Last week, in Unvented Crawl Spaces, we looked at the six major components of good crawl space design.
This week we are going to look at the code section for closed crawl spaces and one process for approaching a closed crawl space using closed cell foam.
Here is the IRC code section regarding unvented crawl spaces:
When creating these designs, make sure you coordinate with the appropriate code department to confirm that your design meets the local code requirements.
Note that the building code only contains minimum requirements for this application and does not have specific guidelines for how the unvented crawl space assembly is created or sequencing of the process.
Let’s look at one process for approaching a closed crawl space, as it relates to spray foam insulation. Once all other crawl space work is complete, this process can be used:
- Install permanent ground vapor retarder material, such as 6-mil poly or greater, lapping the vapor retarder up the perimeter wall and any pylons at least 12 inches
- Secure the vapor retarder as desired and seal the vapor retarder with tape and mastic
- Insulate the interior perimeter wall with closed cell spray foam insulation, to appropriate thickness to achieve desired R-value, overlapping the vapor retarder by at least 6 inches
- Leave a minimum 3” termite inspection band between the top of the foam insulation and the top of the stem wall
- Leave a minimum 3” wicking gap between the bottom of the foam insulation and the crawl space floor
- Apply thermal barrier or ignition barrier, if necessary
This is an example of how to approach a crawl space with interior perimeter wall insulation. Remember, you have other insulation options including closed cell foam insulation installed on the exterior of the perimeter wall or either open cell or closed cell installed to the underside of the sub-floor.
Stay tuned next week as we continue to discuss the interesting world of spray foam insulation.
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