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Last Updated: Monday, January 15th, 2001, Created: Monday, January 15th, 2001

Should the vapour barrier go to the floor in the basement?

One of our viewers is about to insulate his basement and he has been told that he should not run the vapour barrier all the way to the floor. Fact or fiction?

You should run the vapour barrier wherever there is insulation to keep the moisture on the warm side of the wall. And in a basement installation, you should wrap the vapour barrier around and under the insulation to prevent moisture from sneaking in from the bottom of the insulated wall.

So the real question is: should the insulation go all the way to the floor? The answer, with one exception, is yes. We used to be worried about freezing the footings on the outside if we insulated to the floor, but research has shown that insulating right to the floor will not affect the footing under the wall. In addition, you will never get a warm comfortable basement unless you insulate the entire wall. You will also notice in the graphic that there is a moisture barrier right against the concrete wall starting at ground level and going down under the wall, then the vapour barrier all the way up on the warm-in-winter side of the insulation. The protection against ground moisture does not go all the way to the top, to allow for moisture to escape at the top towards the outside.

The one exception is a field stone foundation. Here you have poor mortar and probably poor drainage on the outside. The wall has always been warm. If you freeze this delicate wall, you may create problems. Hence, if you are insulating on the inside it is a good safety measure to insulate a fieldstone foundation no more than one foot into the ground. If however you want to insulate on the outside, you can go as deep as you want since everything you do will just make that old wall dryer and warmer.

Keywords: Basement, Insulation, Vapour Barrier, Walls

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