Glossary of Roofing Terms


Under most insurance policies, claim reimbursement begins with an up-front payment for the ACV, actual cash value, of your damage.

Algae discoloration:

A type of roof discoloration caused by algae. Commonly called fungus growth


A bituminous waterproofing agent applied to roofing materials during manufacturing.


Bubbles that may appear on the surface of asphalt roofing after installation.


A package of shingles. There are 3, 4, or 5 bundles per square depending on the style of shingle

Counter flashing:

That portion of the flashing attached to a vertical surface to prevent water from migrating behind the base flashing.


A row of shingles or roll roofing running the length of the roof.


The surface installed over the supporting framing members to which the roof is applied.


The horizontal, lower edge of a sloped roof

EDPM/Ethylene Propylene Diene Monomer:

a synthetic rubber most commonly used in single-ply roofing because it is readily available and simple to apply. Seaming and detailing has evolved over the years and is fast, simple and reliable with many membranes including factory applied tape, resulting in a faster installation.


Fibrous material saturated with asphalt and used as an underlayment or sheathing paper.

Fiber glass mat:

An asphalt roofing base material manufactured from glass fibers.


Pieces of metal or roll roofing used to prevent seepage of water into a building around any intersection or projection in a roof such as a vent pipes, chimneys, adjoining walls dormers and valleys.


The upper portion of a sidewall that comes to a triangular point at the ridge of a sloping roof.

Ice and Water Shield:

IWS is an underlayment of asphalt polymers, formed into a rolled sheet. The asphalt makes it vapor-tight, and the polymers make the asphalt elastic and sticky. This protective barrier is able to stretch and seal around nails driven through it. Placing IWS a minimum of 24″ past the interior wall line at the eave and in the valleys provides your first line of defense to ice damming.

Ice dam:

Condition formed at the lower roof edge by the thawing and refreezing of melted snow on the overhang. Can force water up and under shingles, causing leaks.


That portion of the roof structure that extends beyond the exterior walls of a building.


The degree of roof incline expressed as the ratio of the rise, in feet, to the span, in feet.


The supporting framing member immediately beneath the deck, sloping from the ridge to the wall plate.


Roofing over any existing roofing without first removing it.

Recoverable depreciation:

If you have replacement cost coverage with your insurance policy, as most do, when your roof is repaired or replaced you submit a final bill to receive the balance of this depreciated amount. This can take weeks to receive and will come payable to any person or bank that’s named on any mortgage.

Roof Vent:

Any outlet for air that protrudes through the roof deck such as a pipe or stack. Any device installed on the roof, gable or soffit for the purpose of ventilating the underside of the roof deck.

Shake Redeck:

Installing a composite roofing system with OSB or plywood over the slat decking where a shake roof used to be.


A unit of roof measure covering 100 square feet.

Step flashing:

Flashing application method used where a vertical surface meets a sloping roof plane.

Three-tab shingle:

Low cost asphalt shingle seen on income property or used for ridge caps with other shingle types.

“Torch Down” or Modified Bitumen:

A single-ply rolled roof similar to ice-and-water shield, but impregnated with a mineral-based wear surface. Torch-down systems involve heating the adhesive as the material is unrolled.

TPO/Thermoplastic Polyolefin single-ply roofing:

This roofing material can be fully adhered, mechanically fastened, or ballasted. TPO seam strengths are reported to be three to four times higher than EPDM roofing systems. This is a popular choice for “Green” building as there are no plasticizers added and TPO does not degrade under UV radiation. It is available in white, grey, and black. Using white roof material helps reduce the “heat island effect” and solar heat gain in the building.


Roll type material applied to the deck before shingles are installed. Several types are available for different situations, felt being the common one.


The internal angle formed by the intersection of two sloping roof planes to provide water runoff.