Roofing Terminology, Explained in Plain English

Measurement and quantity

• Square — 100 square feet of roof area. Roofing is bought and bid by the square, not the sheet. A 30-square roof is 3,000 sq ft.
• Bundle — a package of shingles. Most architectural shingles run 3 bundles per square; some heavier products run 4 or 5.
• Pitch (slope) — rise over 12 in. of run. A 6/12 roof rises 6 in. per foot. Steeper roofs cost more to install and change what materials are allowed.
• Coverage — the actual area a bundle covers once the shingles are lapped at their exposure. Always less than the raw shingle area.
• Exposure — the portion of each shingle course left visible after the next course laps over it.

Parts of the roof

• Ridge — the horizontal peak where two slopes meet. Capped with ridge shingles, often over a ridge vent.
• Hip — an external angled edge where two slopes meet, running down from the ridge to a corner.
• Valley — the internal angle where two slopes meet. The hardest-working part of the roof and where leaks start.
• Eave — the lower edge, over the wall line, usually with an overhang.
• Rake — the sloped edge at a gable end.
• Fascia — the vertical board at the eave that gutters hang on.
• Soffit — the underside of the overhang, usually vented to feed intake air into the attic.

Layers, from the deck up

• Decking (sheathing) — the plywood or OSB structural surface. Everything else fastens to it.
• Underlayment — the water-shedding layer over the deck. Synthetic has largely replaced felt.
• Ice and water shield — a self-adhering membrane in valleys and around penetrations. Out here its job is wind-driven rain, not ice.
• Drip edge — metal flashing at eaves and rakes that directs water off the edge instead of behind it.
• Starter strip — a purpose-made first course that seals the bottom edge of the field shingles against wind uplift.
• Field shingles — the main body of the roof.
• Hip and ridge cap — shingles made or cut to cover the hips and ridge.

Flashing and penetrations

• Flashing — metal that seals a transition. Step flashing at a wall, counter flashing over it, valley metal in a valley.
• Pipe boot — the collared flashing that seals around a plumbing vent. The rubber gasket is often the first thing on a roof to fail.
• Chimney cricket — a small peaked structure behind a chimney that diverts water around it rather than letting it pond.

Ventilation

• Ridge vent — continuous exhaust vent along the peak.
• Soffit vent — intake at the eave. Ridge vent without soffit intake does very little.
• Turbine / static vent — spot exhaust vents used where a continuous ridge vent is impractical.
• Balanced ventilation — roughly equal intake and exhaust area. Unbalanced systems pull conditioned air out of the house instead of moving attic air.

Terms on the estimate

• Tear-off — removing the existing roof down to the deck. Priced by the square and by how many layers come off.
• Deck repair — replacing rotted or damaged sheathing found after tear-off. Usually a unit price, since nobody knows the count until the old roof is off.
• Re-roof / overlay — installing new shingles over an existing single layer. Cheaper up front, but you never see the deck and the roof runs hotter.

Frequently asked questions

How many bundles of shingles are in a square?

Three bundles per square for most architectural shingles. Heavier designer or premium products can run four or five bundles per square — check the wrapper, since it affects both the count and the load weight on the roof.

What roof pitch can shingles be installed on?

Asphalt shingles are standard on 4/12 and steeper. Between 2/12 and 4/12 they can be used with a doubled underlayment or membrane detail per the manufacturer. Below 2/12 you need a low-slope membrane or metal system, not shingles.

Do I really need drip edge?

Yes. Without it, wind-driven rain runs back under the shingle edge and rots the deck and fascia. It is inexpensive and it is required by current code on eaves and rakes.

What is the difference between a re-roof and a tear-off?

A tear-off removes everything to the deck so the sheathing can be inspected and repaired. A re-roof lays new shingles over one existing layer — cheaper, but the deck stays hidden and the assembly runs hotter, which shortens shingle life.

Products in this guide

• RoofingShingles, underlayment, drip edge and accessories
• Plywood & OSBDecking for tear-off repairs
• InsulationAttic insulation and ventilation planning
• HardwareFasteners and jobsite supplies

See every product line we carry

Keep reading

• RoofingBest Roofing Materials for West Texas
• InsulationInsulation Guide
• SidingVinyl Siding Guide
• All guides in the resource center