Glossary of Terms


The definitions of terms included in this glossary are those pertinent to the roofing trade and are not necessarily those found in standard dictionaries. Some of the terms included are colloquial in nature and are used with the meanings applicable only to the roofing trade.

Absorption The ability of a material to accept quantities of gases or liquids

Adhesive A substance used to adhere materials together

Aggregate Any granular material including crushed stone, slag, or gravel

APP Atactic Polypropylene or torch-on cap sheet

Atactic A polymer featuring a random arrangement of pendent groups on each side of the carbon chain

Backing Lumber placed behind or between other members to give support and strength

Back-Mopping Mopping the back or underside of roofing material

Barge Rafter Same as fascia board. But on the rake or gable end of the roof

Base Sheet The first layer of roofing applied on the deck. Also, a dry or slip sheet

Bitumen A class of amorphous, black or dark colored, (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, soluable in carbon disulfide, and found in asphalts, tars, pitches and asphaltites. A generic term used to denote any material composed principally of bitumen.

Bleeding The draining or loosening of saturants from the roofing material

Blister A swelling and separating of the top layer of roofing from the underlayment. A bladder like air pocket

Bond To fasten or stick together

Buckles Bends, crumples, or curls in roofing

Built-Up Roof Roof formed by a number of layers of roofing mopped together with hot asphalt abbreviated as BUR

Cap Sheet A finish roofing material, used as a covering for a built-up roof

Cap Nails A tin flat disk and nail, giving greater holding area to the nail head. Used in windy areas and on soft roofing materials. (A requirement for fiberglass felts)

Cant Strip A beveled strip used to break the 90 degree angle where the roof meets walls or curbs

Caulking To make water tight by plugging with Vulkem caulking

Condensation The change from vapor to liquid form, as from steam to water

Coping The top covering of a wall; may be metal, tile, masonary, or wood. Also called metal cap or parapet cap.

Conductor Head Collects water from scupper or drain pipe and funnel it into a down pipe (usually on outside of the wall)

Counterflashing Flashing that extends over another flashing

Course A continuous row or layer of shingles or other roofing material

Cricket A relatively small elevated area of a roof constructed to divert water out of a dead or flat valley or around other projections

Curb A protective rim

Cured Completely dry; moisture free

Dead Load Rafters Sheeting, roof membrane, shingles, shakes, tile, actual weight of roof and the roof structure

Debris Accumulated rubbish, trash, and fragments on roof

Deck or Substrata The roof surface to be covered; a small platform used for walking

Diverter A piece of metal bent at right angles to change the flow of rain water

Downspout A pipe or conductor to carry the water from a roof

Drain An outlet designed to capture or direct the flow of water from a roof

Drip Edge A metal flashing or other over hanging component intended to control the direction of dripping water

Dry Rot Wood decay caused by a fungus that consumes the cellulose portion of the wood, leaving a soft skeleton that readily crumbles to a powder. Wood structures that are inadequately ventilated and constantly exposed to moisture are especially vulnerable to dry rot.

Eaves The projecting lower edge of a roof

Exposure The portion of roofing exposed to the weather

Elasticity The property of a membrane allowing it to return to its original size and shape after the removal of stress

Elongation Lengthening or stretching ability to accommodate movement

Fascia Board A board attached to the bottom of rafters acting as a finishing board

Felt A roofing material manufactured from cellulose fibers of rags, paper, wood or fiberglass

Fishmouth An open seam or a ripple on the roof surface

Flood Coat The top layer of an asphalt which the rock is embedded on a rock surfaced built-up roof

Flush A term applied to surfaces that are level and form a single, unbroken surface

Gauge A metal thickness measurement

Granule Aggregate commonly used to surface cap sheets, shingles, and other surfaced roof coverings

Gravel Crushed stone or rock used for surfacing roofs

Gutter A trough installed along the eaves to carry off water

Hatch An opening in the roof; an access hole to the attic

Heat Welding Method of melting or fusing together sheets of thermoplastic and polymer modified bitumen

Hem Edge created by folding metal back on itself

Hoist Lifting device

HVAC Heating, ventilating, and air conditioning equipment

Ice Dam A mass of ice formed near transitions from warm to cold roof surfaces

Impregnate To cause, to be filled or permeated with; to saturate

Infrared Thermography Roof analysis technique used to measure the temperature gradient of a roof surface to locate areas of moisture

Insulation Materials used to reduce the flow of heat

Intake Ventilation Ventilation system that allows for the flow of fresh air into the building

Irish Flax An imported brownish roll fiber material used for flashing purposes

Joint The point at which two or more surfaces are united

Kettle A metal vessel for heating asphalt

Laminate To join layers of material together via heat and/or pressure

Lap The part of a roofing membrane that covers any portion of another section of membrane and is then sealed to form a watertight connect

Low-slope roofs A category of roofs that have a slope at or less than 3:12 (14 degrees)

Live Load Moving roof installation equipment, wind, snow, ice or rain (temporary weight on the roof)

Mastic A thick adhesive mixture of preparations such as asphalt; used for repairing roofs

Mat A thin layer of fiber which reinforces the membrane

Mechanically fastened membrane Membranes that have been attached at defined intervals to the substrate using fasteners or other mechanical devices

Membrane A flexible or semi-flexible sheet of thermoset, thermoplastic, or modified bituminous material whose primary function is waterproofing

Metal Edging A metal trim used around the outside edges of a roof

Modified Bitumen A bitumen modified by one or more polymers

Modifier Any compound that is added to a formulation to obtain certain performance enhancements

Mopping An installation of bitumen applied with a mop or mechanical device to the substrate or to the felts of a Built-up roof or modified bitumen membrane.

Nailer A piece of dimensional lumber or plywood which serves as a receiving medium for the fasteners

Overflow A roof drain in wall, above outlet elevation, for excess water or back-up to roof drain

Overhang The length of rafter projecting beyond the wall line

Ozone Resistance A property of a material to resist the effects of ozone exposure

Parapet A low wall above the roof level

Partially Attached A method of roofing assembly in which the membrane has been spot affixed to a substrate using an adhesive or mechanical device

Penetration Any element (e.g., pipes, conduits, HVAC supports) that pass through the roof

Pigment A compound used to impart color

Pinhole A tiny hole in the roof coating, film, foil, membrane or laminate components

Pipe Boot Pre-fabrications flashing component used to flash around a circular penetration

Pipe Collar Where pipe flashing meets the pipe

Pipe Flashing A preformed sheet metal unit (1 piece flashing) used at a pipe penetration through roof

Pitch The slope of a roof, indicated by the relation of the rise 10″ high

Pitch Pocket A flange, open-bottomed metal enclosure placed around a penetration and filled with hot bitumen or flashing cement

Platform A raised area in which equipment is et-on usually 6″ to 10″ high to the span

Ply A layer of roofing material

Pourable Sealer A two-part sealer used at difficult-to-flash penetrations

Primer A thin asphalt base sprayed or brushed on roof or sheet metal before applying asphalt

PVC Roof Membrane Polyvinyl chloride (PVC) resin is the largest volume member of the vinyl family. PVC membranes are grease resistant, which makes them an ideal choice for commercial buildings such as restaurants and apartments where cooking residue is discharged through vents on the roof. PVC membrane is reinforced with fabric, which provides increased strength and stability.

Rake The slope of a roof; the sloping edge on a gable roof that may be covered with a bargeboard

Recover (Reroof) To apply a new roof over an old roof

Red Rosion Red slip sheet used under a base sheet

Reflectivity The ability of a material to reflect light and heat

Reinforced Membrane A membrane reinforced with felts, mats, fabrics, or other fibers

Ridge The point on a double-sloping roof at which the rafters meet the ridge pole

Ridge Shingles Units of roofing made for ridge covering

Roof Curb A raised frame used to mount mechanical units on the roof

Rot Decay that attacks wood. The two major types are dry rot and wet rot

Rubber A material, at room temperatures, is capable of recovering substantially in shape and size from large deformations

Scupper A hole or gutter bordering a deck; to let water run through a wall to a conductor head

Sealant A material that is used as an adhesive to form a seal

Sealant Backing A material place in a joint before applying sealant

Seam A joint formed by joining two separate sections of material

Self-Adhering Membrane A membrane that adheres to the substrate and overlaps without the use of additional adhesive

Sheathing (Sheeting) The boards or other material used for covering the frame or roof structure

Single-ply membranes Roof membranes that are applied using just one layer of membrane material Most common are TPO or PVC

Slip Sheet A light sheet of paper applied over roof sheathing to prevent the roofing from bonding to sheeting. May be called dry sheet

Solid-Mopping A continuous mopping of a surface, with no area left unmopped

Solvent Any liquid used to dissolve another material

Splice Joining of overlapping materials

Spot-mopping A mopping pattern in which hot Bitumen is applied in roughly circular areas. A grid of unmopped perpendicular bands is left on the roof

Square A unit of measure of roofing area equal to 100 square feet 10′ by 10′ area = 100 sq. ft

Storm Collar A narrow strip of metal formed to fit around vent pipes

Tappered Fiberboard Wood pulp that is molded into a sheet and used for feathering bumps or edges of plywood or roof sheeting

Tear-Off To remove completely an existing roofing membrane

Tear Resistance The load required to tear a material when the stress is concentration on a small area of the specimen by the introduction of a prescribed flaw

Termination A method of anchoring the free edges of the membrane to the roofing system

Thermal Shock The stress producing phenomenon resulting from sudden temperature changes in a roof membrane when for example; a rain shower follows brilliant sunshine

Thermoplastic A material that softens when heated and hardens when cooled

Torch-On / Cap Sheet Granular cap sheet required to be heat welded in place with a torch

TPO Roof Membrane Thermoplastic polyolefin membrane is based on polymers defined by ASTM D 5538, Practice for Thermoplastic Elastomers — Terminology and Abbreviations, as a thermoplastic elastomer – olefinic. A thermoplastic elastomer is a diverse family of rubber-like materials that, unlike conventional thermoset rubbers, can be reprocessed and recycled like thermoplastic materials. Thermoplastic polyolefins are in the thermoplastic elastomer family and are commonly referred to as TPO in the single-ply roofing industry.

Turbine / Whirly Vent A wind driven vent to draw heat from the attic, usually 12″ to 14″ in diameter. UV. APP, and to a lesser extent, SBS is sensitive to UV (Ultra Violet) light and both will weather best when protected from UV exposure

Ultraviolent A form of radiation that is potentially damaging to certain chemical compounds in the roofing membrane

Valley The angle formed by the meeting of two roof slopes

Valley Metal Sheet metal used in a valley usually 24″ wide

Vapor Retarder Material installed to restrict the flow of water vapor through the roofing assembly

Vegetative Roofs A roof system composed of a waterproof substrate and an area of planting

Water Absorption The amount of water absorbed by a material within a specific period of time

Waterproof A property of a material to resist water

Web / Yellow Jacket A woven cloth or organic filaments used in repairs or reinforcement of mastic

Weld (Heat Weld) By joining of metal together by heat fusionSBS Styrene Butadiene Styrene. An SBS modified asphalt combined with a polyester or fiberglass core

Weep Holes Small holes whose purpose is to permit drainage of water that accumulates inside a building component

Z-Bar Metal flashing used especially on walls where roof, plaster, or wood siding meet