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408.1 Overlap Vapor Retarder

Francis Vineyard

Francis Vineyard

Registered User
Joined
Jan 1, 2010
Messages
3,105
Location
Charlottesville, VA
In 2006 Virginia amended this section to specifically overlap the vapor retarder but left this out in 2009. Is it specified to overlap the vapor retarder for vented crawl space where installed in the 2009 and 2012 as it does with conditioned crawl and under slabs?

Thanks for your help,

Francis
 
2009 IRC - R408.1 Ventilation. The under-floor space between the bottom of the floor joists and the earth under any building (except space occupied by a basement) shall have ventilation openings through foundation walls or exterior walls. The minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 150 square feet (14 m2) of under-floor space area, unless the ground surface is covered by a Class 1 vapor retarder material. When a Class 1 vapor retarder material is used, the minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 1,500 square feet (140 m2) of under-floor space area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of the building.

2009 IRC - R406.3.2 Below-grade moisture barrier. A 6-mil-thick (0.15 mm) polyethylene film shall be applied over the below-grade portion of exterior foundation walls prior to backfilling. Joints in the polyethylene film shall be lapped 6 inches (152 mm) and sealed with adhesive. The top edge of the polyethylene film shall be bonded to the sheathing to form a seal. Film areas at grade level shall be protected from mechanical damage and exposure by a pressure preservatively treated lumber or plywood strip attached to the wall several inches above finish grade level and extending approximately 9 inches (229 mm) below grade. The joint between the strip and the wall shall be caulked full length prior to fastening the strip to the wall. Other coverings appropriate to the architectural treatment may also be used. The polyethylene film shall extend down to the bottom of the wood footing plate but shall not overlap or extend into the gravel or crushed stone footing.
 
Irregular pieces of plastic cover the crawl space floor; some it barely over laps to where it appears to be butted end to end, but the soil is not visible. At one time it used to be required overlap 6 inches.

Keystone R406.3.2 is the plastic applied outside of wood foundation walls.
 
Gregg that's specific for unvented crawl space. Virginia had it required to be overlap in the last code cycle then left it out. Same in IBC 1203.3: reduced ventilation allowed when floor is covered. The idea that soil can be added so there is no standing water in the crawl and at minimum cover it without the specific language to lap and seal the barrier over the soil for a reduction in passive ventilation opening if that’s what the code allows is absurd IMO. Then again to begin with passive ventilation doesn't work all that great.

Francis
 
Energy code states the same thing. Somebody was snoozing, And it does not make any sense to have removed the verbiage.
 
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