Confused by roofing jargon? This glossary defines 40+ roofing terms — from decking and flashing to squares and valleys — in plain English for homeowners.
Square: The standard roofing unit of measurement. One square equals 100 square feet of roof surface. A 2,000 sq ft roof has 20 squares. All roofing material quantities are calculated in squares.
Pitch: The steepness of a roof, expressed as rise over run (e.g., 6:12 means the roof rises 6 inches for every 12 inches of horizontal run). Low pitch = 2:12–4:12. Medium = 4:12–8:12. Steep = 8:12+.
Roof deck / sheathing: The plywood or OSB panels nailed to your rafters that form the structural surface of your roof. Everything else — underlayment, shingles — sits on top of this.
Underlayment: A water-resistant or waterproof layer installed directly on the roof deck, beneath the shingles. Felt paper (15 or 30 lb) is traditional. Synthetic underlayment is stronger and more durable. Ice-and-water shield is a self-adhering waterproof membrane used in vulnerable areas.
Architectural shingles: Also called dimensional or laminate shingles. A multi-layer asphalt shingle that's thicker and more durable than 3-tab, with a dimensional appearance. The current residential standard.
TPO: Thermoplastic polyolefin. A heat-weldable flat roofing membrane that's the current industry standard for low-slope roofs. White, reflective, and durable.
Drip edge: A metal flashing installed along roof edges that directs water away from the fascia and into gutters. Required by most building codes.
Flashing: Sheet metal (usually aluminum or galvanized steel) used to seal roof transitions — around chimneys, vents, skylights, and where the roof meets a wall. The most common source of roof leaks.
Valley: The V-shaped channel formed where two roof planes meet. Valleys concentrate water flow and are a common leak point. Open metal valleys and closed-cut valleys are the two main styles.
Ridge: The horizontal peak where two sloping roof planes meet. Ridge caps cover this area and are a high-wear location.
Hip: A sloping edge of a roof where two planes meet at an angle (as opposed to a gable, where the wall extends up to the ridge). Hip roofs are more wind-resistant than gable roofs.
Soffit: The underside of the roof overhang. Perforated soffits provide attic ventilation. Rotted soffits are a sign of water damage or poor ventilation.
Fascia: The vertical board running along the eave where gutters are attached. Often the first thing to show water damage from clogged or failing gutters.
Ice dam: A ridge of ice that forms at the eave when heat escapes through the roof deck, melts snow, and the meltwater refreezes at the cold edge. Forces water under shingles.
Starter strip: A row of roofing material installed at the eave before the first course of shingles, providing a waterproof base at the most vulnerable edge.
ACV (Actual Cash Value): Insurance term. Pays the depreciated value of your roof, accounting for age and wear. Lower payout than RCV.
RCV (Replacement Cost Value): Insurance term. Pays the full cost to replace your roof with like materials regardless of age. Better coverage, higher premiums.
Manufacturer warranty: Covers defects in roofing materials. Typically 25–50 years for architectural shingles. Often requires professional installation and registration.
Workmanship warranty: Covers the contractor's installation quality. Varies widely — 1 year to lifetime depending on the contractor. Get it in writing.
Tear-off: Removing the existing roofing material before installing new. Adds cost ($0.50–$2.00/sq ft) but is required when adding layers would exceed building code limits or when the deck needs inspection.