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Crawl space - absent vapor barrier

Joined
Oct 19, 2009
Messages
427
Location
Lincoln
Given:

I am not the AHJ but the designer for this project.
Applicable code: 2012 IRC R408
Contractor/developer wants to have only three large vents for the crawl space where highlighted in orange. None of these are located within 3 feet of the building corners.
Building location is in the most arid climate of Arizona where ground moisture is not a concern.

Question:

I have designed a hybrid solution that shows exposed earth where there will be minimal ventilation. For the corners of the crawl space that do not have vents located within 3 feet of the corners, I have called for vapor barrier to cover the earth - which is what is required for a non-vented crawl space. The contractor insists that nobody uses vapor barrier in crawl spaces because it is not practical / needed in this arid climate. Is that really okay?
 

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  • VaporBarrier.pdf
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Mark K

Platinum Member
Joined
May 12, 2010
Messages
1,815
Vapor barriers in just the corners is a waste of money. Any moisture from the soil will be evenly distributed in the crawl space. I believe the most effective solution is to provide ventilation.
 

north star

Sawhorse
Joined
Oct 19, 2009
Messages
4,062
% ~ % ~ %

Bay Point,


Is there some applicable Code section, or local
Ordinance that would not require the vents to
be located within 3 ft. of the corners ?.......If not,
then install as the Code section requires.........The
contractor does not have a legal position to

override the adopted Codes or Ordinances.

% ~ % ~ %
 

Paul Sweet

Sawhorse
Joined
Oct 17, 2009
Messages
1,601
Location
Richmond, VA
The 2021 IRC section 408.2 has an exception for vents within 3 ft. from corners where the ground is covered with a class 1 vapor retarder and vents are placed to provide cross ventilation.
 
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