Choosing the Right Vapor Retarder for Crawlspace Encapsulation

This post first appeared on the Green Building Advisor Website.

When I first started working in the trades, back in the mid 1990’s, I was working for my brother as an apprentice electrician.  We had an agreement, he would perform any work needed in attics, I got crawlspaces.  Some of the work we were performing was on seasonal cabins that were being updated for use during Minnesota’s cold winter.  These cabins were constructed decades earlier, built very close to the earth.  Sometimes there were even stumps from the trees that were cut down to make room for the cabin that were left under the structure, in the crawlspace.  More than once, I was sure the fire department was going to have to be called to extract me from under one of these cabins.  Most were vented crawlspaces, some you couldn’t tell if they were vented or unvented, and very few had any type of vapor retarder or soil gas mitigation system present.

One of the many crawlspaces I’ve spent time in. This one featured a puddle of raw sewage and unsealed ductwork. This was a vented crawlspace in a very cold climate, no insulation in the floor system or on the crawlspace walls.

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Vapor Control in Walls with Continuous Insulation-IRC Chapter 7 vs Chapter 11

This article first appeared in the January/February 2024 issue of the Journal of Light Construction.  www.jlconline.com

The International Residential Building Code is supposed to provide clarity into how builders construct homes.  In the IRC’s own words, The IRC was created to serve as a complete, comprehensive code regulating the construction of single-family houses, two-family houses (duplexes) and buildings consisting of three or more townhouse units.”  Usually, the codes do a decent job giving us options on how we should build homes with the occupant’s safety and health as our number one priority.  Codes also address energy efficiency and building durability.  Sometimes though, codes can be quite confusing.  How we handle vapor retarders when using continuous insulation is one of those areas.

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