What are the layers of a roof?
Most of them are covered for good the day the roof goes on. Here's what each one does, from the deck up.
Roof decking
The deck is the wood the roof is fastened to. On newer homes it's plywood or OSB in sheets. Many older homes here have plank decking, boards laid across the rafters.
After tear-off we walk the bare deck, photograph it, and replace soft or delaminated decking with 7/16 inch OSB. New shingles can't fix a deck that won't hold a nail.
On North Central Dr in Beavercreek, in September 2026, the bare plank deck went under new sheathing before anything else went on.
How many layers of shingles can a roof have?
In Ohio, two at most. The residential code doesn't allow a new roof to go over an old one "where the existing roof has two or more applications of any type of roof covering. (opens in a new tab)" We don't lay a new roof over an old one at all. Every roof we replace is torn off to the deck. On North Central Dr in Beavercreek we took three layers off in September 2026, and on Spaulding Rd in Dayton, three more in May 2026.
Ice and water shield
Ice and water shield is a membrane that sticks directly to the deck. It goes where water is most likely to get under the shingles: the eaves, the valleys, and around anything that comes through the roof.
Ohio requires an ice barrier from the lowest edge of the roof to at least 24 inches inside the exterior wall line.
We install two rows at the eaves, one row in every valley, along every roof-to-wall transition and around everything that comes through the roof.
Roof underlayment
Underlayment covers the rest of the deck, under the shingles. On a normal slope, Ohio's minimum is one layer, lapped 2 inches.
We put down two layers of synthetic underlayment and overlap them 24 inches, so every square foot of the deck has two layers over it.
Gutter apron and drip edge
Metal covers the edges of the deck. We use gutter apron at the eaves, where the gutters hang, and drip edge at the rakes, the sloped edges at the gable ends. Gutter apron vs drip edge explains the difference.
Roof flashing
Flashing is the metal that seals the places where the roof meets something else: a wall, a chimney, a skylight, a pipe. In the leaks we investigate, the cause is usually one of these details, not the shingles. Why roofs leak goes through them.
Starter strip, shingles, and hip and ridge caps
Starter strip runs along the edges and gives the first row of shingles something to seal to. Shingles cover the field. Hip and ridge caps cover the peaks, where two slopes meet.
We install these three as one Owens Corning Duration system: Owens Corning starter strip, Duration shingles, and Owens Corning hip and ridge caps, installed to the manufacturer's specifications. We do not mix in parts from other brands.
What should I ask a roofer about the layers?
Ask how many rows of ice and water shield they will install, how many layers of underlayment, and what the overlap is. Ask whether the old roof comes off to the deck. We install two rows of ice and water shield at the eaves and two layers of synthetic underlayment overlapped 24 inches. It's the part of the roof you'll never see.
Roof ventilation
Ventilation isn't a layer, but the layers above depend on it. Air comes in at the soffit and leaves at the ridge. Before we install a ridge vent we confirm there's enough intake at the soffit to feed it. How attic ventilation works covers what Ohio requires.
Every one of these is part of a roof replacement from us.
Jobs behind this article
Next step: the questions to ask each roofer when you compare estimates.
