Glossary · Insulation & windows

Condensation

Also called: window condensation · interstitial condensation · hidden condensation · attic frost

Water that forms when humid air touches a surface colder than its dew point, on windows, cold pipes or hidden inside walls and attics.

What it means

Condensation you can see, such as on windows, is a sign indoor humidity is high for the outdoor temperature. Hidden condensation inside walls, attics and rim joists happens when moist indoor air leaks or diffuses into the building envelope and meets cold surfaces. Over time it feeds mould and rot.

Why it matters in an audit

Auditors look for condensation stains and attic frost because they point to air leaks and humidity problems that need fixing before or along with insulation.

Sources

Learn more here

Related terms

Dew point The temperature at which air becomes saturated and water starts to condense on surfaces, like water beading on a cold glass.
Relative humidity (RH) How much moisture the air holds compared with the most it could hold at that temperature, shown as a percentage.
Air barrier The continuous layer of materials in walls, ceilings and floors that stops air from leaking through the building envelope.
Vapour barrier / vapour retarder A layer that slows water vapour moving through walls and ceilings, to keep it from condensing inside the structure.
Mould Fungi that grow on damp surfaces indoors; they can damage materials and affect health, and moisture is always the root cause.
Low-e glass Window glass with a thin, invisible metal coating that reflects heat, keeping more warmth in during winter and out in summer.

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