Homes that are built with raised floor construction are prone to becoming damaged with moisture, rot and mildew. Unpleasant odors permeating the building interior from beneath may be a symptom of a crawlspace gone bad.
Coding usually requires only perimeter wall venting for the purpose of keeping the crawlspace dry. In cases of dampness where hot, humid outside air enters the vents and condenses when it touches cold earth or the underside of air-conditioned floors, these vents add to the problem. Sealing the space becomes the best solution.
Before closing up the crawlspace, condition it and dry it out first. Spray the frame with a borate water solution that will sanitize it, kill bugs and mildew, while not harming humans and animals. Remove, repair or replace any rotten wood. Cover the ground with temporary poly sheeting and run dehumidifiers to dry out the space thoroughly.
Once the area is completely dry, build a conditioned crawlspace:
- install a continuous vapor barrier of 12 millimeter poly sheeting sealed with waterproof mastic
- screw foam insulation to foundation walls, minimum of R-11 and fire-rated
- add an interior floor drain with backflow preventer sealed to the vapor barrier and attached to exterior perimeter foundation drains to keep outside rain and ground water out of the space and drain any leaking crawlspace water sources
- air-seal with caulk, adhesive, air-sealing foam, gaskets or adhesive membranes any exterior entry doors; joints between the top of the foundation wall and the mud sill, between the mud sill and the rim joist and between the rim joist and the sub-floor; around ducts, pipe conduits and any penetrations through the wall or rim joist
- attach a small fan and duct to the underside of the first floor to bring conditioned air through the crawlspace at a rate not less than 1 cfm per 50 square feet of horizontal floor area. Get professional help in the case of radon mitigation systems.
In effect, the crawlspace becomes a mini-basement and keeps the underside of the building healthy. Conditioned crawlspaces are not recommended for areas that are in designated flood zones, or in marine climates without an installed air handler or return ducts.
You may want to add a humidity sensor like Smart Home Products Z-Wave Temperature/Humidity Sensor, or the Meade Humidity Sensor soon to be available on Amazon, to alert you if a new humidity problem occurs beneath the building. See the article below on the new moisture sensor chip developed by Cornell University that connects via wifi and can log moisture changes and send real time feedback. It was designed to be installed in grapevines to record plant moisture but works in concrete curing and should work in crawlspaces as well.
For more information, view the crawlspaces website and watch the attached video for an example of one company encapsulating a crawlspace. For help in the Greenville, South Carolina area, contact a company like Foothills CrawlSpace at 866.546.6301, Falcone Crawl Space & Structural Repair at 866.651.8989, or All-Dry of the Carolinas Basement Systems at 855.808.7083.