Dew Point

LISTEN...


Added insulation and a new airtight layer on the exterior of a building runs the risk of changing the DEW POINT in framed assemblies. Consult with an Energy Advisor to make sure this assembly is done correctly!

Here's a graphic example of condensation happening in a wall:

Inside temp / humidity =20 deg. C and 50%. Outside temp / humidity = -5 deg. C and 80%

The diagram above shows a typical wood frame construction section view with fairly basic layers:

  1. Gypsum drywall,
  2. Poly vapour barrier,
  3. Insulation in stud cavities @ 24" o.c.,
  4. OSB,
  5. House wrap,
  6. Back vented siding

Note that around layer #4, 5 and 6, our assembly is experiencing moisture as the dew point is on the warm side of the sheathing. This could be happening because of air leakage and transported moisture through the assembly.

The water droplets in the diagram represent condensation. The point in temperature where moisture laden air (vapour) changes to condensation (water) is called the Dew Point.


Previous page
« Airtightness, insulation and drying

Next page
Dealing with Dew Point »