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Roofing Terminology P-R

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metal roofing

PARAPET WALL- A low wall around the perimeter of a roof deck.

PARGE COAT- A thin application of plaster for coating a wall.

PASS- The term used to describe the application of one layer of Spray Polyurethane Foam (SPF). The speed of a pass will determine foam thickness.

PASS LINE- The distinct line formed between two passes of SPF. This line is the top skin of the bottom pass of the SPF.

PAVER STONES- Usually pre-cast concrete slabs used to create a traffic surface.

PENETRATION- Any object that pierces the surface of the roof.

PENTHOUSE- A relatively small structure built above the plane of the roof.

PERLITE- An aggregate formed by heating and expanding siliceous volcanic glass. Perlite in a fluffy heat expanded form is used in lightweight insulating concrete, fire-resistant rigid insulation board (R = 2.78 per inch) and potting soil.

PERMEABILITY- The rate of flow of a liquid or gas through a porous material.

PHASE CONSTRUCTION- In roofing the practice of applying the felt plies of the built-up roofing membrane in two or more operations, separated by a delay of at least one day.

PHOTO-OXIDATION- Oxidation caused by rays of the sun.

PIPE BOOT- A prefabricated flashing piece used to flash around circular pipe penetrations. Also known as a Roof Jack.

PITCH- A term frequently used to designate coal tar pitch.

PITCH PAN OR POCKET- A bottomless metal box placed on the roof around irregular projections. These are subsequently filled with coal tar pitch or mastic to create a weather tight seal.

PLASTICIZERS- Material incorporated into rubber and plastic in order to increase their flexibility and workability.

PLASTIC CEMENT- A term used to describe Type I asphalt roof cement. Plastic cement should not be used on vertical surfaces.

PLY- A single course of roofing felts or reinforced membrane.

PLYWOOD- Wooden panels formed by gluing thin sheets of wood together, with the grain of adjacent layers arranged at right angles.

POINTING- The process where joints between masonry units, brick, etc., are filled with mortar.

PONDING- The accumulation of water at low-lying areas on a roof.

POLYMER- A substance consisting of large molecules which have been formed from smaller molecules of similar make-up.

POLYURETHANE- Any of various polymers with a urethane base.

PONDING- A condition where water stands on a roof for prolonged periods due to poor drainage and/or deflection of the deck.

POP RIVETS- Fasteners used to join pieces of metal that are installed by either compressed air assisted or hand operated guns. Unique in that they are installed from one side of the work.

POROSITY- The density of substance and its capacity to pass liquids.

POUR COAT- The top coating of bitumen on a built-up roof.

POWER VENTS- Electrically powered fans used to move air from attics and structures.

PRECAST- Concrete building components which are formed and cured at a factory and then transported to a work site for erection.

PREVAILING WIND- The most common direction of wind for a particular region.

PRIMER- A material of relatively thin consistency applied to a surface for the purpose of creating a more secure bonding surface.

PROJECTION- Any object or equipment which pierces the roof membrane.

PROTECTION BOARD- Heavy asphalt impregnated boards which are laid over bituminous coatings to protect against mechanical injury.

PUNCTURE RESISTANCE- The ability of a material to withstand being pierced by a sharp object.

PURLINS- A horizontal structural member spanning between beams or trusses to support a roof deck.

PVC- Polyvinyl Chloride.

QUARTER SIZED- Term for the size of hand sealant dabs, size of a U.S. 25¢ piece.

R-VALUE- The measure of a material’s resistance to heat flow. The higher a material’s R-value, the more it insulates.

RAFTER- The structural member extending from the downslope perimeter of a roof to the ridge or hip and is designed to support the roof deck and roof system components.

RAGGLE BLOCK- A specially designed masonry block having a slot or opening into which the top edge of the roof flashing is inserted and anchored.

RAKE- The angle of slope of a roof rafter, or the inclined portion of a cornice.

REFLECTIVE- A term referring to a material that has a white or shiny metallic surface.

REGLET- A horizontal slot, formed or cut in a parapet or other masonry wall, into which the top edge of counterflashing can be inserted and anchored.

RE-IMPREGNATE- To replace oils and bitumen in the components of the solvent based BUR which through weathering and oxidation, have been lost.

RESIN- The “B” component in SPF that is mixed with the “A” component in order to form polyurethane. Resin contains a catalyst, fire retardants, a blowing agent, Polyol, and a surface active agent.

RIDGE- The line where two planes of roof intersect, forming the highest point on the roof that runs the entire length of the roof.

RIDGE CAP- Material applied over the ridge or hip of a roof.

RIDGE COURSE- The final course of roofing applied that covers the area where two or more roof planes intersect.

RIDGE VENT- An exhaust venting device located at the ridge of a roof that works in conjunction with a starter or under eave soffit vent and is used to ventilate attics. Ridge vents and their cooperative starter or soffit vents should be installed at a 1-1 ratio in order to function properly.

ROOF- The assembly of interacting components designed to weatherproof and normally to insulate a buildings surface, separated from adjacent assemblies by walls or changes in elevation.

ROOF COATING- A bituminous material, either a cutback or an emulsion, to protect the surface of the BUR but not necessarily to re-impregnate it.

ROOF DECK- That component in building construction, which forms a platform on which the remainder of the BUR components are placed.

ROOF DRAIN- The termination or fitting at the roof of an interior drain or leader, for draining rain water from nominally flat roofs.

ROOF LOUVERS- Rooftop rectangular shaped roof vents. Also called box vents, mushroom vents, airhawks, soldier vents.

ROOF PLANE- A roofing area defined by having four separate edges. One side of a gable, hip or mansard roof.

ROOF SEAMER- A mechanical device used to crimp metal roof panels and make the seams watertight, OR a machine used to weld membrane laps of PVC (Thermoplastic) roofing material.

ROOF SLOPE- The angle made by the roof surface plane with the horizontal plane and expressed as the amount of vertical rise for every twelve inch (12″) horizontal run. For instance, a roof that rises four inches (4″) for every twelve inch (12″) horizontal run, is expressed as having a “four in twelve” slope; often written as “4-12.” Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also known as the Pitch of a roof.

ROOF SYSTEM- General term referring to the waterproof covering, roof insulation, vapor barrier, if used and roof deck as an entity.

RUN- The horizontal distance between the eaves and the ridge of the roof, being half the span for a symmetrical gable roof.

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