The importance of using vapour barrier in a crawlspace.

One of the most misunderstood areas of the home is the crawlspace.  There has been disagreement on several parts of the crawlspace for decades. The big questions are;  do you heat the area or keep it at the outside temperature, should the walls be insulated and vapour barrier applied, and do you need to have any vapour barrier on the floor.  One thing is for sure, if you don’t do it right you could end up with a result like the one shown.

First of all if heat is present in the crawl space you will need to try your best to separate the heat from the cold. When the heat and cold come into direct contact with each other frost develops as you can see in this picture. When it warms up outside the frost melts and the wood becomes damp. Before you know it the framing/skirting is rotted and mouldy. The best prevention for this is to insulate and vapour barrier the walls. The vapour barrier stops the transfer of moisture and the insulation slows down the heat transfer. The result is a more comfortable and healthy home, not to mention a solid foundation.

If the home is for seasonal use and the crawlspace is not heated then you don’t need to insulate the skirting walls. But you still should put down vapour barrier on the soil so the ground moisture does not enter the crawlspace. I often see crawlspaces with very damp soil. It is crucial that this soil moisture be kept out of the crawlspace. Therefore you need to lay a sheet of 6mm poly over the soil and seal it around all the edges as much as possible.  With the advent of the spray foam industry we now can insulate and vapour barrier in one application. A few inches of foam will make a tremendous difference in the comfort of your home or summer cabin. There is much more to be said about crawlspaces but little space to say it. Feel free to call us for more on this and other topics.


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