We hear it all the time, “my basement is wet/damp/musty in the spring and summer – but that’s alright, it’s supposed to be like that. We just run the dehumidifier for 6 months straight and empty it once or twice a day.” When a basement/crawlspace has high moisture, so does the rest of the house. The natural path for air to move throughout a home is up, which means that too is the natural path for moisture. This can lead to condensation on windows, mold/milder on surfaces, and overall sub par indoor air quality.
Original existing ground cover over a dirt floor - unsealed and ineffective
If your home has standing water in the basement or is built over ledge,then maybe there is nothing you can do other than exterior grade and drainage work…but for many there are alternative solutions. This Post addresses decreasing moisture content in basements/crawlspaces with exposed dirt floors.
Even if your basement/crawlspace is bone dry and you have an exposed dirt floor, you should still install ground cover. Why? although
Tools of the Trade
moisture may not be a concern, other gases could be. In the northeast Radon is an issue, and if your Radon level is not that high but you still want to reduce it, this solution is much less money than installing a Radon Remediation system.
Many home already have a vapor barrier/poly laid out over exposed dirt; HOWEVER, it is not sealed at the seams or the edges near the foundation wall. Vapor is like air and water, it will find a way out unless sealed tightly!
The Solution: At the least, use
Sealed Ground Cover over a dirt floor - Vapor Tight
*6 mil poly sheets (any hardware store). Cut sections to cover the exposed area(s) and leave enough excess to run up the foundation wall an extra 8-12″. If you have to overlap sections of poly we like to have at least a 2-4′ overlap. Purchase enough strapping (1×3″ sections) to run around the perimeter of the exposed area. Lay out your first section of poly on the ground and run up the foundation walls approximately 8-12″. **Sandwich the poly sheet between the foundation wall and strapping and adhere strapping to wall (anywhere from 3-6″ up from the bottom of the floor) – we like to use 22 caliber concrete nail shots but you could also use concrete screws. Continue this process around the entire perimeter of the foundation wall making sure that the pieces of strapping abut seamlessly creating no gaps for vapor to escape through (3 shots per 8′ section of strapping should suffice).
If you have to overlap sections of poly, make absolutely
Seal around all protusions with ground cover and quality tape
sure that you thoroughly tape the seams with high quality building tape. We like to use Dow tape used for rigid board insulation and we usually apply 2 sections of tape per seam.
If done properly, you can usually feel the improved air quality within 15-30 minutes. The air will feel dryer and the smell will be cleaner.
*If your basement has crushed stone on the floor, is used for storage, or has high traffic – you may want to use reinforced poly as it will hold up better to wear and tear.
**If your foundation wall is stone or not a flat enough surface to get a
The complete package: ground cover fully sealed at all edges and seams - spray foam applied to perimeter joist - non condensing moisture management system
tight seal with just strapping against the poly, you may need to first adhere sections of 2×4″ to the foundation wall and then install low expanding closed cell foam where there are gaps between the 2×4″ and foundation wall. Then you can sandwich the poly between the strapping and 2×4″ with screws.
