Section 322.38. Vapor retarders.

 

(1)   General.

(a) Definition. Under this section, a vapor retarder is a material with no intrinsic thermal or structural properties that has a rating of 1.0 perm or less when tested in accordance with ASTM standard E 96, Procedure A.

(b) Continuity.

1. The vapor retarder shall be continuous. All joints in a vapor retarder consisting of sheet material shall be overlapped 6 inches and taped or sealed, except as provided in subd. 2. Rips, punctures, and voids in the vapor retarder shall be patched with vapor retarder materials and taped or sealed. Seams that are not over a framing member shall be taped or sealed.

2. Taping or sealing a vapor retarder is not required around doors and windows, behind bathtub enclosures, and at top and bottom wall plates, if the retarder is held to those materials in an airtight manner by other building components, such as gypsum wallboard.

(2)   Frame assemblies.

(a) General. Except as provided under par. (c) , all frame walls, frame floors and frame ceilings that comprise the thermal envelope, shall have a vapor retarder installed on the warm-in-winter side of the thermal insulation.

(b) Coverage. The vapor retarder shall cover the exposed insulation and the interior face of the framing.

(c) Exceptions.

1. Where the vapor retarder is omitted, as allowed under subds. 2. to 4. , all sources of air leakage, such as between double top or bottom plates or between double studs, shall be caulked or sealed.

2. No vapor retarder is required in the box sill.

3. No vapor retarder is required where batt insulation is provided with foil or kraft paper backing on the warm-in-winter side and the nailing tabs are tightly fastened to the warm-in-winter face of the framing members.

4. No vapor retarder is required over cavities that have at least 50% of the required R-value provided by spray-applied foam having a perm rating of 1.0 or less, unless required by the foam manufacturer.

5. A vapor retarder for a floor over an open, unheated area may consist of 5/8-inch tongue-and-groove oriented-strand board, or 3/4-inch tongue-and-groove CDX plywood, which is exposure-rated plywood.

(3)   Concrete floors.

(a) Except as allowed under par. (d) , a vapor retarder shall be installed directly under the concrete floor slab or under the base course of concrete floor slabs.

(b) Vapor retarder material shall be at least 6 mils in thickness or shall be a reinforced material.

(c) Joints in the vapor retarder shall be overlapped at least 6 inches and taped or sealed.

(d) A vapor retarder is not required under the slab of an unconditioned attached garage.

(4)   Concrete or masonry basement walls. A non-rigid sheet vapor retarder with a perm rating of 0.1 or less is prohibited in all of the following locations:

(a) On a concrete or masonry wall which is below grade to any extent.

(b) On an insulated frame wall constructed in front of a concrete or masonry wall which is below grade to any extent.

CR 08-043 : cr. Register March 2009 No. 639 , eff. 4-1-09; CR 09-104 : r. (3) (d), renum. (3) (e) to be (3) (d) Register December 2010 No. 660 , eff. 1-1-11; correction in (3) (a) made under s. 13.92 (4) (b) 7. Register December 2010 No. 660 ; CR 15-041 : renum. (1) (b) to (1) (b) 1. and am., cr. (1) (b) 2., am. (2) (c) 4., cr. (2) (c) 5. Register December 2015 No. 720 , eff. 1-1-16.