Home / Glossary

Plain-language definitions of common roofing terms — squares, valley, ridge, underlayment, drip edge, ice-and-water shield, flashing, and the impact/fire/wind rating classes.

ACV / RCV

Actual cash value (ACV) is the depreciated value of your roof at the time of loss; replacement cost value (RCV) is the cost to replace it new. Many hail policies pay ACV first and release the withheld "recoverable depreciation" after the work is completed and invoiced.

Class 4 (UL 2218 impact)

The highest impact-resistance class under UL 2218, the steel-ball drop test. A Class 4 covering withstands a 2-inch steel ball dropped from 20 feet without the underside cracking. It reduces — but does not eliminate — hail damage risk.

Class A (fire)

The highest roof-covering fire classification under UL 790 / ASTM E108, corresponding to severe fire-test exposure (maximum resistance to flame spread, burning brands, and fire penetration). Classes B and C denote moderate and light exposure.

Drip edge

A metal flashing installed along the eaves and rakes that directs runoff away from the fascia and into the gutter, protecting the deck edge from water intrusion. Its installation is commonly required by building code.

Eave

The lower edge of a roof, typically overhanging the exterior wall. Eaves are where gutters, drip edge, and eave ice-and-water protection are installed.

Fascia

The horizontal board mounted at the eave along the ends of the rafters, to which the gutter is usually attached. It closes off and protects the rafter tails.

Flashing

Sheet-metal or membrane components that seal transitions and penetrations — around chimneys, walls, valleys, vents, and skylights — to keep water out of vulnerable joints. Most roof leaks originate at failed flashing.

Granule

The ceramic-coated mineral surfacing on asphalt shingles that provides color and shields the asphalt from ultraviolet degradation. Granule loss accelerates aging — a particular concern under Colorado's high-altitude UV.

Hip

The external angle formed where two sloping roof planes meet at a downward-sloping ridge. A hip roof slopes on all sides, with no vertical gable ends.

Ice dam

A ridge of ice that forms at a roof's eave when melting snow refreezes, trapping water behind it that can back up under the roof covering. Ice-and-water shield at the eaves is the primary defense.

Ice-and-water shield

A self-adhering, waterproof membrane applied at eaves, valleys, and penetrations to protect against leaks from ice dams and wind-driven rain. In cold climates it is typically required along eaves; it seals around fasteners that are driven through it.

IRC / IBC (International Codes)

The International Residential Code (IRC, for one- and two-family homes) and International Building Code (IBC, for commercial buildings) are the model codes that Colorado jurisdictions adopt — by edition, with local amendments — to govern roofing work.

Low-slope roofing

Roofing on pitches below roughly 3:12, which relies on a continuous waterproof membrane rather than shedding. Single-ply membranes (TPO, EPDM, PVC), modified bitumen, and built-up roofs are low-slope systems.

Oil-canning

The visible waviness or buckling that can appear in the flat areas of standing-seam and other flat metal panels. It is an aesthetic characteristic, not a structural defect.

Penetration

Any object that passes through the roof surface — a plumbing vent, flue, skylight, or conduit. Each penetration must be flashed and sealed to prevent leaks.

Rake

The inclined edge of a roof over a gable end, running from eave to ridge. Rake edges receive drip edge and starter courses to resist wind uplift.

Ridge

The horizontal line at the top of a roof where two sloping planes meet. It is capped with ridge shingles or ridge caps and is frequently the location of a ridge vent.

Ridge vent

An exhaust vent installed along the ridge that lets warm, moist attic air escape. Paired with intake vents at the soffit or eave, it drives passive attic ventilation, reducing heat and moisture buildup.

Roof deck (sheathing)

The structural surface — usually plywood or OSB on residential roofs — fastened over the rafters or trusses, onto which underlayment and the roof covering are installed. Deteriorated decking is replaced during a reroof.

SBS-modified (rubberized) asphalt

Asphalt modified with styrene-butadiene-styrene polymer to add flexibility and elasticity. SBS modification helps shingles absorb impact and tolerate temperature swings, and is common in impact-resistant (Class 4) products.

Single-ply membrane

A low-slope roofing sheet installed in large panels and seamed together — TPO, PVC (both thermoplastic, heat-weldable) or EPDM (a synthetic rubber). Common on flat commercial and some residential roofs.

Soffit

The underside of a roof overhang, spanning from the fascia back to the wall. Vented soffits provide the intake air for attic ventilation.

Square

The roofing unit of area equal to 100 square feet (a 10 ft x 10 ft area). Roofs are estimated, sold, and installed by the square — a "20-square roof" covers 2,000 square feet of roof surface.

Starter strip

The first course of shingles (or a purpose-made starter product) installed at the eave and rake. Its adhesive bonds the first exposed course and improves wind resistance at the roof's edges.

Steep-slope roofing

Roofing on pitches of roughly 3:12 and greater, where water sheds by gravity. Shingles, tile, slate, and metal panels are steep-slope systems. Contrast with low-slope roofing.

Tear-off

Removal of the existing roof covering (and often underlayment) down to the deck before installing a new roof. A full tear-off, versus re-covering over the old roof, is required by some codes and lets the deck be inspected.

Underlayment

The water-resistant layer installed over the roof deck and beneath the primary roof covering. It provides a secondary barrier against wind-driven rain and protects the deck during installation. Materials include asphalt-saturated felt and synthetic underlayments.

Valley

The internal angle formed where two sloping roof planes meet, channeling a large volume of runoff. Valleys are lined with metal or membrane and are a common leak point if improperly flashed.