Accepted Answer

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If a crawlspace is vented, it is ideal to treat it as an outdoor space (no different than an attic space), and insulate the floor between the crawlspace and living space. If you have heating/ cooling and water pipes running thru the crawlspace then you have a conflict and it has to be treated as an indoor space; in this case you would not insulate the floor, but insulate the perimeter of the foundation and not vent it.

 

I would insulate the floor with batt insulation and then a layer of 2" rigid insulation should be applied to the bottom of the floor joists with all joints taped and sealed with spray foam. This provides an air and thermal barrier between the crawlspace and the house above. The batt insulation by itself, is only acting as a filter since moisture can still migrate thru it; and it will do this all by itself because humidity in the air is always trying to balance itself out; and it will migrate from crawlspace to house with no problem, without the rigid insulation.

 

If the crawlspace has soil for the floor and is vented then lay one layer, on the soil, of 6 mil polyethylene vapor barrier with all joints overlapped 6-12 inches; no need to tape joints. Run poly up concrete sidewalls, but no need to seal, just secure to hold it in place. If it is not vented, the polyethylene joints need to be taped and sealed to the concrete sidewalls.

 

 

If you need further help or clarification on this answer, please do not hesitate to reply to this post.

 

Thanks for asking your question at Just Answer.

Best of Luck, Brian

 

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Expert:	Brian
Pos. Feedback:	99.2 %
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Answered:	11/2/2009

Architect

Licensed Architect- 12 years, L.E.E.D. AP, Former Remodeling Contractor- 10 years