Ice and Water Shield Installation in Southfield, MI

Every shingled eave in Michigan needs an ice barrier under Michigan Residential Code R905.2.7.1, either two layers of underlayment cemented together or a self-adhered sheet of polymer-modified bitumen. Measured from the eave's edge, it must reach at least 24 inches inside the exterior wall line. A township code handout quoting the same code adds that the rule covers unheated attached garages too, and exempts only detached buildings with no heated space. This is the strip that takes the backed-up water when an ice dam forms, so it's the one place on the roof where you shouldn't accept a shortcut.

A valley carries the water from two roof planes, and in winter it fills with snow that melts last. The code (R905.2.8.2) says valley linings go in to the shingle manufacturer's instructions before the shingles. GCP's data sheet for its high-temperature membrane names valleys among the leak-prone spots self-adhered membrane is made for. A full-width membrane centered in the valley, then the valley shingled or metal-lined over it, is the detail to ask for.

Wherever the roof meets something vertical, water has a seam to find. Membrane turned up the chimney, the skylight curb or the sidewall gives the step and counter flashing a sealed backup. The code requires step flashing at sidewalls and a cricket behind any chimney wider than 30 inches. The membrane goes under all of that. The flashing itself is covered on chimney flashing repair.

Shingles are allowed down to a 2:12 pitch, but between 2:12 and 4:12 the code calls for double underlayment, because water drains slowly and wind pushes it uphill. Many roofers cover those shallow sections, like porch roofs, rear additions and dormer tie-ins, entirely in membrane. Below 2:12, shingles aren't allowed at all, and the section needs a membrane roof instead (see flat roofing).

Metal roofs run hot in summer sun, and standard membranes aren't made for that. High-temperature versions are. GCP rates its Ice & Water Shield HT up to 260°F, says it can sit exposed up to 120 days before the roof goes on, and markets it specifically for metal roof assemblies. On a metal roof, ask for an HT-rated product by name in the estimate.

The rest of the deck doesn't need membrane. The code accepts #15 felt or an approved synthetic underlayment: one layer on slopes of 4:12 and up, side laps of 2 inches, end laps staggered 6 feet. Most roofers use synthetic for the field and stop the membrane where the code and the trouble spots end. Ask which one the estimate names, because "underlayment" alone could mean either.