 | |
 | |
 | |
| | |
| |
| | |
| |
| | |
| |
| | |
| |
 | |
Vapour-Barrier Materials
Requirements for Vapour Barriers
The vapour barrier is an important component of the house envelope; it provides some protection from moisture damage to the structure and the insulation materials.
To be effective, the vapour barrier must be:
- resistant to the flow of water vapour
- durable
It must be installed on the warm side of insulation.
The vapour barrier does not need to be perfectly continuous like an air barrier, but it should cover as much of the building envelope as possible. Although it needs to be located on the warm side of the insulation, the vapour barrier can be installed part way into the wall, provided that no more than one third of the insulating value of the wall is on the warm side of the vapour barrier. This should be reduced to one quarter or less of the insulating value in very cold climates or in buildings with high moisture sources, such as swimming pools.
Like an air barrier, the vapour barrier can be made up of different materials; even some existing building components such as plywood, paint or vinyl wallpaper may form part of the vapour barrier.
Vapour-Barrier Components
The effectiveness of vapour-barrier material is measured in terms of its "perm" rating. The lower the perm rating, the more effective the vapour barrier.
Among the materials that are considered to be effective vapour barriers are:
- polyethylene
- aluminum foil
- some types of paints
- some types and thicknesses of insulation
- vinyl wallpaper
- exterior-grade plywood
In most older houses, the layers of oil-based primer paint and varnish finishes can function as an adequate vapour barrier for walls and ceilings. Areas that most often require special applications of vapour barriers include interlocking ceiling tiles and new drywall. Pay special attention to areas of high humidity, such as kitchens and bathrooms.
Choosing Vapour-Barrier Materials
Any material used as a vapour barrier should be durable and resistant to moisture flow. You should also consider the following factors:
- Is the material easy to install?
- Can it also act as insulation or an air barrier?
- Is it appropriate to the other work being done on the home?