crawlspace3 good crawlspace2

If your house was built with a crawlspace then the area under your house is not all too different from a bear cave. It’s a dirty, dark, smelly space with various bugs and animals living in it. Because of these conditions the majority of us don’t even consider the crawlspace as part of our house.  The reality is that your crawlspace is an integral component to the heating, cooling, comfort and indoor air quality of your home. Lets take a closer look at whats happening in the crawlspace and how these conditions play a role in what happens inside our homes. 


Moisture is one of the common issues where the vented crawlspace is left vulnerable. There are a variety of avenues for moisture to enter the crawlspace where over time it will invite mold and insects and eventually giving way to a compromise of the structural integrity and the indoor air quality of the home. The first pathway for moisture to move into the crawlspace is through the exposed dirt surface at the floor of the crawlspace. As the the ground around the house retains moisture from rainfall the moisture content of the soil in the crawlspace will also increase raising the overall humidity level of the air in the crawlspace. The summer months of the year means increased air temperature which has a greater capacity for holding moisture. Opening foundation vents is meant to alleviate excessive moisture build up in the crawlspace with cross-ventilation, however, this is an inevitable backfire because as the warm air moves through the crawlspace the moisture in the air will then condensate on cooler surfaces like water lines, duct work, wood framing, insulation and foundation walls. Moisture will also move through block walls looking to dry out. Just like hot moves to cold, wet moves to dry. 



The classic vented crawlspace is typically insulated at the ceiling with fiberglass batt insulation. One of the pitfalls to insulating with fiberglass batts in the ceiling is the exposure to moisture. Over time moisture will permeate the fibers and tiny air gaps; the very system it depends on to act as insulation. As the insulation becomes more and more water logged in becomes less and less effective and eventually pulls away from the sub-floor above and falls out of the joist cavity. 

The conditioned air in our homes naturally rises as it is heated leaving cooler air at the floor. Couple this with the void of any heat in the crawlspace or air sealing around penetrations from the crawlspace into the living space and we have even more cool air being drawn to the floor of our living space. 


So how do we keep moisture out of the crawlspace and keep our floors warmer while increasing the efficiency of our homes? The solution is simple. 

1-Make sure the grading around the house is moving bulk moisture away from the foundation. 

2-Run all downspouts at least five feet away from the foundation. 

3-Install a 6 mil (12 mil is ideal) poly vapor barrier on the crawlspace floor and seal it at the walls, peers and seams. 

4-Seal off foundation vents. 

5-Provide a HVAC supply vent in the crawlspace and create a return path to the unit. 

6-Insulate the walls and rim joist of the crawlspace with a monolithic application of closed cell spray foam insulation. Install at a depth of 2 inches.

-For homes with high moisture levels or flooding a sump pump and/or a dehumidifier should be included.