Roofing Terminology

This page includes a list of Roofing Terminology and their definitions, to help you better understand.

 

A:

ADHERED
:a roof component which is glued, bonded, or sealed.

AMBIENT TEMPERATURE
:the temperature of the air — air temperature.

APPLICATION RATE
:the quantity (mass, volume or thickness) of material applied per unit area.

AREA DIVIDER
:a raised, double wood member, attached to a properly flashed wood base plate, that is anchored to the roof deck — used to relieve thermal stresses in a roof system lacking expansion joints.

ASBESTOS
:a group of natural, fibrous, and impure silicate materials.

ATACTIC POLYPROPYLENE
:a group of high molecular weight polymers, formed by the polymerization of propylene.

 

B:

BALLAST
:a heavily weighted anchoring material, such as aggregate, used to hold (or assist in holding) a roof membrane in place.

BASE FLASHING
:strips of roof membrane which are installed in the area allocated for vertical flashing.

BLISTER
:a spongy, raised portion of a roof membrane (ranging, in area, from 1″ in diameter to a barely detectable height) that results from pressure buildup from gases (most commonly air and/or water vapor) trapped within the membrane system, which usually involves the delamination of the underlying plies.

BOND
:the adhesive and cohesive forces holding two separate roofing components together in close contact.

BONDED
:to be glued or adhered (see adhered).

BOOT
:the covering of flexible materials (may be preformed to a particular shape) used to seal the space around a penetration.

BROOMING
:to embed a single ply of roofing material, in which is smoothed out with a broom, to ensure contact with the adhesive underneath.

BTU
:(British Thermal Unit) — The heat energy required to raise the temperature of 1 pound of water 1° Fahrenheit.

BUCKLE
:an upward, elongated, tenting displacement of a roof membrane (frequently occurs over insulation or deck joints), which may be an indication of movement within the roof assembly, and is usually associated with improper installation.

BUTYL
:a rubber like material produced by copolymerizing isobutylene with a small amount of isoprene — manufactured in sheets or blended with other elastomeric materials in the creation of sealants and adhesives.

 

C:

CANT
:a beveled strip of wood/wood fiber that, when a horizontal and vertical surface intersect, fits into the angle of said intersection — the 45° slope of the exposed surface of the cant strip provides a gradual angular transition from the horizontal surface, to the vertical surface (good angle for flashings).

CAPILLARY
:when the surface of a liquid (that which is in contact with a solid) is elevated or depressed, which is dependent upon the relative attraction of the molecules of the liquid for each other, and for the molecules of the solid.

CAULKING
:a waterproof filler and sealant used at ambient temperatures — remains plastic for an extended time after application.

COMMERCIAL BUILDING
:buildings meant for the public and the industrial field — usually have low-slope roof systems.

CONDENSATION
:the conversion of water vapor (or other gases) to liquid form as the temperature drops or the atmospheric pressure rises (see dew-point).

COPING
:the (covering) piece placed on top of a wall that is exposed to the weather — usually sloped to shed water from the roof.

COUNTER FLASHING
:the elastomeric or formed metal sheeting, which is secured on/into a wall, curb, pipe, rooftop unit, or other such surfaces, to shield the top edges and joints of a base flashing — to be continuously coated by a specific roofing material, with allowance made for a specific lap.

CRACK
:a separation or fracture occurring in the roof membrane/deck, generally caused by thermally induced stress or substrate movement.

CREEP
:the permanent deformation of a roofing material in the roof system, caused by the movement of the roof membrane that results from continuous thermal stress or loading.

CRICKETS (and Saddles)
:a raised area built into an existing roof system to help water flow to drainage areas.

CURB
:a raised member used to support roof penetrations (such as skylights, mechanical equipment, hatches, etc.) above the level of the roof surface.

CUTOFF
:a seal for materials that is designed to prevent lateral water movement into the edge of a roof system where the membrane of the roof terminates at the end of the day’s work, or used to isolate sections of the roof system — usually removed before the continuation of work.

 

D:

DAMP PROOFING
:the treatment of a surface or structure to resist the passage of water in the absence of hydro-static pressure.

DEAD LEVEL
:a term used to describe an absolutely horizontal roof — zero slope (see slope).

DEAD LOADS
:non-moving rooftop loads, such as mechanical equipment, air conditioning units, and/or the roof deck itself.

DECK
:the structural surface to which the roofing or waterproofing system (including insulation) is applied.

DEGRADATION
:a deleterious change in the chemical structure, physical properties, or appearance of a material, due to natural or artificial exposure.

DELAMINATION
:the separation of the plies in a roof membrane system, or the separation of laminated layers of insulation.

DEW-POINT
:the temperature at which water vapor starts to condense in cooling air at the existing atmospheric pressure and vapor content.

DRAIN
:a device that allows for the draining of water from the roof area.

DRAINAGE
:a system that allows water to run off a roof.

 

E:

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 the stress.

ELASTOMERIC
:the term used to describe the elastic, rubber like properties of a material.

END LAP
:the distance of overlap where one ply extends beyond the end of the immediately adjacent ply.

EPDM
:(Ethylene Propylene Diene Monomer) — commonly referred to as a “rubber roof”.

EPOXY
:a class of synthetic, thermo-setting resins that produce tough, hard, chemical resistant coatings and adhesives.

EMC
:(Equilibrium Moisture Content) — the moisture content of material stabilized at a given temperature and relative humidity, expressed as percent moisture by weight; the typical moisture content of a material in any given geographical area.

EXPANSION JOINT
:a structural separation between two building elements, designed to minimize the effect of the stresses and movements of a building’s components, and to prevent theses stresses from splitting or ridging the roof membrane.

EXPOSURE
:the time during which a portion of a roofing element is exposed to the weather.

EXTRUSION
:a manufacturing process which consists of forcing batched and formulated material through an orifice.

 

F:

FABRIC
:a woven cloth of organic or inorganic filaments, threads, or yarns.

FACER
:a surfacing applied at the factory on some insulation boards.

FACTORY MUTUAL
:an organization that classifies roof assemblies for their fire characteristics and wind-uplift resistance for insurance companies in the United States.

FERRULE
:a small metal sleeve placed inside a gutter at the top, which acts as a spacer in the gutter to maintain its original shape — a spike is nailed through the gutter into the fastening board.

FIELD
:the open part of a roof.

FISHMOUTH
:a membrane defect consisting of an opening in the edge lap of a felt in a built up membrane — a consequence of an edge wrinkle.

FLASHING
:components that make a watertight seal between the field of a roof and any walls or penetrations.

FULLY_ADHERED
:an installation method where a membrane is totally adhered (see adhered).

 

H:

HEAT WELDING
:a method of melting or fusing together the overlapping edges of separate sheets of thermoplastics and polymer modified bitumen’s.

HORIZONTAL FLASHING
:flashings that are installed around objects on the flat surface of a roof.

HYGROSCOPIC
:the term used to describe a material which attracts, absorbs, and retains atmospheric moisture.

 

I:

INCLINE
:the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal unit of run.

INFRARED THERMOGRAPHY
:a practice of roof analysis where an infrared camera is used to measure the temperature differential of a roof surface to locate areas of underlying moisture.

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.

IRMA
:(Inverted Roof Membrane Assembly) — A patented, proprietary variation of the “Protected Membrane Roof Assembly” in which Styrofoam Brand insulation and ballast are placed over the roof membrane (IRMA and Styrofoam are registered trademarks of the Dow Chemical Corporation).

 

L:

LAP
:the part of the roof or flashing that overlaps or covers any portion of the same, or another type, of adjacent component.

LIFE CYCLE COSTING
:a method of economic analysis that takes into account the expected costs over the useful life of an asset.

LIGHT REFLECTANCE
:the percentage of light that is not absorbed by the surface of the material.

LIVE LOADS
:temporary loads that the roof structure must be designed to support, for example, people, installation equipment, rain, snow, ice, etc.

LOOSE LAID MEMBRANES
:membranes that are not attached to the substrate except at the perimeter — typically held in place with ballast.

LOOSE LAID and BALLASTED
:an installation method where a membrane is only attached in a few places and mainly held down by ballast.

LOW TEMPERATURE FLEXIBILITY
:the ability of a membrane to remain flexible after it has been cooled to a low temperature.

LOW SLOPE ROOF
:a roof with a slope of 3″ per foot, or less.

 

M:

MANUFACTURER’S BOND
:a security company’s guarantee that it will stand behind a manufacturer’s liability to finance membrane repairs, occasioned by ordinary wear within a period generally limited to 5, 10, 15, or 20 years.

MECHANICALLY ATTACHED
:when material is attached to a deck with screws or other fasteners.

MECHANICALLY FASTENED
:an installation method where a membrane is attached to a deck with fasteners.

MECHANICALLY FASTENED MEMBRANES
:membranes attached at defined intervals to the substrate.

MEMBRANE
:a flexible or semi-flexible roof covering/waterproofing layer whose primary function is the exclusion of water.

METAL FLASHING
:frequently used as through wall flashing, cap flashing, counter flashing, or gravel stops (see flashing).

METAL ROOF SYSTEM
:a roof system made of metal panels.

MILDEW
:a superficial coating or discoloring of an organic material due to fungal growth.

MODIFIED BITUMEN
:composite sheets consisting of a polymer (e.g. atatic polypropylene (APP) or styrene butadiene styrene (SBS)), often reinforced, and sometimes surfaced with various types of mats, films, foils, and mineral granules.

MOISTURE RELIEF VENT
:a venting device through the roofing membrane to relieve moisture vapor pressure from within the roof assembly.

MOLE RUN
:a meandering ridge in a roof membrane that is not associated with insulation or deck joints.

 

N:

NAILABLE
:when parts of a roof system can be mechanically fastened to a deck.

NEOPRENE
:a synthetic rubber (polychloroprene) used in sheet applied elastomeric roof membranes or flashings.

NIGHT SEAL
:method used to temporarily seal a membrane edge during construction to protect the roof assembly from water penetration.

NON-VULCANIZED MEMBRANE
:a membrane manufactured from thermoplastic compounds that retain its thermoplastic properties throughout its service life.

NUCLEAR TESTING
:a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflected neutrons are measured to ascertain presence of moisture.

 

O:

ORANGE PEEL
:a surface condition that shows a fine texture resembling the texture of an orange.

ORGANIC
:being or composed of hydrocarbons or their derivatives, or matter of a plant or animal origin.

 

P:

PARAPET WALL
:a perimeter wall which extends above the roof.

PEEL STRENGTH
:the average force required to peel a membrane from the substrate to which it has been bonded.

PENETRATION
:any object which passes through the roof.

PERLITE
:an aggregate used in lightweight insulation, concrete, and in preformed perlite insulation boards, which is formed by heating and expanding siliceous.

PERM
:a unit of water vapor transmission defined as 1 grain of water vapor/ per square foot/ per hour/ per inch of mercury pressure difference.

PERMEANCE
:an index of a materials’ resistance to water vapor transmission (see perm).

PHASE APPLICATION
:the installation of a roof system or waterproofing system during two or more separate time intervals.

PITCH POCKET
:a flange, open bottomed, metal container that is placed around columns or other roof penetrations, and is filled with hot modified bitumen and/or flashing cement to seal the joint.

POLYMERS
:chemical compounds — in modified bitumen roof systems, they are added to bitumen to change its chemistry.

PONDING
:when water on a roof assembly stays instead of completely draining.

POSITIVE DRAINAGE
:the drainage condition in which consideration has been made for all loading deflection of the deck and additional roof slope has been provided to ensure complete drainage of the roof area within 24 hours of rainfall.

POURABLE SEALER
:a type of sealant often supplied in two parts and is typically used to fill pitch pans.

PRIMER
:a thin liquid bitumen applied to a surface to improve the adhesion of subsequent application of bitumen.

PROTECTED MEMBRANE ROOF
:an insulated and ballasted roof assembly in which the membrane is covered by the insulation and ballasted — sometimes referred to as “inverted roof assembly”.

PSYCHOMETRIC CHART
:a diagram relating to the properties of humid air with temperature.

PURLINS
:metal channels or beams that support a structural metal roof system.

PVC
:(Polyvinyl Chloride) — usually associated with a thermoplastic, singly ply roof membrane system.

 

R:

RAKE
:the sloped edge of a roof at the first or last rafter.

RE-COVER
:installing a new roof system on top of an existing roof system.

REFLECTIVITY
:the ability of the surface of a material to reflect the infrared energy of a light source.

REGLET
:a groove in a wall or other surface adjoining a roof surface for use in the attachment of counter flashing.

REINFORCED MEMBRANE
:roofing or waterproofing membrane reinforced with felts, mats, fabrics, or chopped fibers.

RELATIVE HUMIDITY
:the ratio of the weigh of moisture in a given volume of air vapor mixture to the saturated (max.) weight of water vapor at the same temperature, expressed as a percentage.

RE-ROOFING
:the practice of applying new roofing material over existing roofing materials.

RIDGING
:an upward, “tenting” displacement of a roof membrane, frequently occurring over insulation joints, deck joints, and base sheet edges — generally associated with improper application.

ROOF ASSEMBLY
:an assembly of interacting roof components (including the roof deck) designed to weatherproof and, normally, to insulate a building’s top surface.

ROOF DECK
:the bottom part of a roof assembly — a roof system is supported by a deck.

ROOF MEMBRANE
:the watertight part of a system.

ROOF SYSTEM
:a system of interacting roof components (not including the roof deck) designated to weatherproof and, normally, insulate a building’s top surface.

RUBBER
:a polymeric material which, at room temperature, is capable of recovering substantially in shape and size after removal by force.

R-VALUE
:the resistance to heat transfer of a material.

 

S:

SBS
:(Styrene Butadiene Styrene) — High molecular weight polymers that have both thermoset and thermoplastic properties formed by the block copolymerization of styrene and butadiene monomers. These polymers are used as the modifying compound in SBS polyer modified roofing membranes to impart rubber like qualities to the asphalt.

SEAL
: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 — cures to a resilient solid.

SELF ADHERING MEMBRANE
:a membrane that can adhere to a substrate and to itself without use of adhesives — under surface is protected by a release paper.

SELVAGE JOINT
:a lapped joint designed from membrane — 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.

SELVAGE
:an edge or edging that differs from the main part of a sheet.

SHARK FIN
:an upward curled felt side or lap/end lap.

SHINGLING
:the procedure of laying parallel sheets so that one longitudinal edge of each felt overlaps and the other longitudinal edge under laps an adjacent sheet — usually shingled on a slope to have water flow over, rather than against, each lap.

SINGLE-PLY SYSTEMS
:systems that have only one layer of roofing membrane.

SLIP SHEET
:a sheet material placed between two components of a roof assembly to ensure that no adhesion occurs between them and/or to prevent possible damage from chemical incompatibility, wearing, or abrasion of the membrane — often associated with PVC membranes.

SLOPE
:the incline of a roof — the tangent of the angle between the roof surface and the horizontal (measured in inches per foot).

SNOW LOAD
:a load imposed on buildings due to snowfall — categorized as live or environmental load.

SOIL STACK
:a sanitation pipe that penetrates the roof — used to vent plumbing fixtures (stink stacks).

SOLVENT WELDING
:a process where a liquid solvent is used to chemically weld or join together two or more layers of certain membranes — usually thermoplastics.

SPF
:(Sprayed Polyurethane Foam) — a foamed plastic material formed by spraying two components, PMDI and a resin, to form a rigid, fully adhered, water resistant, and insulating membrane.

SQUARE
:the term used to describe 100 square feet of roof area.

STRESS CRACK
:external or internal cracks within a material caused by long-term stress.

STRIPPING
:the technique of taping joints between insulation boards on deck panels.

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 (i.e. a large stack of insulation boards placed on top of a structural steel deck).

 

T:

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.

TAPERED INSULATION
:insulation that is made so the material has slope.

TAPING
:see STRIPPING.

TEAR OFF and REROOF
:the removal of all roof system components down to the structural deck followed by the installation of a new roof system.

TEAR STRENGTH
:the maximum force required to tear a material.

TEST CUT
:a sample of the roof membrane — usually 4 inches x 40 inches in size — that is cut from a roof membrane to diagnose the condition of the existing membrane (i.e. to detect leaks or blisters).

THERMAL CONDUCTANCE (C)
:a unit of heat flow that is used for a specific thickness of material or for materials of combination construction (i.e. laminated insulation).

THERMAL CONDUCTIVITY (K)
:the heat energy that will be transmitted by a conduction through 1 square foot of 1 inch thick homogeneous material, in one hour.

THERMAL INSULATION
:a material applied to reduce the flow of heat.

THERMAL RESISTANCE
:an index of material applied to reduce the flow of heat.

THERMAL SHOCK
:the stress producing phenomenon resulting from sudden temperature changes in a roof membrane (i.e. when a rain shower follows brilliant, hot sunshine).

TPO
:(Thermoplastic Olefin Membrane) — A blend of polypropylene and ethylene-propylene polymers, in which colorant, flame retardants, UV absorbing substances, and other proprietary substances can be blended with the TPO to achieve the desired physical properties.

THERMOPLASTIC
:materials that soften when heated and harden when cooled.

THERMOSET
:a material that solidifies or “sets” irreversibly when heated — usually associated with cross-linking of the molecules induced by heat or radiation.

THERMOSTATS and THERMOPLASTICS
:two types of single-ply membranes.

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 exterior.

TIE-OFF
:a seal used to terminate a roofing application at the adjacent roofing system.

TUCK POINTING
:the process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.

 

U:

UNDERLAYMENT
:a material installed between a deck and roof system.

 

V:

VALLEY
:the area on a roof surface where two downward slopes meet.

VAPOR MIGRATION
:the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

VAPOR PRESSURE GRADIENT
:a graph, analogous to a temperature gradient, indicating the changes in water vapor pressure at various cross sectional planes through a roof or wall system.

VAPOR RETARDER
:a material designed to restrict the passage of water vapor through a wall or roof — should have a perm rating of 0.5 or less.

VENT
:an opening designed to convey water vapor or other gas from inside a building/building component, to the atmosphere to relieve vapor pressure.

VERTICAL FLASHING
:a flashing which is installed at upturned edges.

 

W:

WATERPROOFING
:the treatment of a surface or structure to prevent the passage of water under hydro-static pressure.

 

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