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COMMERCIAL ROOFING GLOSSARY

Alligatoring
Shrinkage cracking of the bituminous surface of built-up roofing or the exposed surface of smooth-surface roofing, producing a pattern of deep cracks with the scaly look of an alligators hide.
Asphalt
A highly viscous hydrocarbon produced from the residuum left after the distillation of petroleum used as the waterproofing agent of a built-up roof.
Ballast
An anchoring material (such as rounded river rock, gravel, or pre-cast concrete pavers), which is used to resist wind, uplift forces and hold roof membranes in place.
Bitumen
A generic term for either the asphalt or coal tar pitch used in the roofing industry.
Blister
A spongy, raised portion of roofing membrane, ranging in size from 25mm(1”) in diameter and barely detectable to as much as 4.6m2 (50ft2) in area and 300 mm(12”) high. Blister result from the pressure of trapped air or water vapour.
Built-Up Roof
Is a roof consisting of multiple plies of roof felts laminated together with bitumen. Built-up roof material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet.
Cricket
A wood-framed structure that diverts water away from chimneys, walls or other vertical roof projections and penetrations; also called a saddle.
Deck
The substrate over supportive framing to which roofing material is applied; also called decking or sheathing.
Drip edge
Flashing made of steel or other non-corrosive material that is placed along the eaves and rake edges at a 90ΒΊ angle to let water runoff drop clear of fascia and into the gutters.
Eave
A roof edge that extends past the exterior wall line.
Emulsion
An intimate mixture of bitumen and water, with uniform dispersion of the bitumen globules, achieved through a chemical of clay emulsifying agent.
EPDM
Ethylene Propylene Diene Monomer (or Terpolymer which is simply a product consisting of three distinct monomers). EPDM is classified as a Thermoset material which means it is either fully-cured prior to being installed or that it cures during natural weathering after installation.
Fascia
Vertical roof trim located along the perimeter of a building, usually below the roof level, to cover the rafter tails at the eaves. Also called the boards behind the gutter.
Felt
Material of interwoven fibers saturated with asphalt and used as a protective under layer between shingles and decking; also called tarpaper.
Fishmouth
An opening formed by an edge wrinkle in a felt where it overlaps another felt in a built-up roofing membrane.
Flashing
Metal or other flexible material used to seal the roof and prevent leaks around any projection or intersection, such as pipes, chimneys, dormers, valleys or adjoining walls.
Flat or low slope roof
A roof with a pitch of less than three feet of rise over a twelve-foot run; this type of roof needs a sealed system installation.
Flood Coat
The top layer of bitumen in an aggregate-surfaced built-up roofing membrane.
Gravel
Coarse granular aggregate, having rounded edges, resulting from the natural erosion of rock.
Hip
The external angle formed by the intersection of two sloping roof planes; from the ridge to the eaves.
Ice/Leak barrier
A self-adhering and self-healing membrane applied to the roof deck and designed to protect against water infiltration from ice buildup or wind-driven rain.
Laminated shingles
Strip shingles made with fiberglass mat and asphalt that are laminated, or textured, to create a three-dimensional effect. Also called dimensional or architectural shingles. There are also shingles that are called dimensional though they are made from a single material, not two materials laminated together.
Loosely Laid Membrane
Membranes, which are not attached to the substrate except at the perimeter of the roof. They are held in place with appropriate and adequate ballast.
Membrane
The portion of the roofing system that serves as the waterproofing material. Can be composed of one material or several materials laminated together.
Modified Bitumen
Is a bitumen modified by one or more polymers such as Atactic Polypropylene (APP), styrene butadiene styrene (SBS).
Permeability
The rate of flow of a liquid or gas through a porous material.
Pitch changes
The variation in the degree of roof incline, which is expressed as the ratio of the rise to the span, in feet.
Pitch Pocket (A.K.A. Pitch Pan)
A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with grout and a pourable sealer to seal around the penetration in order to seal it from against moisture entry. Pitch pockets are a good source of leaks and should be avoided if possible. For an example on how to properly fill a pitch pocket, click here.
Plumbing boot
A prefabricated covering, usually of flexible material, used to seal around a penetration; also called a pipe boot.
Ply
A layer of roofing membrane. A four-ply membrane has at least four plies of felt at any vertical cross section cut through the membrane.
Ponding
The accumulation of water at low-lying areas on a roof.
Primer
A liquid bituminous material applied to a surface to improve adhesion of heavier application of subsequently applied bituminous materials.
Protected Membrane Roof (PMR)
A roof assembly in which the insulation and ballast are placed on top of the membrane component. Commonly referred to as an "inverted roof assembly."
PVC
PVC stands for Polyvinyl Chloride. It is one of the pioneering single-ply roof materials. The first known PVC roofing membrane was produced by a company called Trocal and was installed in Germany in 1966. Within a few short years, Trocal PVC covered millions of square feet all over the world and single-ply roofing was setting the stage for market dominance.
Rafter
The structural member supporting the deck and roof system components, extending from the down slope perimeter to the ridge or hip.
Rake
The inclined edge of a sloped roof over a wall from the eave to the ridge, and usually perpendicular to the eave and ridge.
Ridge
The horizontal external angle formed by the intersection of two sloping roof planes, i.e., where the two sides of a roof meet at the highest point.
Ridge vent
A type of roof exhaust vent that ventilates the attic along the ridge or hip line where the roof deck has been cut back; works in conjunction with soffit vents under the eaves.
Roof ventilation
A static, wind- or power-operated system for removing hot air and moisture from the air under your roof. Includes ridge vents.
Shed roof
A roof containing only one sloping plane; a single-pitch roof, with no hips, ridges, valleys or gables. Also called a half gable. The area at the top is called a clearstory.
Single Ply Membrane
Roofing membranes that field-applied using a pre-manufactured sheet of single layer membrane material (either homogenous or composite) rather than multiple layers.
Smooth-Surfaced Roof
A built-up roofing membrane with a coating of hot asphalt, asphalt emulsion or asphalt cutback.
Soffit
The finished underside of the eaves, or roof overhang, which can be enclosed or exposed.
Soffit vent
An intake vent in the soffit area of the house that provides attic venting at a lower portion of the roof deck and good circulation with other forms of venting such as ridge or roof vents.
Substrate
The surface upon which the roofing membrane is placed – structural deck or insulation.
TPO
Thermoplastic Olefin or Polyolefin membranes are single-ply roof membranes constructed from ethylene propylene rubber.
Valley
The internal angle formed by the intersection of two sloping roof planes running from the eaves to the ridge, allowing water to run off.
Vapour Retarder
A material designed to restrict the passage of water vapour through a wall or roof assembly.
Water shield
A watertight barrier used to seal water out at the eaves and rakes, in valleys, and around chimneys and skylights.

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