Roof Deck Replacement in Southfield, MI

Plywood is thin wood veneers glued in cross layers. OSB (oriented strand board) is wood strands pressed with resin. Angi notes OSB is the more common choice because it costs less, while plywood is stronger. Whichever is used, APA, the engineered wood association, recommends a 1/8-inch gap at panel edges and ends so the sheets can expand without buckling the roof. Panels also need the right thickness for the rafter spacing; the grade stamp on each sheet says so.

Many older houses have a plank deck: solid boards running across the rafters, sometimes with gaps between them. The Michigan Residential Code lets asphalt shingles go on solid sheathing or 1-inch nominal boards. Wide gaps, split boards and boards worn thin by decades of nails are where problems start, because shingle nails have to go at least 3/4 inch into the sheathing. When planks are too gapped or too thin to hold nails, plywood or OSB goes over the boards or replaces them. Angi lists plank decking at $3 to $7 per square foot, against $2 to $5 for solid sheathing.

Rot shows up where water sits longest: along the eaves under ice dams and backed-up gutters, in valleys, and around chimneys and skylights. It's often invisible until the shingles come off. From the attic you may see dark stains, soft spots or sheathing peeling apart in layers. The fix is to cut back to sound wood, centered on rafters, and patch with new panels of the same thickness so the roof stays flat. Rotted eave decking often goes with rotted fascia; the soffit and fascia page covers that trim.

A sag between rafters, where the deck dips like a hammock, usually means sheathing that's too thin or wet for too long. New sheathing fixes it. A sag along the ridge or a bowed rafter is a different job: cracked rafters get sistered, with a new board bolted alongside, and a ridge that drops may need collar ties or a beam. Heavy snow loads, an extra layer of shingles and old notches cut for vents all add up. Structural work like that may need an engineer's or the city's sign-off, so ask the contractor how they'll handle it before the roof is opened.

Most deck work happens during a tear-off, the one time the whole deck is visible. The roofer walks it after the old shingles come off, marks soft and delaminated sheets, and replaces them before underlayment goes down. The contract should price this up front: a per-sheet or per-square-foot price for replacement decking, so nobody negotiates with the roof open. Get photos of the sheets that were replaced. For the rest of the re-roof, see roof replacement.