R-Value: The measure of a material’s resistance to heat flow. The higher a material’s R-value, the better it’s insulating properties.

Racking: The method of installing asphalt shingles in which the shingles are installed straight up to the ridge rather than horizontally. If this method is used with 3-tab shingles, the throats of every second course will line up.

Rafter: The structural member which extends from the roof eave to the ridge or hip and is designed to support the roof deck and roof system components.

Rake: The sloped perimeter edge of a roof that runs from the eaves to the ridge. The rake typically runs perpendicular to the eaves and ridge.

Rake-Starter: A starter strip placed along rake edges for use in asphalt shingle roofing. See also "Bleeder Strip".

RCI: Roof Consultants Institute

RCMA: Roof Coatings Manufacturers Association

Re-Cover (Overlay): The installation of a new roof system over an existing system without removing the existing system.

Reglet: A groove in a wall or other surface adjoining a roof surface for use in the attachment of a counterflashing.

Reinforced Membrane: A roofing membrane that has been strengthened by adding a polyester scrim, glass fibers or another reinforcing material.

Relative Humidity: The amount of water vapor in the air compared to the amount of water vapor that the air can hold at a given temperature. For example, if the relative humidity is 50 percent, then the amount of water vapor in the air is half of what the air could actually hold at that temperature.

Re-roofing: The procedure of installing a new roof system.

Ridge: The line where two planes of a roof intersect at their highest edges.

Ridge Cap: Material applied over the ridge or hip of a roof to create a watertight installation.

Ridge Vent: An exhaust venting device located at the ridge of a roof that works in conjunction with a starter or under eave soffit vent and is used to ventilate attics.

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

Roof Assembly: A term used to describe all of the roof components including structural roof deck, insulation, membrane and flashings.

Roof Cement: See "Asphalt Roof Cement", "Coal Tar Roof Cement" or "Plastic Roof Cement".

Roof Curb: A raised frame used to structurally mount and waterproof rooftop equipment such as HVAC units, exhaust fans, roof hatches or skylights.

Roofer: An individual who installs roof systems and materials.

Roof Jack: (1) A steel bracket fastened to the roof that is used to support toe boards. (2) A term used to describe a Pipe Boot or Flashing Collar.

Roof Overhang: That portion of the roof that extends beyond the exterior wall line of the building.

Roof Seamer: (1) A mechanical device used to crimp metal roof panels and make the seams watertight. (2) A machine used to weld membrane laps of PVC or other thermoplastic roof membranes.

Roof Slope: The angle formed by the roof surface plane with the horizontal plane of the building. Expressed as the amount of vertical rise for every twelve inches of horizontal run. For example, a roof that rises four inches for every twelve inch (12") horizontal run, is expressed as having a "four in twelve" slope; often written as "4:12." Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also referred to as the Pitch.

Roof System: Multiple roof components assembled to provide waterproofing (and sometimes insulating) capabilities for a structure.

Rosin Paper: Non-asphaltic material used as slip sheets and sheathing paper in roof systems. Also referred to as Rosin-Sized Sheathing Paper.

Run: The horizontal dimension of a slope.


Saddle: A small structure designed to facilitate drainage of water away from flashing components.

Sag: Settling or drooping of base flashings that have not been properly secured to a surface.

Saturated Felt: Felt that has been saturated with bitumen.

SBS: Styrene Butadiene Styrene. A polymer sometimes used to modify asphalt.

Scrim: Woven or non-woven material used to reinforce membranes; it is usually laminated or coated to produce the membrane.

Scuttle: A unit that provides access to the roof from the interior of the building. See also "Hatch".

Sealant: Generic term for a multitude of materials used to seal joints or junctures against moisture or weather.

Seam: A line, ridge, or groove formed from fitting, joining, or lapping two components.

Self-Adhering Membrane: A type of membrane whose bottom surface will stick or adhere to a substrate without the use of an additional adhesive material.

Self-Sealing Shingle: Asphalt shingles with adhesive strips that will soften and stick to the underlying course of shingles when heated by the sun. Designed to minimize the risk of wind uplift.

Self-Tapping Screws: A screw with a small drill-bit like tip that will drill its own hole and eliminate the need to pre-drill a hole.

Self-Vulcanizing Membrane: Membrane that is initially thermoplastic in nature but that cures (vulcanizes) from exposure to the elements.

Selvage Edge: That portion of a granule-surfaced membrane that is designed to be overlapped by the succeeding membrane course.

Shark Fin: A curled corner or lap in a membrane.

Shed Roof: A roof with only one sloping plane.

Shelf Life: The length of time between the manufacture of a material and when the material is no longer suitable for use.

Shingle: (1) A single piece of prepared roofing material for use in steep slope roof systems. Can be used to refer to a variety of materials, such as asphalt, wood, clay, cement or slate. (2) To install a shingle roof system.

Shingle Fashion: Refers to the overlapping of succeeding courses of roofing materials.

Side Lap: The longitudinal overlap of adjoining materials.

Siding: Exterior wall finish materials applied to the outside of a structure.

Sill: The bottom framing member of a door or window opening.

Sill Flashing: Flashing material(s) used to waterproof the bottom framing member of a door or window opening.

Single Coverage: One layer of roofing material.

Single-Lock Standing Seam: A standing seam system with one overlapping interlock between two seam panels.

Single-Ply Membranes: Roofing membranes that are applied in one layer. Common single ply roof membranes include PVC, EPDM, TPO, Hypalon and Modified Bitumen membranes.

Single-Ply Roof System: Roofing systems where the principal component consists of a single-ply membrane.

Skylight: A transparent or translucent item that is designed to admit light to the interior of the structure.

Slag: Residue from blast furnaces that is sometimes used for the surfacing on aggregate-surfaced built-up roof systems.

Slate: A fine-grained metamorphic rock that splits into thin, smooth-surfaced layers used in steep slope roofing applications.

Slip Sheet: Sheeting material placed between roofing components to prevent those components from adhering to one another or to prevent material damage due to component incompatibility. Slip Sheets may be polyethylene, rosin-sized sheathing paper, or other material.

Slope: The angle of incline of a roof expressed as a percent or as a ratio of rise to run. See Roof Slope or Pitch.

SMACNA: Sheet Metal and Air Conditioning Contractors National Association

Smooth Surfaced Roof: A roof without a gravel surfacing.

Snow Guard: Devices secured to the roof to prevent snow and ice from sliding off the roof’s surface.

Snow Load: A roof load resulting from snow accumulationl. Snow load is an important structural consideration when roofs are designed in areas subject to significant snowfall.

Soffit: The underside of a roof overhang.

Soffit Vent: An intake ventilation device located in the soffit.

Softening Point: The temperature at which bitumen will begin to flow.

Softening Point Drift: change in the softening point of bitumen.

Soil Pipe: A pipe that penetrates a roof and is used to vent a building’s plumbing. Also referred to as a Plumbing Vent Pipe.

Solder: Any one of various fusible alloys, usually tin and lead, used to join metallic parts.

Solid Mopping: To continuously apply hot asphalt or coal tar leaving no areas without bitumen.

Solvent: (1) A liquid capable of dissolving other substances such as bitumen. (2) A liquid that is part of a substance and is used to make that substance easier to work with. Once applied, the solvent evaporates and leaves the working characteristics of the substance. Examples are solvent-based adhesives and solvent-based mastics.

Solvent Weld: To weld materials using a liquid solvent. Sometimes used in the application of thermoplastic roof systems, in lieu of heat welding.

Spall: A chip, fragment, or flake from concrete or masonry.

Special Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV. This asphalt can be used on roofs with slopes up to 6 in 12 (50%).

Specification: Written requirements for a construction project; contains but is not limited to the following: the scope of work, methods of construction and materials.

SPF: Sprayed Polyurethane Foam.

SPF Compounds: Refers to the Isocyanate and resin components used to make polyurethane foam.

SPI: The Society of the Plastics Industry

SPI/SPFD: The Society of the Plastics Industry/Sprayed Polyurethane Foam Division

Splash Guard: A fabricated metal pan or masonry block that is placed below a leader pipe or downspout and is used to help protect the roof membrane on a lower roof level or to prevent soil erosion when placed on the ground.

Splice: To join along ends.

Splice Plate: A metal plate placed above or below the joint between two adjacent pieces of metal.

Splice Tape: A self-adhering (usually double-sided) tape used for splicing membrane materials. Commonly used in the installation of EPDM rubber membrane roof systems.

Split: The separation of a material resulting from tensile forces.

Sprayed Polyurethane Foam (SPF): A monolithic sprayed-on roofing material with a high R-value; formed when isocyanate ("A" component) and resin ("B" component) are mixed at a 1:1 ratio.

SPRI: Single Ply Roofing Institute

Sprinkle Mopping: To scatter hot bitumen over a surface.

Spud: To remove the top surfacing of a roof by scraping it with special tools called spud bars or power spudders.

Spud Bar: A long-handled tool with a stiff flat blade on one end (usually 4" or 6" wide) that is used to scrape and remove the top surfacing of a roof down to the membrane.

Square: (1) 100 square feet of roof area (9.29 m2) in the USA. (2) 10 square meters (107.639 ft.2) of roof area using the metric system of weights and measures.

Stainless Steel: A highly corrosion resistant steel alloy containing either chromium, nickel, or copper.

Stair Step: The diagonal method of laying shingles.

Standing Seam: A type of metal roof system where the longitudinal seams on adjacent panels are turned up, overlapped and folded in various ways in order to prevent moisture entry and interlock the panels.

Starter Course: The primary course of roofing materials. The Starter course is installed along the roof eave and is usually covered by the first course of roofing.

Starter Plies: Felt or ply sheets that are cut into widths that are proportionate to the reciprocal of the number of plies being installed. For instance, with a three-ply built-up roof, the first starter ply would be one-third of the roll width, the second two-thirds of the roll width installed over it, and then a full ply over those.

Starter Strip: Strips of shingles (usually 3-Tab shingles with the tabs cut off) or roll roofing material that is laid along the eave line of the roof prior to the application of the first course of shingles. The starter strip is used to fill in the gaps created by shingle cutouts and joints.

Static Load: Roof loads that do not move such as HVAC units. See, also, Dead Load.

Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. This asphalt can be used on roofs with slopes up to 3 in 12 (25%).

Steep-Slope Roof: A roof with a slope exceeding 3 in 12 (25%). Deemed appropriate to receive water-shedding type roofing materials such as asphalt shingles, wood shakes and shingles, concrete or clay tile, etc.

Steep-Slope Roofing Materials: Roofing materials that depend on their water-shedding capabilities to keep moisture from entering a building. These materials are generally installed on roofs with slopes that equal or exceed 3" in 12" (25%).

Steeple: A tall tower forming the superstructure of a building, such as a church or temple, and usually surmounted by a spire.

Step Flashing: Pieces of metal or other material that are used to flash roof projections such as chimneys, walls, curbs, etc. The pieces are installed between each course of roofing and generally have a vertical flange equal in length to that of the horizontal flange.

Strapping: Installing roofing felts so that they run parallel with the slope. Not a recommended installation method for slopes that are 1:12 or less.

Strip Flashing: Pieces of membrane material that are used to flash metal flashing flanges such as gravel stop. Also referred to as Stripping.

Strip Mopping: Hot bitumen applied in parallel bands.

Strip Shingles: Asphalt shingles that are manufactured in strips without cutouts used to create the effect of individual shingle tabs.

Styrene Butadiene Styrene (SBS): The modifying agent used in SBS modified asphalt roofing materials that increases the elasticity of the material.

Substrate: The surface upon which the roofing is installed. Roof decks and adjoining walls (behind the base flashings) are both examples of a substrate.

Sump: A depression around roof drains and scuppers to help facilitate roof drainage.

Surface Erosion: The effect on a surface after being worn away from abrasion or weathering.

Surfacing: The top-most layer of the roof system designed to protect the system from damage.


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