Click on a letter from the below alphabet for a definition of roofing terms.

 # |  A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

#14 Screw - #14 represents the gauge (thickness) of wire used to manufacture the screw.

10' / 120" Laps - Term used to identify the style of deck sheet. The membrane width between tabs on the sheet will be 120" with 6" fastening tabs. A 10' lap system will be "picture framed" on the exposed perimeter edges of the building using a 7' 6" deck sheet and having a 31" reverse lap. This can also be accomplished by ordering 2 tabs to be built into the deck sheet, one tab at 31", and the second at 91" from the beginning. The remainder of tabs will be spaced at 120".

5' / 60" Laps - Term used to identify the style of deck sheet. The membrane between the tabs on the sheet will be 60" with 3" fastening tabs. A 5' lap system will utilize a minimum 24-36" wind tab on outside exposed edges. This can be accomplished by ordering the deck sheet with a 31" reverse tab.

28" Laps - Term used to identify the style of deck sheet. The membrane between the tabs on the sheet will be 28" with 3" fastening tabs. Typically used to enhance wind uplift or substrates with low pull out value with a standard 31" reverse tab.

3 Mil Slipsheet - Also known as visqueen, a .003 inch (three thousands of an inch) thick polyethylene or polypropylene plastic sheeting used for separating incompatible products from Duro-Last membrane.

31" Reverse - A reverse lap with the fastening tab falling 31" from the beginning of the deck sheet (may also act as a "Wind Tab").

63" Reverse - A reverse lap with the fastening tab falling 63" from the beginning of the deck sheet.



Alligatoring - Surface cracking due to oxidation and shrinkage stresses, which shows as mounding of an asphalt surface, resembling the hide of an alligator.

ANSI - American National Standards Institute.

ARP Material - Asphalt Resistant Polymer / Asphalt Resistant Product.

Asphalt Shingles

Asphalt - a. A dark brown to black substance found in natural beds and is also obtained as a residue in petroleum or coal tar refining that consists chiefly of hydrocarbons. b. Ansphaltic composition used for pavements and as a waterproof cement.

ASCE-7 - American Society of Civil Engineers. ASCE-7 provides the basis for Duro-Last to determining the fastening patterns and deck sheet designs for roofs that are in high wind zones, or buildings over 40' in height, considering information such as the building height, location, wind zone speeds, pull tests, and parapet wall heights. Other factors will also have a direct impact on the design.

Asphalt - A dark brown or black substance found in a natural state or, more commonly, left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt may be further refined to conform to various roofing grade specifications.

Asphalt Shingle - A shingle manufactured by coating a reinforcing material (felt or fibrous glass mat) with asphalt and having mineral granules on the side exposed to the weather.

Attic - The open space between the underside of the roof sheathing and the upper side of the ceiling directly below the roof.

Auger Fastener - A nylon screw type fastener used in decks such as lightweight concrete, gypsum and tectum. For Duro-Last installations, a 7/16" – 9/16 pilot hole.



Back Seal - Duro-Last approved sealant that is used between the membrane and substrate, such as Duro-Last caulk or strip mastic.

Ballast - Aggregate such as river rock or concrete pavers used as an anchoring material to hold roofing material in place.

Base Sheet - A heavy sheet of felt sometimes used as the first ply in built-up roofing.

Base Flashing - A. That portion of the flashing that is attached to or rests on the roof deck to direct the flow of water on the roof, or to seal against the roof deck. b. A material applied to the base of a wall extending above a roof, as a protection for the junction of the wall, and the roof.

Bitumen - Bitumens are mixtures of hydrocarbons of natural or pyrogeneous origin; or combinations of both, frequently accompanied by their non-metallic derivatives, which may be gaseous, liquid, or solid, and which are completely soluble in carbon disulfide. In the roofing industry the word covers both asphalt and coal tar pitch.

Blind Nailing - Shingles nailed in such a location that when the next shingle is applied, the nails of the first shingle do not show.

Blisters (structural) - The more evident and serious blisters are structural blisters. They are caused by the expansion of trapped air and water vapor or other gases. Air and moisture trapped within the construction tend to expand during a rise in air temperature of from the heat of the sun. This expansion causes the plies of the roofing to seperate and bulge the roof surface in a balloon effect.

Block Method - Method of applying shingles in vertical rows from eave to peak instead of horizaontal rows. This method makes shading more noticeable and can lead to improper fastening. Also called straighth up method.

Bond - Adherence between elements of the roof system.

Boot - A covering made of flexible material, which may be preformed to a particular shape, used to exclude dust, dirt, moisture, etc., from around a penetration. Also, a flexible material used to form a closure, sometimes installed at inside and outside corners.

Breather Vent (away)

Breather - A type of roof vent consisting of a hooded flanged pipe 2" to 8" in diameter, penetrating the roofing membrane to allow escape of moisture from insulation.

Bridging - When membrane or base flashing is unsupported at a juncture.

Buckling - Warping or wrinkling of the roof membrane.

Built-up Roofing - layers of roofing felt bonded together on site. A protective surface coating of gravel or slag is sometimes embedded in a heavy top coating of hot bitumen.

Building Code - The minimum construction requirements established generally by national organizations of experts and adopted completely or in altered form by local governing authorities.

BUR - Built Up Roof. A semi-flexible multi-ply roof, consisting of plies or layers of saturated or coated felts, fabrics, or mats with bitumen between each layer. BUR roofs are normally surfaced with mineral aggregate, liquid coating or granule-surfaced cap sheet.

Butyl Tape - A sealant tape sometimes used between metal roof panel seams and/or end laps. It is also used to seal other types of sheet metal joints, and in various other sealant applications.



Calendar Process - The process by which the top layer and bottom layer of thermoplastic PVC film is created. These 2 films are laminated to a polyester scrim to create the Duro-Last membrane used for roof deck sheets and accessories.

Cant - A beveled or triangular-shaped strip of wood, insulation, or other material designed to serve as a gradual transitional plane between the horizontal surface of a roof deck and a parapet wall or other vertical surface. Cants are NOT required by Duro-Last, and when possible should be removed.

Carpet Roll - A deck sheet that is rolled onto a 25' long cardboard tube. These are rolled up in the length of lap direction and can not be longer than 25'. The ideal length is 23' 6" long to protect the ends of the sheet from being damaged in shipping. When the deck sheet is unrolled, the fastening tabs will be exposed one at a time for fastening.

Cap Flashing - Portion of flashing built into a vertical surface to prevent the flow of water behind the base flashing. The cap flashing overlaps and caps off the top of the base flashing.

Caulking - The physical process of sealing a joint or juncture, or sealing and making weather-tight the joints, seams or voids between adjacent surfaces by filling with a sealant.

CDR Ring - Composite Drain Ring. A pair of rings made of a composite material used as a compression water cut-off in the Duro-Last drain boot. See detail 2020 and data sheet.

Cement Asphaltic Plastic - A mixture of asphalt, solvent and mineral stabilizer used to adhere flashings or to fill pan flashings.

Closed Valley with shingles laced through.

Closed Valley - A valley where the flashing is covered by shingles.

Chalk Line - A line made on the roof or other flat surface by snapping a taut string or cord dusted with colored chalk.

Chemical Resistance - The ability of a material to withstand contact with specified chemicals without a significant change in properties.

Cleat - A continuous metal strip or angled piece, used to secure metal components.

Clip - A non-continuous metal component or angle piece used to secure two or more metal components together..

Closed Curb Flashing - A curb flashing that is custom fabricated at the factory using Duro-Last membrane. It is made to slide over the top of the curb frame and flash (waterproof) the four sides of the curb. Closed flashings are welded to the deck sheet and terminated at the top.

Closed Curb Flashing With Top - A curb flashing custom fabricated at the factory using Duro-Last membrane. It is made to slide over the top of the curb frame, enclosing the top and four sides. A closed curb with top flashing needs only to be welded to the deck sheet.

Coal Tar Pitch - A bituminous material produced by distilling crude tar residue derived from the cooking of coal. It is used as the waterproofing material for tar and gravel built-up roofing.

Concealed Nailing - Application of roll roofing in such a manner as to conceal or cover all nail heads used to fasten the roofing to nail able decks.

Condensation - The change from water vapor to liquid water, resulting from a drop in temperature of an air vapor mixture.

Conductor - A pipe for conveying rainwater from a roof gutter to a drain or from a roof drain to a storm drain.

Coping - The cap or highest covering course of a wall, usually overhanging the wall and having a sloping top to carry off water.

Counter Flashing - Strips of metal, roofing, or fabric inserted and securely anchored to the regle or attached to a vertical surface above the plane of the roof and turned down over the face flashing to protect the base flashing.

Course - Row of shingles that can run horizontally, diagonally or vertically.

Cold Tar Pitch - A coal tar-derived product used as the waterproofing agent in dead-level or low-sloped built-up roof membranes and membrane waterproofing systems, conforming to ASTM Specification D 450, Type I.

Combustible - Capable of burning.

Compatible Materials - Two or more substances that can be mixed, blended, or attached without separating, reacting, or affecting the materials adversely.

Concrete Nails - A nail specially designed for installation into concrete. For Duro-Last installations, pre-drill the concrete deck with a 3/16" masonry bit a minimum of 1½” deep to seat the concrete nail a minimum 1” deep. See data sheet.

Concrete Screw - A square drive, #14 screw with high-low threads, specially designed for installation into concrete. For Duro-Last installations, pre-drill the concrete deck with a 3/16" masonry bit a minimum of 1½” deep to seat the concrete screw a minimum 1” deep. See data sheet.

Contractor Responsibilities - The contractor is responsible for following all applicable plumbing, building, electrical and safety codes, using standard roofing practices and proper safety procedures, and following OSHA guidelines. The contractor must also assure that the installed system meets or exceeds all project specifications as well as all local and other safety rules, regulations, and codes.

Control Joint - A groove that is formed, sawed, or tooled into a concrete or masonry structure to regulate the location and amount of cracking and separation resulting from the dimensional change of different parts of the structure, thereby avoiding the development of high building stresses.

Conterflashing - 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.

Coping Cap - The covering piece on the top of a parapet wall, usually made of metal, masonry, or stone.

Core Cuts - A series of sample cut outs that are taken through the existing roof, typically down to the roof deck. Core cuts determine the thickness, moisture, and make up of the existing roofing assembly, as well as the type and length of fastener to be used.

Core Cutter - A tool used to make core cuts into the existing roof assembly. May be purchased through the Duro-Last sales department.

Corners 12" x 18" - Outside corners commonly used for emergency field fabrication of curb flashings or on parapet walls that are wider then average.

Corners – Drip Edge & Gravel Stop - Duro-Last extruded 2" & 4" drip edge and gravel stop corners are mitered at 90° and are available in outside corners only.

Cracking - After long exposure, a fissure or fissure pattern appearing on the shingle of roofing due to weathering of the asphalt.

Curbs on top of
Duro-Last flat roof.

Curb - A wall of wood or masonry built above the level of the roof, surrounding a roof opening such as for installation of roof fans or other equipment.

Canted Curb - A curb or frame that is placed over an opening through the roof to support equipment such as air conditioners or other large units. If the curb or frame has a beveled 45-degree cant, it is called a "canted curb." Order a Duro-Last curb flashing with a 12" skirt to accommodate the canted curb.

Cure - A process whereby a material forms permanent molecular linkages by exposure to chemicals, heat, pressure and/or weathering.





Data Sheet - Provides a detailed description of the product and lists basic uses and installation guidelines.

Dead Load - The total weight of all installed materials and the constant weight of a roof used to compute the strength of all supporting framing members.

Deck/Roof Deck - The structural component of a roof that provides the substrate to which the roofing or waterproofing system is applied.

Deck Sheet / Roof Section - A custom pre-fabricated section of Duro-Last membrane that covers a portion or all of the roof deck. Deck sheets can be made up to 2,500 square feet using 40 mil material, with no single dimension greater than 100’ feet in width or length, or 2000 square feet using 50 mil material, with no single dimension greater than 80’ in width or length. 40-mil membrane weighs 25 lbs. per square and 50-mil weighs 33 lbs. per square.

Dormer - A seperate smaller roofed structure that projects from a sloping roof to provide more space below the roof anf to accommodate a vertical window.

Downspout - A pipe conveying rainwater from a roof gutter to a drain.

Drip Edge - A modified L-shaped flashing used along the eaves and rakes. The drip edge directs runoff water into the gutters and away from the fascia.

Drain: An outlet on the roof used to collect and direct the flow of runoff water from a roof area.

2-Inch Adapter Drain is a drain flashing made with a 1/4" washer welded to a Duro-Last skirt used on drains that are 2" or less.

Drain Boot with CDR Rings is an inverted stack flashing made of Duro-Last membrane material designed to line the pipe, and 2 composite (compression) rings that are used inside the drain for water cut-off. Caulk is used between the drain and the drain boot at the point where the CDR rings will be fitted. Once the CDR rings are in place inside the drain boot, the strings are cut to give compression, preventing water from backing in under the system.

PVC Drain is sold through Duro-Last and is a either a 3" or 4" PVC bowl style roof drain with a cast iron strainer. See detail 2011 & data sheet.

Leaf Strainer is a flexible plastic strainer for 3” and 4” drains only.

Scupper Liner is a through-wall drain flashing with a 6" skirt on one or both ends.

Vinyl Coated Metal Scupper is a vinyl coated metal through-wall drain flashing with a 6" skirt on one or both ends.

Drill Bit / SDS - A drill bit with a titanium carbide tip and a Slotted Drill Shank (SDS). Typically used with a hammer drill.

Drill Bit / Straight - Straight shank bit with a carbide tip.

Drill Bit / TE-CX - Hilti TE-CX is a Slotted Drill Shank (SDS) bit with a solid carbide tip.

Duro-Cap Metal Edge System - 24 gauge galvanized steel or aluminum with Kynar coating or mill finish designed to snap on to Duro-Last extruded fascia and gravel stop edge details.

Duro-Flash Counterflashing - A 1/8" x 3" extruded pad with an attached Duro-Last 6" skirt available in 10' lengths. The pad is secured on or into a wall, curb, unit etc. to cover and protect the upper edge of the membrane base flashing, and field welded to the curb or parapet flashing.

Duro-Fold Underlayment - 3/8" thick fanfold underlayment is made of extruded polystyrene, has 1.25# density, and is covered on both sides with a polyethylene facer.

Duro-Last Fasteners - Mechanical securement devices such as screws and nails.

Duro-Last Membrane 40 Mil - Duro-Last material, nominal .040 inches thick. See Data Sheet.

Duro-Last Screws - Duro-Last #14 heavy-duty screws are for use in wood, steel and lightweight concrete decks. Two styles are available: P-3 or square drive head. We also offer spade or drill point and all are Factory Mutual approved. A Duro-Last #15 heavy-duty screw is also available for deck types that are sub-standard.



Eave - The horizontal roof overhang that extends outward and is not directly over the exterior walls or the buildings interior.

Edge Details - Rigid edge terminations that help make rooftop perimeters watertight.

2" & 4" Drip Edge is made from rigid, extruded vinyl, and has an attached 6" skirt. It is fastened 8" on center to the deck or wood nailer with approved fasteners and the skirt is heat-welded to the field membrane. Drip edge can be installed on any flat edge including the top of the parapet wall.

2" & 4" Gravel Stop is made from rigid, extruded vinyl, and has an attached 6" skirt. It is fastened 8" on center to the deck or wood nailer with approved fasteners and the skirt is heat welded to the field membrane. Gravel stop can be installed on any flat edge including the top of the parapet wall. Kynar coated metal Duro-Cap covers are also available on request.

Fascia Bar 1 ¾” "& 4" with Cover is made from rigid, extruded vinyl. It is fastened 6" on center and may be used as perimeter detail and as termination on any square or rectangular penetration. Kynar coated metal Duro-Cap covers are also available on request.

Termination Bar is a ridged, extruded vinyl termination bar and shall be fastened 6" on center to the deck or wood nailer with approved fasteners. Termination bar may be used as perimeter detail and as termination on any square or rectangular penetration.

Elk - Shingle manufacturer based out of Texas, provides elegant and innovative shingles.

Ell - An extension of a building at right angles to its length.

Embossed - The molded, textured or raised side of the Duro-Last material.

End Lap - The amount of overlap at the end of a ply on the application of roll roofing.

Encapsulate - To enclose or wrap with membrane.

Escutcheon Washer - Used to seal around small round penetrations on vertical surfaces such as parapet walls. See detail 7010 and data sheet.

Expansion Joint - A planned, controlled joint placed between two roof surfaces or between two sections of a built-up roof. Expansion joints allow roofs to expand without causing harm to building.

Exposure - Portion of shingle that is exposed to the weather.



Face Nailing - Nailing with the nails placed in the exposed area or face of the shingle.

Factory Mutual - Factory Mutual Research Corporation (FMRC) is a testing agency that tests and measures wind uplift resistance, fire spread, and hail damage characteristics.

Factory Weld - A pre-fabrication weld that is made in-house under controlled, ideal factory conditions using a dielectric or hot air process. Duro-Last will pre-fabricate about 80% of welds on any project under quality controlled conditions to reduce contractor fabrication in the field. Factory welds are also used to pre-fabricate custom ordered deck sheets, curbs, parapets and accessories.

Fastening Tab - During the fabrication process of a deck sheet or parapet flashing, a 3" tab is incorporated into the bottom side of the deck sheet or back side of the parapet flashing to attach the membrane to the substrate. Tabs are located on the bottom side of the factory weld to insure all fastening is done on the underside of the sheet.

Fascia - A wood trim board used to hide the cut ends of the roof's rafters and sheathing. The gutter system is usually nailed to the fascia.

Duro-Last fastening tab.

Felt - A very general term used to describe roll roofing materials, consisting of a mat of organic or inorganic fibers.

Felt (glass) - A non-woven mat of flexible glass fiber, formed by spreading fibrous material over a screen and pressing it together to form a sheet.

Felt (15 & 30) - Asphalt or coal tar saturated felt weighing approximately 15 or 30 pounds per 100 square feet.

Fire Wall - Any wall built for the purpose of restricting the spread of fire in a building. Such walls of solid masonry or concrete usually divide a building from the foundations to about a meter above the roof.

Fire-Resistant - Material that is resistant to catching on fire.

Fish Mouthing - The raising of a portion of the butt edge (lower edge) of a shingle. This curved short section tapers back into the shingle. Usually, only the front part of the shingle is affected. Often the reslut of moisture absorption followed by moisture evacuation in the shingle.

Field Weld - A 1-1/2" wide weld that fuses membrane together by using a hot air welder and silicone roller, and/or auto-welder. These welds are created on the job site to connect all roofing deck sheets and components together to form Duro-Last’s monolithic, water tight roofing system. See detail 1010.

Fire Rating - UL Standards for External Fire Testing for Roof Coverings (UL 790). The requirements cover the performance of roof covering materials exposed to fire conditions originating from sources outside of buildings on which the coverings are installed. The UL 790 rates roof coverings as having a Class A, B, or C fire ratings.

Flashing (eaves) - Treatment of the edge of a roof with metal.

Flashing - Metal strips used to form a watertight seal between the items butted up against the shingles. Flashing is used along walls, chimneys and dormers. Metal is usually 28 gauge galvanized sheet metal, but may be lead, copper, tin or aluminum.

Flute - The metal rib high point on metal substrates/decks. A valley is typically the area between two flutes and may need to be filled using an appropriate flute filler when installing Duro-Last’s metal retrofit system, the Duro-Shield system.

FR10/50 ATLAS - Fire retardant mat (fire barrier sheet).

Full Reverse - A reverse lap with the fastening tab located 63" from the beginning of the deck sheet. The remaining tabs on the sheet fall in the normal direction.



Gable - The triangular end of an exterior wall from the level of the eaves to the ridge of a double-sloped roof.

GAF - Shingle manufacturer based in New Jersey. Have been in business since the l886, GAF has a wide variety of shingle styles and colors.

Gambrel Roof - A type of roof which has its slope broken by an obtuse angle, so that the lower slope is steeper that the upper slope. A double-sloped roof having two pitches.

Grande - Elk's newest shingle offering. More than40% bigger than standard shingles. Has a 90 mph wind warranty.

Gravel Stop - A gravel guard used at the rakes and eaves of a built-up gravel coated roof.

GripPull - A stand-up tool with Visegrips and pulleys, used to pull wrinkles out of the Duro-Last deck sheet during installation.

Gutter - A channeled metal component installed along the down slope perimeter of a roof to convey runoff water from the roof to drain leaders or downspouts.



Half Sheet - Also known as a “half tabs” or “28” laps.”

Header - The beam into which the common joists are fitted when framing around a roof opening.

Head Lap - The overlapping of shingles or roofing felt at their top edge.

Walk behin heat welder used in welding Duro-Last seams.

Heat Welding - A hot air process where two seperate pieces of material are welded together.

Hip Roof - A roof, which rises by inclined planes from all four sides of a building. The line where two adjacent sloping sides of a roof meet is called the hip.

Hot Air Weld - See field weld.

Hot Pipe - A round roof penetration that is consistently 110 degrees Fahrenheit or more in temperature.

HVAC Units - Heating, ventilation, and air conditioning equipment.



Inside / Outside Corners 6” x 6” - Corners made of Duro-Last membrane, installed for aesthetic reasons. Outside corners are required at any transition where the deck material must be cut to bend over an edge or wall. Inside corners are optionally used at the installers discretion.

Insulation - Material such as poly-isocyanurate, or expanded or extruded polystyrene, used under the roof membrane to prevent the passage of heat. An appropriate separator sheet must be used when installing Duro-Last membrane over incompatible insulation.









Lap Cement - A cut back asphalt used for cementing the laps of roll roofing.

Lap - The distance between factory welds on a deck sheet.

Live Load - The total weight of all installed equipment and materials and all variable weight that will move across a surface.



Mastic - A tape like sealant used as water block.

Membrane - A saturated cotton or burlap fabric used for certain built-up roofing applications. Also a waterproofing system or roof covering.

Metal Anchors - Also known as “mollies.” Zinc plated and designed to be driven into a 1/4” hole and set with a hammer.

Mil - A unit of measure. One mil is equal to 0.001 inches, or 25.4 micrometers. Often used to indicate the thickness of a roofing membrane.

Moisture Relief Vent - A venting device installed through the Duro-Last roofing membrane to relieve moisture vapor pressure from within the roofing system.

Monolithic - Formed from or composed of a single material; seamless.



Nailer - Also known as blocking, a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, providing a receiving medium for fasteners used to attach membrane or flashing.

Nailing Strips - Strips of wood placed at the eaves of all types of roof decks except wood, and at the tops of masonry expansion or ventilation curbs for attaching the flashing. Also called nailers.

Night seal or Night tie-in - Materials and/or methods used to temporarily seal a membrane edge during construction to protect the uncompleted roofing assembly from water penetration. Usually removed when roofing application is resumed.



Open Curb or Stack Flashing - A curb or stack flashing made to be wrapped around a roof curb or pipe stack and must be welded closed and welded to the deck sheet and then terminated at the top. Open curbs are produced with an additional 3" of membrane for vertical field welding the item closed.

Open Valley, shingles peel away from valley metal .

Open Valley - A valley where the flashing is exposed to the weather. (NOT A GOOD PRACTICE)

Overhang - That portion of roofing extending beyond the deck. As related to the roof structure, that part of the roof structure which extends beyond the exterior walls of a building.





Panduit Band - A smooth, flat stainless steel band used in conjunction with sealant and caulk to terminate round stack flashings.

Panduit Tool - A tool used to tighten a panduit band for a watertight termination on a round stack flashing.

Parapet Wall - The part of a perimeter wall that extends above the roof.

Parapet Wall Flashing - A custom made flashing for a wall on a roof with fastening tabs spaced 28" or less.

Penetration - A measure of the viscosity of a bitumen.

Penetration - Any construction such as pipes, conduits, and HVAC supports that pass through the roof surface.

Pitch - Height from the joist to ridge divided by rafter length, which translates to rise in inches per horizontal foot or ratio of pitch. Ratio is an portion up to full pitch (24" in 12").

Pitch Pan or Pocket - Usually a rectangular flanged metal collar placed around metal supports that project above a roof deck. The pitch pan is placed on top of the roofing underlayment.

Pipe Flashing / Round Flashing - Custom made flashing, either open or closed and used for round roof penetrations such as vent and soil pipes. Duro-Last will prefabricate custom rounds up to 999 inches in diameter.

Ply - A single layer or thickness of roofing material. Built-up roofs are described as three, four ply, etc., according to the number of layers used to build up the membrane.

Polyglass - Maker of self-adhered underlayments. Have a wide array of products for every type of roof system.

Polyvinyl Chloride - PVC is a synthetic thermoplastic polymer prepared from vinylchloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers and other modifiers. Rigid forms are used in pipes; flexible forms are used in the manufacture of sheeting and roof membrane materials.

Polyglass TU Plus - Self-adhered Modified Rubber Tile and Metal underlayment. This membrane is glass fiber reinforced, with a high strength polyester fiber fabric on the upper surface.

Polyglass UDL - family of products are high strength, polyolefinic, multi-laminate roof covering underlayments manufactured using highly durable structures and formulated with anti-skid protection on the top surface to provide significantly enhanced slip resistance, even during wet and slippery conditions.

Ponding - The collecting of water in shallow ponds on the top surface of roofing. Certain roofs are designed for the ponding water to a shallow depth over the whole surface of the roof deck, to aid in summer cooling. Many flat roof systems void their warranties if ponding water sits on the deck for more than 48hrs.

Positive Drainage - Slope that has been designed into a roof area to ensure drainage within 48 hours after the end of rainfall, when conditions are conducive to drying.

Primer - A cut back asphalt coating of thin consistency used on concrete or metal preparatory to applying a built-up roof.

Purlin - Boards laid from gable to gable on which the common rafters sit.

Pre-Fabricate - To make or pre-assemble custom sized roof deck sheets and accessories at the Duro-Last factory under optimal, quality-controlled conditions. About 80% of Duro-Last welds are done at the factory under ideal conditions.

Pull Test - A test of a fastener using a Pull Tester on a deck/substrate to determine the fastener spacing for a roof installation. The less the pull, (measured in pounds of resistance) the greater the quantity of fasteners that will be needed along the deck sheet fastening tab. The greater the pull, the fewer fasteners that will be needed. Consult the Duro-Last Specification Manual to calculate the proper fastening spacing along the fastening tab (not to exceed 18” on center).

Pull Tester - Tool that measures the pounds of pull-out resistance on a Duro-Last approved fastener.






Rafters - The lumber supports that make up the roof structure. Usually 2" x 12" lumber. The roof sheathing is nailed to the rafters.

Reverse Lap - The first lap or laps on a deck sheet that “work” or “point” in the opposite direction of the rest of the laps on the sheet. This is done to help start a deck sheet in the right position and wrinkle free, and to locate the bulk of the material away from the edge or parapet wall.

Reverse Tab - The tab on the underside facing the opposite of the regular tabs and the first tab to come out of the roll. This tab is created from a “reverse lap,” and its primary purpose is for ease of installation. Reverse tabs can only be ordered at the beginning of the deck sheet and are used to start the deck sheet by giving the installer an edge to align the deck sheet to a snapped chalk line.

Reglet - A groove in the vertical wall adjacent to a roof surface, above the top of base flashing into which the metal counter flashing is placed and rigidly held in place; it is either formed in concrete or consists of a metal insert.

Ridge with ridge vent installed.

Ridge - The horizontal line where two opposite sloping sides of a roof join at the highest point of the roof, hip, or dormer. On double sloped gable roofs sometimes called the comb.

Ridge Cap - Formed shingles, shake or tile used to cover the ridge of a building. Make sure that specially designed cap products are used. Many roofers will use materials not made for this purpose.

Roll Roofing - Any roofing material, which comes from the dealer in rolls. More specifically it applies to mineral surfaced asphalt, or composition roofing.

Roll Roofing (granule surfaced) - Roll roofing finished on one side with colored granules.

Roll Roofing (smooth surfaced) - Roll roofing which is coated on both sides with either a smooth or veined surface.

Roll Goods - Duro-Last uses 64” wide roll goods to pre-fabricate deck sheets.

Roof System - A system of interacting roof components, generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.

Roof Trak II Walkway Pads - A non-skid walkway pad for rooftop protection in heavily traveled areas such as around large units that require service.

Roof - A protective covering that covers or forms the top of a building.

Roof Drain - The termination or fitting at the roof of an interior drain or leader for draining rainwater from normally flat roofs.

Roof Insulation - Any medium or low density material used as part of the roofing system to reduce heat loss through the roof. A variety of insulation materials are being used including wood fibers, glass fibers, cork, plastics and poured lightweight.

Roof Span - Distance from outer wall to opposing outer wall of a building covered with a roof.

Run - The horizontal distance between the face of a wall and the ridge of the roof.



Saturated - Soaked or filled with moisture. A core sample of an existing assembly is considered saturated when droplets of moisture can be squeezed from the sample.

SB-240 Mastic - Trowelable mastic ideal for parapet walls. Use SB-240 mastic to adhere the parapet wall flashing to the wall. Mechanical attachment is still required.

Knitting machine that manufactures the scrim.

Scrim - A key component of the Duro-Last roofing system. The scrim is weft inserted creating a grid-like appearance. If the Duro-Last membrane is ever punctured the scrim tightens up preventing the tear from gaining in size.

Scupper - An outlet in the wall of a building or a parapet wall for drainage of overflow water from a floor or roof directly to the outside. Special scupper drains connectd to internal drains are also sometimes installed at roof and wall junctions.

Self-Healing - A term used in refrence to bitumen which melts with the heat from the sun's rays, and seals over cracks that earlier formed in the bitumen from other causes.

Selvage - The un-surfaced strip along a sheet or roll roofing which forms the under portion at the lap in the applicatin of the roof covering.

Sealant - Duro-Caulk - Caulk used in conjunction with an approved termination to create a weathertight seal. Only caulk supplied by Duro-Last is approved for warranty without deviation.

Separator - Term used to describe the means of keeping two non-compatible materials from coming into contact with each other.

Side Lap - The horizontal distance one shingle overlaps adjacent shingle in the same course; also the horizontal distance one sheet of roofing overlaps adjacent sheet.

Single Coverage - Method of applying roof shingles to provide only one complete layer of roof protection. Many special shingles for re-roofing are designed for single coverage for reasons of economy.

Single-Ply Membranes - Roofing membranes that are field applied using only one layer of membrane material (either homogeneous or composite) rather than multiple layers.

Skirt - Membrane material attached to an accessory, such as curbs, stacks, drip edge, gravel stop, drains etc. The skirt is used for overlapping onto a deck sheet for the purpose of field welding a watertight assembly. Standard skirts are 6” but can also be ordered larger.

Sky Light - Glass opening in roof to admit light.

Slateline - GAF shingle made to mimic conventional slate roofing, a highly attractive shingle with a pronounced shadow effect.

Slipsheet - A separator sheet placed between the Duro-Last roof assembly and a non-compatible component on the existing roof, to ensure that plasticizer migration or breakdown does not occur. It also protects against possible damage from chemical incompatibility, wearing, or abrasion of the membrane.

Soffit - A board or sheet that extends from the fascia to the buildings siding and hides the bottom of an overhang. Soffit may or may not contain ventilation slots depending on the attic venting system used.

Startercourse of shingles.

Starter Course - The first course of shingles installed on a roof, starting at the lower left edge of the eave.

Step Flashing - Metal shingles or plates used in a stair-step pattern under regular shingles. Step flashing is the recommended flashing whenever a wall or chimney is above the roof line.

Standard Sheets - A Duro-Last deck sheet that generates no waste during fabrication, and minimizes labor in the field. This is done by using all full or half sheets during manufacture. Using full reverses with full last laps on field sheets and/or 31" reverses with full last laps will optimize deck sheet manufacture, and may also qualify an order for discounts. See the "Standard Size Sheet List" in the Duro-Last price list for more information. Price list is only available to registered Duro-Last contractors, sales representatives, and representatives of Duro-Last Roofing, Inc.

Start Piece - The start piece is the lap, that the reverse lap and standard laps are welded to. The start piece will have the reverse tab and the first standard tab, ”pointing” in opposite directions. The start piece is the first panel used in the fabrication of the deck sheet, and it’s also the first tab that the contractor uses to start the deck sheet on the roof. The Duro-Last contractor will snap a line a set distance from the edge of the building or from a previous installed deck sheet, and will adjust the reverse tab on the start panel to that snapped line.

Strip Mastic - ¾” wide butyl tape used for back seal only. Available in cases of 10 rolls, 350’ total.



Tab - Weather exposure surface of a shingle between the cutouts.

Tack Claw - A tool used to check field seams for proper welding.

Termination - The method of anchoring and/or sealing free edges of the membrane in a roofing or waterproofing system.

Thermoplastic - Type of single-ply membrane that can be heat welded and includes a re-inforcement layer of polyester (scrim), which provides increased strength. Thermoplastic membranes are light in color and will usually result in energy savings.

Titanium Dioxide - Used in thermo-plastic roofing membranes to reflect UV rays and to protect the polymers in the roofing material.

Tie-In - The transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roofing or waterproofing system.

Truss - A combination of members such as beams, bars and ties, usually arranged in triangular units to form a rigid framework for supporting loads over relatively long spans as in wide span roof construction.

Two-way Air Vent - Used to ventilate the Duro-Last roofing system.



UV / Ultraviolet - Invisible light radiation, adjacent to the violet end of the visible spectrum, with wavelengths from about 200 to 400 nm. (nanometers).

Underlayment - A sheet material that is used to separate the roof deck and the roof system.



Valley - The horizontal line formed along the depressed angle at the bottom of two inclined roof surfaces.

Vapor Barrier - A material that prevents the passage of water or water vapor through it.

Velux - One of the world leaders in skylight manufacturing. Uses all glass skylights instead of plastic bubbles that are common in the industry today.

Vent on a shingle roof

Vent - An outlet for air; vent pipe in a plumbing system; a ventilating duct.

Vent Pipe - A vertical pipe providing an escape for foul gasses from a sanitary fixture. For a number of fixtures the vent pipes lead into a larger vertical pipe to the outside through the roof called a vent stack.

Vinyl Coated Metal - 24 gauge, hot-dipped galvanized, grade G-90 metal with a 17 mil Duro-Last film laminated to one side. Available in white, tan, or gray colors.



Waterproof - The quality of a membrane, membrane material, or other component to prevent water entry.

Wind Load - Force exerted by the wind on a structure or part of a structure.

Water Vapor - Moisture as a gas in air. Warm air can hold more water vapor than cold air. Water vapors in the air crates a pressure much like any other gas. Cold air has a relatively low vapor pressure.

Wind Load - Force exerted by the wind on a structure or part of a structure.

Wind Requirements - Duro-Last has special fastening requirements for roofs 40’ and over and roofs in high wind zones. The Duro-Last Engineering Services department can perform wind calculations using ASCE-7, which determines fastening patterns for roofs in high wind zones considering the building’s height, location, wind zone, pull tests, wall heights etc.

Wind Tab - A fastening tab that must be located 24” to 36” from a parallel exterior edge or wall when the wall is 24” or less in height. Normally a 31” reverse tab (or series of 31” reverse tab) is used as a wind tab. See 31” reverse.

Wind Uplift - The force caused by the deflection of wind at roof edges, roof peaks or obstructions, causing a drop in air pressure immediately above the roof surface.

Wrinkle - A slight ridge caused by folding, rumpling or creasing. In roofing usually refers to the common wrinkle pattern that forms over the joints or insulation.

Wood Nailer - #2 grade lumber or better is required as a hard surface for edge fastening in any situation where 1-inch or greater of insulation is added to the roof perimeter edge.













Duro-Last Glossary Terms - View