Roofing Terms, in Plain English

Actual Cash Value, or ACV, is one way an insurance policy can value a roof claim. It pays the cost to replace the roof minus depreciation for its age and wear. In plain terms, ACV reflects what the old roof was worth at the time of the loss, not what a brand-new roof costs. An older roof has depreciated more, so an ACV settlement on it is smaller. Whether your policy pays ACV or full replacement cost is spelled out in your policy.

Class 4 impact-resistant shingles are shingles that earned the highest rating, Class 4, in an industry test that drops a steel ball to simulate hail impact. They are built tougher, often with a reinforced backing, so they resist the bruising and cracking that hail causes on ordinary shingles. Because they hold up better in hailstorms, many insurers offer a premium discount for homes that install them, though the discount and terms depend on your insurer and policy.

Drip edge is a strip of metal flashing installed along the edges of a roof, at the eaves and the rakes, before the shingles. It guides rainwater off the roof and into the gutters instead of letting it run back underneath and soak the fascia and the deck. Drip edge is a small, inexpensive piece, but leaving it out lets water wick into the wood at the most vulnerable edge of the roof, where rot starts.

The fascia is the long, straight board that runs along the lower edge of the roof, capping the ends of the rafters where the roof meets the gutters. Gutters are usually mounted directly to the fascia, so it carries their weight and the water they collect. A sound fascia keeps the roof edge looking clean and gives the gutters something solid to hang from, while a rotted fascia can let gutters pull loose and water get behind them.

Flashing is the thin metal that seals the joints and edges where a roof meets something else, such as a chimney, a wall, a skylight, or a valley. Its job is to direct water away from those seams so it cannot sneak underneath the shingles. Flashing is one of the most important leak-stopping parts of a roof, and most roof leaks start at failed or poorly installed flashing rather than in the open field of shingles.

Ice and water shield is a self-adhesive, waterproof membrane installed in the most leak-prone areas of a roof, such as valleys, around chimneys and skylights, and along the eaves. Unlike standard underlayment, it sticks directly to the decking and seals tightly around nails, creating a watertight barrier. It is used as added protection in the spots where wind-driven rain and water backup are most likely to force their way under the shingles.

A roof insurance deductible is the portion of a covered claim that the homeowner pays out of pocket before the insurance company pays the rest. If a covered roof claim is approved, the insurer pays the covered repair or replacement cost minus your deductible, and that deductible is always the homeowner's responsibility. Deductibles can be a flat dollar amount or a percentage of the home's insured value, and the specific amount is set in your policy.

A pipe boot is the flashing that seals around a pipe where it passes through the roof, such as a plumbing vent. It is usually a metal flange with a rubber collar that fits snugly around the pipe to keep water out. Pipe boots are a very common source of roof leaks, because the rubber collar dries out, cracks, and fails years before the surrounding shingles do. A cracked pipe boot is one of the most frequent and easily fixed leak causes.

Replacement Cost Value, or RCV, is the more generous of the two ways an insurance policy can value a roof claim. It pays the full cost to replace the damaged roof with a new one of similar kind and quality, without subtracting for age or wear. Many RCV policies pay in two parts: an initial amount up front, then the withheld depreciation once the work is completed and documented. Whether you have RCV or Actual Cash Value coverage is defined in your specific policy.

A ridge vent is a vent that runs along the peak, or ridge, of a roof and lets hot, humid air escape from the attic. Paired with intake vents low on the roof, it creates a steady flow of air that keeps the attic cooler and drier. Proper ridge ventilation protects the roof from heat and moisture damage, helps shingles last their full life, and can lower cooling costs during hot summers.

Roof decking, also called sheathing, is the layer of wood that forms the solid base of the roof. It is usually plywood or OSB nailed across the rafters, and everything else, the underlayment and shingles, attaches to it. The decking gives the roof its strength and a flat, sound surface to fasten to. Because it is hidden until the old roof is torn off, decking damage is the most common reason a final replacement price comes in above the estimate.

A roof overlay is when a new layer of shingles is installed directly over the existing old roof, without tearing the old shingles off first. It is faster and cheaper than a full tear-off because it skips the removal and disposal work. The tradeoff is real: an overlay hides any rot or damage in the decking, adds weight to the roof, traps heat, and usually does not last as long. Most building codes also limit a roof to no more than two layers.

Roof pitch is the measure of how steep a roof is. It is written as a ratio of vertical rise to horizontal run, such as 6:12, meaning the roof rises 6 inches for every 12 inches it runs horizontally. A higher first number means a steeper roof. Pitch affects how a roof sheds water, what materials can be used, and how much a replacement costs, because steeper roofs are slower and more dangerous to work on.

A roof tear-off is the complete removal of the old roofing materials down to the bare wood decking before a new roof is installed. Stripping everything off lets the crew inspect and repair the decking, install fresh underlayment, and start the new roof on a sound base. A full tear-off is the proper way to replace a roof, even though it costs more in labor and disposal than simply layering new shingles over the old ones.

A roof valley is the V-shaped channel formed where two sloped sections of roof meet and run downward together. Valleys collect and carry a large volume of rainwater off the roof, which makes them one of the busiest and most leak-prone areas. Because so much water funnels through them, valleys are flashed and built with extra care, and a failed valley is a common source of leaks on an older or poorly installed roof.

A roofing square is the unit roofers use to measure and price a roof. One square equals 100 square feet of roof surface, or a 10 foot by 10 foot area. Material and labor are figured by the square, not by the home's floor space, so a roof is quoted in squares rather than total square feet. A typical single-family home has a roof somewhere in the range of 15 to 30 squares.

Granules are the tiny mineral pebbles bonded to the surface of an asphalt shingle. They give the shingle its color and, more importantly, shield the asphalt underneath from the sun's ultraviolet rays. As long as the granules stay put, the shingle is protected. When they wear off or get knocked loose by hail or age, the bare asphalt is exposed, dries out, and the shingle starts to fail. Granule loss is one of the clearest signs a roof is aging or storm-damaged.

The soffit is the underside of the roof overhang, the surface you see when you stand under the edge of the roof and look up. Besides finishing off the overhang, the soffit usually houses the intake vents that pull fresh air into the attic. A healthy, vented soffit is a key part of attic ventilation, and a damaged or rotted soffit is often the first visible sign of a water or pest problem at the roof's edge.

Starter strip shingles are a special first row of shingles installed along the edges of a roof, underneath the visible first course. They have a strip of adhesive positioned to seal down the bottom edge of the shingles above them and they leave no gaps where the shingle seams fall. This locks the roof's edge against wind uplift and blocks water from getting under the first row, which is why proper starter is essential at the eaves and rakes.

Underlayment is the protective layer installed directly on the roof decking, underneath the shingles. It acts as a second line of defense against water, so if wind drives rain under the shingles or a shingle is lost in a storm, the underlayment keeps the deck and the home below it dry. Modern roofs use either a felt paper underlayment or a tougher synthetic underlayment, with synthetic now the common choice for its strength and water resistance.