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Crawlspace Insulation - What is the Best Method?

Updated on December 20, 2012

Crawlspaces are usually the last place you would ever think of trying to insulate, but they are actually one of the most under insulated and air sealed areas of a home.  There are a lot of different methods used to insulate crawlspaces.  I will stick to the most efficient methods and practices for efficiency and moisture control.

Heated Crawlspace

Heated crawlspaces are the preferred variety because it takes less material and it allows you the ability to control the moisture in the crawlspace by making it part of the conditioned space.  In order to heat a crawlspace, very little is needed.  If you have duct work or hot water lines that are uninsulated, chances are you are heating your crawlspace already.  keeping the heat in is a different story.

The only insulation material that is acceptable for crawlspaces in closed cell polyurethane spray foam insulation.  The main reason for this is it's water resistant characteristics.  The general method of preparing the crawlspace starts with the floor, which is probably dirt or gravel.  Laying 6 mil poly vapor barrier down on the ground will keep the moisture under the vapor barrier.  Running the vapor barrier 1/3 of the the way up the walls and overlapping seams by a foot will ensure that all areas are covered.  By using the polyurethane spray foam to seal the vapor barrier to the wall you are creating a continuous seal that allows no moisture in the crawlspace.  There should be 3 inches on the walls and box sills and all seams should be sprayed as well with a flash coat after they have been taped. 

If you do not have duct work or hot water pipes that run through the crawlspace, you will want to add a few light bulbs.  Each light bulb gives off around 1200 BTU/HR of heat.  That will be sufficient enough to keep the space a nominal temperature. 

Unheated Crawlspace

This method insulated the floor joist spaces rather than the walls. Although this method works fine,  it is not recommended for a few reasons.  If plumbing or wire repairs ever have to be done, it is a big mess.  Also, if cable wires are spray foamed they may not work properly.  This happened to me a few times and it is not fun to trouble shoot.  The biggest reason not to perform this method is you cannot properly control the moisture making this a possibly unhealthy situation.  Closed cell spray foam is still the only material that is acceptable for crawlspaces.  Fiberglass cannot be used and cellulose is not a very good application.

If you are unsure about what types of energy improvement to do on your home or have questions about other methods, please hire an energy consultant.  They will walk you through the process of showing you the energy improvements that will work for your family and budget.  Depending on what state you live in, there may be rebates available also.


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      RMICorporation 7 years ago

      Do not forget to include your intumesent coating, as most spray foams cannot be left exposed.