Dew point describes air at a stated moisture content. It is not a fixed line inside a wall and does not replace moisture assessment.
Meaning
Dew point is reached when air at a given moisture content cools to saturation. It depends on the initial state, so there is no single value for every room and season.
What happens in a wall
Temperatures, vapour pressures and material moisture vary through an assembly. Real conditions can include rain, construction moisture and air transport.
Simplified model
A Glaser-type assessment has defined assumptions and scope. It does not cover every transient mechanism or demonstrate that rain or air leakage is harmless.
Risk and assessment
Surface risk depends on temperature and humidity near the surface. Complex layers, drying or recurring wetting may require transient modelling with appropriate inputs.
Common mistakes
Saying the dew point is in the insulation and therefore safe is not evidence. Assess water sources, accumulation, drying and material sensitivity.
| Item | Parameter | Check / result |
|---|---|---|
| Air | Temperature + moisture | State |
| Wall | Transport | Mechanism |
| Model | Assumptions | Limits |
What this means for your project
Ask which mechanism was assessed and which were excluded. For a problem following rain, investigate water entry before changing vapour layers without evidence.
Sources and scope of review
- ISO 13788:2012 — Surface humidity and interstitial condensation
- PNNL / Building America — Moisture control for residential buildings
Related reading
- The Thermal Envelope: How to Define It Correctly
- Thermal Bridges: Where They Occur and Why They Matter
- Airtightness: What It Is and Why It Matters