Evidence Policy

Why "Evidence-Informed"

Residential indoor air quality sits at the intersection of building science, materials science, environmental health, and clinical medicine. No single research discipline covers the full scope. Controlled studies on long-term health outcomes from specific building assemblies are rare — the variables are too many, the timelines too long, and the sample sizes too small for the kind of randomized controlled trials that produce definitive conclusions.

The Good Air Standard does not wait for definitive proof that a material or practice causes harm before recommending alternatives. It applies the precautionary principle: where evidence suggests risk and lower-risk alternatives exist at reasonable cost, the standard recommends the lower-risk option. This approach is disclosed transparently so that homeowners and builders understand what the recommendations are based on and can make informed decisions.

Evidence Categories

Category 1: Peer-Reviewed Research (Highest Weight)

Published research in peer-reviewed journals on indoor air quality, building science, environmental health, and materials science. This includes emissions testing studies, health outcome studies, building performance research, and systematic reviews.

How used: Primary basis for material category evaluations, VOC threshold references, and health-related claims. When peer-reviewed research directly addresses a question, it takes precedence over other evidence categories.

Limitation acknowledged: Publication bias, study design limitations, and the gap between laboratory conditions and real-world building performance. The standard cites specific studies rather than making broad claims about "scientific consensus."

Category 2: Established Standards and Building Codes

Published standards from recognized bodies: ASHRAE, ICC (International Code Council), ASTM, EPA, WHO, CDPH (California Department of Public Health), CARB (California Air Resources Board), and international equivalents.

How used: As baseline requirements that the Good Air Standard builds upon. The standard treats code compliance as a floor, not a ceiling. Certification thresholds (GREENGUARD Gold, CDPH v1.2) are used as screening criteria with their limitations disclosed.

Category 3: Building Science Field Data

Published research and case studies from building science organizations and practitioners: Building Science Corporation, RDH Building Science, Oak Ridge National Laboratory Building Technologies Research, Fraunhofer Institute, and similar institutions. Includes hygrothermal modeling, assembly performance monitoring, and failure analysis.

How used: Primary basis for assembly design recommendations, moisture management strategies, and failure mode identification. Building science field data directly informs which assemblies are "forgiving" and which trap moisture.

Category 4: Manufacturer Emissions Testing (With Verification)

Product emissions test data published by manufacturers, tested to recognized standards (CDPH v1.2, ASTM D5116, ISO 16000 series). This includes Safety Data Sheets (SDS), technical data sheets, and third-party certification test reports.

How used: For material-level recommendations where specific product categories are evaluated. The standard requires published test data — not marketing claims or certification badges alone. See Are Green Certifications Enough? for how certification data is interpreted.

Limitation acknowledged: Manufacturer-funded testing may be subject to selection bias (testing favorable products or conditions). The standard looks for independent third-party testing where available.

Category 5: Practitioner Field Experience (Lowest Weight, Highest Practical Value)

Documented experience from builders, indoor air quality professionals, building performance consultants, and environmental health practitioners who work with chemically sensitive clients. This includes installation practices, failure patterns, and material performance observations that may not appear in published research.

How used: To inform practical recommendations — installation sequences, common failure modes, contractor communication strategies, cure timeline observations. Field experience is explicitly labeled when it forms the basis for a recommendation rather than published research.

Limitation acknowledged: Anecdotal, subject to confirmation bias, not controlled. The standard uses field experience to supplement, not replace, higher-weight evidence categories.

What Is NOT Accepted as Evidence

• Manufacturer marketing claims without test data. "Low-VOC," "green," "healthy," "natural" on packaging or marketing materials are not evidence of emissions performance.
• Forum posts, blog articles, and social media. These may identify questions worth investigating but are not sources for the standard itself.
• Testimonials. Individual success or failure stories are not generalizable without supporting data.
• Unpublished or proprietary research. If it cannot be reviewed, it cannot be verified.

Conflict Resolution

When evidence categories conflict:

1. Peer-reviewed research takes precedence over all other categories.
2. When peer-reviewed research is absent or inconclusive, building science field data and established standards guide the recommendation.
3. When multiple peer-reviewed sources conflict, the standard notes the conflict, presents both positions, and applies the precautionary principle (recommend the lower-risk option).
4. Manufacturer data that contradicts independent research is noted but does not override independent findings.

How This Policy Applies to Content

Every content page on this site includes an "Evidence Basis" section that identifies the primary sources for that page's claims. This allows readers to evaluate the evidence behind any specific recommendation rather than accepting the recommendation on authority alone.