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Roofing Terms for Non-Roofers

Below are some of the most common roofing terms and what they mean. This is not meant to be an exhaustive list but to give some of the basics so that you can more easily converse with your flat roofer.


Accelerated Weathering: a testing process for materials in which they are exposed to harsher than normal temperatures, water, light, etc., to magnify and measure the effect these processes have on the material.

Adhere: to stick two surfaces together. This uses asphalt or roofing cements in built-up roofing or with contact cement or a heat welder for single-ply membranes.

Aggregate: river rock, stone, marble chips, etc., used as a ballast for your roofing system (weight that holds your roof on).

Aging: the effect of time and environment on your roofing materials.

Aluminum: a non-rusting metal often used for roofing and flashing.


Ballast: heavy material used to hold (or assist in holding) on your waterproofing material.

Base Ply: the bottom ply of roofing in a roofing membrane or system.

Base Sheet: a tar coated felt sheet used as the first layer in multi-ply and tar and gravel roof systems.

Batten: a narrow metal bar used to hold the roof membrane or base flashing in place.

Bitumen: typically referring to asphalt or coal tar, this is a viscous or solid substance used to stick membranes together and waterproof them. Bitumen is a by-product of petroleum production and is also used in roads.

Blackberry (also Blueberry or Tar-Boil): a blister or bubble in the tar, often indicating water damage or weakening of the roofing system.

Blister: a pocket of air trapped between layers of felt or membrane or membrane and substrate. Can easily be ruptured if walked on.

Blocking: wood attached above the deck and below the waterproofing membrane used in areas where extra support for the membrane is needed.

Brooming: a process in which a broom or squeegee is used to ensure full adhesion of roof membranes.

Buckle: an upward bent or tent in the roof membrane most commonly occurring over joints in the roof.

Building Code: regulations established detailing loads, procedures, and construction requirements for buildings. These codes ensure that buildings are made suitable to weather and environmental conditions for the area taking into account things such as snow weight, winds and earthquake activity and their effect on buildings. These codes also set out requirements for acceptable use of buildings, requiring specific standards be met depending on number of people expected and the use the building will be put to.

Built-Up Roof Membrane (commonly referred to as BUR or Tar and Gravel): a multi-ply roof membrane that has layers of felts alternating with layers of bitumen (tar). These are usually surfaced with aggregate and bitumen (tar and gravel) or a top coating. *Please note that here at Northern Seal we do not install this type of roofing system*

Butyl-Tape: a sealant tape sometimes used for temporary seals at the end of each workday, temporary repairs and as temporary waterproofing between different types of materials.


Canopy: an overhanging or projecting part of a roof, typically seen over doorways.

Cant Strip: is used on older roofing systems in areas where the roof meets a vertical surface to make the transition between the two planes easier on the roofing material.

Cap Flashing: metal shield used to cover the upper edges of roof me ***

Cap Sheet: a granule surfaced (like shingles) sheet used to top some built-up or modified bitumen roof membranes.

Capillary Action: the process by which water can move laterally through seams even when the roof is sloped the proper way.

Caulking: (1) the process of sealing a joint or juncture, (2) sealant used to fill joints and seams to make them weather proof.

Chalk Line: a line made on a roof by holding down both ends of a string covered in chalk and then snapping it in the centre. This gives a straight line which will wash off easily with water.

Chimney: a framed structure that projects through and above a roof requiring specific flashing to ensure waterproofing.

Cladding: the material used to cover the exterior walls of a building or parapet walls.

Coating: surface material used either for protection or decoration.

Coated Felt: a felt membrane that has been saturated with asphalt and then coated on both sides with a harder asphalt coating.

Cohesion: the strength with which a substance sticks to itself.

Cold Process Built-Up Roof: alternating layers of felts, mats or fabrics with roof cements or adhesives that are not significantly heated in the application process. These usually rely on solvents.

Combustible: able to be burned.

Compatible Materials: two or more substances that can be attached or put together without having to worry about them negatively affecting each other. Non-compatible materials must be separated to keep them from reacting.

Concealed Screw Method: a method of roofing in which screws go into lower layers of materials and are then covered by adhered waterproofing membrane.

Condensation: when water vapour or other gases turn to liquid state as temperatures drop.

Contact Cements: adhesives that glue different roofing products together. They stick things together immediately on contact when the contact cement has been applied to both surfaces.

Contamination: when a surface or material becomes unclean and must either be cleaned before use or must be completely discarded.

Coping: a type of flashing that goes over a wall to protect it from the weather.

Counterflashing: metal sheeting that has been bent and secured to a wall, curb, pipe or other projection to protect the area where the roofing membrane ends.

Curb: (1) a raised part of the roof supporting penetrations (skylights, hatches, etc.) above the surface of the roof. (2) a low raised perimeter wall

Cure: using chemicals, heat, pressure or time to allow a material to form its molecular bonds and achieve its desired characteristics.

Cure Time: time required for the curing process.


Dead Level: a roof with no intentional slope to the roof drains.

Dead Loads: permanent loads on the roof caused by the structure, mechanical and electrical equipment and the roof system itself.

Deck: the base onto which the roof is applied, it may be metal or wood but must be able to support the dead and live loads which it will be required to carry.

De-lamination: separation of laminated layers.

Design Loads: loads required by building codes or governing bodies which give specifications for the design of a building.

Dew Point Temperature: temperature at which water vapor condenses into liquid water causing condensation.

Downspout: conduit used to carry water to a lower roof level, the ground or to a water runoff system.

Drain: an outlet wherein water is collected and directed to flow off the roof.

Drip Edge: metal flashing with a lower edge that projects outward and directs dripping water away from your building.

Dynamic Load: any load which moves around or changes (people, wind pressure, electronic equipment, etc.).


Eave: edge of a roof that projects beyond the wall

Elastomeric Coating: a coating system that is able to be stretched to at least twice its original length and return to its original dimensions.

EPDM (Ethylene Propylene Diene Monomer): a rubber roofing material that comes in large sheets and all seams and detail work is done with solvents and glues. It is not a weldable product. You have probably seen it used as pond liner.

Expansion Joint: a separation between two building elements which allows movement without damaging either of the elements or the roofing system.


Factory Seam: a seam made by the manufacturer of a product (e.g. a preassembled roofing product).

Fading: any lightening in colour.

Fascia: the part of your roof where the eaves trough is installed.

Fasteners: any of a wide range of things used to secure your roof into place (e.g. nails, screws, cleats, clips, bolts, etc.)

Field Seam: a seam made by your roof installer.

Field of the Roof: main portion of the roof, not including perimeter and siding.

Fishmouth (Wripples or Edge Wrinkle): a half-cylindrical or half-conical opening (looks like a fishes mouth) which forms at an edge or seam, caused by movement during the installation process.

Flaking: when layers of a material, especially a coating or surface layer, separate uniformly.

Flame Retardant: a substance added to a material to reduce its tendency to burn.

Flange: a portion of flat material used to transition roofing products to drains, skylights, roofing vents, etc.

Flash Point: the temperature at which a roofing product that contains solvents (e.g. glues, primers, cleaners) will dry. Below this temperature these products are unworkable.

Flashing: metal used to protect the perimeter and any penetrations of the roofing system.

Flashing Cement: trowel grade roofing tar that can be used as a temporary waterproofing material that can be used around roof penetrations and the perimeter. This is not a long-term solution.

Flashing Collar (Storm Collar or Flashing Boot): a flashing product used to cover and seal pipe vents and other penetrations.

Flood Coat: the top layer of a tar and gravel roof into which gravel is embedded into liquid-tar.

Flood Test: when water is temporarily and deliberately left on your roof to test the waterproofing.


Galvanized Steel: steel coated with zinc to prevent corrosion.

Granule: small pieces of rock used to surface cap sheets, shingles and other roof coverings.

Gravel: small pieces of rock used as ballast to hold your roofing system in place.

Gravel Stop: a raised lip or mesh around the perimeter of a building or around drains to prevent gravel from falling off of the perimeter of the building or into drains.

Gutter: a channeled part of the roof that leads water from the roof to a drain or downspout.


Heat Welding: using heat to melt overlapping layers of roofing material together to form a continuous sheet.

Hoist: a lifting device sometimes needed to get products onto the roof.

“Hot” or “Hot Stuff”: roofers term for hot tar.

Humidity: the amount of moisture in the atmosphere, often expressed as a percentage, in which 100% is the point at which the atmosphere can hold no more and it rains. Warmer air can hold more moisture than cooler air before it releases as rain.

HVAC: heating, ventilating and air conditioning equipment.


Ice Dam: a wall of ice formed by meltwater meeting a colder part of the roof and refreezing. This can cause water to back up under roofing materials and cause or aggravate leaks.

Impact Resistance: the ability of a roofing material to resist damage from falling objects, foot traffic or other things which may pierce the roof.

Infrared Thermography: the use of infrared cameras to identify areas of the roof with temperature differences in order to locate leaks, wet insulation or damaged decking.

Inverted Roof Membrane Assembly: when insulation and ballast are placed over the roofing membrane instead of the insulation being underneath.


Joist: metal or wood beams running parallel to support the roof of a building.


Lap: how thick the weld or sealant is on overlapping roofing material.

Lap Cement: a roofing cement made to adhere overlapping layers of roofing material.

Lap Seam: wherever overlapping roofing materials are seamed, sealed or bonded together.

Lead: a soft metal often used for different types of flashings.

Loose-laid Membranes: roofing membranes that are only mechanically attached at the perimeter of the roof. They are held in place over the rest of the roof by ballast (stone, gravel, paving stones, etc.).


Mansard: decorative steep-sloped roof around the perimeter of a building.

Mansard Roof: a steep roof that meets up with a flat roof at its high point.

Mechanically-Fastened Membranes: roofing membranes that are attached to underlying layers with screws, nails, plates or other fasteners.

Membrane: the material used on your roof to make it waterproof.

Metal Flashing: pieces of sheet metal that are bent to go around edges of a roof to cover where the membrane meets the wall. Includes many types, including through-wall flashing, cap flashing (coping), counterflashing, step flashing, etc.

Meter: 39.37 inches

Mil: a unit of measure used to indicate the thickness of a roofing membrane. 1000mil is one inch.

Mildew: a fungus that grows on the surface of a material in damp conditions.

Mineral-Surfaced Roofing (or Sheet): roofing material with mineral granules in the surface or top layer (e.g. shingles).

Modified Bitumen: tar impregnated sheets modified with either plasticisers or rubber additives. The most common type of modified bitumen today is rubber modified. This type of roof can be installed either cold process or hot process, hot process being more common.

Mopping: the process of applying hot tar to roofing felts or other materials.


Neoprene: a liquid rubber used in roof flashings.

Night Seal (or Night Tie-Off): a seal that is made to temporarily protect the roof section that has already been done in case of rain. This seal is usually removed when work on the roof recommences.


Open-Webbed Steel Joist (OWSJ): the roof supports on large steel constructed buildings running between the large I-beams in your building. Often used to support safety tie off points on the roof or HVAC units.


Pallet: a wooden base used to store shipping materials.

Parapet Wall: the wall surrounding the perimeter of a building, usually more than a foot in height.

Penetration: (1) anything that passes through the roof, (2) the hardness of a material, measured by measuring how far a needle goes into the material under specific conditions (time, temperature, pressure).

Pitch-Pocket (Pitch-Pan): a flashing detail designed to waterproof irregular penetrations. It consists of a steel or rubber sleeve often filled with a two part epoxy sealer.

Plastic Cement: another name for trowel-grade tar, often containing fibers for added support. This product can often be used when the roof is wet to make emergency seals.

Pliability: how flexible a material is.

Ply: a layer of membrane in a roofing system. Single-ply systems are a single layer of roofing membrane instead of a roofing system made of building up multiple layers.

Polyvinyl Chloride (PVC): A rigid polymer plastic that is fairly UV stable. Chemical plasticizers are added during manufacture to make the sheets flexible enough to be used as a flat roofing material. PVC is a thermoplastic, meaning it can be welded to itself to form water proof seals with heat. PVC roofs begin to fail as the plasticizers degrade in the sunlight (UV).

Ponding: water that remains on low areas of the roof instead of flowing off.

Positive Drainage: a condition in which the roof has been designed and sloped so that all water is able to drain from it within 48 hours of a rainfall.

Primer: refers to a variety of compounds designed to clean and prepare surfaces to receive glues or peel-and-stick roofing products.

Puncture Resistance: the ability of a roofing membrane to resist puncture by a sharp object.


Rafter: refers to wooden beams that support the sub-structure of your roof.

Reinforced Membrane: a roofing or waterproofing membrane that has been reinforced, usually with a nylon mesh, to increase puncture resistance and rigidity, and decrease thermal expansion.

Ridge: the highest point of a roof where two roof areas meet.

Roof Assembly: all components of a roofing system (including roof deck, vapor barriers, insulation, membranes and fasteners).


Sag: (1) when areas of the roof or structure settle over time resulting in standing water which further aggravates the sagging problem, (2) a term referring to improperly installed vertical roofing components resulting in rippling or buckles.

Saturated Felt: felt that has been partially saturated in tar.

Seam Strength: the force needed to separate the layers of a seam in membrane material.

Self-Adhering Membrane: a membrane that already has glue on one side and is made to stick to itself without additional glues.

Self-Drilling Screw: a screw that drills and taps its own hole into steel.

Sill: the bottom horizontal frame of an opening such as a window or door.

Sill Flashing: flashing below a window or door.

Skylight: a window set into the roof in order to allow light to enter a building.

Slope: the angle of a roof, often expressed as a percent or ratio. Flat roofs have up to 10 percent slope or a 3 foot rise over 12 feet.

Snow Guard: things attached to the roof to keep snow in place and prevent it from building up in certain parts or sliding off of the roof.

Snow Load: the weight of snow on a roof.

Soil Stack (Stink Pipe): a pipe that penetrates the roof to vent plumbing lines.

Spalling: when concrete or other masonry starts to crumble or break away from a building.

Splash Block: a block placed below a downspout in order to prevent erosion from water running off of a roof.

Square: 100 square feet of roof area.

Starter Sheets: most manufacturers of singly-ply membranes require a perimeter course of material that is narrower than the regular roof rolls. (e.g. While we will use 10’ wide rolls on the roof, there will be a perimeter sheet that is 5’ wide).

Substrate: the insulation or deck of the roof onto which the waterproofing membrane of the roof is applied.

Sump: an intentional lower area around a drain or scupper that promotes drainage.


Test Cut: a sample of the roof that is used to diagnose the condition of the roofing components including age, decay, thickness and weight.

Thermal Shock: when a roof experiences a wide temperature fluctuation in a short amount of time resulting in rapid expansion or shrinking of the roofing membrane. Over time this contributes to premature aging.

Tie-Off: a place to tie off fall-arrest ropes that complies with WSIB standards.

Tongue and Groove Planks: a type of wood often used in old wood construction buildings with interlocking edges similar to hardwood flooring.


Ultraviolet (UV): a wavelength of light that is invisible to humans but which causes degradation to the chemical structure of many types of roofing products. These products must therefore be protected from the sun to ensure proper function throughout their service life.

Underlayment: a product used to provide a break between the roof deck and the roof system.


Vapor Retarder: material used to slow or stop water vapor from moving through a roof assembly.

Vent: an opening used to allow air to pass from inside a building to outside.

Ventilator: a roofing accessory designed to allow moisture to escape from underneath the roofing membrane.


Wind Uplift: the upward force caused by wind moving horizontally across the surface of your roof (e.g. wind blowing across a tarp will often cause it to rise).