![]() ![]() Using a cold-side vapor barrier would almost guarantee moisture condensation in the insulation in winter - a very undesirable condition that reduces the effectiveness of the insulation and is just asking for a mold contamination problem. at or above 33-percent relative humidity (RH) will have a higher vapor pressure than crawlspace air at 40 degF and 90-pecent relative humidity (RH), and moisture will tend to move, if at all, from the warmer house to the cooler crawlspace. Since warm air holds more moisture than cold air, warmer air generally has the higher vapor pressure.įor example, air at 68 degF. First, remember that moisture moves from a point of high vapor pressure to a point of low vapor pressure. Moisture migration and relative humidity remain two of the least-understood topics builders face. John Mascaro, Mascaro Construction, Philadelphia PA In the winter, when the house is hot and dry, it seems the vapor barrier should be on the cold side of the insulation. If you place a vapor barrier on the warm side of the insulation between a heated area and an unheated crawlspace, will moisture from the crawlspace migrate into the insulation and condense? The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss. I could reach out and literally grab and crush rotted floor joist bottoms by the handful. I have observed extreme strucutral damage from rot in a clean looking crawl space sporting a nice concrete rat slab but where a poly vapor barrier stapled to the joist bottoms trapped and accumulated moisture, finally water, in the floor structure. Wet insulation means lost insulation value, risk of mold contamianation, and in some cases structural damage from rot or wood destroying insects. The photo at left shows what can happen when a vapor barrier is placed on the cold side of a building floor - in this case over a damp or wet crawl space or basement. If the crawl area is actually wet from surface runoff, roof spillage, ground water, or plumbing leaks, the amount of water pumped into the home can be much larger and more harmful. Carson Dunlop's comment that a dirt crawl can contribute several gallons of moisture per day into a home is the best case. ![]() Our page top sketch showing the effects of covering a dirt floor in a crawl space is courtesy of Carson Dunlop Associates (found at page bottom, Click to Show or Hide). Crawl Space Ground Covers to Help Control Crawl Space Moisture ![]() We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. Which way does the insulation vapor barrier or kraft paper go over a basement or crawl space: facing up (towards the floor above) or facing down (towards the crawl space or basement floor)? This article discusses the proper location and placement of moisture barriers or vapor barriers in crawl spaces to crawl space moisture.ĭoes the vapor barrier go "up" towards the warm side or underside of the floor above, or does the vapor barrier go "down" facing the crawl space or basement interior?Īnd what difference does proper crawl space moisture barrier placement make to overall building moisture problems? We have no relationship with advertisers, products, or services discussed at this website. InspectAPedia tolerates no conflicts of interest.
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