Glossary

The Scoring System

Two-Question Test

The pair of questions every wall has to answer: can it dry itself out, and can you inspect it when something goes wrong. These are the first two scoring axes (Drying Ability and Inspectability).

Chemical Question

The third scoring axis, asked alongside the Two-Question Test: does the assembly minimize and disclose its chemical load. Scored as the VOC Tier.

Drying Ability

How well an assembly dries after it gets wet. Scored Fast (dries to both sides), Moderate (one side or slowly), Poor (minimal), or None (vapor-closed, no drying path).

Inspectability

Whether you can examine the assembly when something goes wrong, without demolition. Scored Open (examinable without demolition), Partial (some access), or Sealed (destructive removal required).

VOC Tier

The chemical-disclosure score for every wet-applied layer. Scored Zero-VOC, Near-Zero after cure, Documented, or Undisclosed (which fails the standard).

Verdict

The single conclusion read from the three axes: Recommended, Conditional (acceptable only under a stated condition), or Not Recommended. The verdict follows the scores.

The Four Mold Inputs

What mold needs to grow: spores, warmth, moisture, and a food source. Spores and warmth are not controllable in a home; moisture and food source are — which is why the rubric focuses on drying and on keeping organic material out of the wet zones.

Building-Science Terms

VOC (volatile organic compound)

A carbon-based chemical that evaporates into the air at room temperature. Building materials, finishes, and adhesives can emit VOCs, which is the chemical load the standard tries to minimize.

Off-gassing

The release of VOCs from a material over time after installation. Some materials off-gas for hours, others for weeks or months.

Near-zero after cure

A material that emits meaningfully only during a defined, disclosed cure period and then settles to near-zero emissions. This is a passing VOC tier when the cure window is stated.

Drying path

A route for moisture inside an assembly to escape — inward, outward, or both. An assembly with no drying path traps any moisture that enters.

Vapor barrier vs. vapor retarder

A vapor barrier largely stops water vapor from passing through; a vapor retarder slows it. A barrier on the wrong side, or on both sides, can trap moisture and block drying.

Vapor-open (vapor-permeable)

A material or assembly that lets water vapor pass through, allowing the wall to dry. The opposite of vapor-closed.

Rainscreen / drainage gap

A ventilated air space behind the cladding that lets water drain and the wall dry outward, instead of trapping moisture against the sheathing.

Drainage plane / WRB (water-resistive barrier)

The continuous layer (often a housewrap) that sheds bulk water to the outside of the wall and directs it away from the structure.

Mineral wool

Insulation spun from stone or slag. Inorganic, does not feed mold, and unlike fiberglass does not hold liquid water against the framing — a common substitution in recommended assemblies.

OSB (oriented strand board)

Engineered wood sheathing made from wood strands and adhesive. Organic and mold-susceptible when wet; unlike plywood it swells permanently after saturation.

Hygroscopic

Able to absorb and release moisture from the air. Some materials (like lime or hemp) buffer humidity this way; others simply hold water where it causes harm.

Thermal bridging

Heat (and the condensation risk that follows) taking a shortcut through a conductive material such as a steel stud, bypassing the insulation. Continuous exterior insulation reduces it.

Inorganic envelope

A wall built from materials that contain no food for mold (masonry, mineral board, mineral wool, steel), so trapped moisture cannot become a mold problem in the structure itself.

Health Terms

MCS (Multiple Chemical Sensitivity)

A condition in which a person reacts to low levels of chemicals — including building-material VOCs — that most people tolerate. A primary reason this standard prioritizes low, disclosed chemical loads.

CIRS (Chronic Inflammatory Response Syndrome)

An inflammatory illness associated by some clinicians with exposure to water-damaged buildings and the mold and microbial byproducts in them. Often cited alongside MCS as a reason to reduce mold risk in construction.

For the full scoring definitions and how a verdict is derived, see the scoring rubric; for how evidence and independence are handled, see how we evaluate systems.

Reviewed by Zen Watcher, Good Air Homes.