Do I really need a vapor barrier?
In many colder North American climates, vapour barriers are a required part of building construction. You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good.
What happens if you don’t install a vapor barrier?
If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface, moisture problems can occur. Of course, you can have moisture problems here even without the exterior vapor barrier because of what Bill Rose calls the rule of material wetting.
How does smart vapor retarder work?
A smart vapor retarder reacts to changes in relative humidity (RH) by altering its physical structure. When the air is humid in the summer, the moisture penetrates through the pores into the building interior, allowing building materials to dry out.
Is plywood a vapor barrier?
Latex painted gypsum board (one coat of latex paint) is a Class III vapor retarder. Plywood sheathing and oriented strand board (OSB) have perm values of greater than 1 perm when using the wet cup test. Therefore, a kraft-faced batt (Class II vapor retarder) is required on the interior of this assembly.
Should you put plastic behind drywall?
Normally interior walls do not require a vapor barrier, but there are some situations where it is highly recommended. A continuous plastic vapor barrier behind the drywall will protect the interior walls of these areas from water damage.
What is a smart vapor retarder?
One solution to the changing conditions of a house during the annual cycle is to install a vapor retarder whose permeance (a measure of how readily water vapor can pass through) varies based on the humidity. These are often referred to as smart vapor retarders.
Do I need a vapor barrier behind drywall?
Normally interior walls do not require a vapor barrier, but there are some situations where it is highly recommended. The paint acts as a vapor barrier as well. A continuous plastic vapor barrier behind the drywall will protect the interior walls of these areas from water damage.
Will a vapor barrier reduce humidity?
A vapor barrier blocking evaporation of ground moisture will lower the relative humidity in the crawl space and hopefully the mustiness you complain of.