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By: Jasna Aleksandrova

In our last of our crawlspace series of blogs we’re going to talk about retrofitting sealed crawlspaces.

Sealed crawl spaces proved that they outperform naturally vented crawl spaces with vent openings usually on opposite sides of the crawl space wall. This outperforming over the vented crawl space usually counts for better energy efficiency and better moisture control. New building strategies always imply that the crawl space should be sealed and this is the reason why almost every new home usually is build with the sealed crawl space. Aside of this rule are homes in the areas where floods are common and they need to be build with vented crawl space with larger opening in the walls. Although sealed crawl spaces are better performers in terms of energy efficiency and moisture control, if they are not constructed and insulated properly when firstly build, then they are potential problem maker if earth gases like radon and methane exist in the soil, and also again, there are possibilities of moisture problem. Problems with earth gases and moisture will affect the quality of the air in the whole house, especially on the ground floor. If this is the case then although maybe relatively new build the sealed crawl space needs serious retrofitting.

Retrofitting for moisture problem

Every time when retrofitting is necessary, before the beginning to take these retrofitting actions, a good retrofitting strategy is needed. If the problem is moisture then firstly must be determined the source of the moisture. The reasons can be several like problems with the drainage system of the roof, or miscalculated slope angle around the house, or maybe high water table level around the house. After realizing the source of the problem corrective actions can be done. Cleaning the gutters and directing the downspouts away from the foundation of the house if the problem is drainage of the roof. Then, if the problem is miscalculated slope angle, making a steeper angle of the slope around the house to prevent water building up around the foundation should be done. High water table level sometimes requires placing the insulation on the exterior of the crawl space, and after excavating the foundation also installing new foundation insulation for moisture protection, and installing drainage system for the foundation.

Retrofitting for humidity and soil gas problem

When the problem in the crawl space is humidity, or gases form the soil like radon and methane then different retrofitting actions should be done. First action is to install thick insulation on the interior walls of the crawl space. This is necessary if insulation is not placed on the exterior of the crawl space. For preventing gases like radon and methane to enter the house perforated plastic pipes should be installed in the ground of the crawl space and directed outside. Then the ground should be layered with thick polystyrene insulation boards. This insulation should be fitted on the rim joist area which supports the ground floor of the house, and also on the crawl space side of the ground floor, which is the ceiling of the crawl space. After installing the insulation the floor of the crawl space, the walls and the ceiling, then everything should be sealed with polyethylene plastic, minimum 6 millimeters thick. For best performance the plastic should be taped at seems and sealed on the walls and ceiling of the crawl space. By doing this retrofitting actions the sealed crawl space will remain warm, and humidity and gas free.

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