Hey, Captain Crawl Space, What is the benefit of sealing the crawl space?
– Mike D. from Lee Hall
Old Crawl Space Thinking:
Dirt floors add moisture to the house-
So, vents were added to allow moisture to escape- or at least that was the plan. Instead, reality is that in the winter, the vents let cold air in. So builders tried to insulate the floor to keep the cold out. Still, the floors are cold. The cold air in the crawl space cools the warm air ducts leading to higher heating bills and inefficiencies.
In the summer, the vents let warm humid air in. The lower temperature crawl space cools the entering warm air and causes the Relative Humidity to go way up. This causes condensation to form on everything in the crawl space, mold grows on the floor joists and wood rot begins. Often, wet, heavy fiberglass insulation sags due to weight and gravity and falls to the floor. In the summer and winter, warm air moves upwards- this draws damp (moldy and smelly) air from the crawl space upstairs. Mold, wood rot, and poor energy performance are very common from Va. Beach to Richmond.
Clearly, the old way did not work.
New Crawl Space Thinking:
1) Fix groundwater seepage (if necessary) with a sump pump and drain lines.
2) Seal off the earth completely with a strong vapor barrier.
3) Seal Vents and other outside air leaks.
4) Insulate crawl space walls to prevent cold air from entering through porous block.
5) Dehumidify the air.
The result is lower humidity and any HVAC unit or duct work in the crawl space is now part of the conditioned living space. This makes the air system more efficient, and mold and rot conditions have been remediation.