Cambridge Builders Website

Some of our new houses now feature sealed crawlspaces.

How it’s done:

·    There are no foundation vents installed in the foundation walls.

·    A vapor barrier is installed in the crawlspace.  Unlike a traditional vapor barrier which is supposed to cover 80-90% of the ground inside the crawlspace, in a sealed crawlspace design, the vapor barrier covers 100% of the ground, it is extended up the outside foundation walls and all of the joints in the vapor barrier are sealed.  A 3-4 inch space at the top of the foundation walls is left exposed so that proper termite inspections can be performed.

·    Instead of insulating the floor system of the house, the outside foundation walls are insulated with a foam board.  Again, a 3-4 inch space at the top of the foundation walls is left exposed so that proper termite inspections can be performed.

·    The wood band around the exterior of the floor system framing may be insulated but doing so is not required.

·    A small amount of conditioned air (1 small duct) from the HVAC system is blown into the crawlspace.  A return air duct is not required because of the air that is normally exchanged with the house.

Benefits of a Sealed Crawlspace:

·    Much lower moisture levels in the crawlspace.  This greatly reduces mold growth and the chances of and wood rot.  This also makes it more difficult for insects to live and reproduce in the crawlspace.

·    Because some air is inevitably exchanged between the crawl space and the first floor of the house, reducing the amount of mold in the crawlspace improves the air quality inside the house.  Almost every traditional crawlspace contains some mold.

·    Energy efficiency is significantly increased for several reasons:

·    Typical fiberglass batt insulation only functions at its full potential when it is enclosed on all six sides to prevent air from moving through the insulation.  Insulated floors are never enclosed on the bottom.  Insulating the perimeter foundation walls eliminates the need for fiberglass batt insulation in the floor system.

·    The HVAC ducts in the crawl space are in a conditioned air space instead of an unconditioned air space.  Even though the ducts are insulated, they still loose heat in the winter and gain heat in the summer when they are in an unconditioned space.

·    There is less thermal impact from air exchange between the crawlspace and the first floor of the house because the air that is exchanged with the crawlspace is now conditioned.

·    Floors stay warmer in the winter.

Note:  The first house with a sealed crawlspace that we sold was inspected in April 2007 by a home inspector hired by the buyers.  The home inspector stated that he had inspected approximately 7 houses over the previous 2 days and the moisture content of the wood in those crawlspaces ranged from 12-15%.  He determined that the moisture content of the wood in the house with the sealed crawlspace was 8% on the day he inspected it.