Parts of a Roof — Every Component Explained

Why understanding roof components matters

When a contractor gives you a roof replacement quote, knowing what each component is — and why it matters — helps you compare quotes accurately. A low bid that omits ice & water shield or uses inferior underlayment is a worse value than a higher bid with the full system, even if the line items look similar at first glance.

The roofing system components

Roof Decking

The structural foundation of your roof — typically 7/16" or 1/2" OSB (oriented strand board) or plywood sheathing attached to your rafters. Everything above it sits on the decking. When Atlas Roofing does a tear-off, we inspect every inch of decking for rot, mold, or damage before installing the new roof. Any compromised decking is replaced — installing a new roof on bad decking is a common shortcut that causes premature failure.

Ice & Water Shield

A self-adhering rubberized membrane applied directly to the decking at eaves, valleys, and other vulnerable areas before underlayment goes down. In Northeast Ohio, ice & water shield is not optional — it's what prevents ice dam water from infiltrating your home. The GAF standard requires it at all eaves and valleys. Atlas Roofing uses GAF WeatherWatch as our standard, with Grace Vycor Pro available as an upgrade for maximum protection.

Underlayment

A second layer of water-resistant material installed over the decking (and over the ice & water shield at eaves). Synthetic underlayment like GAF FeltBuster has largely replaced traditional felt paper — it's lighter, stronger, tear-resistant, and provides better secondary protection if shingles are damaged. Atlas Roofing uses GAF FeltBuster as our standard underlayment.

Starter Strip

A specially designed first row of material installed along eaves and rakes before the first course of shingles. Starter strips have a pre-applied adhesive that seals the bottom edge of the first shingle course — preventing wind from lifting the first row. Skipping starter strip or using cut-down shingles instead is a common installation shortcut.

Shingles

The visible surface layer — typically architectural (dimensional) asphalt shingles on Northeast Ohio homes. Each shingle course overlaps the one below it, shedding water from top to bottom. Atlas Roofing installs GAF Timberline HDZ as our standard shingle. The specific nailing pattern, exposure, and alignment matter significantly for wind resistance.

Ridge Cap Shingles

Specially designed shingles that cover the peak (ridge) of the roof, sealing the most exposed part of the system. GAF Seal-A-Ridge cap shingles have pre-applied adhesive for a watertight seal. Standard cut shingles used as ridge cap are an inferior substitute.

Ridge Vent

A continuous vent strip installed along the ridge that allows hot, humid attic air to escape. Paired with soffit vents at the eaves (intake), ridge vents create the balanced airflow that prevents heat buildup, extends shingle life, reduces ice dam risk, and prevents moisture damage to attic insulation. Atlas Roofing installs GAF Cobra ridge vent on all complete replacements.

Flashings

Metal (typically aluminum or galvanized steel) installed wherever the roof meets a vertical surface — chimney bases, sidewalls, dormers, and skylights. Flashing failure is one of the most common causes of roof leaks. Properly installed flashing is step-flashed at sidewalls (interwoven with shingle courses) and counter-flashed at chimneys. Atlas Roofing replaces all flashings on full replacements.

Drip Edge

A metal flashing installed along eaves and rakes that directs water away from the fascia and into the gutters. Often skipped or installed incorrectly — it should go under the underlayment at eaves and over it at rakes. Missing or improperly installed drip edge is a frequent source of fascia rot.