Crawlspaces and Basements

Nearly every home in Vermont is built with a basement or a crawlspace. Even homes on slabs require a frost-wall foundation due to the heavy and prolonged freeze we enjoy in this climate.

Crawlspaces

Crawlspaces require special attention because there is often just a bare earth floor, from which moisture rises. There has been some argument in recent years about whether the crawlspace should be part of the conditioned building envelope. We believe that, in our climate, that they should be considered a part of the living space, and sealed and insulated accordingly.

The procedure we use to retrofit these areas is as follows:

  • Cover earthen floor with 6 mill polyethylene air / vapor barrier and seal all joints.
  • Foam seal the floor barrier to the foundation wall.
  • Foam seal the rim joist to the base of the foundation.
  • Seal all penetrations through the foundation wall.
  • Seal any ducts that run through the crawlspace and insulate.
  • Seal plumbing, electrical and ventilation chases that enter the living space. This is to reduce insect and rodent infiltration.
  • Do not insulate the floor joists above the crawlspace.

Basements

As with crawlspaces, basements are often damp and drafty. To help prevent this condition, we seal the rim joist around the entire perimeter with foam sealant to about 6 inches below the top of the foundation. We also seal any penetrations through the foundation walls, such as dryer vents, service entrances for gas, water, electric, etc. The floor joists should not be insulated.

We are careful to ensure that there is an adequate supply of air for combustion appliances like dryers, furnaces and water heaters. The ideal arrangement is to use direct vent, or sealed combustion, appliances. These draw air from outdoors, and are not susceptible to backdrafting the way conventional appliances are. In this situation, it is desirable to have a slight negative pressure in the basement to help prevent soil gases from entering.

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