Updates on Wisconsin's Uniform Dwelling Code

Questions and Answers about Wisconsin's Uniform Dwelling Code
See Comm 20-25 online

Comm 22.38(3)(d) - Edges of the vapor retarder shall extend up the edges of the slab at least to the top of the slab.
Question:  Do I need to extend my vapor retarder up the edges to the top of the floor slab in every case?

Answer (Dec. 1, 2009):  No.  The vapor retarder shall be provided beneath the entire concrete floor slab, but need not extend up the edge to the top of the slab provided the floor slab is cast over a code-complying footing and is tight against the wall the footing is supporting or, if it is not poured over the footing, is cast tight against the concrete footing itself.

A concern has been expressed that the code requirement placing the vapor retarder between the edge of the slab and the wall or footing could create an open joint that could be a route for bulk moisture to migrate from the sub-grade into the building interior. The foundation which the floor slab extends over, or is cast against, provides an equivalent degree of protection from the propagation of moisture in the soil beneath the foundation that a vapor retarder alone would provide.

Note:  This Q&A is for a concrete floor slab cast against concrete walls or footings.  Concrete floor slabs cast against wood foundations shall have a vapor retarder installed in accordance with the adopted installation standard ANSI/AF&PA PWF specified in Table 21.24-2.