Creating the Perfect Crawlspace

The best way to design a crawlspace that accentuates your building envelope and does not allow unwanted moisture into the home is to treat them as if they were miniature basement2013.08.08.Blog_Crawlspaces spaces. Crawlspaces should be insulated, sealed and all exposed masonry should be covered to prevent condensation.

From the US Department of Energy: “Most building codes require vents to aid in removing moisture from the crawl space. However, many building professionals now recognize that building an unventilated crawl space (or closing vents after the crawl space dries out following construction) is the best option in homes using proper moisture control and exterior drainage techniques.

If you have or will have an unventilated crawl space, the best approach is to seal and insulate the foundation walls rather than the floor between the crawl space and the house. This strategy has the advantage of keeping piping and ductwork within the conditioned volume of the house so these building components don’t require insulation for energy efficiency or protection against freezing. The downside of this strategy is that rodents, pests or water can damage the insulation, and the crawl space must be built airtight and the air barrier maintained.”

Seal crawlspaces with a vapor barrier along the floor and walls that is at least 6-mil or more. This will prevent moisture from entering the home, termites from gaining access to lumber and soil gases from leaching into the flooring system. Attach the vapor barrier mechanically at the edges and seal all seams with tape. Consider installing a thin 2-3 inch concrete slab over the vapor barrier for increased insulation.

Where crawlspaces are below grade, they must have perimeter footing drains to move moisture away from the home. All crawlspaces should provide adequate drainage for any floods or plumbing issues that may be experienced. Always ensure that the grade slopes away from the foundations.

Crawlspaces can be conditioned or vented. Vented crawlspaces allow air to move through, but care must be taken with the design to ensure that moisture and water is kept out.

Conditioned crawlspaces must be included as part of the homes heating and cooling systems so that they stay dry and maintain the same temperature as the house. This would mean heating and AC for extra cubic space and possibly larger equipment to handle it. Conditioned crawlspaces also need to be vented through pipes and require a blower fan to circulate air.

In homes where radon is a hazard, you can vent your crawlspace with perforated plastic piping in the gravel under the vapor barrier. Run the piping up through the roof to ensure that the radon is safely vented. You can also control radon by installing a passive radon system in the crawlspace floor.

If your crawlspace has been exposed to moisture during the construction process, it will need temporary dehumidification. Never utilize your crawlspaces as storage and regularly check that crawlspace perimeters are secure in order to prevent animals, moisture and insects from entering.

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