Condensation risk check
What it examines
Section titled “What it examines”Two questions:
- Does vapour condense anywhere in the structure, and if so, how much.
- Can the structure dry out over the summer, or does the moisture accumulate year on year.
The second is the more important: a structure tolerates seasonal condensation if it dries out afterwards. What it does not tolerate is accumulation.
Why it is critical in a framed structure
Section titled “Why it is critical in a framed structure”Because the structure is closed: moisture that gets between the sections cannot simply evaporate. In a thick brick wall moisture spreads out and dries; here it stays where it formed.
Add to that the fact that corrosion of steel needs exactly this — sustained moisture.
What affects the result
Section titled “What affects the result”The order of the layers
Section titled “The order of the layers”The basic rule: vapour permeability should increase outwards. The vapour control layer goes on the inside and the permeable layer outside.
Thermal bridges
Section titled “Thermal bridges”The cold spot is where the vapour condenses. So good thermal bridge handling is also moisture protection. The steel thermal bridge.
The internal moisture load
Section titled “The internal moisture load”How the building is used: how many people, how much cooking, whether there is mechanical ventilation.
Airtightness
Section titled “Airtightness”Air flowing out through a gap carries far more moisture into the structure than diffusion does. Airtightness.
When the simple calculation is not enough
Section titled “When the simple calculation is not enough”The simplified, steady-state procedure is sufficient for many cases. Where the build-up is unusual, the load is high or the structure is sensitive, a transient calculation is warranted, handling the seasonal cycle and the moisture storage of the materials.
What to do with the result
Section titled “What to do with the result”- If condensation occurs and does not dry out: change the build-up, do not accept it.
- If it is borderline: the quality of the work decides — the continuity of the membrane and the airtightness are then critical.
- If it passes comfortably: look at the connections separately anyway, because the surface calculation does not include them.
The point
Section titled “The point”The moisture calculation is not bureaucracy but the only way to “see inside” the structure before it is built.