Glossary

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Glossary


A

ABRASION RESISTANCE
The ability of a membrane to resist being worn away by contact with a moving abrasive surface, such as foot traffic, mechanical equipment, wind-blown particles, etc.
ACCELERATED WEATHERING
The process in which materials are exposed to a controlled environment where various phenomena – such as heat, water, condensation, and light – are altered to magnify their effects, thereby accelerating the weathering process. The physical properties that result from this exposure are then measured and compared to those of the original unexposed material.
ADHERE
To cause two surfaces to be held together by adhesion. Single-ply membranes are often “partially” or “totally adhered” to a substrate with the use of contact cements, such as air-cured phenolic-neoprene mixtures, or other similar adhesives. See ADHESION, ADHESIVE, BOND.
ADHESION
The combined ultimate strength of the molecular forces and the mechanical interlocking achieved between the adhesive and the surfaces bonded. See ADHERE, ADHESIVE, BOND.
ADHESIVE
A substance capable of holding materials together by surface attachment. These substances may be used to adhere or attach various roofing materials and components, such as single-ply membranes, flashings, insulation boards, etc. Before adhesives are applied, their compatibility with other roofing materials and components should be ensured through consultation with the membrane supplier. Failure to do so could result in the degradation of these materials and in poor adhesion. See ADHERE, ADHESION, BOND.
AGGREGATE
(1) crushed stone, crushed slag or water-worn gravel used for surfacing a built-up roof;
(2) any granular mineral material.
ALLIGATORING
The cracking of the surfacing bitumen on a built-up roof, which produces a pattern of cracks similar to an alligator's hide; the cracks may or may not extend through the surfacing bitumen. Usually caused by oxidizing of the asphalt due to weathering and/or shrinkage stresses.
ALLOY
A combination of two or more chemically different polymers which have been re-formed through processing into a new material from which the original materials cannot be separated.
APPLICATION RATE
The quantity (mass, volume or thickness) of material applied per unit area.
AREA DIVIDER
See CONTROL JOINT.
ASBESTOS
A group of natural, fibrous, impure silicate materials.
ASPHALT
A dark brown to black cementitious material in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing.
ASPHALT, AIR BLOWN
An asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening point and modify other properties.
ASPHALT FELT
An asphalt-saturated felt or an asphalt-coated felt. A mat of organic or inorganic fibres in sheet form impregnated with bitumen supplied in roll form.
ASPHALT MASTIC
A mixture of asphaltic material and graded mineral aggregate that can be poured when heated but requires mechanical manipulation to apply when cool.
ASPHALT, STEAM BLOWN
An asphalt produced by blowing steam through molten asphalt to modify its properties, normally used for highway bitumen.
ASTM
American Society for Testing Materials
ATACTIC POLYPROPYLENE
A group of high molecular weight polymers formed by the polymerization of propylene. Both atactic (amorphous, non-crystalline) and isotactic (highly crystalline) polymers are formed during the polymerization. The atactic polymer is the primary modifier used in combination with bitumen, although a small quantity of the isotactic polymer may be used as well.

B

BACKMOPPING
Applying hot asphalt to what will be the concealed side of a material (insulation sheet, felt, etc.) before turning it over and arranging it in place.
BACKNAILING
The practice of blind nailing (in addition to hot-mopping) all the plies of a substrate to prevent slippage.
BALLAST
An anchoring material, such as rounded river rock, gravel, or pre-cast concrete pavers, which is used to hold single-ply roofing membranes in place and to stabilize the roof system from wind uplift forces. Although ballasting materials differ greatly in size, composition, and weight, they are typically applied at the rate of ten (10) pounds or more per square foot of roof area. Thus, ballast should only be applied to those roof structures able to support this added weight. Also, ballast materials should be large and heavy enough to resist being blown off the roof, yet light and smooth enough to avoid damaging the membrane.
BASE FLASHING
See FLASHING.;BASE PLY
The base ply is the first ply when it is a separate ply, and not part of a shingled system.
BASE SHEET
A saturated and coated felt placed as the first ply in some multi-ply built-up roof membranes, also a modified and / or saturated and coated sheet used in modified bitumen roofing systems.
BATTEN
A narrow metal band or plate, usually of galvanized steel or aluminium, which is used to fasten or hold in place a single-ply membrane, to prevent its displacement. Also known as a “strip fastener.” See MECHANICALLY FASTENED MEMBRANES.
BITUMEN
The generic term for an amorphous, semi-solid mixture of complex hydrocarbons derived from any organic source. Asphalt and coal tar are the two bitumens used in the roofing industry.
BITUMINOUS
Containing or treated with bitumen. Examples: Bituminous concrete, bituminous felts and fabrics, bituminous pavement.
BITUMINOUS EMULSION
(1) A suspension of minute globules of bituminous material in water or in an aqueous solution;:(2) A suspension of minute globules of water or an aqueous solution in a liquid bituminous material (invert emulsion).
BLISTER
A spongy raised portion of a roof membrane, ranging upwards in size from 25 mm (1") in diameter and of barely detectable height. Blisters result from the pressure build-up of gases entrapped in the membrane system. The gases most commonly are air and / or water vapour. Blisters usually involve delamination of the underlying membrane plies.
BOND
The adhesive and cohesive forces holding two roofing components in intimate contact.
BROOMING
Embedding a ply of roofing material by using a broom to smooth out the ply thereby ensuring contact with the adhesive under the ply.
BTU
British thermal unit - the heat energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit (1 BTU = 0.252 kilocalories (kcal)). See KILOCALORIE.;BUILT-UP ROOF MEMBRANE
A continuous, semi-flexible roof membrane assembly consisting of plies of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, generally surfaced with mineral aggregate, bituminous materials, or a granule-surfaced roofing sheet.
(Abbreviation: BUR.)
BUR
Abbreviation for Built-up Roof.
BUTT JOINT (BUTT SPLICE)
A joint or seam formed by joining separate sections of membrane at the edges without overlap (i.e. edge to edge). Once the edges have been joined, the seam is usually covered and sealed with a narrow strip of membrane material or compatible tape.
BUTYL
A rubber material produced by copolymerizing isobutylene with a small amount of isoprene. Butyl is manufactured into various sheet goods, blended with other rubber materials, and is often used to make sealants.

C

CALENDERING
A manufacturing process by which polymeric membranes and sheeting are produced. The finished material is formed by passing it between the nips of a series of large counter-rotating steel rollers which produces a film or sheet of uniform thickness The device used for this purpose is a calender.
CANT STRIP
A bevelled strip of wood or wood fibre that fits into the angle formed by the intersection of a horizontal surface and a vertical surface. The 45o slope of the exposed surface of the cant strip provides a gradual angular transition from the horizontal surface to the vertical surface.
CAP FLASHING
See FLASHING, see COPING.
CAPILLARITY
The action by which the surface of a liquid (where it is in contact with a solid) is elevated or depressed, depending upon the relative attraction of the molecules of the liquid for each other and for those of the solid.
CAP SHEET
A granule-surfaced coated sheet used as the top ply of a built-up roof membrane or flashing or also in modified bitumen roofing systems.
CAULKING
A composition of vehicle and pigment, used at ambient temperatures for filling joints, that remains plastic for an extended time after application.
CGSB
Canadian General Standards Board.
CHLORINATED POLYETHYLENE (CPE)
A synthetic elastomer, used for single-ply membranes, which is composed of high molecular-weight polyethylene which has been chlorinated, a process which yields a flexible rubber-like material. See PLASTOMERIC MEMBRANES.
CHLOROSULFONATED POLYETHYLENE
A synthetic, rubber-like elastomer, based on high molecular-weight polyethylene with pendant sulphonyl chloride groups, usually formulated to produce a self-vulcanizing membrane. Chlorosulfonated polyethylene (CSM or CSPE is marketed by DuPont under the trade name HYPALON). See ELASTOMERIC.
COAL TAR PITCH
A dark brown to black, semi-solid hydrocarbon formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterproofing agent in dead-level or low slope built-up roofs. (For specification properties, see CSA A123.4-M1979 Types A and B.)
COATED BASE SHEET (OR FELT)
Felt that has been impregnated and saturated with asphalt and then coated on both sides with harder, more viscous asphalt to increase its impermeability to moisture; a parting agent is incorporated to prevent the material from sticking in the roll.
COEFFICIENT OF THERMAL EXPANSION
The change in length of a material as a function of temperature. A dimensionless coefficient, it is usually reported in mm/mmoC (or inches/inchoF).
COLD PATCH
A method of repairing a BUR using plastic asphalt cement with either a glass mat or saturated cotton membrane, instead of hot asphalt.
COLD-PROCESS ROOFING
A continuous, semi-flexible roof membrane, consisting of plies of felts, mats, or fabrics that are laminated on a roof with alternate layers of cold-applied roof cement and surfaced with a cold-applied coating.
COLOUR STABILITY
The ability of a material to retain its original colour, even after long exposure to strong sunlight and / or other harsh environmental conditions, including air pollutants, acid rain, extremes of temperature, etc. Colour stability may be especially important for white or specially pigmented materials which may have been deliberately selected for their high degree of reflectivity or aesthetic effect.
COMPRESSIVE STRENGTH
The ability of roofing materials and components to resist deformation or other damage caused by the weight or compression of either “live” or “dead loads.” High compressive strength may be especially important in insulation boards.
CONDENSATION
The conversion of water vapour or other gas to liquid as the temperature drops or the atmospheric pressure rises. See DEW POINT.
CONTACT CEMENTS
Adhesives which may be used to adhere or bond together various roofing components. The adhesive is applied in a liquid state to the two surfaces to be joined, and then allowed to dry before the surfaces are mated. The bond is formed immediately as the surfaces touch. Because contact cements form a bond immediately upon mating the surfaces, great care must be taken to ensure that the membrane is positioned properly. Any attempt to lift or reposition a misaligned and cemented membrane could result in damage to the membrane and / or in poor adhesion.
CONTROL JOINT
A raised, double-wood member attached to a properly flashed wood base plate that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where no expansion joints have been provided. Also referred to as an area divider.
COPING
The covering piece placed on top of a wall that is exposed to the weather. It is usually sloped to shed water.
COPOLYMERIZATION
A chemical reaction that results in the bonding of two or more dissimilar monomers to produce large, long-chain molecules which are copolymers.
COUNTERFLASHING
Formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, rooftop unit or other surface to cover and protect the upper edge of a base flashing and its associated fasteners.
COVERAGE
The surface area to be continuously coated by a specific roofing material, with allowance made for a specific lap.
CPE
Abbreviation for “chloronated polyethylene”.
CRAZING
A series of hairline cracks in the surface of weathered materials.
CRACK
A separation or fracture occurring in a roof membrane or roof deck, generally caused by thermally induced stress or substrate movement.
CRCA
Canadian Roofing Contractors Association.
CREEP
The permanent deformation of a roofing material or roof system caused by the movement of the roof membrane that results from continuous thermal stress or mechanical loading or gravity.
CRICKET
A superimposed construction placed in a roof area to assist drainage. Also sometimes referred to as a SADDLE.
CROSSLINK
A chemical phenomenon by which polymers are cured or vulcanized. A crosslink is a chemical bond formed between the long chain molecules in the block polymer. This bond connects adjacent molecules and prevents their relative displacement (molecular slippage) when the material is stressed.
See VULCANIZATION.
CSA
Canadian Standards Association.
CSM
The designated nomenclature for “chlorosulfonated polyethylene” by ASTM D-1418.
CSPE
A common abbreviation for “chlorosulfonated polyethylene”.
CURB
A raised area on which a skylight or fan or other accessory is to be placed.
CUTBACK
Any bituminous roofing material that has been solvent-thinned. Cutbacks are used in cold-process roofing adhesives, flashing cements, and roof coatings.
CUTOFF
A material seal that is designed to prevent lateral water movement into the edge of a roof system where the membrane terminates at the end of a day's work. It is also used to isolate sections of the roof system. Cutoffs are usually removed before the continuation of work.

D

DAMPROOFING
Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.
DEAD LEVEL
The term used to describe an absolutely horizontal roof. Zero slope. See SLOPE.
DEAD-LEVEL ASPHALT
A roofing asphalt that has a softening point range of 60oC to 68oC (140oF to 154oF) and that conforms to the requirements of CSA A123.4-M1979 Type 1.
DEAD LOADS
Non-moving rooftop loads, such as mechanical equipment, air conditioning units, and the roof deck itself.
DECK
The structural surface to which the roofing or waterproofing system (including insulation) is applied.
DEFLECTION
A bending or arching of the deck which results in a surface which deviates from truly flat and level.
DELAMINATION
Separation of the plies in a roof membrane system or separation of laminated layers of insulation.
DEW POINT
The temperature at which water vapour starts to condense in cooling air at the existing atmospheric pressure and vapour content.
DIMENSIONAL STABILITY
The change in length and / or width of a material that results from exposure to elevated temperatures over time. Expressed as a percent.
DISC FASTENERS
A wide variety of devices with mechanical assemblies used to attach single-ply membranes and/or insulation boards to a substrate or deck. Disc attachments generally consist of a square or circular shaped plate with a hole in the centre, through which a screw or nail-like clip may be inserted. They are generally set in place with a drill-like device.
DOUBLE POUR
The application of the top coating of bitumen and gravel surfacing of a built-up roofing in two separate applications. This is accomplished by embedding a quantity of gravel in the first pour coat of bitumen then brooming off the loose gravel and re-pouring and re-gravelling.
DRAIN
A device that allows for the flow of water from a roof area.
DRIP EDGE
The formed edge on metal installed at the eaves of a roof.
DRIPPAGE
Bituminous material that drips through the roof deck or at the edge of the roof or at roof openings.
DROPBACK
A reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air. Also called “fallback”. See SOFTENING POINT.
DRY SHEET
An unsaturated felt or paper used in certain applications to help prevent bitumen drippage (not to be confused with a saturated felt “laid dry” meaning “unmapped”).

E

EDGE LAP
The overlap of the edge of a ply over a previous ply. Also called “side lap”.
EDGE STRIPPING
Application of felt strips cut to narrower widths than the normal width of the full felt roll. They are used to cover joints.
EDGE VENTING
The practice of providing regularly spaced protected openings along a roof perimeter to relieve moisture vapour pressure.
ELASTOMER
A macromolecular material that returns rapidly to its approximate initial dimensions and shape after substantial deformation by a weak stress and the subsequent release of that stress.
ELASTO-PLASTIC
A term used to describe the whole range of synthetic rubber and plastic materials used in the manufacture of single-ply roofing membranes.
ELASTOMERIC
The term used to describe the elastic, rubber-like properties of a material.
ELONGATION
The ability of a roofing membrane material to be stretched or elongated by the application of a force.
See ULTIMATE ELONGATION.
EMBEDMENT
(1) The process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive;
(2) The process of placing a material into another material so that it becomes an integral part of the whole material.
EMBRITTLEMENT
The loss of flexibility, elasticity, or ductility of a material. The transition of a flexible material to a brittle material.
EMULSION
The intimate dispersion of an organic material and water achieved by using a chemical or clay emulsifying agent.
ENDLAP
The overlap of the start of a roll over the previous roll.
EPDM
Designated nomenclature by ASTM for a terpolymer of ethylene, propylene, and a diene.
EPDM LAP SEALANT
A material used to caulk the exposed edge of field seams of EPDM membranes. See FIELD SEAM, SEAM, SEALANT.
ETHYLENE PROPYLENE DIENE MONOMER (EPDM)
An elastomeric material synthesized from ethylene, propylene, and small amounts of diene monomer. EPDM is widely used in single-ply roofing membranes. It may be used alone or in EPDM / butyl blends. See ELASTOMERIC.
EQUILIBRIUM AT A MOISTURE CONTENT
(1) The moisture content of a material stabilized given temperature and relative humidity, expressed as a percent moisture by weight;
(2) The typical moisture content of a material in any given geographical area.
EQUIVISCOUS TEMPERATURE (EVT) RANGE
The optimum application temperature of asphalt. It is the temperature range at which a viscosity of 125 centistokes is attained, plus or minus 14oC (25oF).
EXPANSION JOINT
A structural separation between building elements designed to minimize the effect of the stresses from splitting or ridging the roof membrane. (See Construction Details in RCABC Roofing Practices Manual).
EXPOSURE
(1) The transverse dimension of a roofing element not overlapped by an adjacent element in any roof system. The exposure of any ply in a membrane may be computed by dividing the felt width minus 50 mm (2") by the number of shingled plies; thus, the exposure of a 914 mm (36") wide felt in a shingled, four-ply membrane should be 216 mm (8-1/2")
(2) The time during which a portion of a roofing element is exposed to the weather;
(3) The portion or extent of a roof unit which is left exposed to the weather.
EXTENSIVE VEGETATIVE ROOF ASSEMBLIES
Roof top gardens having minimal plant species diversity, irrigated only to establish plants, and typically having a soil depth of less than 150 mm or 6 inches.
EXTRUSION
A manufacturing process which consists of forcing molten polymers through an orifice called a “die”. The shape and dimensions of the die orifice determine the shape and dimension of the finished product. Extrusion is one method by which single-ply roofing membranes may be manufactured.

F

FABRIC
A woven cloth of organic or inorganic filaments, threads, or yarns usually used for reinforcements in certain membranes, assemblies and flashing details.
FACTORY MUTUAL (FM)
An organization that classifies roof assemblies for their fire characteristics and wind-uplift resistance for insurance companies in the United States.
FACTORY SEAM
A splice made by the manufacturer during the assembling of narrow width material into large sheets.
FACTORY SEAM STRENGTH
The force required to cause a seam (created by the membrane supplier) to fail in peel or shear. Expressed in units of force or force per unit area, or as a percentage of the strength of the sheet itself.
FASCIA
The vertical trim board at the eave. The gutter is attached to the fascia.
FASTENERS
Any of a wide variety of mechanical fastening devices and assemblies, including clips, screws, or bolts, which may be used to secure battens, discs, termination bars, and wood nailers to the deck or other suitable substrate.
FELT
A fabric manufactured from cellulose (wood) fibres (organic felts). The manufacturing process involves mechanically interlocking the fibres of the particular felt material in the presence of moisture and heat. Roofing felts are also manufactured using glass fibres or woven or non-woven polyester and (less commonly) asbestos fibres.
FIELD SEAM
A splice made in the field which joins two sheets together using adhesive, splicing tape, heat, or solvent-welding. See FACTORY SEAM.
FISHMOUTH
(1) A half-cylindrical or half-conical opening formed by an edge wrinkle;
(2) In shingles, a half-conical opening formed at a cut edge. Openings occurring at the lapped edge of applied felts or in prepared roofing.
FLASHING
A continuation of the roofing proper to cover any element of the roof structure departing from the roof deck incline.
  • BASE FLASHING
The extension of the roofing membrane over the cant and up the vertical surface.
  • CAP FLASHING
The covering, usually sheet metal, which covers the base flashing, or capping a higher wall such as a parapet.
  • COUNTER FLASHING
Sometimes used for the lower portion of the sheet metal flashing when the metal flashing is divided into two pieces.
  • GRAVEL STOP
A formed strip of material, usually metal, nailed around the edges of a gravelled roof to prevent the gravel from rolling or washing off and to add a finished appearance to the roof. It may be combined with the fascia flashing.
  • STEP FLASHING
Individual pieces of flashing material used to flash the sides of chimneys and dormers and similar projections on steeper sloped roofs which are usually shingled. The individual pieces are overlapped and stepped up the slope.
  • THRU-WALL FLASHING
Flashing extending completely through a masonry wall to prevent water infiltrating behind lower elements of the flashing system and roofing system.
FLASH POINT
The temperature at which asphalt becomes volatile and can burst into flame.

G

GLASS FIBRE MAT
A thin mat composed of glass fibres with or without binder used as reinforcing or carrier sheet for a roofing membrane.
GLAZE COAT
(1) The top layer of asphalt in a smooth-surfaced built-up roof assembly;
(2) A thin protective coating of bitumen applied to the lower plies or top ply of a built-up roof membrane when application of additional felts or the flood coat and aggregate surfacing are delayed.
GRAVEL
Coarse, granular aggregate, containing pieces approximately 6 mm (1/4") to 19 mm (3/4") in size and suitable for use in aggregate surfacing on built-up roofs.
GRAVEL STOPS
See FLASHING.
GUM PAN
See PITCH POCKET.

H

HEADLAP
The minimum distance, measured at 90o to the eaves along the face of a shingle or felt, from the upper edge of the shingle or felt to the nearest exposed surface.
HEAT AGING
Controlled exposure to elevated temperatures over time.
HEAT WELDING
A process or method of melting and sealing or fusing together the overlapping edges of separate sections of thermoplastic or uncured elastomeric roofing membranes by the application of heat and pressure. Small, portable “hot air” or “heat welding” devices are available which can, without the use of chemicals or adhesives, heat seal or fuse together overlapping edges to form waterproof seams.
HOLIDAY
An area where a liquid-applied material is missing.
HORIZONTAL APPLICATION
The roofing materials are laid parallel to the eaves and at right angles to the slope.
“HOT STUFF” OR “HOT”
The roofer's term for hot bitumen.
HYGROSCOPIC
The term used to describe a material which attracts, absorbs and retains atmospheric moisture.
HYPALON
A registered trademark of E.I. duPont de Nemours, Inc., for “chlorosulfonated polyethylene” (CSPE).

I

ICE DAM
A build-up of ice at the eave drainage area or in the valley of a sloping roof. This build-up may cause water to back up under the roofing.
INCLINE
The slope of a roof expressed either in percent or in the number of vertical units or rise per horizontal unit of run. See SLOPE.
INORGANIC
Being or composed of matter other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.
INSULATION
A material applied to reduce the flow of heat.
INTENSIVE VEGETATIVE ROOF ASSEMBLIES
Roof top gardens with diverse plant species, irrigated for maintenance and typically having a soil depth equal to or more than 150 mm or 6 inches.
INVERTED ROOF
See PROTECTED MEMBRANE.
IRMA ROOF
See PROTECTED MEMBRANE.

J

K

KETTLE TEMPERATURE
The temperature of the hot material in the kettle. Also see EQUIVISCOUS TEMPERATURE (EVT) RANGE.
KILOCALORIE
Kilogram-calorie or, more commonly, kilocalorie (kcal) is the heat energy required to raise the temperature of 1 kilogram of water one degree Celsius (1 kcal = 3.97 BTU). See BTU.

L

LAP
That part of a roofing membrane which overlaps or covers any portion of another section of membrane which is then sealed to form a watertight connection.
LAP CEMENT
A cut-back asphalt used for cementing the laps in roll roofing or a proprietary adhesive used with certain types of single-ply roofing membranes.
LIVE LOADS
Any mobile roof installation equipment; also includes wind, snow, ice or rain.
LOOSE-LAID MEMBRANES
Membranes which are not attached to the substrate except at the perimeter of the roof. Loose-laid membranes are held in place with appropriate and adequate ballast, such as round river washed stone, gravel, pavers, etc. This assembly may only be used on roof structures able to support the added weight of the ballast, which is generally applied at the rate of ten pounds or more per square foot of roof area.
LOW TEMPERATURE FLEXIBILITY
The ability of a membrane or other material to remain flexible (resist cracking when flexed) after it has been cooled to a low temperature. Low temperature flexibility is important, especially in a membrane which is to be installed during the winter and/or in a cold climate. See LOW TEMPERATURE RESISTANCE.
LOW TEMPERATURE RESISTANCE
The lowest temperature at which a material does not fracture or crack under prescribed impact and flexing conditions. Expressed in oC (or oF).
See LOW TEMPERATURE FLEXIBILITY.

M

MASTIC
A sealant that has a “non-sag” consistency to prevent the material from flowing away from the joint or surface to which it is applied. Mastics are usually applied using a standard caulking gun, a trowel, or a knife. See SEALANT.
MAT
A thin layer of woven, non-woven, or knitted fibre which serves as reinforcement to the membrane.
MECHANICALLY FASTENED MEMBRANES
Generally used to describe single-ply membranes which have been positively attached at intervals to the substrate, usually with various fasteners and other mechanical devices such as battens. Mechanical fastening makes it possible to install membranes over certain substrates, such as gypsum or lightweight concrete fills, which may not accept adhesive or heavy ballasting. Mechanical fastening permits the membrane to float free between the fasteners, and allows greater movement between the membrane and the substrate than in a fully adhered system.
MEMBRANE
A flexible or semi-flexible roof covering or waterproofing layer, whose primary function is the exclusion of water.
MESH
The square or circular opening of a sieve.
METAL FLASHING
See FLASHING; metal flashing is frequently used as through-wall flashing, cap flashing, counter flashing or gravel stops.
MIL
A unit of measure used to indicate the thickness of a roofing membrane. One mil is equal to 0.001 inches or 25.4000 microns (normally applies only to American manufactured materials). Often incorrectly used as an abbreviation of millimetre.
MILL DECK
A wood roof deck constructed of members placed on edge vertically and spiked or nailed together.
MINERAL GRANULES
Opaque, natural, or synthetically coloured aggregate commonly used to surface cap sheets and roofing shingles.
MINERAL STABILIZER
A fine, water-insoluble inorganic material, used in a mixture with solid or semi-solid bituminous materials.
MINERAL SURFACED ROOFING
Built-up roofing materials whose top ply consists of a granule-surfaced sheet. Usually refers to organic roll roofing rather than “elastomeric” or “plastomeric” preformed sheets.
MINERAL SURFACED SHEET
A felt that is coated on one or both sides with asphalt and surfaced with mineral granules.
MODIFIED BITUMEN
A material consisting of bitumen which has been modified through the inclusion of one or more polymers and may contain stabilizers and other additives. Modified bitumen roofing membranes usually also contain a reinforcing material such as glass fibre and / or polyester. See ATACTIC POLYPROPYLENE, STYRENE-BUTADIENE-STYRENE, and STYRENE-BUTADIENE-RUBBER.
MODIFIED PROTECTED MEMBRANE
A roofing system wherein the roofing membrane is applied over a portion of the insulation and under the other portion of insulation which is ballasted. The usual ratio is one-third of the insulation under and two-thirds over the membrane.
MODULUS
The measure of a material's stiffness. Since polymeric materials do not exhibit traditional elastic behaviour, the modulus is not a constant. For a polymeric material, the modulus is reported as the tensile stress required at a given elongation. Expressed as force per unit area at a given percent elongation.
MOP-AND-FLOP
An application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations, are coated with adhesive, and are then turned over and applied to the substrate.
MOPPING
An application of hot bitumen applied to the substrate or to the felts of a built-up roof membrane with a mop or mechanical applicator.
  • SOLID OR FULL MOPPING
A continuous mopping of a surface, leaving no unmopped areas.
  • SPOT MOPPING
mopping pattern in which hot bitumen is applied in roughly circular areas, leaving a grid of unmopped, perpendicular bands on the roof. Seldom used and rarely recommended.
  • SPRINKLE MOPPING
A random mopping pattern wherein heated bitumen beads are strewn onto the substrate with a brush or mop. Seldom used and rarely recommended.
  • STRIP MOPPING
A mopping pattern in which hot bitumen is applied in parallel bands. Seldom used and rarely recommended.
MSMRCA (now RCABC)
The Master Sheet Metal and Roofing Contractors Association of B.C., which is now the Roofing Contractors Association of British Columbia.

N

NAILING
(1) In the Exposed Nail Method, nail heads are exposed to the weather; or
(2) In the Concealed Nail Method, nail heads are concealed from the weather.
NAILING STRIPS
Strips of wood (also called nailers) which are fastened on walls, curbs and steep / sloping non-nailable roof decks to allow the anchoring of flashings. Also used to prevent insulations and any required roof membrane from sliding.
NEOPRENE
A synthetic rubber (polychloroprene) used in liquid-applied and sheet-applied elastomeric roof membranes or flashings.
NINETEEN-INCH SELVAGE
A prepared roofing sheet with a 432 mm (17") granule-surfaced exposure and a non-granule-surfaced 483 mm (19") selvage edge. This material is sometimes referred to as NIS or as Wide-Selvage Asphalt Roll Roofing Material Surfaced with Mineral Granules. See MINERAL SURFACED ROOFING.
NON-VULCANIZED MEMBRANE
A membrane manufactured from thermoplastic compounds that retain their thermoplastic properties throughout the life of the membrane.
NON-WOVEN
A term used to describe the random arrangement of reinforcing fibres (glass, polyester, etc.) in a mat or scrim
NRCA
National Roofing Contractors Association (U.S.A.)

O

ORGANIC
Being composed of hydrocarbons or their derivatives, or matter that is of plant or animal origin.
OVERHEATING
Heating the material in the kettle in such a manner that its characteristics are altered. This alteration can take place either by prolonged heating at proper kettle temperature or by heating for shorter periods at higher than recommended kettle temperature.

P

PARAPET
A low wall along the edge of a roof which is frequently an extension of the perimeter wall of the building structure.
PERLITE
A friable aggregate used in lightweight insulating concrete and in pre-formed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.
PERM
A unit of water vapour transmission defined as one grain of water vapour per square foot per hour per inch of mercury pressure difference (one inch of mercury = 0.49 psi).
PERMEANCE
An index of a material's transmission resistance to water vapour. See VAPOUR.
PHASED APPLICATION
The installation of a roof system or waterproofing system during two or more separate time intervals.
PIB
Abbreviation for “polyisobutylene”.
PICTURE FRAMING
A rectangular pattern of ridges in a roof membrane over insulation or deck joints.
PITCH (SEE TAR)
A short form reference to coal tar pitch. The word may also refer to slope or to the angle above the horizontal of the roof incline.
PITCH POCKET
A flanged, open-bottomed, metal container placed around columns or other roof penetrations that is filled with hot bitumen and / or flashing cement to seal the joint. The use of pitch pockets is not recommended by RGC. Also called “gum pan”.
PLASTICIZER
A chemical substance (e.g. an organic compound) added to natural or synthetic resins for the purpose of increasing flexibility, and facilitating processing and workability.
PLASTIC
Any of a large group of synthetic materials, usually produced by the polymerization of various organic compounds, which can be formed (i.e. molded, cast, extruded, etc.) into flexible sheets or membrane.
PLASTIC CEMENT
Although all caulking cements could be called plastic cement, there is a commonly held acceptance in the roofing industry that plastic cement means bituminous cement. These can be either asphalt or coal tar base with the former much more common. These are a mixture of bitumens, asbestos fibres, filler and suitable solvent.
PLASTOMERIC
A term used to describe any of a large group of plastic-based materials possessing elastic, rubber-like properties.
PLASTOMERIC MEMBRANES
A broad group of plastic-based materials in sheet form, which possess elastomeric properties. Plastomeric materials may be manufactured from a variety of polymers, including various compounds and / or blends or alloys.
PLY
A layer of felt in a built-up roof membrane system. A four-ply membrane system has four plies of felt. The dimension of the exposed surface (the “exposure”) of any ply may be computed by dividing the felt width minus 50 mm (2") by the number of plies; thus, the exposed surface of a 914 mm (36") wide felt in a four-ply membrane should be 216 mm (8-1/2"). See EXPOSURE.
POLYCHLOROPRENE (NEOPRENE)
A synthetic elastomer produced by the polymerization of chloroprene, and used in liquid-applied and sheet-applied roof membranes and flashings. Neoprene may be installed as both a cured (vulcanized) and an uncured (non-vulcanized) sheet membrane.
POLYESTER
A polymeric resin which is generally cross-linked or cured, and made into a variety of plastic materials and products. Polyester fibres are widely used as the reinforcing medium in reinforced flexible sheet membranes as they can provide high tensile strength, tear and puncture resistance.
POLYISOBUTYLENE (PIB)
A synthetic uncured elastomer produced by the co-polymerization of isobutylene and isoprene. PIB roofing membranes are composed of polyisobutylene, and various other reinforcing fillers and stabilizers.
POLYMER
A natural or synthetic chemical compound of high molecular weight, or a mixture of such compounds, formed when small individual molecules, called monomers, are combined and linked together to form large long-chain molecules, called polymers.
POLYMERIC ALLOYS
A physical blend of two or more polymers, combined to modify a given physical property, e.g. tensile strength.
POLYMERIZATION
The process whereby single molecules, called monomers, are combined to form large, chain-like molecules, called polymers. Heat, pressure, and / or chemicals may be used to “trigger” this process, which, depending upon the raw materials used, can produce a wide variety of plastics and synthetic rubbers, a number of which are used in the fabrication of single-ply roofing membranes.
POLYVINYL CHLORIDE (PVC)
A thermoplastic polymer, synthesized from vinyl chloride monomer. See PLASTOMERIC MEMBRANES, THERMOPLASTIC.
POND (PONDING)
The collection of water in shallow pools on the top surface of roofing usually caused by a roof surface that is incompletely drained. Good drainage is essential to good roof design.
POSITIVE DRAINAGE
The drainage condition in which consideration has been made for all loading deflections of the deck, and additional roof slope has been provided to ensure complete drainage of the roof area within 24 - 48 hours of rainfall.
PREPARED ROOFING
A general term applied to all asphalt roll roofing and shingles.
PRIMER
A thin, liquid bitumen applied to a surface to improve the adhesion of subsequent applications of bitumen. Also refers to non-bituminous adhesion enhancers used in proprietary roofing systems and caulking materials.
PROTECTED MEMBRANE
A roofing system wherein the roofing membrane is applied at the structural deck level and the insulation is placed above the membrane and ballasted. Also called inverted or upside-down roof.
PVC
Abbreviation for Polyvinyl Chloride.

Q

R

RAKE
The sloped edge of a roof at the first or last rafter.
RCABC
Roofing Contractors Association of British Columbia.
RE-ENTRANT
An inside corner of a surface wall intersection which may produce stress concentrations in the roofing or waterproofing membrane.
REGLET
A groove in a wall or other surface adjoining a roof surface for use in the attachment or counter flashing, or actual insertion of the roof membrane.
REINFORCED MEMBRANE
A roofing or waterproofing membrane reinforced with felts, mats, fabrics, or chopped fibres.
RELATIVE HUMIDITY
The ratio of the weight of moisture in a given volume of air-vapour mixture to the saturated (maximum) weight of water vapour at the same temperature, expressed as a percentage.
REROOFING
The practice of applying new roofing materials over existing roofing materials; or removal of existing roofing materials and replacement with new. Also and more correctly called Replacement Roofing.
RGC
Roofing Contractors Association of B.C. Guarantee Corp.
RIDGE
The horizontal where roofs sloping in different directions join at the highest point.
RIDGE CAPPING
Waterproofing units applied along the ridge to cover the join between roof surfaces. Ridge capping may be asphalt shingles, wood shingles or shakes, tiles, roll roofing, or metal shaped for the purpose.
RIDGING
An upward “tenting” displacement of a roof membrane, frequently occurring over insulation joints, deck joints, and base sheet edges.
RIEI
Roofing Industry Educational Institute.
ROLL ROOFING
The term applied to smooth-surfaced or mineral-surfaced coated felts.
ROOF ASSEMBLY
An assembly of interacting roof components (including the roof deck) designed to weatherproof, and normally insulate, a building's top surface.
ROOF DIVIDER
A low wall used to break up a large roof area into smaller sections in order to prevent the build-up of stress in the system which could be greater than the roof's ability to withstand.
ROOFER
The trade name for the workman who applies roofing materials.
ROOF SYSTEM
A system of interacting roof components (NOT including the roof deck) designed to weatherproof, and normally insulate, a building's top surface.

S

SADDLE
See CRICKET.
SATURATED FELT
A felt that has been partially saturated with low softening point bitumen.
SCREEN
An apparatus with apertures for separating sizes of material.
SCRIM
A woven, non-woven, or knitted fabric, composed of continuous strands of material used for reinforcing or strengthening flexible sheet membranes. Scrim may be incorporated into the membrane by laminating or coating.
SCUPPER
An overflow through a parapet wall. A type of eave drain through a flashing detail which connects to a rainwater leader.
SEAL
(1) A narrow closure strip made of bituminous materials;
(2) To secure a roof from the entry of moisture.
SEALANT
A mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movement is expected; it may cure to a resilient solid or remain in a mastic or semi-mastic state. Also called “caulking”.
SEAM
A joint formed by mating together two separate sections of roofing membrane. Seams may be sealed in a variety of ways, including hot-air welding, solvent welding and adhesive bonding. Regardless of the method used, however, all seams should be permanently joined together to assure watertight integrity and to be able to withstand all strains and stresses caused by application, wind uplift, installation equipment and foot traffic.
SEAM STRENGTH
The force or stress required to separate or rupture a seam in the membrane material. See SEAM.
SELF-ADHESIVE MEMBRANES
Single-ply membranes which can adhere to a substrate and to itself at overlaps without the use of an adhesive. The undersurface of a self-adhesive membrane is protected by a “release paper”, which prevents the membrane from bonding to itself during shipping and handling. Later, as the membrane is unrolled, the release paper is peeled away and the self-adhering undersurface is applied to the substrate. Successful application of a self-adhesive membrane requires a clean and dry substrate and the application of firm, uniform pressure.
SELVAGE
An edge or edging that differs from the main part of a fabric, or granule-surfaced roll roofing material.
SELVAGE JOINT OR EDGE
A lapped joint designed for mineral-surfaced cap sheets. The mineral surfacing is omitted over a small portion of the longitudinal edge of the sheet below in order to obtain better adhesion of the lapped cap sheet surface with the bituminous adhesive.
SHARK FIN
An upward-curled felt side lap or end lap.
SHEATHING PAPER
A medium to heavy breather-type building paper or felt, usually asphalt treated, secured to wall or roof deck before the application of the covering material. Most commonly used under shingles in residential construction. Also referred to as UNDERLAYMENT.
SHINGLE
(1) A small unit of prepared roofing material designed to be installed with similar units in overlapping rows on inclines normally exceeding 1:4 (3" in 12");
(2) To cover with shingles;
(3) To apply any sheet material in overlapping rows like shingles.
SHINGLING
(1) The procedure of laying parallel felts so that one longitudinal edge of each felt overlaps and the other longitudinal edge underlaps an adjacent felt. (See PLY.) Normally, felts are shingled on a slope so that the water flows over that rather than against each lap;
(2) The application of shingles to a sloped roof.
SIDE LAP
See EDGE LAP.
SIEVE
An apparatus with apertures for separating sizes of material.
SINGLE-PLY MEMBRANES
Roofing membranes that are field applied using just one layer (usually) of membrane material (either homogeneous or composite) rather than multiple layers. However, the manufacture of the single-ply sheeting may involve lamination or several layers of the same or different materials.
SINGLE-PLY ROOFING
A roofing system in which the principal roofing component is a single-ply flexible membrane of elastomeric, plastomeric, or modified bituminous compounds.
SINGLE-PLY SYSTEM ASSEMBLIES
There are six major types of single-ply roofing systems assemblies:
(1) Loose-laid (4) Totally-adhered
(2) Self-adhesive (5) Mechanically-fastened
(3) Partially-adhered (6) Protected Membrane Roof Assembly
SLAG
A hard, air-cooled aggregate that is left as a residue from blast furnaces. It is used as a surfacing aggregate and should be surface-dry, graded and free of sand, clay, or other foreign substances at the time of application.
SLIP SHEET
Sheet material, such as reinforced kraft paper, polyester scrim, or polyethylene sheeting, placed between two components of a roofing system (such as membrane and insulation) to ensure that no adhesion occurs between them, and to prevent possible damage from chemical incompatibility.
SLIPPAGE
The relative lateral movement of adjacent components of a built-up roof membrane. It occurs mainly in roof membranes on a slope, sometimes exposing the lower plies to the weather.
SLOPE
The tangent of the angle between the roof surface and the horizontal. The incline or pitch of a roof surface. Example 1:50 (approximates 20 mm in 1 m [1/4" per foot]).
SMOOTH-SURFACED ROOF
A built-up roof membrane surfaced with a layer of hot-mopped asphalt, cold-applied asphalt-clay emulsion, cold-applied asphalt cutback, or sometimes with an unmopped inorganic felt.
SOFTENING POINT
The temperature at which bitumen becomes soft enough to flow. The softening point of asphalt is measured by the “ring-and-ball” test ASTM Standard D36. The softening point of coal tar pitch is measured by the “cube-in-water” test ASTM Standard D5.
SOFTENING POINT DRIFT
A change in the softening point of bitumen during storage or application. See DROPBACK.
SOLID-MOPPING
See MOPPING.
SOLVENT CLEANERS
Heptane, hexane, white gas, and unleaded gas, used to clean the membrane prior to applying the splicing adhesive in some single-ply roofing systems. Also may be aromatic solvents such as Xylene, Toluene or Methyl Ethyl Ketone (MEK).
SOLVENT WELDING
A process used to chemically weld or join together two or more layers of certain membrane materials (usually thermoplastic), by applying a solvent, such as tetrahydrofuran (or THF), to the overlapping surfaces and mating them when the bonding surfaces become tacky. Used most often in welding or sealing seams.
SPECIAL STEEP ASPHALT
A roofing asphalt that has a softening point of approximately 104oC (220oF) and that conforms to the requirements of ASTM Standard D312, Type IV (U.S. designation).
SPLICE
See SEAM.
SPLICING TAPE
Cured or uncured synthetic rubber tape used for splicing in lieu of “contact adhesives”.
SPLIT
A separation in roofing material resulting from movement of the substrate. See CRACK.
SPOT-MOPPING
See MOPPING.
SPREAD COATING
A manufacturing process in which the compound (plastisol) is prepared in mixers and then fed to individual coaters. The mixture is cold until after it is spread onto the supporting base (reinforcement). After coating, the membrane passes through a heating channel which causes it to change from a paste to a solid.
SPRINKLE-MOPPING
See MOPPING
SPUNBOND POLYESTER MAT
Continuous filament, uniformly dispersed polyethylene terepthalate fibre mat. A binder is used to stabilize the mat, which serves as reinforcement to the membrane.
SQUARE
The common industry term used to describe 100 square feet of roof area (approximately 10 m2).
SQUARE BUTT
A term commonly applied to strip-type asphalt shingles.
STABILIZER
An ingredient in the formulation of single-ply membranes added to improve certain physical properties which are important for processing, storage, workability, and performance.
STACK VENT
A vertical outlet in a built-up roof system designed to relieve any pressure exerted by moisture vapour between the roof membrane and the vapour retarder or deck.
STARTER STRIP
A roofing material applied at the eaves and serving as a base for the first course of roofing.
STEEP ASPHALT (Type 3 Asphalt)
A roofing asphalt that has a softening point range of 90oC to 98oC (194oF to 208oF) and that conforms to the requirements of CSA A123.4-M1979 Type 3.
STRAWBERRY
A small bubble or blister in the flood coating of a gravel-surfaced roof membrane which has penetrated to the gravel surface and is exposed to the weather.
STRIP MOPPING
See MOPPING.
STRIP FASTENER
See BATTEN.
STRIPPING OR STRIP FLASHING
(1) The technique of sealing a joint between metal and the built-up roof membrane with one or two plies of felt and hot-applied or cold-applied bitumen; the technique of taping joints between insulation boards on deck panels;
(2) Base ply flashing and surface protection of built-up membranes at parapets, etc.
STYRENE-BUTADIENE RUBBER
High molecular-weight polymers having rubber-like properties, formed by the random copolymerization of styrene and butadiene monomers. Polymers of this type are often cross-linked to give maximum rubber-like properties in service. These polymers are sometimes used as the modifying compound in certain modified bitumen roofing membranes.
STYRENE-BUTADIENE-STYRENE COPOLYMER (SBS)
High molecular-weight polymers which have both elastomeric and thermoplastic properties, formed by the block copolymerization of styrene and butadiene monomers. The three block copolymer formed has a centre block of butadiene with end blocks of styrene. These polymers are sometimes used as the modifying compound in certain modified bitumen roofing membranes.
SUBSTRATE
The surface upon which the roofing or waterproofing membrane is applied, i.e. the structural deck or insulation.
SUPERIMPOSED LOADS
Loads that are added to existing loads. For example, a large stack of insulation boards or other material placed on top of a roof deck.

T

TAB
The portion of an asphalt shingle projecting below the following course and separated from the adjacent tab by a slot.
TALC
A fine white powder which may be present on the surface of vulcanized EPDM or other membranes, used in the manufacturing process to prevent adhesion of the membrane to itself. The same purpose can also be served by the use of mica dust or in some cases, sand.
TAPERED EDGE STRIP
A tapered insulation strip used to
(1) elevate the roof at the perimeter and at curbs that extend through the roof;
(2) provide a gradual transition from one layer of insulation to another.
TAPING
Technique of taping joints between insulation or overlay boards to prevent drippage of bitumen.
TAR
A brown or black bituminous material, liquid or semi-liquid in consistency, in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum oil-shale, wood, or other organic materials. Rarely used. The term tar and gravel really means asphalt, felt, and gravel roofs.
TARRED FELT
A felt that has been saturated with refined coal tar.
TEST CUT
A sample of the roof membrane, usually 100 mm x 1000 mm (4" x 40") in size, that is cut from a roof membrane to:
(1) Determine the weight of the average inter-ply bitumen moppings;
(2) Diagnose the condition or components of the existing membrane.
RGC recommends that the test cut procedure NOT be used as the only means of determining the quality of a roof system.
THERMAL SHOCK
The stress-producing phenomenon resulting from sudden temperature changes in a roof membrane (for example, when a rain shower follows brilliant sunshine).
THERMOPLASTIC
Polymers which soften when heated and harden when cooled. This process is repetitive provided the material is not heated above the point at which decomposition occurs.
THERMOPLASTIC ELASTOMERS
Compounds formulated from materials traditionally used for vulcanized rubber. Curing agents are controlled in the compound so cross-linking does not occur, and the final product exhibits the properties of a thermoplastic material.
THERMOSET
A material that solidifies or “sets” irreversibly when heated. This property is usually associated with cross-linking of the molecules induced by heat or radiation.
THROUGH-WALL FLASHING
A water-resistant membrane or material assembly extending through a wall and its cavities, positioned to direct any water entering the top of the wall to the exterior.
TOTALLY ADHERED
A roofing assembly in which a single-ply membrane has been fully adhered to a substrate, usually with the aid of an appropriate contact or water-based adhesive or emulsion. Totally adhered membranes are often installed on roofs which, because of their slope, construction, or other factors, cannot support adequate ballast, or into which mechanical attachment is difficult.
TPO
Abbreviation for Thermoplastic Polyolefin

U

ULTIMATE ELONGATION
The amount a membrane sample stretches during tensile testing before it ruptures. Usually expressed as a percentage of the original length.
ULTRAVIOLET (UV)
Ultraviolet radiation from the sun is known to be potentially damaging to certain bitumens and chemical compounds used in roofing membranes. Formulations with stabilizers and UV absorbers effectively inhibit the potentially deleterious effects of UV exposure. Mineral surfaced sheets and roofing gravel are typical reflectants.
UNDERWRITERS LABORATORIES (UL)
An organization that classifies roof assembles for their fire characteristics and wind-uplift resistance for insurance companies in United States.
UNDERWRITERS LABORATORIES CANADA (ULC)
An organization that classifies roof assembles for their fire characteristics and wind-uplift resistance for insurance companies in Canada.

V

VALLEY
The junction of two sloping roof planes at the lower end of the slope. Opposite of a ridge or hip.
VAPOUR MIGRATION
The movement of water vapour from a region of high vapour pressure to a region of lower vapour pressure.
VAPOUR-PRESSURE GRADIENT
A graph, analogous to a temperature gradient, indicating the changes in water vapour pressure at various cross-sectional planes through a roof or wall system.
VAPOUR RETARDER
A material designed to restrict the passage of water vapour through a wall or roof. In the roofing industry, a vapour retarder should have a perm rating of 0.5 or less. Commonly misnamed “vapour barrier”.
VENT
An opening designed to convey water vapour or other gas from inside a building or a building component to the atmosphere, thereby relieving vapour pressure.
VERMICULITE
An aggregate used in lightweight insulating concrete, formed by the heating and consequent expansion of a micaceous mineral.
VERTICAL APPLICATION
The sheets of roofing materials are run up and down the slope of a roof rather than along the horizontal.
VISCOSITY
The measure of flow resistance of a fluid at a specific temperature and pressure. Viscosity is the reciprocal of fluidity. Hot asphalt flows and mops easily - it has low viscosity and high fluidity. Liquid asphalt below its equiviscous temperature range has a viscosity substantially greater than 125 centistokes - it has high viscosity and low fluidity.
VULCANIZATION
Any of various processes by which natural or synthetic rubber or other polymeric materials may be cured or otherwise treated (i.e. exposed to chemicals, heat, or pressure) to render them non-thermoplastic, and which improves their elastic properties through this chemical change.

W

WATER CUTOFF
See CUTOFF.
WATERPROOFING
Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.
WIND UPLIFT
The loss of attachment between a roof system or components in a roof system resulting from wind-induced pressures. Wind that is deflected around and across the surfaces of a building causes a drop in air pressure immediately above the roof surface; as a result the air in the building will flow beneath the membrane and roof deck and lift the roof upward. Wind uplift may also be caused by the introduction of wind underneath the membrane and roof edges, where it can cause the membrane to balloon and pull away from the substrate. Roof loss by wind can be avoided, or prevented, by proper installation and adequate adhesion, attachment, or ballasting.

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General Information