Glossary of Roofing Terminology
This glossary is
intended to help you understand terms you will encounter as you plan
your roofing project
(Please Note: This roofing glossay is not in precise alphabetical order)
The ability of a material to accept within its body
gases or liquid, such as moisture.
(1) The degree of attachment between two surfaces held together by
interfacial forces—mechanical or chemical or both; (2) the
of attachment or bonding between application of the same substance; (3)
the combined ultimate strength of the molecular forces and the
mechanical interlocking achieved between the adhesive and the surface
bonded. Adhesion is measured in shear and peel modes.
American National Standards Institute.
polyurethane coating: A
polyurethane coating that contains a
specific class of isocyanates based on a long straight chain molecular
structure. Normally used in finish coats that are exposed to the
elements. It is noted for its good weather resistance.
temperature: The temperature
of the air existing on all sides;
rate: The average quantity
(mass, volume or thickness) of
material applied per unit area.
temperature: The temperature
of a material, such as hot asphalt,
when applied to the roof.
shingle: A shingle
manufactured by coating a reinforcing
material (paper felt or fiberglass mat) with an asphalt-based coating
and having mineral granules on the side exposed to the weather. See
A group of naturally occurring, fibrous impure silicate materials.
This material is often found in older roofing system felts
and poses a serious health risk if disturbed without following proper
Asphalt Roofing Manufacturers Association.
To cause two surfaces to be held together by the combined strength of
the molecular forces and the mechanical interlocking achieved between
adhesive and the bonded surface.
A cementing substance that produces a steady and firm attachment or
adhesion between two surfaces.
(1) Crushed stone, crushed slag, water-worn gravel or marble chips used
for surfacing a built-up or polymer-modified bitumen roof system; (2)
any granular material.
American Institute of Architects.
barrier: The assembly of
materials used in building construction
to reduce or retard the uncontrolled passage of air into and out of the
Cracking of a surfacing bitumen, asphalt, coating or mastic or coating
on a spray polyurethane foam (SPF) roof system that occurs during the
aging process in which the loss of volatile oils and the oxidation
brought about by solar radiation produces a pattern or cracks similar
to an alligator’s hide; the cracks may or may not extend
the surfacing material.
flashing: A term used for a
flashing located at the juncture of
the top of a sloped roof and a vertical wall, chimney or steeper-sloped
A person technically qualified and professionally licensed to practice
architecture; that is, designing and dministering the
construction of buildings.
A dark brown to black cementitious material in which the predominating
constituents are bitumens found in a natural state or more commonly
left as a residue after evaporating or otherwise processing crude oil
or petroleum. See “bitumen.”
The practice of nailing the concealed portion of a roofing ply, steep
roofing unit or other components in a manner such that the fasteners
are covered by the next ply, or course, and are not exposed to the
weather in the finished roof system. Hot-mopped roofing felts and
polymer-modified bitumen sheets may be backnailed to prevent slippage.
Also referred to as “blindnailing.”
Rolling a coating by hand, normally behind the spray or power roller
applicator, to ensure better coverage and adhesion.
coat: The first coat of a
(1) Cap or cover; (2) in a metal roof, a metal closure set over, or
covering the joint between, adjacent metal panels; (3) in a steep-slope
roof system, a strip of wood or metal usually set in or over the
structural deck, used to elevate and/or attach a primary roof covering;
(4) in a single-ply membrane roof system, a narrow plastic or metal bar
that is used to fasten or hold the roof membrane and/or base flashing
(1) A class of amorphous, black or dark-colored, (solid, semi-solid or
viscous) cementitious substances, natural or manufactured, composed
principally of highmolecular-weight hydrocarbons, soluble in carbon
disulfide, and found in asphalts, tars, pitches and asphaltites; (2) a
generic term used to denote any material composed principally of
bitumen, typically asphalt or coal tar.
(1) A raised portion of a roofing membrane resulting from local
internal pressure, such as an enclosed pocket of air, which may be
mixed with water or solvent vapor, trapped between impermeable layers
of felt or membrane or between the membrane and substrate; (2) the
similarly formed surface swelling in coated prepared roofing such as
asphalt shingles; (3) separation of a coating from a substrate; may be
caused by water absorption and the resultant swelling or subsurface
(1) The adhesive and/or cohesive forces holding two components in
positive contact; (2) a surety; typical types are: bid, performance and
payment; (3) a guarantee relating to roof system performance.
(1) A covering made of flexible material that may be preformed to a
particular shape, used to exclude dust, dirt, moisture, etc., from
around a penetration; (2) a flexible material used to form a closure,
sometimes installed at inside and outside corners.
To cast or distribute granular or aggregate surfacing material.
An upward, elongated displacement of a roof membrane frequently
occurring over insulation or deck joints. A buckle may be an indication
of movement within the roof assembly.
code: The minimum
construction requirements established
generally by national organizations and adopted completely or in
altered form by local governing authorities. Building code controls
design, construction, quality of materials, use and occupancy,
location, and maintenance of buildings and structures within the area
for which the code was adopted.
edge: The lower, exposed edge
of a shingle, tile or shake.
joint: A joint formed by
adjacent, separate sections of
material, such as where two neighboring pieces of insulation abut.
A material, such as minimum nominal #1-1⁄ 2 inch size or #4,
alternatively, #3, #24, #2 or #1—as specified in ASTM
D448—smooth river stone, crushed stone, standard precast
pavers or interlocking, beveled, doweled or contoured fit lightweight
concrete pavers, which employs its mass and the force of gravity to
hold a roof membrane system in place.
flashing (membrane base flashing):
Plies or strips of roof
membrane material used to closeoff and/or seal a roof at the
horizontal-to-vertical intersections, such as at a
roof-to-wall juncture. Membrane base flashing covers the edge of the
field membrane and extends up the vertical surface. See
ply: The bottom or first ply
in a built-up or polymermodified
bitumen roof system when additional plies are to be subsequently
seam: A name applied to a
common standing seam metal panel
profile that may use a square- or rectangular-profile snap-on cap or
may be attached to and formed around a beveled wood or metal batten.
Containing or treated with bitumen, e.g., bituminous concrete,
bituminous felts and fabrics, and bituminous pavement.
waterproofing method available for
positive-side waterproofing only; cold or hot bituminous application
with reinforcing material.
(1) Sections of wood (which may be preservativetreated) built into a
roof assembly, usually attached above the deck and below the membrane
or flashing, used to stiffen the deck around an opening, act as a stop
for insulation, support a curb, or serve as a nailer for attachment of
the membrane and/or flashing; (2) wood cross-members installed between
rafters or joists to provide support at cross-joints between deck
agent: A chemical substance
applied to a suitable substrate to
create bond between it and a succeeding layer. See
(1) An instance of a membrane or base flashing unsupported at a
juncture; (2) occurs in steep-slope roofing when the nesting method is
not used in re-covering, such as roofing over standard-size asphalt
shingles with metric-size asphalt shingles.
Embedding a ply or membrane by using a broom or squeegee to smooth it
out and ensure contact with the adhesive under the ply or membrane.
A sheet (membrane, felt, etc.) lap facing upslope allowing water to hit
against the edge of it rather than facing downslope to allow water to
run over it smoothly.
roof (BUR): A continuous,
semi-flexible roof membrane consisting
of multiple plies of saturated felts, coated felts, fabrics or mats
assembled in place with alternate layers of bitumen and surfaced with
mineral aggregate, bituminous materials, a liquid-applied coating or a
granule-surfaced cap sheet.
rubber: A synthetic elastomer
based on isobutylene and a minor
amount of isoprene. It can be vulcanized and features low permeability
to gases and water vapor. Butyl rubber is manufactured into various
sheet goods, blended with other rubber materials, and is often used to
tape: A sealant tape
sometimes used between metal roof panel
seams and/or end laps; also used to seal other types of sheet metal
joints and in various sealant applications.
A slight convexity, arching or curvature (as of a beam, roof deck or
strip: A beveled strip used
to modify the angle at the point
where the roofing or waterproofing membrane meets any vertical element.
flashing: (1) Usually
composed of metal, used to cover or shield
the upper edges of the membrane base flashing or wall flashing; (2) a
flashing used to cover the top of various buildings components, such as
parapets or columns. See “flashing” and
concrete: A poured-in-place
roof deck material composed of
Portland cement, water, a foaming agent or pregenerated foam and air.
It’s oven-dry density is about 24 to 32 pounds per cubic foot.
A powdery residue on the surface of a material.
The formation of a friable powder on the surface caused by the
disintegration of the binding medium
by weather factors.
A continuous metal strip, or angled piece, used to secure metal
components. See “clip.”.
A noncontinuous metal component or angle piece used to secure a metal
panel to a substrate or two or more metal components together. See
tar: A dark brown- to
black-colored, semisolid hydrocarbon
produced by the distillation of coal.
pitch: A coal tar used as the
waterproofing agent in dead-level
or low-slope built-up roof membranes and membrane waterproofing
systems, conforming to ASTM D450, Type I.
base sheet: A coated felt
intended to be used as a base ply in a
built-up or polymer-modified bitumen roof membrane.
felt (sheet): (1) An asphalt
felt that has been coated on both
sides with harder, more viscous asphalt; (2) a fiberglass
that has been simultaneously impregnated
and coated with asphalt on both sides.
rolled: The process of
forming steel into sheets, panels or
shapes on a series of rollers at room temperature.
ridge: A term used to
describe an installation of finishing
slate shingles or wood roofing at the ridge of a roof whereby the
shingles on one side project beyond to the apex of the ridge.
head: An enlargement or catch
basin at the top of a downspout or
leader to receive rainwater from a gutter or scupper.
The covering piece on top of a wall exposed to the weather, usually
made of metal, masonry or stone.
The decorative horizontal molding or projected
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.
(1) The term used for a row of roofing material that forms the roofing,
waterproofing or flashing system; (2) one layer of a series of
materials applied to a surface (e.g., a five-course wall flashing is
composed of three applications of roof cement with one ply of felt or
fabric sandwiched between two layers of roof cement).
The surface area uniformly covered by a specific quantity of a
particular material at a specific thickness.
Fine, random cracks forming a network on the surface of a membrane,
coating or film.
A relatively small area of a roof constructed to divert water from a
horizontal intersection of the roof with a chimney, wall, expansion
joint or other projection.
(1) A raised member used to support roof penetrations, such as
skylights, mechanical equipment, hatches, etc., above the level of the
roof surface; (2) a raised roof perimeter relatively low in height.
A sheet, often granule-surfaced, used as the top ply of some built-up
or polymer-modified bitumen roof membranes and/or flashings.
action: (1) The action by
which the surface of a liquid where it
is in contact with a solid is elevated or depressed epending
the relative attraction of the molecules of the liquid for each other
and for those of the solid; (2) the siphoning of liquid into a joint or
void between two adjacent surfaces.
An ingredient that initiates a chemical reaction or increases the rate
of a chemical reaction when combined with another chemical.
cement-based compounds and various
additives that are mixed and packaged for use in a dry form; the
packaged mixture is then mixed with water and liquid bonding agents to
a workable concrete-like consistency.
fiber deck: Treated wood
fibers bonded together with Portland
cement or other resinousor cementitious-type binder that are compressed
and molded to form a structural material. Examples of product trade
names are Tectum and Insul-rock.
Stone, masonry, prefabricated metal or woodframed structure containing
one or more flues projecting through and above a roof
polyethylene (CPE): A
thermoplastic material used for single-ply
roof membranes composed of highmolecular- weight polyethylene that has
been chlorinated with a process that yields a flexible rubber-like
material. CPE can be vulcanized but usually is used in a
polyethylene (CSPE or CSM):
best known by the DuPont trade name Hypalon,® a synthetic,
rubber-like thermoset material, based on highmolecular-weight
polyethylene with sulphonyl chloride, usually formulated to produce a
self-vulcanizing membrane. Membranes in vulcanized and
nonvulcanized forms are used; classified by ASTM D5019.
roof cement: A trowelable
mixture of processed coal-tar base,
solvents, mineral fillers and/or fibers. Classified by ASTM D4022,
“Coal Tar Roof Cement, Asbestos Containing.”
A fluid material applied in the field as a film to the roof surface to
provide weather protection to the original roof substrate.
Designed for or capable of being applied without heating as contrasted
to hot-applied. Coldapplied materials are furnished in liquid state,
whereas hot-applied materials are furnished as solids that must be
heated to liquefy before application.
board roof insulation: Rigid
board insulation generally
composted of perlite or wood fiberboard factorybonded to
polyisocyanurate or polystyrene.
strength: The property of a
material that relates to its ability
to resist compression loads.
joint: A groove that is
formed, sawed or tooled in 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 stresses.
roof: A roof system that uses
products made of highly reflective
and emissive materials for its top surface. Cool roof surfaces can
remain at markedly lower temperatures when exposed to solar heat in
service than surfaces of roofs constructed with traditional
non-reflective roofing products.
board: An insulation board
used over closed cell plastic foam
insulation (e.g., polyisocyanurate) to prevent blistering when used in
conjunction with hot bituminous membranes. Suitable cover-board
insulations are glassfaced siliconized gypsum board, fiberglass board,
perlite board, wood fiberboard or mineral fiberboard. Cover boards are
also recommended between polyisocyanurate insulation and single-ply
membranes to protect the polyisocyanurate.
waterproofing: A compound of
cement, quartz or silica sand and
other active chemicals that are mixed and packaged for use in a dry
powder form. The packaged mixture is then mixed with water and applied
to a concrete surface where it penetrates into the pores of concrete.
The weight of a structure itself, including the weight of fixtures or
equipment permanently attached to it.
A structural component of the roof of a building. The deck must be
capable of safely supporting the design dead and live loads, including
the weight of the roof system, and the additional live loads required
by the governing building codes and provide the substrate to which the
roof or waterproofing system is applied. Decks are either
noncombustible, (e.g., corrugated metal, concrete or gypsum) or
combustible (e.g., wood plank or plywood).
(1) The movement of water vapor from regions of high concentration
(high water vapor pressure) toward regions of lower concentration; (2)
spreading of a constituent in a gas, liquid or solid tending to make
the composition of all parts uniform; (3) the spontaneous movement of
atoms or molecules to new sites within a material.
stability: The degree to
which a material maintains its original
dimensions when subjected to changes in temperature and humidity.
A vertical pipe or conduit used to carry runoff water from a scupper,
conductor head or gutter of a building to a lower roof level or to the
ground or storm water runoff system; also called a conductor or leader.
load: The external force, for
example, from the weight of ice
and snow, applied to a steep-slope roof system component forcing the
edge: A metal flashing or
other overhanging component with an
outward projecting lower edge intended to control the direction of
dripping water and help protect underlying building components.
load: Any load that is
nonstatic, such as a wind load or moving
(bowing, sagging): (1) The
deformation of a structural member as
a result of loads acting on it; (2) any displacement in a body from its
static position or from an established direction or plane as a result
of forces acting on the body.
A floor slab, metal wall panel, roof panel or the like having a
sufficiently large in-plane shear stiffness and sufficient strength to
transmit horizontal forces to resisting systems.
movement: In roofing and
waterproofing, dimensional changes in
dissimilar interfacing materials characterized by different and
incompatible rates of change of dimensions, such as membranes and
flashing materials, resulting from a temperature change or change in
loading. See “thermal movement.”
A structure projecting from a sloping roof usually housing a window or
standing seam: In a metal
roof panel or metal cap, a standing
seam that uses a double overlapping interlock between two metal panels.
See “standing seam.”
mat: A fabric composite or a
nondegradable plastic configured to
allow drainage of water, typically with adhered filter fabric to
prevent growth medium and fines from blocking the drainage path.
course: A separate layer of
material that provides a location
for moisture to move laterally through a protected-membrane roof
system. A drainage course relieves hydrostatic pressure from a
material’s surface and the associated weight of water.
(or dry-in felt): Usually the
underlayment or the process of
applying the underlayment for steep-slope roofing. In low-slope
roofing, it is usually called a temporary roof.
The lower edge of a sloping roof; that part of a roof which projects
beyond the wall.
Polyepichlorohydrin, commonly referred to as epichlorohydrin. See
The property of a body that causes it to tend to return to its original
shape after deformation (such as stretching, compression or torsion).
A macromolecular material that returns rapidly to its approximate
initial dimensions and shape after substantial deformation by a weak
stress and subsequent release of that stress.
coating: A coating that is
capable of being stretched at least
twice its original length (100 percent elongation) and recovering to
its original dimensions. electro-galvanized: A method of application of
corrosion- resistant zinc coatings for fasteners.
lap: The distance of overlap
where one ply, pane or piece
extends beyond the end of the immediately adjacent underlying ply,
panel or piece.
(bitumen-stop): A continuous
membrane edge seal formed at the
perimeter and at penetrations by folding the base sheet or ply over the
plies above and securing it to the top of the membrane. The envelope
prevents bitumen seepage from the edge of the membrane.
A class of synthetic, thermosetting resins that produce tough, hard,
chemical-resistant coatings and adhesives.
propylene diene terpolymer (EPDM): A
terpolymer of ethylene,
propylene and diene with the residual unsaturated portion of the diene
in the side chain to provide for vulcanization. It is a thermosetting
EPDM is an acronym for “ethylene propylene diene M-class
rubber,” which is a name assigned to this material within the
classification established in ASTM D1418.
A process in which heated or unheated material is forced through a
shaping orifice (a die) in one continuously formed
shape, as in film, sheet, rod or tubing.
joint: A structural
separation between two building elements
that allows free movement between the elements without damage to the
roof or waterproofing system.
The practice of providing regularly spaced or continuously protected
(louvered or otherwise shielded) openings along a roof edge or
perimeter, used as part of a ventilation system to dissipate heat and
An encrustation of soluble salts, commonly white, deposited on the
surface of stone, brick, plaster or mortar; usually caused by free
alkalies leached from mortar or adjacent concrete as moisture moves
The ratio of the extension of a material to the length of the material
prior to stretching. Usually, elongation is expressed as a percentage
of the original length.
(1) The process of pressing/positioning a felt, aggregate, fabric, mat
or panel into hot bitumen or adhesive to ensure contact at all points;
(2) the process of pressing/positioning granules into coating in the
manufacture of factory-prepared roofing, such as shingles.
(1) Infrared emissivity is a measure of the ability of a surface to
shed some of its absorbed heat (in the form of infrared radiation) away
from the surface; emissivity is expressed as a percentage or a decimal
factor; (2) the ratio of radiant energy emitted from a surface under
measurement to that emitted from a black body (the perfect emitter and
absorber) at the same temperature.
Ethylene propylene diene M-class rubber, also called ethylene propylene
diene terpolymer. See “ethylene propylene diene
(ECH): A synthetic rubber
including two epichlorohydrin-based
elastomers. It is similar to and compatible with EPDM.
(1) Weathering, wearing away or degradation; (2) wearing away of a
coating by chalking or the abrasive action of water or windborne
particles or grit.
interpolymers (EIPs): A group
of thermoplastic compounds
generally based on PVC polymers from which certain single-ply roofing
membranes can be formulated.
polystyrene (EPS): A type of
plastic foam insulation product
having predominately closed-cell structure manufactured from expanded
polystyrene beads in a molding process; boards or blocks are formed.
See “insulation.” expansion: The increase in length
volume of a material or body caused by temperature, moisture or other
(1) A woven cloth or material of organic or inorganic filaments,
threads or yarns used for reinforcement in certain membranes and
flashings; (2) geotextile membranes used as a protective or separating
layer in roof and waterproofing systems.
A flexible sheet manufactured by the interlocking of fibers with a
binder or through a combination of mechanical work, moisture and heat.
Felts are manufactured principally from wood pulp and vegetable fibers
(organic felts), asbestos fibers (asbestos felts), glass fibers
(fiberglass felts or ply sheets) or polyester fibers.
A relatively inert ingredient added to modify physical characteristics.
A heavy bead of waterproofing compound or sealant material generally
installed at the point where vertical and horizontal surfaces meet to
obtain a more gradual transition through the 90-degree angle at the
base of a vertical flashing.
(FRT) plywood: Plywood that
has been impregnated under pressure
with mineral salts; in the event of fire, the burning wood and salts
emit noncombustible gases and water vapor instead of the usual
The projecting edge of a rigid or semirigid component, such as an edge
metal flashing flange.
point: The lowest temperature
at which vapors above a
combustible substance ignite in air when exposed to an ignition source.
Components used to weatherproof or seal roof system edges at
perimeters, penetrations, walls, expansion joints, valleys, drains and
other places where the roof covering is
interrupted or terminated. For example, membrane base flashing covers
the edge of the field membrane, and cap flashings or counterflashings
shield the upper edges of the base flashing.
Mats or felts composed of fibers, sometimes used as a membrane backer
The tendency of material or product to crumble or break into small
resistance: Resistance to
cycles of freezing and thawing that
could affect applications, appearance or performance.
(1) In steep-slope roofing, a board that is nailed to the ends of a
roof rafter; sometimes supports a gutter; (2) in low-slope roofing, the
vertical or steeply sloped roof or trim located at the perimeter of a
building. Typically, it is a border for a low-slope roof system.
Any of a wide variety of mechanical securement devices and assemblies,
including nails, staples, screws, cleats, clips and bolts, that may be
used to secure various components of a roof assembly.
Insulation composed principally of cellulose fibers usually derived
from paper, paperboard stock or wood, with or without binders. See
base sheet: A
fiberglass-reinforced base sheet for built-up roof
system construction, impregnated and coated with asphalt and surfaced
with mineral matter; classified by ASTM D4601 as Type I or Type II.
fabric: A tightly woven
fabric, typically polyester or
polyethylene/polypropylene, used to restrict the flow of fine particles
and other contaminants while allowing water to pass freely through. It
is used to protect drainage systems from clogging.
A term used to describe a deck surface condition. A sharp raised edge
(generally in concrete) capable of damaging a roof membrane or vapor
cement: A trowelable mixture
of solvent-based bitumen and
mineral stabilizers that may include asbestos or other inorganic or
organic fibers. Generally, flashing cement is characterized as
vertical-grade, which indicates it is intended for use on vertical
surfaces. See “asphalt roof cement” and
(pour) coat: The surfacing
layer of bitumen into which surfacing
aggregate is embedded on an aggregate-surfaced built-up roof.
Approvals: Commonly referred
to as FM, a research and testing
business unit of FM Global (a commercial and industrial property
insurer) that classifies roofing components and assemblies for their
fire, traffic, impact (hail), weathering and ind-uplift
steel: Steel coated with zinc
for corrosion esistance.
gable: The vertical
triangular portion of the end of a building
having a double-sloping roof from the level of the eaves to the ridge
of the roof.
(1) A roof that has two pitches on each side of a central ridge where
the upper roof areas have less slope than the lower roof areas; (2) a
roof with two inclines on each slope.
coat: (1) The top layer of
asphalt on a smoothsurfaced built-up
roof membrane; (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.
stop: A flanged device,
frequently metallic, designed to prevent
loose aggregate from washing off the roof and to provide a continuous
finished edge for the roofing.
deck: A mixture of calcined
gypsum binder and wood chips or
other aggregate; when mixed with water, sets to a conglomerate mass;
used for poured gypsum roof decks.
Glass fibers bonded into a sheet with resin and suitable for
impregnation with asphalt in the manufacture of bituminous
waterproofing, roof membranes and shingles.
Opaque, natural or synthetically colored aggregate commonly used to
surface cap sheets, shingles and other granule-surfaced roof coverings;
also referred to as mineral or ceramic granules.
(1) Used at the bottom of a steep-slope roof system valley, a large
flat metal piece(s) wider than the valley to help prevent buildup at
the base of the valley either from debris or ice-dam formations. (2) A
plate used to connect two or more members or to reinforce a joint.
board panels: Cementitious
board stock with noncombustible core
primarily comprised of gypsum that is commonly used as a barrier board,
thermal barrier or cover board in a roof assembly.
A channeled component installed along the downslope perimeter of a roof
to convey runoff water from the roof to the drain leaders or downspouts.
(1) The distance of overlap measured from the uppermost ply or course
to the point where it laps over the undermost ply or course; (2) the
head lap area.
welding: A method of melting
and fusing together the overlapping
edges of separate sheets or sections of polymer-modified bitumen,
thermoplastics or some uncured thermoset roofing membranes by the
application of heat (in the form of hot air or open flame) and pressure.
The edge created by folding metal back on itself.
To be installed by heating the underside of the sheet with a propane
torch or other heating device, melting the polymer-modified bitumen on
the bottomside and adhering the sheet in the molten material.
sloping line along the outer angle formed by the meeting of two sloping
sides of a roof with eaves that meet at a right angle.
roof: A roof that rises by
inclined planes from all four sides
of a building to form hips at the intersection of adjacent roof slopes.
International Building Code. A model building code published by the
International Code Council (ICC); applies to all construction except
detached one- and twofamily dwellings and townhouses.
dam: A mass of ice formed at
the transition from a warm to a
cold roof surface, frequently formed by refreezing meltwater at the
overhang of a steep roof causing ice and water to back up under roofing
International Residential Code; a model building code published by the
International Code Council (ICC); applies to detached one- and
two-family dwellings and townhouses.
The slope of a roof expressed in percent or in units of vertical rise
per units of horizontal run.
Any of a variety of materials designed to reduce the flow of heat from
or into a building. See “thermal insulation.”
shingles: Individual shingles
that mechanically attach to one
another to provide enhanced wind resistance without reliance on sealing
A highly reactive organic chemical containing one or more isocyanate
groups. A basic component in spray polyurethane foam (SPF) systems and
some polyurethane coating systems.
Any of the small timbers, metal or wood beams arranged parallel to one
another and spanning from wall to wall to support a floor, ceiling or
roof of a building.
unit of energy or work in the SI system; equals the work done by a
force of 1 newton, which acts over a distance of 1 meter in the
direction of the force.
A lower downspout section used to direct water away from a wall.
flashing (diverter): A metal
flashing detail installed at the
eave end of a roof-to-wall transition designed to direct runoff
way from the wall or wall cladding.
That part of a roofing, waterproofing or flashing component that
overlaps or covers any portion of the same or another type of adjacent
cement: An asphalt-based roof
cement formulated to adhere
overlapping plies or asphalt roll roofing.
seam: Occurs where
overlapping materials are seamed, sealed or
built-up roof: A continuous,
semi-flexible roof membrane
consisting of multiple plies of felts, mats or fabrics laminated
together with alternate layers of roof cements and surfaced with a
liquid-applied coating with or without aggregate surfacing.
(1) The action of removing soluble constituents from a solid into a
solution; (2) the dissolving out of soluble substances when water seeps
through a roof system.
The direction opposite that from which the wind is blowing. The side
sheltered from the wind. For comparison, see
concrete: (1) Concrete with a
density of less than 115 lb/ft3;
(2) Poured deck fill composed of a combination of two or more of the
following: gypsum, vermiculite, perlite, wood fibers and air-entrained
roofs: A category of roofs
that generally includes weatherproof
membrane types of roof systems installed on slopes at or less than 3:12.
A decorative steep-sloped roof on the perimeter of a building.
safety data sheet (MSDS): A
written description of the chemicals
in a material or product and other pertinent data, including such
things as safe handling and emergency procedures. In accordance with
OSHA regulations, it is the manufacturer’s responsibility to
produce MSDSs and the employer’s responsibility to
their contents to employees.
fiber: Insulation composed
principally of fibers manufactured
from rock, slag or glass, with or without binders.
The application of hot bitumen with a mop or mechanical applicator to
the substrate or plies of a bituminous membrane.
A thick adhesive material used as a cementing agent for holding
waterproofing membrane in place.
fastened membrane: Generally
used to describe a membrane that
has been attached to the substrate at defined intervals.
A flexible or semiflexible roof covering or waterproofing whose primary
function is to exclude water.
A unit of measure, one mil is equal to 0.001 inches; often used to
indicate the thickness of a roof membrane.
roofing: Roofing materials
with a surface or top layer
consisting of a granule-surfaced sheet.
An application procedure in which roofing elements (insulation boards,
felt plies, cap sheets, etc.) are initially placed upside down adjacent
to their ultimate locations; coated with adhesive or bitumen; and
turned over and adhered to the substrate.
Acrylonitrile butadiene polymer blend. One proprietary NBP membrane is
commonly referred to as nitrile-butadiene copolymer.
(1) The installation of new metal roof deck directly on top of existing
metal roof deck; (2) a method of reroofing with new asphalt shingles
over existing shingles in which the top edge of the new shingle is
butted against the bottom edge of the existing shingle; also known as
A synthetic rubber (polychloroprene) used in liquid- or sheet-applied
elastomeric roof membranes or flashings.
(Sometimes referred to as “blocking”); a piece or
lumber and/or plywood secured to a structural deck or walls that
provides a receiving medium for the fasteners used to attach membrane
or flashing. See “blocking (1).”
National Fire Protection Association; an international nonprofit
organization. Its mission is to reduce the worldwide burden of fire and
other hazards on the quality of life by providing and advocating
consensus codes and standards, research, training and education. NFPA
publishes the NFPA 70, “National Electrical Code”
National Roofing Contractors Association.
The period of time after an adhesive has been applied and allowed to
dry during which an effective bond can be achieved by joining the two
Occupational Safety and Health Administration; a government agency in
the U.S. Department of Labor. Its mission is to maintain a safe and
healthy work environment.
drainage: Component(s) in a
roof or waterproofing drainage
system used to protect it against damage from a water load imposed by
blocked or partially blocked primary drainage system; e.g., overflow
scupper, overflow interior drain.
board (OSB): A mat-formed
panel product with oriented layers
resulting in directional properties. OSB is comprised primarily of wood
strands bonded with exterior adhesive formulations under heat and
pressure. Design capacities are referenced to the primary and secondary
structural axes, which typically correspond to the manufacturing
machine and cross-machine directions, respectively. The primary
direction is often referred to as the strength direction.
Any material installed on top of a waterproofing assembly.
bottom flat part of a roofing panel that is between the ribs of the
(1) A layer of material, usually applied by the spray method, that is
allowed to reach cure before another layer (“pass”)
applied; (2) a term used to explain a spray motion of the foam gun in
the application of the spray polyurethane foam (SPF) material. The
speed of the pass controls the thickness of the SPF.
felt: Bitumen-saturated felt
perforated with closely spaced
small holes to allow air and moisture to escape during application of
built-up roofing; depending on the type of material or specific use,
can be classified in accordance with STM D226, D2626 or D4897
(1) The time rate of vapor transmission through unit area of flat
material of unit thickness (values in reference sources are quoted for
unit thicknesses) induced by unit vapor pressure difference between two
specific surfaces under specified temperature and humidity conditions.
The English (inch•pound) unit of measurement for permeability
(grains•in.)/(h•ft2•in. Hg), which is
to as “perm•inch” units; (2) The property
of a porous
material that permits a fluid (or gas) to pass through it; commonly
refers to water vapor permeability of a sheet material or assembly and
defined as water vapor permeance per unit thickness.
cement: A roofing industry
generic term used to describe asphalt
roof cement that is a trowelable mixture of solvent-based bitumen,
mineral stabilizers, and other fibers and/or fillers; generally it is
intended for use on relatively low slopes, not vertical surfaces. See
“asphalt roof cement” and “flashing
(PIB): A product formed by
the polymerization of isobutylene;
may be compounded for use as
a roof membrane material.
foam board: A thermal
insulation composed of polyisocyanurate
foam with adhered facers; commonly called iso or isoboard; classified
in accordance with ASTM C1289.
coating: A one- or two-part
solvent-based coating that contains
polyisocyanate monomer and a hydroxyl containing resin, that reacts
during cure to form elastomeric coating.
The excessive accumulation of water at lowlying areas on a roof that
remains after 48 hours after precipitation under conditions conducive
drainage: The drainage
condition in which consideration has been
made during design for all loading deflections of the deck and
additional roof slope has been provided to ensure drainage of the roof
area within 48 hours of precipitation.
(1) A thin, liquid-applied solvent-based bitumen that may be applied to
a surface to improve the adhesion of subsequent applications of
bitumen; (2) a material that is sometimes used in the process of
seaming single-ply membranes to prepare the surfaces and increase the
strength (in shear and peel) of the field splice; (3) a thin
liquidapplied material that may be applied to the surface of spray
polyurethane foam (SPF) to improve the adhesion of subsequent
application of SPF protective coatings.
The part of a perimeter wall that extends above a roof.
A support or base for rooftop components such as pavers, pipes and
small rooftop units.
(1) Any construction (e.g., pipes, conduits, HVAC supports) passing
through a roof; (2) the consistency of a bituminous material expressed
as the distance, in tenths of a millimeter (0.1 mm), that a standard
needle penetrates vertically into a sample of material under specified
conditions of loading, time and temperature (ASTM D5 is the test method
used for bituminous materials). A cone is sometimes used for special
purposes instead of a needle.
An aggregate used in lightweight insulating concrete and preformed
perlitic insulation boards, formed by heating and expanding siliceous
(pitch-pan): A flanged,
open-bottomed enclosure made of sheet
metal or other material placed around a penetration through the roof,
properly stripped in to the roof membrane and filled with grout and
bituminous or polymeric sealants to seal the area around the
deck: A wood deck of planks
usually 15⁄ 8 inches to
31⁄ 2 inches thick and 6 inches to 8 inches wide laid on the
tongued-and-grooved or splinted edges and spiked together.
The material property of being flexible or moldable.
A layer of felt or ply sheet in a built-up roof membrane or roof system.
foam: A cellular, unfaced,
preformed rigid thermal insulation
produced by the polymerization of polyisocyanates in the presence of
polyhydroxyl compounds, catalysts, cell stabilizers, and blowing
agents; classified in accordance with ASTM C591.
bitumen: (1) A bitumen
modified by including one or more
polymers (e.g., atactic polypropylene, styrene butadiene styrene); (2)
composite sheets consisting of a polymer-modified bitumen often
reinforced with various types of mats or films and sometimes surfaced
with films, foils or mineral granules.
chloride (PVC): A synthetic
thermoplastic polymer prepared from
vinyl chloride. 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.
concrete: Concrete in which
the reinforcing cables, wires or
rods are tensioned before there is load on the structural member,
holding the concrete in compression for greater strength.
membrane roof (PMR): An
insulated and ballasted roof assembly in
which the insulation and ballast are applied on top of the membrane
(sometimes referred to as an inverted roof assembly).
resistance: The ability of a
material to withstand the action of
a penetrating or puncturing object.
See “polyvinyl chloride (PVC).”
A groove or slot often cut in a masonry wall or other vertical surface
adjoining a roof for inserting an inset flashing component such as a
The sloped edge of a roof at or adjacent to the first or last rafter.
A component in a two-piece counterflashing that may be surface-mounted
to a wall, inset into a raggle or embedded behind cladding. It is used
for ease of installation and future maintenance and repair or
replacement. See “reglet.”
membrane: A roof or
waterproofing membrane that has been
strengthened by the addition or incorporation of one or more
reinforcing materials, including woven or nonwoven glass fibers,
polyester mats or scrims, nylon or polyethylene sheeting.
cap: A material or covering
applied over the ridge of a roof.
assembly: An assembly of
interacting roof components including
the roof deck, vapor retarder (if present), insulation and membrane or
primary roof covering designed to weatherproof.
paper (specifically rosin-sized sheathing paper):
paper used as a sheathing paper or slip sheet in some roof systems.
See “thermal resistance (R)”
racking: A method of asphalt
shingle application also referred
to as the “straight-up method,” whereby shingle
applied vertically up the roof rather than laterally or across and up;
requires placing a part of a shingle under product already in place
every other course, which may result in a less than recommended number
of nails being used for fastening.
Defined as the reflectance of an opaque, optically flat surface or
coating of thickness sufficient to be a completely opaque. Reflectivity
is a property of a material, while “reflectance” is
property of a sample of the material.
A sheet-metal receiver for the attachment of counterflashing. A reglet
may be surface-mounted, inset into a raggle or embedded behind cladding.
Highest point on a roof, represented by a horizontal line where two
roof areas intersect, running the length of the area.
vent: A ventilator located at
the ridge that allows the escape
of warm and/or moist air from the attic area or rafter cavity.
curb: Raised frame used to
mount mechanical units such as air
conditioning units, exhaust fans, skylights, etc., on a roof.
Horizontal dimension of a slope.
A small tapered/sloped roof area structure that helps to channel
surface water to drains; frequently located in a valley. A saddle is
often constructed like a small hip roof or pyramid with a
See “styrene butadiene styrene copolymer (SBS).”
A woven, nonwoven or knitted fabric composed of continuous strands of
material used for reinforcing or strengthening membranes.
membrane: A membrane that can
adhere to a substrate and to
itself at overlaps without the use of an additional adhesive. The
undersurface of a selfadhering membrane is protected by a release paper
or film, which prevents the membrane from bonding to itself during
shipping and handling.
life: (1) The period of time
a building component or system will
function successfully without replacement or excessive repair assuming
reasonable or expected periodic maintenance is performed; (2) the
number of years of service a material, system or structure will provide
before rehabilitation or replacement is required.
(1) A small unit of prepared roofing designed for installation with
similar units in overlapping rows or courses on inclines normally
exceeding 3:12 slope; (2) to cover with shingles; (3) to apply any
sheet material in succeeding overlapping rows like shingles.
membranes: Roof membranes
that are fieldapplied using just one
layer of membrane material (either homogeneous or composite) rather
than multiple layers.
roofing: A roof system in
which the principal roof covering is a
single-layer flexible thermoset or thermoplastic membrane.
Relative lateral movement of adjacent components of a roof membrane. It
occurs mainly in roofing membranes on a slope, sometimes exposing the
lower plies or even the base sheet to the weather.
guard: A series of devices
attached to the roof in a pattern
that attempts to hold snow in place, thus preventing sudden snow or ice
slides from the roof; any device intended to prevent snow from sliding
off a roof.
vent: A manufactured or
custom built air inlet source located at
the downslope eave or in the soffit of a roof assembly.
welding: A process where a
liquid solvent is used to chemically
weld or join together two or more layers of certain membrane materials
plate: A metal plate placed
underneath the joint between two
pieces of metal.
Cured or uncured synthetic rubber tape used for splicing membrane
(1) A blade of leather or rubber set on a handle and used for
spreading, pushing or wiping liquid material on, across or off a
surface; (2) to smooth, wipe or treat with a squeegee.
roofs: A category of roofing
that generally includes
water-shedding types of roof coverings installed on slopes exceeding
flashing: Individual pieces
of sheet-metal material used to
flash walls, around chimneys, dormers and such projections along the
slope of a roof. Individual pieces are overlapped and stepped up the
The surface upon which a roofing or waterproofing membrane is applied
(e.g., in roofing, the structural deck or rigid board insulation).
An intentional depression around a roof drain or scupper that promotes
A felt that has been immersed in hot bitumen; the felt adsorbs as much
bitumen as it can retain under the processing conditions but remains
porous and contains voids.
A drainage device in the form of an outlet through a wall, parapet wall
or raised roof edge typically lined with a sheet-metal sleeve.
A joint formed by mating two separate sections of material. Seams can
be made or sealed in a variety of ways, including adhesive bonding,
hot-air welding, solvent welding, using adhesive tape and sealant.
The ability of a material to be applied around a penetration or at a
roof transition without the need for other flashing materials.
strength: The resistance to
forces that cause or tend to cause
two contiguous parts of a body to slide relative to each other in a
direction parallel to their contact plane.
life: The maximum time
interval during which a material may be
stored and remain in a usable condition according to the material
manufacturer; usually related to storage conditions.
A decrease in one or more dimensions of an object or material.
lap: The continuous
longitudinal overlap of neighboring like
A hard aggregate that is left as a residue from blast furnaces; may be
used as a surfacing material on certain (typically bituminous) roof
A hard, brittle metamorphic rock consisting mainly of clay minerals
used extensively as dimensional stone for steep roofing and in granular
form as surfacing on some other roofing materials.
roof: A membrane roof system
that includes a weathering surface
without mineral granule or aggregate surfacing.
load: The live load due to
the weight of snow on a roof
(expressed in lb/ft2) included in design calculations.
The exposed undersurface of any exterior overhanging section of a roof
stack: A sanitation pipe that
penetrates the roof; used to vent
The distance between supports or beams, girders or trusses.
Bonding or joining of overlapping materials. See
(1) A unit used in measuring roof area equivalent to 100 square feet;
(2) a quantity of material sufficient to cover 100 square feet of a
seam: In metal roofing, a
type of seam between adjacent sheets
of material made by turning up the edges of two adjacent metal panels
and then folding or interlocking them in a variety of ways.
course: The first layer of
roofing, applied along a line
adjacent to the downslope perimeter of the roof area; with steep-slope
water-shedding roof coverings, the starter course is covered by the
flashing: Membrane flashing
strips used for sealing or flashing
metal flashing flanges into the roof membrane.
butadiene styrene copolymer (SBS): High
molecular weight copolymer
with thermoset and thermoplastic properties (thermoplastic elastomer),
formed by the block copolymerization of styrene and butadiene monomers;
used as the modifying compound in SBS polymer-modified asphalt roofing
membranes to impart rubberlike qualities to the asphalt.
insulation: A system of
precut or premolded insulation boards or
a poured insulation fill designed to provide slope to the roof deck
before installing the roof membrane.
A brown or black bituminous material, liquid or semisolid 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.
slate roof system: A term
used to designate a slate roof system
with a range of slate thicknesses mixed throughout; usually uses slates
with rougher texture than standard slate with uneven tails or butts.
A material that softens when heated and hardens when cooled. This
process can be repeated provided the material is not heated above the
point at which decomposition occurs.
olefin membrane (TPO): A
blend of polypropylene and
ethylene-propylene polymers, colorant, flame retardants, ultraviolet
radiation absorbers and other proprietary substances that may be
blended with the TPO to achieve the desired physical properties. The
membrane may or may not be reinforced.
In roofing and waterproofing, 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 roof or waterproofing system.
The process of removing deteriorated mortar from an existing masonry
joint and troweling new mortar or other filler into the joint.
(1) The technique of connecting joints between insulation boards or
deck panels with tape; (2) the technique of using self-adhering
tape-like materials to seam or splice single-ply membranes.
The treatment or method of anchoring and/or sealing the free edges of a
membrane in a roof or waterproofing system.
barrier: In torched membrane
applications over combustible
substrates, an above-deck barrier incorporated into a roof system
before torching as a fire-safety practice. Acceptable thermal barriers
include: minimum 3⁄ 4- inch-thick perlite board insulation,
minimum 3⁄ 4-inchthick fiberglass or mineral wool board
insulation, or minimum 1⁄ 4-inch-thick glass-faced gypsum
elastomer: A material having
the general properties of an
elastomer and capable of being repeatedly softened by heat and hardened
to shape by cooling without significant degradation of the polymer
system; typically more thermally and pressure-sensitive and more
sensitive to solvents than thermoset elastomers.
flashing: A water-resistant
membrane or material assembly
extending totally through a wall and its cavities positioned to direct
water within the wall to the exterior, usually through weep holes.
(torch-down): Method used in
the installation of polymer
modified bitumen membranes characterized by using open flame propane
An identification label or seal affixed to a roofing product or package
with the authorization of Underwriters Laboratories Inc. The presence
of the label indicates the product has met certain performance criteria.
An asphalt-saturated felt or other sheet material (may be
self-adhering) installed between a roof deck and roof covering, usually
used in a steep-slope roof construction. Underlayment is primarily used
to separate a roof covering from the roof deck, shed water and provide
secondary weather protection for the roof area of the building.
The internal angle formed by the intersection of two sloping roof
(1) A single wythe of masonry for facing purposes that may not be
structurally connected; (2) any of the thin layers of wood glued
together to form plywood.
barrier: See “vapor
Layer(s) of material or a laminate used to appreciably reduce the flow
of water vapor into a roof assembly.
The resistance of a material to flow under stress. For bitumen,
viscosity measurements are reported in centipoise (cP or cPs) at a
specific temperature; as viscosity increases, flow rate decreases.
(1) High traffic and high-service-frequency areas on a rooftop,
particularly those leading and adjacent to vents, hatches and heavy
duty air-conditioning units; (2) materials or accessories such as
traffic mats or pavers installed on rooftop surfaces to provide wearing
surfaces for traffic and/or protect a roof system from damage resulting
from rooftop traffic.
and ice-dam protection membrane:
A continuous membrane installed
under steep-slope roofing materials in areas subject to ice damming or
wind-driven rain that prohibits water that gets through the roof
covering from getting into the structure; ice- and water-protection
membranes classified by ASTM D1970 must also seal around fasteners.
membrane: The part of a
waterproofing system that has the
primary function of excluding water; it does not include accessories
such as drainage materials or protection boards. See
The ability of a membrane or roof covering to prevent the passage of
water with a limited amount of hydrostatic pressure.
The process of moisture movement by capillary action.
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.
The ability of individual, overlapping components to resist the passage
of water without hydrostatic pressure.
roof system: A roof system
that depends on gravity for quick
drainage via water shedding to prevent water entry into or through the
Treatment of a surface or structure to prevent the passage of water
under hydrostatic pressure.
assembly: An assembly of
interacting waterproofing components
including the deck, membrane and protection/drainage/insulation course.
system: A system of
interacting waterproofing components
consisting at a minimum of a membrane but may also include protection,
drainage and insulation courses, as well as waterstops, expansion and
control joints, various flashings and counterflashings, and overburden
such as pavers, cast concrete and wire mesh or rebars. It does not
include the substrate.
To join pieces of material together by heat fusion.
valley: A method of valley
construction in which shingles or
roofing from both sides of the valley extend across the valley and are
woven together by overlapping alternate courses as they are applied.
In spray polyurethane foam (SPF) roofing, the volume of foam per unit
weight normally expressed as board feet per pound or board feet per
soft, self-healing metal that reacts with the environment to produce a
soft blue-gray zinc carbonate patina that protects the underlying metal
from corrosion. Zinc is commonly used as sacrificial (galvanized)
coating for a base metal such as sheet steel and iron, in various metal
alloys and in oxide form as a white pigment.
over your head is
important. Hiring the wrong "roofer" to install
can lead to
disaster. Hire a real "roofer",