Burning “ExposHome”: Deriving a Mixture of Combustible Materials in American Homes at the Wildland‐Urban Interface for Health Studies

Abstract

Approximately 39% of U.S. homes are now located in the Wildland‐Urban Interface (WUI) and are at elevated risk of burning during wildfires. WUI fires emit a cocktail of chemicals from the combustion of anthropogenic materials, including compounds that may differ from the burning of biogenic‐only materials. There is currently limited knowledge on the mixture composition of combustible materials in WUI homes, representing a data gap and need to further characterize exposure chemistries and toxicological impacts of WUI‐relevant smoke exposures. To address this issue, this study integrated combustible materials in an average American WUI home to derive what we are referring to as the “Burning ExposHome.” Items such as structural materials, plumbing, furnishings, and appliances were included in the Burning ExposHome. Calculations were based on an average American household, a 2,016 sq. ft. single family home of four bedrooms, using materials typical to California due to the high incidence of WUI fires in that geographic region. All materials were sorted and summed by type of base material such as wood materials, plastics, textiles, and metals. This list is notably modular and detailed per item, allowing for the addition/subtraction of components to address future study designs. In summary, the total combustible mass of an average American home was around 46,500 kg, including 81% wood materials, 6% plastics, and 2% metals. This list of materials serves as a foundational mixture of home materials to integrate into exposure characterization, mechanistic toxicology, and ecological/human health research addressing wildfires occurring at the growing WUI.

Plain Language Summary

Wildfires occurring in the wildland‐urban interface (WUI), which is the area where our built environment encroaches upon the wildland, are becoming an increasingly prevalent issue. As WUI fires burn both trees and structures, they likely release a host of dangerous chemicals not found in wildfires burning only biomass‐based matter. Thus, there are concerns that the health effects associated with breathing in WUI fire emissions could be more damaging than the emissions of fires relegated to only the wildland. However, little research has been completed to determine what combustible items and their amounts are present in a typical home. Our study seeks to fill in this gap by integrating all the combustible items in the average American home, including the structural items, furniture, furnishings, appliances, household chemicals, and sundries. Furthermore, we have calculated the amounts of each item needed to create a 10‐kg mixture that models the average American home, titled the “Burning ExposHome” mixture. Our larger goal is that this list of materials and the Burning ExposHome will spur new research addressing the health effects related to wildfires at the growing WUI to better protect our most vulnerable community members.

Key Points

• We calculated the amounts of all combustible materials present in the average American home

• We produced a 10‐kg mixture modeling wildland‐urban interface (WUI) home materials, titled the “Burning ExposHome” for use in lab settings

• We hope the “Burning ExposHome” will spur research regarding the exposure characterization and mechanistic toxicology of WUI fires

1. Introduction

Wildfires are growing in acreage paralleling a changing environment and lengthening wildfire season; for every 1°C increase in global average temperature, the range of area burned by fires in the western United States could increase anywhere from 73% to over 600% (NASEM, 2022; NRC, 2011). At the same time, humans are encroaching into the wildland. The wildland‐urban interface (WUI), defined as areas where human developments are within or near the border of wildland vegetation, is rapidly expanding. The WUI grew by 41% between 1990 and 2010, and as of 2010, 33.2% of all American homes were in the WUI, which corresponds to at least 44.8 million housing units (Radeloff et al., 2018). WUI homes are not only at increased risk for destruction during wildfires, but also increase the risk of human ignition of wildfires (Radeloff et al., 2018). WUI fires have indeed become an increasingly relevant issue in the US in recent years; 75% of California's 20 most destructive wildfires, defined in terms of structures burned, have occurred within the last 10 years (CAL FIRE, 2025c). The 2018 Camp Fire, which has been labeled a representative WUI fire (NASEM, 2022), destroyed 18,804 structures, including entire towns over 17 days and is the most destructive wildfire in California to date (CAL FIRE, 2025c; NASEM, 2022). Similarly, the 2021 Marshall Fire burned over 1,000 structures and 6,000 acres and remains the most destructive fire in Colorado history (NASEM, 2022). At the time of writing, the 2025 Palisades and Eaton Fires in Southern California were estimated to have damaged or destroyed a combined total of 18,291 structures (CAL FIRE, 2025a, 2025b). Unfortunately, WUI fires like the ones described above will only increase in frequency in the coming years as wildfires continue to worsen and as the WUI expands.

Beyond being ecological disasters, WUI fires are also becoming a growing and especially relevant public health concern. WUI fires have a large human exposure burden due to their adjacency to areas with significant human activity (NASEM, 2022). For example, PM_2.5 concentrations were around four times higher than average coupled with increased metal concentrations during the 2018 Camp Fire in the Bay Area region of California (CARB, 2021), home to over 7 million residents (Bay Area Census, 2010). Research regarding reported health effects of WUI‐fire smoke exposure from the Palisades and Eaton Fires are not available yet, but the fires occurred simultaneously in different areas of Los Angeles County, home to over 10 million residents (US Census Bureau, 2020). While there is still a looming research gap on the health effects specific to WUI fires, smoke from biomass‐only wildfires has also been linked to lung damage, inflammation, and mutagenicity across in vitro models of the airway, animal inhalation models, and humans (Brocke et al., 2022; Kim et al., 2018; Koval et al., 2022; Noah et al., 2025; Rager et al., 2021). Furthermore, it is well documented that children, the elderly, pregnant people, and those with pre‐existing heart and lung conditions are at increased risk of experiencing health effects in response to wildfire smoke exposure (NASEM, 2022). Ultimately, the goal of WUI fire smoke and health research are to inform whether new and innovative public health actions are needed and if traditional approaches being implemented are ineffective. Hence, a consensus study report from NASEM in 2022 identified a pressing need for studies to define WUI fires to aid in the characterization and untangling of the health conditions emerging from WUI fires compared to those in biomass‐only wildfires (NASEM, 2022). Scientists do know the inclusion of anthropogenic materials in housing units and structures burned in WUI fires contributes a unique chemistry and toxicity profile that may not be seen in biomass‐only wildfires (NASEM, 2022). Unfortunately, a rate‐limiting step in delineating the chemistry and exposure characteristics of WUI fires has been the lack data on what items are in homes burned during fires. This missing piece has relegated knowledge of WUI fire health exposures mainly to epidemiological studies or extrapolations from research focused on biomass‐only fires.

To address this knowledge gap, the “Burning ExposHome,” representing a mixture of combustible anthropogenic materials that can be found in a typical home burned during a wildfire event, was created. The Burning ExposHome is based on a single family detached home with overall dimensions, number of bedrooms, and household size selected to represent the average American household at the time of writing. The exterior siding was modeled after homes burned during WUI fires in California, due to the high frequency of burned structures in that geographical region. The smoke generated from burning of the standardized mixture of materials in this WUI home could then be used in in vivo or in vitro WUI fire smoke health research to allow the detailed characterization of the fuels that contributed to the smoke mixture. In the manuscript, usage of the term Burning ExposHome refers to the average American home in the WUI that was modeled and used in calculations. We would like to note that all decisions and components included in the Burning ExposHome are described in detail and are modular, such that future expansions of this data resource can easily add or remove select elements to address specific research questions. An overview of this project is presented in Figure S1 of Supporting Information S1.

2. Methods

2.1. Overview

The goal of the “Burning ExposHome” project was to characterize the combustible components of a “typical home” present at the WUI in the U.S. Given that WUI fires occur along the West Coast, a “typical home” present in California was used in prioritizing material selection; though most attributes are translational and applicable to areas across the U.S. Justification and calculations surrounding each materials‐based decision are described below, alongside the specific sources used in determining these components and relevant weights. Relevant data sources were identified by querying research articles, databases, retail information, or other relevant “gray” literature searches from general search queries. Data sources were determined to be relevant if they contained information on the composition of items, the amount of items in typical homes, and/or the mass of the items that could be used for conversions. A summary of sources used for calculations are shown in Figure 1.

Figure 1.

Overview illustrating the different data sources used to inform each aspect of the combustible materials calculation in an average American home in the WUI.

The organization of the methods are presented as follows: First, data informing an average home size are summarized, followed by identifying major materials sources and rationale for methods used to derive calculations for non‐movable and movable fuel loads in a home. In the results section, calculations for the amount of combustible materials in each item category were performed in the same order as their introduction.

Throughout the calculation process, the worst‐case scenario principle was prioritized as it is more relevant for health studies to capture the higher end of potential toxicities and exposure burden for chemical mixtures rather than the lower end. If presented with choices between different common materials used for the same item, the material that was likely to exhibit higher toxicities at lower doses was prioritized. Similarly, when estimating material amounts (which eventually influence exposure dosing), confronted with ranges of amounts, or rounding numbers, the larger number was usually selected. Similarly, trace compounds (including metals) were also included to capture as many aspects of the home as possible. Although most metals are not typically considered combustible, metal emissions in wildfires are a research gap (Boaggio et al., 2022; NASEM, 2022), so care was taken to include them. Results of this effort were lastly coalesced into a list of prioritized material types and summarized according to relative weight percentages of materials in a WUI home and thus designated as components of the “Burning ExposHome.” The final list still carries the title “combustible materials” even with the inclusion of metals since most materials are indeed combustible.

Many gray literature sources and e‐commerce sites, such as Home Depot or Amazon, were used for material calculations. These sources are referenced in‐text with the website name, with specific websites included in detail in Supplemental Tables and screenshots of key webpages used throughout the calculations included as individual pdfs within “Supplemental Folder 1 Materials Sources.” Items that needed calculations like unit conversions or extrapolations are also included in Table S1 with their unrounded values. Figures and tables were generated using BioRender Software, GraphPad Prism (v 10.4.1), and R Software (v 4.4.2).

2.2. Deriving Dimensions to Represent an Average U.S. Home

Calculations of any component, such as structures, furnishings, and clothing, were related back to the average dimensions for a single detached U.S. home. The average and median single‐detached family home size has remained around 2,000 square feet since the mid 1970s (Sarkar, 2011; US Census Bureau, 1981, 2023a). In 2023, 45% of single‐family homes had four or more bedrooms compared to 44% with three bedrooms, although the number of four plus and three‐bedroom homes have been fairly consistent since 2013 (US Census Bureau, 2023a, 2023b). Since there are more houses with four or more bedrooms than any other configuration, and more bedrooms increase the amount of furnishings and the worst‐case scenario, modeling of a WUI house with four bedrooms was prioritized (US Census Bureau, 2023a, 2023b). In 2023, the average household size was 2.51 people, rounded to three people (US Census Bureau, 2023d). Information about household size affects the amount of food, clothing, toiletries, etc. and were important for establishing amounts of combustible materials for many items. In the end, the “Burning ExposHome” is modeled after a Californian home with wood siding of 2,016 square feet with four bedrooms and three household members (Figure S2 in Supporting Information S1).

2.3. Sources and Rationale for Non‐Movable Loads in a WUI Home

2.3.1. Structural Component Prioritization and Underlying Scientific Sources

To date few resources exist that provide the necessary details to calculate the weight of materials used to build average sized American homes. One resource (Messerschmidt, 2021), represents an unpublished analysis conducted by the National Fire Protection Agency in 2021 and presented to the National Academy of Sciences, Engineering, and Medicine (NASEM). This analysis represented an unofficial accounting of materials used to build a typical American single‐family home of 2,016 square feet in 2020 to determine potential fuel from homes during wildfires (Messerschmidt, 2021; NASEM, 2022). Additionally, a non‐peer reviewed 2016 lifecycle analysis of a typical home conducted by the EPA published the amount of materials used to build a 2,150 square foot home in 1998 (EPA, 2016). Although neither Messerschmidt (2021) or EPA (2016) are exhaustive or peer‐reviewed, both represent the most thorough accounting for housing materials thus far and have been adopted into NASEM study reports on WUI fires (NASEM, 2022). The Messerschmidt (2021) analysis was prioritized for this analysis as it contained more data on combustible materials, which was consistent with this study's focus on modeling a worst‐case scenario of materials burned during a WUI fire. For example, Messerschmidt (2021) included estimations for foam board sheathing and spray polyurethane foam insulation, which are combustible, rather than the incombustible fiberglass insulation in the EPA (2016) study. The EPA, (2016) analysis was still consulted to fill in gaps. Since both houses were very similar in square footage, it was assumed that amounts of materials used would not differ significantly between either and would be applicable to both houses. In fact, most components of the two houses had comparable values when calculated as total percentage of combustible materials. Using this prioritization approach, the Messerschmidt (2021) analysis was used to determine the amount of structural wood, subfloor, sheathing, insulation, roof decking, and roof exterior (asphalt shingles), while the EPA (2016) analysis was used for other items including wood siding, windows, and metal ducting.

Additionally, neither the Messerschmidt (2021) nor the EPA (2016) analysis provide material estimates for garages. However, garages are common in the US. By 2021, garages were in over two‐thirds of all housing units in the US (U.S. DOE, 2022). Within the Pacific region, which includes California, 80% of housing units had garages (U.S. DOE, 2022). Messerschmidt (2021) provided the dimensions of a two‐car garage, which was used to calculate the materials used in a garage.

2.3.2. Exterior Siding Prioritization and Underlying Scientific Sources

Wood siding was selected as the representative exterior siding material due to siding material trends over time within California and broader applicability to other regions. The median age of a California home is 48 years, built in 1977 (US Census Bureau, 2023c). In the West geographical region delineated by the US Census Bureau, 43% of homes built in 1977 had primarily wood siding while 44% had primarily stucco siding. Wood siding steadily lost popularity over time, and by 2011, only 11% of new homes built in the West had wood siding (US Census Bureau, 2024). Using fire damage inspections (CalFire DINS) performed by the California Department of Forestry and Fire Protection (CalFire) in Paradise, California, which was decimated by the 2018 Camp Fire, researchers determined that 86% of single resident family homes in Paradise were built prior to 1990, and only 11.6% of those homes were undamaged in the Camp Fire (Knapp et al., 2021). Further analysis in this study also indicates that the Camp Fire destroyed a disproportionate number of older homes built from the 1940 to 1980s as compared to homes that were not reported to be affected or damaged (Figure 2a). Furthermore, most homes experienced damage due to fires that started from their siding (Figure 2b), demonstrating the importance of selecting accurate siding material for the model. Of the homes that had fires start from their siding, a slight majority of homes had siding material rated “combustible,” while a minority of homes had siding rated “not combustible” (CAL FIRE, 2024). Wood siding used in the West geographical region is the only material regarded as combustible. Considering the median age of the California home and a multitude of evidence from Camp Fire data, wood siding was clearly the best choice for the model. Additionally, across the US, wood siding was a popular siding choice until the 2000s, and over 10% of new homes in the Midwest region still have wood siding. Vinyl siding was also considered as it is combustible and has become the dominant siding material in the Northeast and Midwest, so using vinyl siding would be more reasonable if modeling WUI homes in those regions. However, vinyl siding was and still is practically non‐existent in Western homes (US Census Bureau, 2024), hence the final decision to model the “Burning ExposHome” with wood siding.

Figure 2.

Overview of the age of homes typically burnt and the initial location of fire in/on a home during wildfire events. (A) The reported number of single or double‐story single family homes sustaining different categories of damage severity according to the year they were built during the 2018 Camp Fire. There are only two homes with “Major Damage (26%–50%)” in the data set, out of 12,025 total homes surveyed, so its line is not visible in the plot. Damage severity percentages correspond to the percentage of the home damaged during the fire. (B) Locations of fire initiation on any single or double‐story single family homes that sustained any type of reported damage during the 2018 Camp Fire. Data for both graphs originated from the publicly available CAL FIRE Damage Inspection (DINS) database (created June 2024) on the California Open Data Portal website and were plotted for this study.

2.3.3. Paint Prioritization and Underlying Scientific Sources

Peer reviewed sources identifying the amount of paint used in a typical home could not be found. Amount of interior paint could also vary depending on number of walls and other aspects of internal architecture, although a gallon of paint usually covers 400 square feet (Flora Brothers Painting, 2023). Gray literature sources also offer calculators for the amount of paint for a home's exterior based on the perimeter and height of the home (Behr, 2025), which was used to calculate the amount of paint needed. It was assumed both the exterior and interior of the home would be painted with two coats of paint. Importantly, paint additives can also vary depending on the age of the home and the location used. For example, interior paints have lower levels of volatile organic compounds (VOC) and can be water‐based. Exterior paints may have higher levels of VOCs with increased durability and be oil or acrylic‐based (Lowe's, 2024). Lead‐based paints were also not federally banned until 1978 (U.S. EPA, 2024). Thus, research teams should adjust the composition of the paint used in their mixture according to their goals.

2.3.4. Flooring and Carpets Prioritization and Underlying Scientific Sources

American studies conducted in the 2000s for allergy research found that more than 90% of homes contained carpets or rugs (Cho et al., 2006; Jacobs et al., 2008). Additionally, many property managers require 80% of floor areas to be covered with carpeting for noise reduction (Jacobs et al., 2008). Thus, for ease of calculations and in consideration that many houses also have flooring, the “Burning ExposHome” was made half laminate wood flooring and half carpeting.

2.3.5. Plumbing Prioritization and Underlying Scientific Sources

Plumbing data was from a simulated home plumbing system (HPS) built at an EPA research center to study water quality and corrosion. The HPS was built to simulate the number of fixtures and pipe length of a household of four (Lytle et al., 2021). While no manuscripts using the HPS thus far state the square footage of the household they modeled, with the average American household being around three people in 2,100 square feet with four bedrooms, it was assumed that this modeled home would not differ significantly from the American average. The total length of piping used in the HPS was given as 56 m split between cold and hot water lines in a study supplement (Gomez‐Alvarez et al., 2023). Piping in the HPS is 1/2″ copper pipes (Lytle et al., 2021), which are not combustible, thus, to model the worst‐case scenario, polyvinyl chloride (PVC) and chlorinated polyvinyl (CPVC) piping was chosen for the “Burning ExposHome.” Homes also contain other plumbing items such as drain and vent lines of differing sizing and length than the piping in the HPS. As there is very limited data on the amount of such additional piping items in the typical home, the Burning ExposHome incorporated what is provided in the HPS while acknowledging that this is an underestimate and a current data gap.

2.3.6. Electrical Wiring Prioritization and Underlying Sources

Peer‐reviewed sources for amounts of electrical wiring in an average American home could not be found. Instead, gray literature searches indicated that electricians can estimate the amount of wiring used in an American home through a rule of thumb: 1–1.5 feet of wire per square feet of house (Electrical, 2023; Electrical‐1v, 2023). In this study, 1.5 feet of wire per square feet was used. The “Burning ExposHome” is 2,016 square feet and would use around 3,024 feet or 921.7 m of wiring.

2.3.7. Kitchen Cabinetry Prioritization and Underlying Sources

A 2019 study by the National Association of Home Builder's found that the kitchen accounts for 11.2% of the home's square footage (Emrath, 2019). Kitchen cabinets are commonly made of many materials, which include medium density fiberboard (MDF), solid wood, plywood, or wood veneer (Kitchen Cabinet Kings, 2024). To align with the worst‐case scenario principle, MDF was selected as the wood of choice to model kitchen cabinets.

2.4. Sources and Rationale for Movable Loads in a WUI Home

2.4.1. Furniture Prioritization and Underlying Sources

Calculating combustible components for furniture using consumer websites was found to be extremely inefficient as information about materials used to construct furniture could not be easily obtained. Furniture calculations were instead derived from research focused on calculating fire loads for predicting the speed and intensities of fires. Fire load is defined as the heat energy potential of combustible materials. Studies calculating fire loads tend to survey homeowners about the type of furniture they have and summarize furniture contents directly by weighing the furniture or extrapolating mass based on volume and density (Xie et al., 2018). In one study, the most recent fire load density value listed for North American residential buildings was around 600 MJ/m² (Xie et al., 2018) in 2010, which this study used in calculations detailed further below, as it is more recent, although studies conducted in 1980 found fire load density to range from 300 to 1200 MJ/m². However, one drawback of using these North American studies was that fire loads tended to be determined after surveying one or two rooms in the home, usually the living room or basement, and no masses of the furniture or its components were listed. Additionally, furnishings like decorations, toys, and clutter were not included in calculations. Thus, the 600 MJ/m² value was likely an underestimation of fire load density in typical residences, and it would be difficult to convert the 600 MJ/m² to kilogram amounts or percentages of combustible materials such as wood or plastic in furniture without other information.

Although not based on American homes, a study by Blomqvist et al. calculated fire loads in Nordic homes by obtaining several detailed IKEA furnishing plans for the whole home and was used to supplement missing data on furniture combustible materials. Blomqvist et al. was unique as it dissected each piece of furniture by the amount of combustible materials it was made of with detail; for example, whether the plastic used was polypropylene, polyethylene, or polystyrene, producing tables that summarized the percentage material distribution of all furniture in a home (Blomqvist & Simonson, 2009), which provided the foundation for furniture calculations. IKEA furniture could skew materials toward engineered wood and plastics like melamine, but global usage of engineered wood products in furniture and home construction is rapidly increasing due to its affordability (GlobeNewswire, 2025). The kitchen cabinets modeled in this study are made of MDF for instance. Thus, use of IKEA furniture falls with the worst‐case scenario.

2.4.2. Household Appliances Prioritization and Underlying Sources

Combustible components for household appliances were calculated using lifecycle inventories, which are used for determining the environmental impact of recycling appliances by providing breakdowns of the components used to make appliances. The majority of appliance lifecycle inventories data stem from European‐centric appliances to aid the European Union's waste electrical and electronic equipment directive, which set goals for the collection, treatment, recovery, and recycling of raw materials (European Commission, 2024). A limitation of using lifecycle inventories is that most combustible component amounts data are based on European rather than American consumer appliances. However, the size and components of European versus American consumers likely differ by a negligible amount relative to the totality of all combustible materials in homes, so using lifecycle inventories was most straightforward. American sources were used when available. If only percentages of materials were given in a study, their values were applied to American appliances. Appliances counted in the “Burning ExposHome” included a TV, computer/monitor, refrigerator, dishwasher, washing machine, clothes dryer, microwave, oven, printer, wifi router, wifi modem, thermostat, and vacuum cleaner.

Most homes are likely to contain many personal electronic items such as phones and laptops. These types of smaller electronic items were not included in the final list as it was assumed people would prioritize taking their personal phones and laptops and leave behind larger items like desktop computers and/or monitors during an evacuation.

2.4.3. Textiles Prioritization and Underlying Sources

Furnishings were defined as the lifestyle essentials, personal items, and other miscellaneous items that do not include furniture. Included are textiles, toiletries, household cleaning supplies, bedroom essentials, cardboard boxes, storage bins, books, plastic bags, picture frames, and paper and plastic‐based personal items. For calculating textiles, four furnished bedrooms with bedding and clothing were included in this analysis.

Pillows, pillowcases, sheets, blankets, and clothing were included in the list of textiles in the “Burning ExposHome.” Blomqvist et al. included mattresses and one set of sheets, a thin duvet rated for warm weather, and a pillow and pillowcase per bed, which was deemed an underestimation as most households own several sets of bedding per bed. For example, a bedroom poll by the National Sleep Foundation reported the average number of pillows per person was 2.2, and the average number of bedsheets owned per bed was 3.4 (NSF, 2010). Values were rounded to three pillows and four sheets per room. Subtracting items already included in Blomqvist et al., the extra bedding added to the Burning ExposHome was nine pillows and 12 sheets. Twelve pillowcases were further added; if most Americans have extra sheets per bed, they also have extra pillowcases. Three thicker blankets were also added, one per person, since the one used in Blomqvist et al. was thin and rated for warm weather.

Peer‐reviewed sources for amounts of clothing owned by the average American were not found. An educator on minimal wardrobes conducted an Instagram survey to identify how many pieces of clothing responders owned (Lee, 2024). Data was collected from 2020 to 2024 with 283 responses globally, although most responses, 48%, were from North Americans. Clothing items counted in the study included any clothing except undergarments. The study concluded that the average person owned 144 pieces of clothing and shoes in their wardrobes (Lee, 2024). Shoes are not modeled separately from clothes in this study as shoes were a small portion of the wardrobes surveyed, and the average number of shoes owned per person were not provided. Since the Burning ExposHome includes three residents, a total of 432 pieces of clothing was counted.

To obtain an accurate accounting of the amount of different textile materials in the typical closet, additional resources were consulted. A materials market report by Textile Exchange, most recently updated in 2023, provided percentage breakdowns for different fibers used in the global fiber market in 2022 (Textile Exchange, 2023). The broad categories in the report included plant fibers, animal fibers, manmade cellulosics, and synthetic fibers. This breakdown was used as a proxy for the proportion of different clothing materials found in the WUI home wardrobe. 27% of the fiber market was made of plant fibers, of which cotton was the majority, thus cotton was used to model plant fibers. Animal fibers comprised 2% of the market, and wool was the most represented, thus wool was used for animal fibers. Manmade cellulosics accounted for 6% of the market, which includes materials like rayon, which was used to represent this category. Synthetic fibers were 65% of the market share, a majority of which was polyester (Textile Exchange, 2023), so polyester was used as the synthetic fibers component of the average wardrobe. Except for the polyester textiles, which was counted as a plastic, all other textiles used were counted in the textiles category.

2.4.4. Toiletries and Household Cleaning Supplies Prioritization and Underlying Sources

As noted previously, the average American household size is defined as three people for this model. Thus, three sets of toiletries were counted in the “Burning ExposHome.” Sizes of toiletries were standard sizes. Toiletries included 32‐fluid ounce shampoo, conditioner, and body wash sets, 5.1‐ounce tubes of toothpaste, and toothbrushes. Items like the shampoo, conditioner, body wash, and toothpaste were split apart into their liquid and container portions in the final list. The list of household cleaning supplies in the WUI home model included bleach, a two pack of 24‐fluid ounces of toilet bowl cleaner, 32‐fluid ounces of all‐purpose disinfectant, 16‐fluid ounces of rubbing alcohol, and 15‐ounces of Raid bug spray. The Burning ExposHome was also assumed to have eight toothbrushes and 32 rolls of toilet paper as both values account for extras items stored in homes and are common sets sold.

To split the shampoo, conditioner, body wash, bleach, disinfectant, bug spray, rubbing alcohol, and toilet bowl cleaner into their liquid and container portions, the weight of the overall product was obtained from the seller's website, which included both container and liquid. To obtain the weight of the liquid itself, empty containers of equivalent size were found online, and their weight was recorded, then the weight of the empty container was subtracted from the weight of the full product. For bug spray, the container portion was a metal can, and its value was entered under the metal category. For shampoo, conditioner, body wash, bleach, disinfectant, and rubbing alcohol, the container portion was all high‐density polyethylene (HDPE). The liquid portion for all these items were included in the assorted liquids category. For the toothpaste, using the above method was difficult as we were unable to find empty toothpaste packaging or their weights on purchasing websites. Instead, a blog article where the author took apart an empty toothpaste tube by hand and weighed each of the components was used (Smith, 2020).

2.4.5. Miscellaneous Items Prioritization and Underlying Sources

Most homes cannot be summed up with just a collection of appliances, furniture, bedding, toiletries, and cleaning supplies. Personal items, sundries, and even food are also combustible, but their amounts could vary widely. Research studies have yet to characterize the average amount of clutter in American homes, thus an estimation for miscellaneous items in homes was attempted. Items in this category include books, picture frames, miscellaneous paper products, miscellaneous plastic items, storage items, and foodstuffs.

Books are common items in American homes. According to a YouGov survey where 29,000 Americans were polled about whether they owned books, the median number of books owned per person was 26–50 (Montgomery, 2023). To align with the worst‐case scenario principle, this study assumed 50 books in the “Burning ExposHome.” Most homes also include wall decorations such as photos, which usually have wooden frames. The number of frames could differ in homes with a range of sizes, thus a range of different sizes of picture frames were included in calculations. Miscellaneous paper products are present in homes and encompass items such as paper files, bills, and mail. If a home has a printer, it also likely has at least a ream of paper. Counting the ream of printer paper as the foundation of this category, the rest of the miscellaneous paper products were assumed to add up to another ream of paper. Homes also have miscellaneous plastic items. Most homes have at least one trash can, which indicates a plastic trash bag burden. A collection of plastic grocery bags is also common in most homes and were included in the calculations. Trash and grocery bags tend to be composed of low density polyethylene (LDPE) (Keep California Beautiful, 2007), which was the plastic used to model these items in the home. Homes also contain other plastic miscellaneous items, such as souvenirs or toys, which were also included in calculations as HDPE. If most homes have personal items, they also likely have storage options. Plastic storage bins are common, and most homes likely have more than one plastic storage bin, such as a 4‐pack of Rubbermaid 95‐quart storage bins with lids. Cardboard boxes are also common storage items. In this study, the weight of cardboard boxes was made equivalent to the weight of the plastic storage bins. Food items are also combustible components within homes. To estimate the amount of food in the Burning ExposHome, it was assumed that most Americans would store up to 1 week's worth of food at home, with some added buffer of dry goods and pantry items, which factored into rounding decisions. To ensure the Burning ExposHome mixture would be shelf stable, spaghetti noodles was used as a proxy for all foodstuffs.

3. Results

The overall goal was to calculate all the combustible items in an average home to create a mixture or materials that are representative of an average home in the WUI, termed the “Burning ExposHome” for use in health research. Thus, after all non‐movable and movable loads and their underlying sources were identified, calculations were performed below to determine the amount of combustible materials present in each item. Items included as non‐movable loads that required calculations presented below include flooring and carpeting, plumbing, electrical wiring, and kitchen cabinetry. Items included as movable loads that required calculations include furniture, appliances, textiles from bedding and clothes, toiletries, household cleaning supplies, foodstuffs, and miscellaneous sundries.

The results section is organized as such: Material calculations first for the non‐movable loads then for the movable loads in the average WUI home are described in the same order they were introduced in the section above. Then, combustible materials were organized by their material type into combustible mass categories stratified by structural materials, furniture, appliances, and the whole home. Finally, a table of all combustible materials, their amounts in the home, and the amount needed to make a 10‐kg mixture of the Burning ExposHome was presented. Detailed information on the items in alongside their source website URL, calculations, extrapolations, unit conversions, and unrounded values are provided in Table S1. Also included are item calculations referenced in the following sections by their item number. Final calculations below are rounded for simplicity.

3.1. Material Calculations for Non‐Movable Loads in a WUI Home

3.1.1. Structural Material Calculations

Structural material values for a 2,016 square foot home were directly obtained from either the Messerschmidt (2021) or EPA (2016) studies as outlined above. For the garage Messerschmidt (2021) included the dimensions for a two‐car garage with a roof, which was 576 square feet, roughly 3.5 times smaller than a 2,016 square foot home. Assuming that the structural aspects of the garage include framing lumber, insulation, sheathing, roof decking, roofing shingles, and wood siding, the amount of materials used to build the home was divided by 3.5 to obtain materials for the garage. In the end, the garage contained 4,344 kg of framing lumber, 1,037 kg asphalt shingles, 996 kg wood siding, 850 kg OSB, 850 kg plywood, 283 kg spray polyurethane (PUR), and 36 kg polystyrene foam board.

3.1.2. Paint Material Calculations

To calculate the amount of paint typically needed for the exterior of the home, the perimeter of the home was multiplied by the height of the home. The perimeter of the Burning ExposHome was estimated as 192 feet (Messerschmidt, 2021). The height of the home was not given, but the typical two floor home was 25 feet (Johnson, 2025). Thus, the exterior wall area of the home was estimated as 4,800 square feet. If a gallon of paint covers 400 square feet, then 12 gallons of paint would be needed to paint the exterior. Estimates for the amount of interior paint needed for a 2,000 square foot home are 10 gallons of paint (Flora Brothers Painting, 2023). Since the Burning ExposHome was slightly larger than 2,000 square feet, and assuming most people keep spare paint in their home, an extra gallon of paint was added, resulting in 11 gallons of paint for the interior. Thus, 23 gallons of paint were estimated as required to paint the exterior and interior of the Burning ExposHome with one coat, which corresponds to 46 gallons of paint for two coats. A gallon of paint weighs between 7 and 12 pounds (Ogletree, 2023). To align with the worst‐case scenario, the conversion rate was assumed to be 12 pounds per gallon of paint, which resulted in 552 pounds or 250 kg of paint as an included component of the Burning ExposHome.

3.1.3. Flooring and Carpeting Material Calculations

Weight of laminate flooring was calculated using product specifications for laminate flooring (Item #1), which resulted in 1,241.7 pounds or 563.2 kg of laminate flooring. Laminate wood is 10% melamine and 90% wood fiber (Marutzky, 2007), which was applied to the 563.2 kg total to determine the melamine and wood components of the laminate wood flooring for calculating percentages of base materials. Laminate wood flooring itself was used in the “Burning ExposHome” mixture. Weight of carpeting was calculated using product specifications for polyester carpeting with a face weight of 60 ounces/square yard (Item #2). Assuming half carpeting, this would be 1,008 square feet of carpeting, equivalent to 112 square yards and translating to 190.5 kg of carpeting.

3.1.4. Plumbing Material Calculations

The 56 m of piping in the EPA's model HPS (Lytle et al., 2021) was assumed to be split evenly between ½” PVC and CPVC schedule 40 piping, used for cold and hot water lines, respectively. Schedule 40 piping is the standard for residential buildings (Modern Industrial, 2022). Pipe weights were determined from product information provided by pipe suppliers, which stated that schedule 40 ½” PVC piping was 0.16 lbs/ft (PVC Pipe Supplies, 2024) (Item #3), while schedule 40 ½” CPVC piping was 0.177 lbs/ft (Corzan Material and Piping Solutions, 2024) (Item #4). These conversion rates were multiplied by 23 m to obtain mass of PVC piping.

3.1.5. Electrical Wiring Material Calculations

12‐2 gauge wiring is common in residential structures (Electrical, 2023; Holden, 2023). The weight of the wiring was 0.082 lbs/ft and composed of PVC and copper (Wire and Cable Your Way, 2024) (Item #5) For simplicity and using the worst‐case scenario principle, 0.082 lbs/ft was used as the conversion for the combustible PVC component of electrical wiring. In total, 112.5 kg of 12‐2 gauge electrical wiring was used in the “Burning ExposHome.”

3.1.6. Kitchen Cabinetry Material Calculations

According to the NAHB study, 11.2% of the 2,016 square foot “Burning ExposHome” is the kitchen (Emrath, 2019), which is equivalent to a 226 square feet kitchen (21 square meters). A kitchen of 225 square feet is estimated to need 10 to 12 sheets of plywood to build the required cabinetry (Ply Supply, 2025), thus 12 sheets of 4 × 8 medium‐density fiberboard (MDF) was used to model the cabinetry. A 4 × 8 feet MDF panel is around 100 pounds per sheet (Item #6). Assuming 12 sheets of panel, this equates to 1,200 pounds or around 5,443 kg of MDF cabinetry.

3.2. Derived Material Calculations for Movable Loads in a WUI Home

3.2.1. Furniture Materials Calculation

To apply the Blomqvist et al. percentages of combustible materials in furniture based on Nordic homes to American homes, the median North American fire load density of 600 MJ/m² was divided by the assumed average heat of combustion of all materials, 20 MJ/kg (Blomqvist & Simonson, 2009), to obtain the mass of combustible materials per meter squared (kg/m²). This number was then multiplied by the area of the “Burning ExposHome,” which was 187 m², to obtain 5,610 kg of combustible furniture material, which was then multiplied to the percentage material distribution of furniture in Blomqvist et al. to obtain the percentage material distribution and weights of furniture in the Burning ExposHome. Graphical representation of calculation steps are shown in Figure 3, and calculated values are in Table S2. The furniture components included wood materials, polyurethane foam, ABS, polypropylene, polyethylene, polystyrene, melamine, polyester, nylon, and acrylic, and cotton and wool natural textiles. Since Blomqvist et al. used IKEA furnishing plans, wood materials were assumed to be all MDF in line with the worst‐case scenario principle. Blomqvist et al. also did not specify what type of polyethylene was used. Polyethylene was converted to HDPE as HDPE is more rigid than LDPE, which is more commonly used for films and bags (Cheremisinoff, 2001; Global Plastic Sheeting, 2024) and would likely fit the needs for furniture better.

Figure 3.

An overview of the steps carried out to adapt percentages of combustible materials in furniture calculated by Blomqvist et al. to the average American WUI home.

3.2.2. Household Appliances Materials Calculation

For many appliances, lifecycle inventory reports with metric unit values for combustible materials were available, so those values were directly entered into the final list. If a source did not specify the type of polyethylene, it was assumed to be HDPE. Many sources also include an “other plastics” category, likely due to parts being unspecified mixtures of plastic. Since polyethylene plastic is the most produced plastic in the world (Rodrigues et al., 2019), those values were converted to HDPE. Basic appliances counted in the WUI home model included a TV, computer/monitor, refrigerator, dishwasher, washing machine, clothes dryer, microwave, oven, printer, wifi router, wifi modem, thermostat, and vacuum.

A common standard TV size is 50 inches (Mantel Mount, 2024). About 40% of the weight of a TV is plastic; around 90% of the plastic in a TV is polystyrene and 10% of the plastic in a TV is acrylonitrile butadiene styrene (ABS) (Arends et al., 2015). A 50‐inch television weighs around 26.9 pounds (Item #7). Thus, the amount of ABS is 0.5 kg and amount of polystyrene is 4.4 kg for a TV. The plastic components of monitors are around 25% of its total weight (Mathews, 2024). The plastic components of monitors were around 20% polystyrene, with the remaining 80% of plastic being split between ABS or acrylonitrile‐butadiene‐styrene terpolymer/polycarbonate blend (ABS‐PC; Arends et al., 2015). However, only older PCs use ABS‐PC, while newer PCs use ABS (Wäger et al., 2009). ABS is also less heat resistant; thus to adhere to the worst case scenario, the monitor plastic was assumed to be 20% polystyrene and 80% ABS. A Dell 27‐inch monitor is 14.9 pounds (Item #8), which translates to 6.8 kg total, and thus 1.4 kg of polystyrene and 5.4 kg of ABS.

A study found the components of a refrigerator were 54.83% metal, 22.93% polyurethane foam, 17.42% ABS and polystyrene, 0.94% polyvinyl chloride (PVC), and 0.55% polypropylene (Dong et al., 2024). In the study, the initial ABS and polystyrene components of a refrigerator before the recycling process were not split separately, but the individual plastic component percentages after grinding, cleaning, and sorting was given, which was 9.15% polystyrene and 7.90% ABS (Dong et al., 2024). These values for polystyrene and ABS do not add up to the original 17.42% of ABS and polystyrene as the processing likely led to loss of plastic components. To keep the ratio of ABS and polystyrene intact from beginning to end of the recycling process, the initial 17.42% was split by the final ABS and polystyrene ratio, which resulted in 9.146% polystyrene and 8.274% ABS. Dong et al., 2024 also did not split the metals into their individual components, thus the metal percentages in a European publication of refrigerators was applied to the metals total in Dong et al., 2024) for consistency (Fiore, 2018). This resulted in metals components being 92.0% steel, 4.79% aluminum, and 3.19% copper. Fiore (2018) was not used for the other calculations as it was missing details for types of plastics. Since the Dong et al. (2024) study was based on Chinese refrigerators, the percentages of components were applied to an American refrigerator. The American refrigerator is 308 pounds (Item #9), which is 139.7 kg. Split between the components, this results in 12.8 kg of polystyrene, 11.6 kg of ABS, 32.0 kg of polyurethane foam, 0.8 kg of polypropylene, 70.5 kg steel, 3.7 kg aluminum, and 2.5 kg copper.

Materials and masses for a washing machine were based on a 2005 American industry average washing machine (Bole, 2006). Materials were converted from pounds to kilograms. The washing machine included 1.4% other plastics (Bole, 2006), which was converted to HDPE. Values to model a dishwasher (Fulvio, 2015), air vented tumble dryer for laundry (Ecobilan, 2009), oven (Landi et al., 2019), microwave (Gallego‐Schmid et al., 2018), HP Deskjet D1360 inkjet printer (Grzesik & Terefeńko, 2012), and 1400W bagless vacuum cleaner (Gallego‐Schmid et al., 2016) were given in grams, which was directly used in the material list for this study. Of note, no resources for components of a range cooktop, which are common in the US, could be found, thus an oven was used instead (Landi et al., 2019).

No peer‐reviewed sources determining components in a typical wifi router or modem could be found. Wifi router housing is made of ABS plastic (MKTechnic, 2023) (Item #10). Housing for wifi modems were difficult to find online, so the weight and composition of a wifi router was used instead as both are about the same size. In the end, the wifi router and modem were found to be 82 g of ABS plastic each (MKTechnic, 2023). Thermostat housing tends to be made of plastic and thus would be combustible in a WUI home burn. For simplicity, it was assumed that the entire weight of the thermostat would be attributable to the plastic housing. A Honeywell Home programming thermostat was listed as four ounces (Item #11). No sources described what type of plastic the typical thermostat was made of, so it was assumed to be ABS, which is also used in wifi routers (MKTechnic, 2023) and serves a similar function. The thermostat accounted for 0.1 g of ABS plastic in the WUI home.

3.2.3. Textiles Materials Calculation

Textiles accounted for in the “Burning ExposHome” include bedding and clothing. For bedding, in total, six pillows, nine sheets, 12 pillowcases, and three blankets were counted in addition to what was already include in the Blomqvist et al. furniture calculations. The weight and material of the bedding was determined through information provided by the manufacturer and were found to all be made of polyester (Item #12–15). The sheets weighed 7.9 kg of polyester each, blankets were 6.5 kg each, pillows were 1.9 kg for two, and a four‐pack of pillowcases were 0.4 kg (Item #12–15).

Peer‐reviewed sources that calculated the weight of different clothing items were not available. On average, jeans are 1.5 pounds and shirts are 0.5 pounds (Hardware Decor, 2024). 0.75 pounds was chosen as the weight for each piece of clothing, which is a little less than the average of the two items, as people generally have more shirts than pants/jeans. With 432 pieces of clothing the home, the total mass of clothing is 324 pounds (147 kg). Assuming the average closet is 65% polyester, 27% cotton, 6% rayon, and 2% wool based on the Global Fiber Report (Textile Exchange, 2023), the total mass of clothes is split into 95.5 kg of polyester, 36.7 kg of cotton, 8.8 kg of rayon, and 2.9 kg of wool. The polyester component was grouped under the polyester plastic in the final list, while the rest of the fabrics were entered under the textiles category.

3.2.4. Toiletries and Household Cleaning Supplies Materials Calculation

Toiletry items include shampoo, conditioner, body wash, toothpaste, toothbrushes, and toilet paper. Household cleaning supply items included bleach, disinfectant, bug spray, rubbing alcohol, and toilet bowl cleaner. All items were split into a liquid and container portion.

Shampoo, conditioner, and body wash weighed 2.8, 2.8, and 3.3 kg, respectively, while their container portion was each 0.2 kg of HDPE (Item #16–19). Bleach was 3.9 kg liquid and 0.2 kg HDPE (Item #20–21). Rubbing alcohol was 0.4 kg liquid and 0.03 kg HDPE (Item #22–23). Toilet bowl cleaner and all‐purpose disinfectant were 1.3 and 1.0 kg liquid, respectively, along with 0.1 kg for both containers (Item #24–27). Bug spray was 0.5 kg liquid and 0.1 kg steel (Item #28–29). The total weight of the toothpaste container was 13.2 g, of which 12.9 g was plastic, assumed to polypropylene, and the remaining 0.31 g was aluminum (Smith, 2020) (Item #30). Assuming three 5.1‐ounce toothpaste tubes in the home, the container weight was subtracted from the weight of a full tube (Item #31) to obtain the liquid component weight of 0.4 kg. Eight toothbrushes accounted for 0.2 kg of HDPE (Item #32). A 32‐pack of Cottonelle Ultra Comfort Toilet Paper was listed as 12.43 pounds (Item #33), which converts to 5.6 kg.

3.2.5. Miscellaneous Items Materials Calculation

Items included under this category include books, picture frames, miscellaneous paper products, miscellaneous plastic items, storage items, and foodstuffs, and their calculations are included below.

Fifty books were counted in the “Burning ExposHome.” A website for book sellers states hardcovers weigh one to three pounds and paperbacks weigh six to 12 ounces (Meyers, 2024). The conversion factor of one pound for a book was chosen for a total of 50 pounds of books or 22.7 kg counted as wood materials. Picture frames were included as combustible materials. A 15‐frame set with different sizes was used, which weighed 6 pounds or 2.7 kg of wood materials as frames are primarily cardboard and engineered wood (Item #34). Two reams of paper were included to estimate the amount of miscellaneous paper products in a home. A ream of 500 sheets of printer paper weighs 20 pounds (Item #35), resulting in a total of 40 pounds of paper products, equivalent to 18.1 kg in the WUI home. The miscellaneous plastic bag category in the Burning ExposHome encompassed 110‐13 gallon garbage bags, a typical unit size, found to weigh 4.5 pounds (Item #36). Grocery bags, rounded to 2.5 kg of miscellaneous LDPE plastic bags was also included. For miscellaneous plastic personal items or toys, using the same mass as the miscellaneous paper products seemed reasonable. This added 18.1 kg of HDPE, as polyethylene is the most produced plastic (Rodrigues et al., 2019), and HDPE is more rigid and thus likely more applicable to personal items and/or toys. Plastic storage bins and cardboard boxes were also included. Storage bins were 4‐pack 95‐quart storage bins with lids, made of polypropylene and weighing 8.5 kg total (Item #37). The mass of cardboard boxes were set equal to the mass of plastic storage bins, which resulted in 8.5 kg of cardboard.

Foodstuffs were also included as combustible materials. Using data from the U.S. Department of Agriculture, economists determined that the average American consumed 1,996 pounds of food a year (Aubrey, 2011). This translated to around 5.5 pounds of food eaten per day, assuming 365 days in a year. To account for a week of food plus additional dry goods and pantry items, this number was rounded to 6 pounds of food per person stored at any given day in a home. With the average household being three people, there should be around 126 pounds or 57 kg of food in a home.

3.3. Organizing Calculations Into Combustible Mass Categories

Combustible items were identified and organized by their combustible mass category: structural, furniture, appliances, or furnishings. The weight of each combustible material within the item was recorded in Table S3 in Supporting Information S1. In all, this study calculated the mass of 50 different combustible items in a home, not including the furniture items already counted in the Blomqvist et al. publication used to calculate furniture combustible materials. We found that the total mass of combustible items in an average WUI home was around 46,482 kg. Using these data, the weight of each type of combustible material was then aggregated within the same combustible mass category, for example, all polypropylene plastic within the appliances category was summed and recorded in Table S4 of Supporting Information S1.

3.3.1. Distribution of Combustible Materials in the Whole Home, Non‐Movable Structural Materials, Furniture, Appliances, and Furnishings

For the whole home, 81% of the combustible materials are wood materials (Figure 4). Except for the furnishings category, wood materials accounted for most of the masses of items in all other material categories. Petroleum‐based products, or asphalt shingles, were the second most common combustible material comprising 10% of the total fraction. This may seem surprising, but by weight, the structural materials category, of which petroleum‐based figures prominently in, accounts for almost 87% of all combustible materials in the home. Plastics, which are large portions of the appliances and furnishings category comprised 6% of the materials in the whole home. Metals, mainly from appliances were the fourth most common material in the whole home by weight at 2%. Finally, the textiles, foodstuffs, assorted liquids, and rubber were trace, each comprising less than one percent of the total mass in the whole home.

Figure 4.

Material type and weight percentage of combustible materials in the whole home and further broken down into percentage distributions in structural materials, furniture, appliances, and furnishings categories. Unrounded values are provided in Table S5 of Supporting Information S1.

Most combustible materials within a home are the non‐movable, structural materials. Within this category, wood materials comprised the largest fraction of combustible materials, 81%. Framing, subfloor, roof decking, siding materials, and kitchen cabinetry are all wood based. Petroleum‐based products were the second most common combustible material by weight, comprising 12% of the total fraction. Plastics, which included the polyurethane foam insulation and polystyrene external wall sheathing was also the third most common structural material. Metals counted in structural materials were only comprised of galvanized steel ducting. Paint comprised 1% of the structural materials.

Wood materials were the most common combustible material type in furniture. Polyurethane foam, used for cushions and mattresses comprised 8% of the total and were categorized under plastics, which accounted for 12% of the combustible materials in furniture. Natural textiles, such as cotton and wool, were the third most common combustible material. Final amounts for furniture materials are derived from tables with more detailed material types, which was further used to calculate collapsed mass category, mass, and percentages of combustible materials in the whole WUI home (Table S2). Most combustible materials within household appliances were metals, which comprised 68% of the total weight. The second‐most common material was plastics, forming many of the inner components of the appliances. Trace amounts of rubber, less than a percent, were also present within this category. Furnishings included the majority of the smaller movable load items in a home and had the most varied material composition. Plastics comprised the largest portion of the combustible materials in furnishings, with 45% of the total. The second and third most common item categories were wood materials at 17%, which included items like cardboard and paper, and foodstuffs at 17% of the total. Textiles, mainly from clothing, also accounted for 15% of the total materials. The furnishings category included assorted liquids from the household chemicals and toiletries, which was 5% of the total. Some trace amounts of metal were present as well.

3.4. Materials Breakdown to Create a 10‐kg Burning ExposHome Mixture

After calculating the mass and percentages of combustible items in the WUI home, represented by the “Burning ExposHome,” the values were extrapolated to calculate the grams of each type of material needed to create a representative mixture with a total mass of 10 kg (Table 1). Ten kilograms of total material was chosen as it was a large enough to include trace elements, but still easy to store. Mass values for items that are less than one kg in the average home and less than one g in the 10‐kg mixture would be considered trace items and are provided in scientific notation. These trace items may be negligible in the overall mixture but are still included in Table 1 to demonstrate a full accounting of all materials. Depending on what the “Burning ExposHome” mix will be used for, research teams could apply their own exclusion criteria for items.

Table 1.

Summary of the 61 Prioritized Materials and Their Masses in an Average WUI Home Transformed Into the Amount Needed to Generate a 10‐kg Mixture of the Burning ExposHome

Material number	Material	Mass in average home (kg)	Grams of materials needed for 10 kg mixture (g)
1	Douglas Fir Framing Lumber	19,544	4,205
2	Medium‐density Fiberboard	5,215	1,122
3	Asphalt Shingles	4,667	1,004
4	Wood Siding	4,481	964
5	Oriented Strand Board (paneling)	3,826	823
6	Plywood	3,826	823
7	Spray on Polyurethane (insulation)	1,273	274
8	Metals—Galvanized Steel	621	134
9	Flooring (melamine resin and fiberboard)	563	121
10	Plastics—Polyurethane foam	453	97
11	Fabric—Cotton	292	63
12	Paint	251	54
13	Plastics—Polyvinyl Chloride (PVC)	197	42
14	Carpet (polyester)	191	41
15	Plastics—Polyester	187	40
16	Metals—Steel	144	31
17	Polystyrene Foam Board	162	35
18	Electrical Cables	112	24
19	Plastics—Polypropylene	108	23
20	Plastics—Melamine	84	18
21	Foodstuffs—Spaghetti Noodles	57	12
22	Plastics—Acrylonitrile butadiene styrene (ABS)	24	5
23	Plastics—High‐density polyethylene (HDPE)	23	5
24	Books	23	5
25	Textiles—Wool	21	5
26	Plastics—Polystyrene	21	5
27	Miscelleanous paper products	18	4
28	Metals—Stainless Steel	14	3
29	Plastics—Nylon	10	2
30	Metals—Enameled Steel	9	2
31	Textiles—Rayon	9	2
32	Cardboard	9	2
33	Metals—Aluminum	8	2
34	Toilet Paper	6	1
35	Metals—Copper	6	1
36	Assorted liquids—Bleach	4	1
37	Metals—Painted Sheet Steel	4	1
38	Assorted liquids—Body Wash	3	1
39	Assorted liquids—Conditioner	3	1
40	Assorted liquids—Shampoo	3	1
41	Plastics—Low‐density polyethylene (LDPE)	3	1
42	Chlorinated Polyvinyl Chloride (CPVC)	2	5E−01
43	Assorted liquids—Toilet Bowl Cleaner	1	3E−01
44	Assorted liquids—Disinfectant	1	2E−01
45	Metals—Iron	1	2E−01
46	Plastics—Acrylic	1	1E−01
47	Rubber—Ethylene Propylene Diene Monomer (EPDM)	1	1E−01
48	Plastics—Polyamide	5E−01	1E−01
49	Assorted liquids—Bug Spray Liquid	5E−01	1E−01
50	Assorted liquids—Rubbing Alcohol	4E−01	9E−02
51	Plastics—Ethylene‐vinyl acetate (EVA)	4E−01	9E−02
52	Assorted liquids—Toothpaste	4E−01	8E−02
53	Plastics—Polyoxymethylene	3E−01	6E−02
54	Plastics—Polyethylene terephthalate (PET)	2E−01	4E−02
55	Metals—Chromium	7E−02	2E−02
56	Metals—Brass	6E−02	1E−02
57	Metals—Nickel Chrome Alloy	5E−02	1E−02
58	Plastics—Extruded polystyrene (EPS)	4E−02	9E−03
59	Plastics—Polybutylene terephthalate (PBT)	4E−02	8E−03
60	Metals—Zinc	4E−03	9E−04
61	Plastics—Polycarbonate	4E−03	8E−04
	Total	46,482	10,000

Note. Materials are organized from greatest (top) to least (bottom) amount of relative mass. Grams of materials needed to make the mixture are included in the rightmost column. Unrounded values and percentages are available in Table S6 of Supporting Information S1.

4. Discussion

This study is amongst the first wave of research to characterize the combustible materials in an average American WUI home and results in the derivation of components to include in the “Burning ExposHome” mixture. In the process, some initial steps were implemented to highlight and close research gaps surrounding the amount of materials in an average WUI home and their role in WUI fire emissions. Our main findings mentioned below include implementing a method to calculate furniture combustible materials with limited resources and calculating the amount of metals in a home, a category that has often been overlooked. Furthermore, comparisons of our study's amount of combustible materials indicate they are similar to those generated from previous estimations and help validate our methodology.

The first major finding of this study was that the data needed to calculate combustible materials, particularly furniture materials, are severely lacking as detailed composition data per furniture item are not publicly available. In the end, we utilized one resource (namely, Blomqvist et al. for a Nordic home) in combination with U.S. fire load density data to generate a best estimate of materials in a U.S. home for the Burning ExposHome. The geographical obstacle of applying estimations of furniture materials in Nordic homes to American homes was circumvented by assuming percentages of combustible furniture materials would remain proportional to home size regardless of country. As mentioned earlier, IKEA furniture can differ from traditional furniture materials, but such furniture materials are becoming more popular and falls within the worst‐case scenario. Additionally, research using the CalFire DINs also found that socioeconomic status does factor into the likelihood a home may burn. Lower‐value residences were more likely to be burned during the Camp Fire (McConnell & Braneon, 2024), and may have material distributions that differ from the average American WUI home. Notably, there has yet to be a study that calculates the combustible furniture components for a US home with the same resolution as the Blomqvist et al. study accomplished for a Nordic home, highlighting a research gap that needs addressing for the US and other geographic regions. Calculations of the average mass fraction composition of individual furniture pieces from a range of suppliers would provide data critical to improve the accuracy of future studies. Still, data were deemed suitable here for our initial analysis of combustible materials in homes, particularly upon comparisons to other potential gray literature sources.

A second major result of this study was the calculation of metals in an average home. The lack of metal data in wildfire emissions research is a gap research is trying to close. All wildfires seem to produce some amount of metal emissions, but arsenic, chromium, copper, lead, nickel, and zinc were most associated with structurally destructive fires like the 2018 Camp Fire (Boaggio et al., 2022). Perhaps this should be unsurprising as there is an association between metals and the combustion of structures and vehicles (Boaggio et al., 2022). Previous research suggests metal emissions may even serve as a fingerprint for WUI fires (Holder et al., 2023). While wildfire metal emissions may largely be linked to burning vehicles, metals are present in homes, especially in appliances, which was factored into the decision to model them in the Burning ExposHome. Still, the amount of metal is likely an underestimate as the Blomqvist et al. study and the current study did not calculate masses of any metal in hinges, nails, lighting fixtures etc., largely due to a lack of information. By including metals in the ExposHome, this study hopes to help parse out the contribution of metals in homes to the overall mixture in WUI fires and their implications for human health.

Other studies have attempted to identify the amount of different combustible materials in homes, so comparisons between methodologies are bound to occur. NASEM's Chemistry of Fires at the Wildland‐Urban Interface study report includes Figure 3‐1, demonstrating an effort in the WUI fire community to include structural materials, household chemicals, furnishings, and furniture in models. There are still some differences in components between our and NASEM's study. NASEM's structural category was 97% wood, 2% asphalt shingles, and 2% other (NASEM, 2022), which aligns with a similar study done by Holder et al. that surveyed literature and used emission factors to estimate WUI fire pollution emissions (Holder et al., 2023). Our study's estimates were around 81% wood, 12% shingles, 5% plastics, 2% metals, and 1% paint. These discrepancies in values are likely attributable to differences in methodologies. Our study has a plastics category to accommodate spray‐on polyurethane foam, 2% of the total mass was dedicated to metals, and we included calculations for paint. Furthermore, our study counted whole shingles as combustible as we will be burning whole shingles in our experiments, while NASEM only counted the combustible portions of shingles. NASEM estimated 35,000 kg for wood structural components, which differs from our study's 32,700 kg, largely in part due to the inclusion of wood decking in their estimations for structural wood. Wood decking was not modeled in the Burning ExposHome as there was little evidence it was a common feature in California WUI homes.

In terms of total mass in an average home attributable to home contents, the NASEM figure also included 7,000 kg of contents in the home, split into 40%–90% wood, 12%–26% plastic, and 0%–20% fabric (NASEM, 2022), which is comparable to the 6,240 kg of furniture, appliances, and furnishings categories in this study. The percentages are not directly comparable because this study included categories NASEM did not have, such as metals, foodstuffs, liquids, and rubber. But our study's percentages for wood, plastics, and fabric are within the ranges given in the figure. Overall, it seems clear that our decision to calculate combustible materials by item is a novelty, differences in materials between studies are within the realm of reason, and our study's detailed calculations validate the generalized estimations generated in these previous studies.

On a broader scale, the Burning ExposHome encapsulates a fraction of important materials within a larger mixture of anthropogenic materials burned during WUI fires. This mixture does not capture all the nuances of a WUI home and currently cannot address every environment and research question. For example, while we included a garage in our estimate, we did not include vehicles which are also burned in WUI fires as they are currently being defined by other research groups; though vehicle components can easily be added to the detailed materials list once they become available. Similarly, mobile homes were destroyed at a significantly higher frequency compared to single‐family homes during the 2018 Camp Fire (CAL FIRE, 2024; McConnell & Braneon, 2024). As materials‐based research gaps continue to be addressed, other items burned in WUI fires such as vehicles, different forms of housing, and even asphalt roads can be incorporated with the Burning ExposHome depending on researcher goals. For further flexibility, the materials needed to make a version of the Burning ExposHome without the garage attachment and paint is also included in Table S7 of Supporting Information S1. Additionally, we aim to expand the Burning ExposHome to more fully address data ranges and confidence intervals amongst materials components as data become available for future modeling and experimental purposes. Thus, while capturing just a portion of potential materials burned during wildfire events, the Burning ExposHome contributes major findings to close research gaps in this field of expanding importance. This data organization and summary effort addresses a much‐needed first step in the endeavor to better understand the health effects of WUI fires by introducing the potential for the mixture's use in chemical analyses and in vitro/in vivo toxicology studies.

5. Conclusion

This study defined the mixture of combustible materials in an average American WUI home and created a list of materials and their amounts to facilitate the creation of a standardized “Burning ExposHome” mixture. The goal is for the Burning ExposHome mixture to aid in the characterization of exposure chemistries and toxicological impacts of WUI‐relevant smoke exposures. We would like to emphasize that the Burning ExposHome should serve as a framework that can be easily adapted to different contexts depending on the needs of the research group. We recognize that certain assumptions were made when information was lacking to derive this mixture; though we would like to highlight that the goal of pointing out the limitations of the Burning ExposHome is not to undermine its novelty, but to openly acknowledge the need for more research that can characterize all the components in a WUI fire to better elucidate the health effects of WUI fires so health researchers can protect our most vulnerable populations from the increasing threat of WUI fire smoke exposures.

Disclaimer

This manuscript has been reviewed by the Center for Public Health and Environmental Assessment, United States Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

Conflict of Interest

The authors declare no conflicts of interest relevant to this study.

Supporting information

Supporting Information S1

Supporting Information S2

Table S1

Chou, C. K. , Holder, A. L. , Nored, A. , Walters, G. , Bai, W. , Gilmour, M. I. , et al. (2025). Burning “ExposHome”: Deriving a mixture of combustible materials in American homes at the wildland‐urban interface for health studies. GeoHealth, 9, e2025GH001439. 10.1029/2025GH001439

Data Availability Statement

The CalFire DINS Data set is publicly available here: https://data.ca.gov/dataset/cal‐fire‐damage‐inspection‐dins‐data (CAL FIRE, 2024).

Figures S1, S2 and Tables S1–S7 in Supporting Information S1 can be accessed here: https://doi.org/10.15139/S3/QTXZGH (Chou, 2025a).

Supplemental Folder 1 Materials Sources which includes images of sources used can be accessed here: https://doi.org/10.15139/S3/L3W2OH (Chou, 2025b).