What are the standard ice and water shield measurements?
Short answer. The key measurements are a roll width of about 36 inches, coverage of roughly 200 square feet per roll on many products, side laps of about 3 to 3.5 inches and end laps of 6 inches, a full sheet centered in valleys for 18 inches on each side, and, where an eave ice barrier is required, coverage to at least 24 inches inside the exterior wall line.
Rolls
- Width: about 36 inches.
- Length: commonly about 65 to 75 feet, though smaller rolls exist.
- Coverage: commonly about 195 to 225 square feet per roll before laps.
Laps
- Side laps: about 3 to 3.5 inches along the long edges, often marked by a selvage or printed line.
- End laps: about 6 inches where rolls meet, staggered between rows.
- Underlayment onto membrane: the regular underlayment laps over the membrane's top edge.
Eaves
Where the local code requires an eave ice barrier, it runs from the roof edge to at least 24 inches inside the exterior wall line. Measured up the slope with an overhang, that often takes two rows. Many Georgia jurisdictions do not require it, so check with your building department.
Valleys
One 36 inch sheet centered in the valley gives about 18 inches up each slope. Valleys are measured along their true diagonal length.
Walls and penetrations
- Roof-to-wall joints: a strip on the deck with several inches turned up the wall behind the siding or house wrap.
- Pipes: a square large enough to extend well beyond the pipe boot flange on all sides.
- Chimneys and skylights: membrane on the deck around the full perimeter, turned up the sides per the flashing details.
Conditions
Many products list a minimum application temperature in the 40s, and exposure limits commonly range from about 30 to 120 days. More in ice and water shield in Georgia, and see how roof areas are measured in how roofers measure a roof.