Sealed Crawl Space - Moisture Trap Or Moisture Barrier?
The idea having a sealed crawl space in your home is interesting. First though, what are we talking about? A crawl space, found in Raleigh NC and many other regions of the country, is the area within the foundation walls between the earth and a house's under-floor framing. Traditionally this area is passively ventilated by screened openings in the foundation wall.
Ventilation has some drawl backs. It lets in moist air, cold air and can let in insects and rodents. These factors are a concern to home owners due to potential for odors, molds, decay, higher energy costs, higher maintenance costs, etc.
A sealed under-house area does not share its air with the outdoors; rather it has a pressure fed duct that is tied to the homes HVAC system. The under-floor areas are not insulated as in a standard crawl space; however the inside perimeter foundation walls are insulated. The earth is covered with a polyethylene barrier that extends up onto the inner foundation wall. This helps keep moisture from emanating from the earth and into the crawl space.
During a home inspection, it is critical to assess the crawl area in Raleigh and other regions. A sealed crawl space can create additional concerns and problems if all components are not installed properly.
The last crawl inspection on new home revealed enough moisture that the floor sheathing, framing and foundation wall insulation were covered with condensation. Unfortunately, mold was present as well. The soil under the poly vapor barrier was very soft and squishy; wet, in other words.
A sealed crawl space with the introduction of moisture ends up acting as a trap since there is no external ventilation. The mixing of the home's HVAC air into the crawl space would never be enough to take care of such excessive moisture.
Some of the problems included gaps between the polyethylene vapor barrier and the foundation wall which allowed moisture to seep from the ground into the "sealed" area. There was likely another source of moisture that could not be readily identified.
A sealed crawl space has many benefits and can contribute to a healthy home as long as the whole "system" is functioning properly.
Clear Choice Home Inspections serving Raleigh NC and other surrounding areas. For more Raleigh NC Home Inspector information, visit our site.
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