Weather-resistive barrier

Required water-resistive barrierR703.2#

Exterior walls must provide the building with a weather-resistant exterior wall envelope. The envelope must include a water-resistive barrier behind the exterior veneer and a means of draining water that enters the assembly to the exterior. Approved materials include No. 15 asphalt felt or other approved materials such as labeled house wraps.

LappingR703.2#

The water-resistive barrier must be applied horizontally, with the upper layer lapped over the lower layer not less than 2 inches. Vertical seams must be lapped not less than 6 inches. Laps are shingled so that water draining down the face of the WRB runs over, never behind, the course below.

Flashing integrationR703.4#

Flashing must be installed to prevent moisture from entering the wall or to redirect moisture to the exterior. Flashing is required at the top of and sides of exterior window and door openings, at intersections of chimneys with frame construction, under and at the ends of masonry and wood copings, above projecting wood trim, at wall and roof intersections, and at built-in gutters.

Window and door integration sequenceR703.4, R703.8#

Pan flashing at window and door sills is required. The WRB and flashing must be lapped so that the sill pan sheds onto the WRB below, the jamb flashing laps over the pan legs, and the head flashing laps over the top of the window nailing flange and tucks behind the WRB above. Sealant is not a substitute for correct shingle sequencing.

PenetrationsR703.2#

Penetrations through the WRB (hose bibs, dryer vents, electrical fixtures, gas line sleeves) must be sealed and flashed to maintain continuous drainage to the exterior. Slit-and-tape details are acceptable when the upper cut is covered by WRB or tape that laps over the penetration flange.

Common inspection flags#

Typical WRB failures caught at siding and final inspection:

• House wrap reverse-lapped with the upper course tucked behind the lower
• No pan flashing under a window, with only caulk at the sill
• Head flashing over a window installed on top of the WRB instead of behind it
• Hose bib and dryer vent cut through the wrap with no sealing tape
• Kickout flashing missing where a roof meets a sidewall above a gutter