Roofing Terminology

3-COURSE – A repair method using plastic cement and a mesh membrane. The 3-course applies a thin coat of plastic cement, then embeds the mesh membrane and is covered by a layer of plastic cement.  Slang for this technique is “BULL & WEB”.


ALLIGATORING – Cracking in a thick layer of asphalt. Asphalt requires support from a membrane such as felt or it will separate.


ASPHALT – A primary substance used in roofing. The product comes in 100lb kegs and is melted in a kettle. Once melted the product is spread to adhere to insulation or become the roof when applied with layers of roofing felt or modified bitumen. Gravel is embedded in asphalt for additional roof protection.


BALLAST / GRAVEL – In roofing, gravel is usually ½ to 5/8-inch in size and is used with the built-up roof for protection.  Ballast describes a 2” stone used as a weight to hold down an EPDM roof.


BASE SHEET – A diversely used term. 1) When the deck is wood or lightweight, a base sheet is fastened to the deck and the insulation and roof adhere to the base sheet. 2) In a 2 ply modified bitumen roof system, the first ply is smooth and call the base sheet or modified base sheet. 3) In base flashing, the first ply, the cap sheet and the whole base flashing can be referred to as the base sheet.


BLISTER – In asphalt-based roofing system, moisture can be trapped and cause the membrane to lift.  Blisters will look like bubbles and can be very small to several feet in length.  Avoid stepping on blisters as they can pop or split.


BUILT-UP– Also known as BUR, is an asphalt based roof system where asphalt is spread and a fiberglass felt is rolled into the asphalt. This occurs usually 3-4 times building the roof system up into a 3 or 4 ply roof.  This system can then be topped with a glaze coat of asphalt, aluminium paint or gravel embedded in the asphalt.


CANT STRIP – A piece of insulation wood. Asphalt products are not designed to be bent at a 90-degree angle. At transitions such as parapet walls and curbs, a 45-degree piece of insulation or wood is installed to allow the membrane transition gradually. Visually, the angle at the bottom of the base flashing.


CAP SHEET – When modified bitumen is used, the cap sheet is the final ply. The cap sheet is usually granulated but can be smooth or aluminium coated.


COAL TAR PITCH – Similar to asphalt, but flows and become liquid in high temperatures.


COLLECTOR HEAD – A metal pan installed on the outside of the scupper to catch water and guide into a downspout. Also called CONDUCTOR HEAD.


COPING – Metal installed on top of the parapet wall to protect the top of the wall from water damage. Cover plates or standing seams are installed at joints of metal.


CRICKET – Additional sloped insulation installed to direct water to drainage points or around curbs.


CURB – AC units and exhaust fans are set on metal support called a curb.  The curb then has a base flashing applied to the exterior and is either counter flashed by separate metal or the unit.


DECK – The structural support for the roof system. Common decks are steel, lightweight concrete, gypsum, wood and concrete.


DOWNSPOUT – A metal tube used to direct water to the ground or a lower roof.


ELASTOMERIC – A rubberized coating that can be applied to roofs or walls.


EPDM – A rubber roof system similar to an inner tube.  EPDM material is much stronger and longer lasting than an inner tube.


EXPANSION JOINT – A separation in the building to allow for movement. This separation must be allowed for in the roof. An expansion joint may be two short walls with a cap to allow for movement.  Bellowed expansion material may also be present.


FISHMOUTH – A lifted edge in the lap of felt in a built-up roof or modified bitumen roof.


FLASHING – Used to describe any treatment at penetrations or terminations of the roof. Types of flashing:


BASE FLASHING: Typically made of the roof membrane and usually transitions from the flat roof to a vertical surface such as a parapet wall or curb.


COUNTERFLASHING: Typically a piece of metal which is above the base flashing.


WALL FLASHING: On tall parapet walls, the base flashing is applied first, then the wall flashing will cover the top of the base flashing. A counterflashing may be installed in between or above.


METAL EDGE/GRAVEL GUARD – Metal installed at the perimeter to terminate the roof.


MODIFIED BITUMEN– An asphalt-based roll membrane. Can consist of a smooth surface sheet or a granulated surface. Two variations are APP and SBS.  The product is made with a modified asphalt and a fiberglass or polyester mat.


PARAPET – A wall at the perimeter and above the roof. The parapet either has a lower roof or no building on the non-roof side.


PITCH/TAPER – Roof slope is necessary to get water off the roof. Pitch is the degree of slope, usually rated in inches per foot of the climb. Tapering is a method to create a slope in the roof by adding wedged insulation.


PITCH PAN – When penetration occurs in the roof, a pitch pan or penetration pan must be installed to prevent water from entering the hole.  Pitch pans come in different forms but are usually filled with a flexible pourable sealer.


PLASTIC CEMENT– Asphalt based material commonly used at penetrations and repairs of BUR and modified bitumen roofs. Slang for this material is “BULL”


POLYISOCYANURATE – Foam insulation used for its high R-value.  Commonly called ISO or POLYISO.


PONDING – Low spots in the roof will allow water to settle.  Ponding which evaporates within 48 hours is acceptable.


RUNNER – A support for rooftop equipment. Usually consists of two 4×4 pieces of wood running the length of the equipment.


SCUPPER – Refers to a hole in the parapet wall or cut in the metal edge to allow the roof to drain.


SINGLE PLY– Refers to any of the products in the EPDM, TPO and PVC type of materials. These materials are installed in a single ply.


SLIPPING / SLIPPAGE / SLIDING – Base flashings or wall flashings on a vertical wall, parapet or curb will fall or slide down due to gravity.


SLOPE – Slope is the angle of the roof. In roofing, roofing this is measured in inches per 12 inches.  Low slope roofs are commonly 1/8” per foot or ¼” per foot. Steep slopes are commonly 5/12 to 11/12.


SPUD – Repairing built-up roofs requires removing the gravel in the repair area.  Before the repairs can be made, the area must be spud. This can be performed individually with a spud bar or on a larger area with a spudding machine.


SPLIT – Primarily applies to built-up asphalt roofs. As the roof deteriorates, it will become weak and allow tears.  These tears can be short or several feet in length. Once a split starts, it will continue to split.


STRIP-IN / STRIPPING – Once the metal edge is installed, roof material is applied to cover the fasteners and the metal edge. This material is called the strip-in.


TPO/PVC – Typically white roof membrane similar to vinyl.