Page 234 - Construction Waterproofing Handbook

RESIDENTIAL WATERPROOFING 4.9
For example, siding, and in particular vinyl siding, has become one of the most com-
mon envelope finish systems in both single-family and multifamily construction. Applied
appropriately, the siding acts as a barrier, using ship-lapped design to shed water quickly.
Wood siding and the newer cement-board siding products, while requiring painting, offer
the same protection against water infiltration as does vinyl siding. Questions have arisen
about whether to seal the laps and seams, both vertically and horizontally. In almost every
case the answer is not to seal the seams. Sealing the seams would entrap moisture that does
enter and eliminate the ability of that moisture to escape directly or evaporate. Sealing,
while not necessarily causing water infiltration, might well lead to mold formation on the
substrate and interior areas. In addition, wood siding and wood framing portions of the
structure would be subjected to wood rot if the moisture were entrapped.
The best technique when using siding is to use a plastic or vinyl building wrap applied
to the entire substrate, carefully sealed, and flashed around window and door openings.
Figure 4.2 shows a proper application of building wrap to a residential structure above
grade. This building wrap then can protect against moisture and mold penetrations as well
as minor water infiltration. Again, proper transition detailing at widows and doors when
using building wrap is critical so that the wrap does not act as a negative flashing that

FIGURE 4.2 Building wrap properly applied to a residential
structure above grade.