High-Risk Systems
High-risk systems in the Good Air Standard are building assemblies that create conditions where moisture problems become invisible, irreversible, or both. These are not "bad" systems in every context — but they are systems where the consequences of a single failure are disproportionately severe for occupants with chemical sensitivity or mold illness. The common thread is sealed cavities: wall assemblies where moisture that enters cannot dry out, cannot be detected without demolition, and feeds on organic materials trapped inside. The Good Air Standard evaluates these systems honestly and recommends alternatives.
What Makes a System "High-Risk" for IAQ
The Good Air Standard classifies systems as high-risk when they combine three characteristics:
- Sealed moisture path: Once moisture enters the assembly, it has no drying mechanism — vapor barriers on both sides, closed-cell foam, or impermeable layers that prevent evaporation in either direction.
- Concealed organic material: Wood, paper, adhesive, or other organic material is trapped inside the sealed cavity where mold can colonize without any visible indication on the interior or exterior surface.
- No inspection path: The failure cannot be detected without destructive investigation. By the time symptoms appear (musty smell, visible mold, occupant health effects), the colonization is extensive.
Any system that scores poorly on all three creates a situation where a single construction defect — one flashing failure, one missed sealant joint, one plumbing leak — leads to concealed mold growth that may not be discovered for months or years.
Systems Evaluated
The following building systems are evaluated in detail on their individual pages. Each evaluation includes the assembly description, specific failure modes for indoor air quality, when the system might still work outside the sensitive-occupant context, and recommended alternatives.
ICF — Insulated Concrete Forms
Concrete poured between two layers of expanded polystyrene (EPS) foam. The concrete provides structural mass and thermal storage. The foam provides insulation and stays in place as the interior and exterior finish substrate.
Risk profile: Moisture trapped between foam layers has no drying path. The foam prevents inspection of the concrete surface. EPS off-gasses styrene at low levels. A leak at any point in the envelope — window flashing, penetration, roof-to-wall junction — introduces moisture into a cavity that cannot dry. The homeowner's first indication is often mold on the interior finish surface, by which time the concealed problem is extensive.
SIPs — Structural Insulated Panels
Expanded polystyrene (EPS) or polyurethane foam core bonded between two layers of oriented strand board (OSB). A structural panel system — the foam core and OSB skins together carry structural loads.
Risk profile: OSB is organic and mold-susceptible when wet. The foam core prevents drying. Every panel joint is a potential entry point that requires precision sealing. A single compromised joint introduces moisture to an OSB surface with no drying path and no inspection access. The foam core prevents inspection of the inner OSB face.
Standard Stick-Frame with OSB + Interior Poly
The most common residential construction in the United States. Wood framing, OSB sheathing, fiberglass batt insulation, interior polyethylene vapor barrier, paper-faced drywall.
Risk profile: Interior polyethylene traps moisture in the wall cavity. OSB sheathing and paper-faced drywall are organic. Kraft-faced insulation is organic. Every layer of this assembly provides food for mold, and the vapor barrier prevents inward drying. This is not a sealed high-performance system — it is a standard system that happens to trap moisture.
Spray Foam — Open-Cell and Closed-Cell
Chemical insulation sprayed in liquid form that expands and cures in place. Closed-cell provides structural reinforcement and vapor resistance. Open-cell provides cavity fill without structural properties.
Risk profile: Chemical off-gassing during and after installation — isocyanates, amine catalysts, flame retardants. Sensitive occupants are the highest-risk group for spray foam exposure. Closed-cell foam traps moisture with no drying path. Open-cell foam absorbs moisture. Both prevent inspection of the surfaces they cover. Removal requires mechanical demolition, generating significant dust and chemical exposure.
The Alternative Approach
The Good Air Standard recommends assemblies designed around the opposite principles: drying ability, inspectability, and minimal organic material at moisture-vulnerable interfaces. The Build Options comparison evaluates seven alternative systems that achieve these goals through different strategies:
- Forgiving Wood Assembly — Uses wood but designs for drying and inspectability.
- AAC, CMU, Steel Frame — Inorganic wall cores that do not feed mold.
- LECA — Fully inorganic, vapor-open. Premium custom.
See the Moisture Control Protocol for the foundational principles that all recommended options share.
Last reviewed: August 2026