Reply
Relevant IRC provisions are:
[edit] IRC provisions
[edit] for above grade
N1102.5 IRC 2006: Moisture control. The building design shall not create conditions of accelerated deterioration from moisture condensation. Above-grade frame walls, floors and ceilings not ventilated to allow moisture to escape shall be provided with an approved vapor retarder. The vapor retarder shall be installed on the warm-in-winter side of the thermal insulation
NOTE: *above-grade*
[edit] exterior vapor barrier
COPIED SECTION IRC 2003;
R406.1 Concrete and masonry foundation dampproofing. Except where required to be waterproofed by Section R406.2, foundation walls that retain earth and enclose habitable or us- able spaces located below grade shall be dampproofed from the top of the footing to the finished grade. Masonry walls shall have not less than 3/8 inch (9.5 mm) portland cement parging applied to the exterior of the wall. The parging shall be damp- proofed with a bituminous coating, 3 pounds per square yard (1.63 kg/m2) of acrylic modified cement, 1/8-inch (3.2 mm) coat of surface-bonding mortar complying with ASTM C 887 or anymaterial permitted for waterproofing in SectionR406.2. Concrete walls shall be dampproofed by applying any one of the above listed dampproofing materials or any one of the wa- terproofingmaterials listed in Section R406.2 to the exterior of the wall. R406.2 Concrete and masonry foundation waterproofing. In areaswhere a highwater table or other severe soil-water con- ditions are known to exist, exterior foundationwalls that retain earth and enclose habitable or usable spaces located below grade shall be waterproofed with a membrane extending from the top of the footing to the finished grade. Themembrane shall consist of 2-ply hot-mopped felts, 55 pound (25 kg) roll roof- ing, 6-mil (0.15 mm) polyvinyl chloride, 6-mil (0.15 mm) polyethylene or 40-mil (1 mm) polymer-modified asphalt. The joints in themembrane shall be lapped and sealed with an adhe- sive compatible with the waterproofing membrane.
COMMENT: The above is required for a basement all being considered a vapor barrier on the outside. Then installing a second vapor barrier inside would be trapping moisture between the two vapor barriers breeding mold in that trapped area.
[edit] vapor barrier
IRC § 322.1: Moisture Vapor Retarders/Moisture Control. In all framed walls, floors, roofs, and ceilings making up the building thermal envelope, a vapor retarder must be installed on the warm-in-winter side of the insulation, unless the framed area is ventilated to allow moisture to escape. (Vapor retarders are designed to prevent the movement of moisture-laden air from the warm side of the wall to the cool side. In temperate climates, vapor retarders are placed on the interior (warm in winter) side of the wall cavity; in hot, humid climates, they are placed on the exterior (warm) side of the wall cavity. According to the Asthma Regional Coordinating Council of New England, walls should be designed to dry to both the interior and the exterior and basements should be designed to dry to the interior. Installing vapor barriers interferes with the ability of walls to dry in both directions, so their use should be limited to severely cold climates. Paper-faced cavity insulation should be used in place of plastic interior vapor barriers.)
