It's pretty basic building science that moisture is not a good thing. The combination of wood and water can lead to not only structural issues, but health problems as well.
Minimizing moisture is a key part of durability. The crawl space is only one part of the house where moisture is a concern, but it is the most obvious.
Since 2008 John Marshall Custom Homes has been installing sealed and conditioned crawl spaces on all of our new homes (except those on basement foundations, of course). While nothing is an absolute guarantee that a home will not be subjected to moisture, using sealed and conditioned crawl spaces greatly reduces the opportunities for moisture - and mold - to occur.
The photo above shows the foundation of a new home we are building at 631 James Alexander Way in Davidson, NC. The preliminary stages of the sealed and conditioned crawl space have been installed, including insulation around the foundation walls, and a vapor barrier on the ground and piers. The vapor barrier that is presently installed is a 6-mil temporary barrier which will be replaced by the final 20-mil vapor barrier towards the end of construction.
Later, the wood framing band that sits on top of the foundation walls will have spray foam insulation applied. This type of insulation provides not only insulating properties but also a tight seal against air infiltration. A conditioned air duct will also be run to the crawl space.
To constantly monitor the humidity levels in the crawl space, we will install a humidity sensor in the crawl space and put the display in a prominent location in the house. We also educate the homeowner about the importance of moisture control, and steps to take if the humidity in the crawl space is outside of a desired range.
We've built many homes with typical vented crawl spaces, and have not had issues with them. But, the sealed and conditioned crawl space provides many benefits, and at John Marshall Custom Homes we have decided they are well worth the investment.
Framing on this LEED-certified home starts on August 16. Please check back soon for further updates as the house starts to take shape.
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