Glossary · Insulation & windows
Dew point
Also called: dew point temperature
The temperature at which air becomes saturated and water starts to condense on surfaces, like water beading on a cold glass.
What it means
Air at a given humidity has a specific dew point, and any surface colder than that collects condensation. In winter, window glass, poorly insulated walls and sheathing behind badly detailed insulation can drop below the indoor air's dew point. Lowering indoor humidity or warming the surface prevents it.
Why it matters in an audit
Dew point explains where condensation, mold and rot will start, which shapes advice on insulation, vapor control and ventilation.
Typical numbers
Reference values with their sources. Your auditor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| Definition (NRCan) | Reached at 100% relative humidity | natural-resources.canada.ca ↗ |
| Highest indoor humidity before window condensation at −4°F outside, 70°F inside (NRCan) | Older double-glazed low-e 24%; double-glazed 34%; double-glazed low-e 50%; triple-glazed low-e 67% | natural-resources.canada.ca ↗ |