"Understanding Your Home" by Building Inspector Mark Visser
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Ventilation
The crawl space should be well ventilated to prevent moisture and/or condensation from entering the floor structure.
No ventilation is required if the crawl space opens into a full basement.

These vents should be closed, sealed and insulated during the heating season.
The crawl spave vent shown to the right is the same size as a cement block and has a screen to keep out insects.

Crawl space ventilation


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Crawl Space Ventilation
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Crawl space ventilation. Unheated crawl space. Heated crawl space.

Unheated crawl space. Adequate ventilation should be provided. Insulate water pipes, heating and cooling ducts and ceiling above (main floor). Floors insulated with glass fibre batts should have a vapour barrier on the heated side of the floor.
Heated crawl space. No ventilation is required if the crawl space opens into a full basement. Heat is radiated from uninsulated water pipes and heating ducts. Exterior walls and joist header space should be insulated and covered with a vapour barrier to prevent heat loss in this area.
Exposed dirt floors should be covered with a vapour barrier. If there is a moisture problem, vents should be installed for proper ventilation. These vents should be closed, sealed and insulated during the heating season. Inadequate crawl space ventilation will lead to mildew and eventually, wood rot.
Exposed dirt floor and vapour barrier. Moisture, directly or indirectly, causes more problems in buildings than any other single cause. Moisture can enter the house in many ways. An exposed dirt floor in the craw space could be the cause for high moisture levels in the house.
Exposed dirt floors should have a 6 mil (0.15 mm) polyethylene cover to trap this moisture. Joints should overlap by 6" (150 mm) and be weighted down. If there is any traffic in the crawl space, 2" (50 mm) of sand should be installed to protect the barrier.






8"x16" Crawl space vent is the same
size as a cement block.
It provides
46 sq.in.of ventilation

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