Materials to Avoid

How to Use This Page

This page lists material categories — not specific brands or products. For each category, we explain what the material is, why it poses a risk through an indoor air quality lens, and what lower-risk alternative categories exist. The $79 Build Package includes a material selection guide with specific product examples that meet the Good Air Standard.

Not every material on this list is dangerous in every application. Context matters — climate, assembly design, exposure duration, and occupant sensitivity all affect real-world outcomes. We note where a material might be acceptable outside of our core audience's needs. But for people building or remodeling with indoor air quality as a priority, these are the categories to avoid or replace.

Paper-Faced Drywall (Gypsum Board)

What it is: Standard interior gypsum board with a paper facing on both sides. The most common interior wall and ceiling finish in U.S. residential construction. Inexpensive, widely available, and familiar to every drywall crew.

Why it's a problem: The paper facing is cellulose — organic material that serves as food for mold. When paper-faced drywall is exposed to sustained moisture (from a wall cavity leak, plumbing failure, or condensation), mold colonizes the paper facing readily. Mold on drywall paper is the single most common finding in residential mold inspections. The gypsum core itself is not organic, but the paper facing — the part that faces the wall cavity — is. In a wall assembly where moisture can reach the back side of the drywall, paper-faced board provides a continuous mold food source.

Specify instead: Paperless gypsum board (fiberglass-faced). The gypsum core is the same. The structural and finishing properties are nearly identical. The paper facing is replaced with a fiberglass mat that does not support mold growth. Paperless drywall costs approximately 15–25% more per sheet than standard paper-faced and is available from all major gypsum manufacturers. Some contractors are unfamiliar with the product but the finishing process is the same. It is a direct, drop-in substitution.

Oriented Strand Board (OSB)

What it is: Engineered wood panel made from compressed wood strands bonded with adhesive resin. The dominant exterior sheathing material in U.S. residential construction due to its low cost and structural performance. Also used for subfloor and roof decking.

Why it's a problem: OSB is highly susceptible to moisture damage. Unlike plywood, which handles intermittent wetting and drying reasonably well, OSB swells significantly when wet — particularly at the edges — and does not recover its original dimensions or structural properties after drying. Swollen OSB creates gaps at panel joints, compromises the air barrier, and provides a moisture-damaged organic substrate for mold growth. During construction, OSB sheathing that gets rained on (which is routine) can be permanently damaged before the WRB and cladding are installed. The adhesive resins in OSB also contribute formaldehyde emissions, particularly in the first year after installation.

Specify instead: For wall sheathing: fiberglass-faced gypsum board (same product used for paperless drywall, in a sheathing-rated version), magnesium oxide (MgO) board, or exterior-grade plywood. For subfloor: exterior-grade plywood. For roof decking: plywood or, where structural requirements allow, alternatives per the build option specification. All of these alternatives handle moisture exposure better than OSB and do not swell irreversibly when wet.

Spray Foam Insulation (Open-Cell and Closed-Cell)

What it is: Two-component polyurethane foam mixed and sprayed on-site. Expands to fill cavities. Available in closed-cell (vapor-impermeable, structurally rigid) and open-cell (vapor-permeable, soft, absorbs water) formulations.

Why it's a problem: Chemical off-gassing during and after installation (isocyanates, amine catalysts, unreacted chemicals). Closed-cell foam traps moisture with no drying path. Open-cell foam absorbs liquid water. Both prevent visual inspection of the wall cavity. Off-ratio application (incorrect chemical mix) produces foam that never fully cures and off-gasses indefinitely. People with chemical sensitivities are the highest-risk group for spray foam exposure. Remediation (removal of cured foam) is extremely expensive and destructive.

Specify instead: Mineral wool batts (stone wool or slag wool) for cavity insulation. Mineral wool is inorganic, does not absorb water, does not off-gas, does not support mold growth, and can be removed for inspection. For air sealing, rely on properly detailed sheathing, taped seams, and fluid-applied WRB — not the insulation. See our full spray foam evaluation.

Formaldehyde-Containing Wood Products

What they are: Particleboard, medium-density fiberboard (MDF), hardwood plywood, and some engineered wood products that use urea-formaldehyde (UF) or phenol-formaldehyde (PF) resins as binders. Common in cabinetry, countertop substrates, shelving, interior doors, trim, and furniture.

Why they're a problem: Formaldehyde is a known human carcinogen (IARC Group 1) and a potent respiratory irritant. Urea-formaldehyde resins emit formaldehyde continuously through hydrolysis — a reaction with ambient moisture — which means emissions continue for years and increase with temperature and humidity. MDF and particleboard are the highest emitters because of their high resin-to-wood ratio and large exposed surface area. CARB Phase 2 and EPA TSCA Title VI regulations have reduced emission levels from historic peaks, but regulated levels are still a floor, not a ceiling, and may not be low enough for people with chemical sensitivities.

Specify instead: Formaldehyde-free plywood (bonded with soy-based, PVA, or no-added-formaldehyde phenolic resins). Solid wood where possible. Metal or stainless steel for shelving and cabinetry boxes where appropriate. For cabinetry, specify NAUF (no added urea-formaldehyde) or NAF (no added formaldehyde) core materials. For countertops, specify solid surface, natural stone, porcelain slab, or stainless steel rather than particleboard-core laminate. The Cabinets and Millwork Protocol covers specification details.

Interior Polyethylene Vapor Barriers

What it is: 6-mil polyethylene sheeting stapled to the interior face of wall studs, behind the drywall. Specified or required in some cold-climate building codes to prevent interior moisture from entering the wall cavity during heating season.

Why it's a problem: In any climate with both heating and cooling seasons, interior poly creates a vapor trap. During cooling season, warm humid outdoor air drives vapor inward through the wall assembly. The vapor reaches the cold poly surface (cooled by air conditioning) and condenses. The condensation is trapped inside the wall cavity — the poly prevents inward drying, and the insulation and sheathing prevent outward drying at the same rate moisture accumulates. The result is sustained elevated moisture content in the cavity, mold growth on framing and the back side of the sheathing, and no visible evidence of a problem until damage is extensive. Even in cold climates where the heating season dominates, summer cooling periods and air conditioning use create inward vapor drive conditions that interior poly cannot handle.

Specify instead: A Class III vapor retarder — vapor-retarding primer applied to the interior face of the drywall. This slows outward vapor diffusion during heating season (reducing condensation risk on cold sheathing) while remaining permeable enough to allow inward drying during cooling season. The vapor control strategy must be designed for the specific climate and assembly — see Moisture Control Protocol. If local code requires a vapor retarder, a vapor-retarding primer typically satisfies the requirement without the moisture-trapping risk of poly sheeting. Verify with the local building official.

High-VOC Adhesives, Sealants, and Caulks

What they are: Solvent-based construction adhesives, polyurethane sealants, silicone caulks, and specialty adhesives used throughout residential construction — at subfloor joints, window installations, countertop mounting, trim adhesion, flooring installation, and dozens of other applications. Often the most overlooked VOC source in an otherwise carefully specified home.

Why they're a problem: A home may have 50–100 individual adhesive and sealant applications across the entire build. Each one is small, but the cumulative VOC load from conventional products is significant — particularly during the first 3–6 months after construction when most off-gassing occurs. Many high-VOC adhesives contain toluene, xylene, or formaldehyde-based components. Sealants at window and door penetrations are installed deep in the wall assembly where ventilation is limited, extending the off-gassing timeline. In a home built with zero-VOC insulation, paperless drywall, and mineral paint, conventional adhesives and sealants can be the dominant remaining VOC source.

Specify instead: Zero-VOC or ultra-low-VOC alternatives exist for virtually every adhesive and sealant application in residential construction. Water-based construction adhesive for subfloor. Low-VOC silicone for window and plumbing sealant. Zero-VOC caulk for interior trim. Request SDS (Safety Data Sheets) and emissions testing data for every adhesive and sealant product before purchase. GREENGUARD Gold certification is a useful minimum floor for identifying lower-emission products, but is not sufficient as a sole criterion — it tests to thresholds that may still be too high for people with chemical sensitivities. The $79 Build Package material selection guide includes product examples for every adhesive and sealant category.

Chemically Treated Lumber

What it is: Pressure-treated wood infused with preservative chemicals to resist rot, insects, and fungal decay. Common applications include sill plates, deck framing, posts in ground contact, and structural members in humid or ground-contact locations. Current formulations typically use alkaline copper quaternary (ACQ), copper azole (CA), or micronized copper preservatives (MCA). Older formulations used chromated copper arsenate (CCA), which has been restricted for residential use since 2004.

Why it's a problem: Treated lumber emits copper compounds and biocide residuals, particularly in the first months after treatment. When cut, sanded, or drilled, treated lumber produces dust containing concentrated preservative chemicals. In enclosed spaces (crawl spaces, basements, interior wall cavities), emissions from treated lumber contribute to the indoor chemical load. The copper compounds can also leach into surrounding soil and water. For people building with chemical sensitivity as a concern, treated lumber inside the conditioned envelope is an unnecessary chemical source.

Specify instead: Where ground contact or moisture exposure requires decay resistance, use naturally durable wood species (cedar, redwood, cypress, black locust) or physical barriers (metal sill plate gaskets, capillary breaks) instead of chemical treatment. Where code requires treated lumber at sill plates, specify treatment with borate-based preservatives (lower toxicity than copper-based treatments) and install a capillary break between the treated sill and the foundation. Never use treated lumber inside the conditioned envelope where it is not required by code. Keep all cutting and fabrication of treated lumber outdoors.

Standard Fiberglass Batt Insulation

What it is: Glass fiber insulation in pre-cut batts sized for standard stud cavities. The most widely used residential insulation product in the United States. Inexpensive and universally available.

Why it's a concern (with nuance): Fiberglass batts themselves are inorganic and do not support mold growth. The glass fibers do not off-gas significantly. However, fiberglass batts have two properties that make them a less-than-ideal choice for IAQ-focused builds. First, many fiberglass batts use formaldehyde-based binders to hold the fibers together (though formaldehyde-free options exist). Second, fiberglass batts are not inherently moisture-resistant — they absorb and hold water when exposed to liquid moisture, creating sustained wetting conditions on adjacent materials. When wet, they lose insulation performance and hold moisture against framing and sheathing. They do not wick moisture efficiently and dry slowly.

This is not a blanket condemnation of fiberglass. Formaldehyde-free fiberglass batts in a well-detailed, drying-capable assembly are a legitimate choice. But mineral wool (stone wool) batts offer strictly better moisture performance: they do not absorb water, dry immediately when exposed, and are manufactured without formaldehyde binders. For the same installation method and comparable cost, mineral wool is the better choice for IAQ-focused builds.

Specify instead: Mineral wool batts (stone wool or slag wool). Same cavity insulation, same installation method, superior moisture handling, no formaldehyde binders. Cost is approximately 2–3× per batt compared to standard fiberglass, but insulation is a small fraction of total build cost.

Asphalt-Based Roofing and Waterproofing

What they are: Asphalt shingles, asphalt-based roofing felts, asphalt dampproofing on foundations, and hot-applied asphalt waterproofing membranes. Asphalt shingles are the dominant residential roofing material in the United States.

Why they're a concern: Asphalt products emit VOCs, particularly during initial installation and during hot weather when the asphalt softens. On a roof, most emissions dissipate outdoors and do not directly affect indoor air quality — but in unvented attics (where the roof deck is inside the conditioned envelope) or in hot climates where attic heat drives emissions inward, the contribution can be measurable. Asphalt dampproofing on foundation walls is applied to surfaces that may be partially inside the conditioned space (basements). The VOC concern is modest compared to spray foam or formaldehyde products, but for people building to the lowest possible chemical exposure, metal or tile roofing and membrane waterproofing are available alternatives.

Specify instead: Metal roofing (standing seam or exposed fastener) or concrete/clay tile for the roof — both are inorganic, long-lived, and contribute no VOC load. For foundation waterproofing, specify sheet membrane or cementitious waterproofing rather than asphalt-based coatings. For roofing underlayment, specify synthetic underlayment rather than asphalt-saturated felt.

The Pattern

The materials on this list share common characteristics. They are the default choices in standard residential construction — selected for cost and familiarity, not for indoor air quality performance. Most of them work adequately in most homes for most people. But for people building with chemical sensitivity, mold risk reduction, or environmental health as a priority, they represent unnecessary risk with available alternatives.

The Good Air Standard does not require exotic, unavailable, or prohibitively expensive materials. Every alternative listed above is commercially available, compatible with standard construction practices, and installable by standard residential contractors. The cost premiums are real but modest — typically adding 10–25% to the specific material category, not to the overall project cost.

For the complete material selection guide with specific product examples for every category, see the $79 Build Package. For lower-risk alternatives organized by application, see Lower-Risk Alternatives.