Roofing Terminology
Alligatoring
Surface cracking due to oxidation and shrinkage stresses, which shows as repetitive mounding of
an asphalt surface, resembling the hide of an alligator.
Application Temperature
The temperature of the hot bitumen when applied on the roof which should be not more than
approximately 11ºC (50ºF) less than the correct kettle temperature.
Asphalt
- A dark brown to black bituminous substance that is found in natural beds and is also obtained
as a residue in petroleum or coal-tar refining that consists chiefly of hydrocarbons. - An asphaltic composition used for pavements and as a waterproof cement. Canadian roofing asphalts
are generally from the heavy end of petroleum distillation and can be obtained in a great range of
viscosities and softening points.
Asphalt Primer
A solution of asphalt in petroleum solvent, used to prepare concrete roof decks for the
application of hot asphalt. The primer lays dust and improves the adhesion of the molten asphalt
to the roof deck.
Attic
The open space between the underside of the roof sheathing and the upper side of the ceiling
directly below the roof.
Base Sheet
A heavy sheet of felt sometimes used as the first ply in built-up roofing.
Base Flashing
- That portion of the flashing which is attached to or rests on the roof deck to direct the flow of
water on the roof, or to seal against the roof deck. - A material applied to the base of a wall
extending above a roof, as a protection for the junction of the wall, and the roof. The simple
principle is to turn the membrane up along the vertical surface, so that the roofing forms a large
watertight tray, the only outlets from which are the roof drains to dispose of the water.
Bituminous felts are usually used for a bituminous roofing.
Bitumen
Bitumens are mixtures of hydrocarbons of natural or pyrogeneous origin; or combinations of
both, frequently accompanied by their non metallic derivatives, which may be gaseous, liquid, or
solid, and which are completely soluble in carbon disulfide. In the roofing industry the word
covers both asphalt and coal tar pitch.
Blind nailing
Shingles nailed in such a location that when the next shingle is applied, the nails of the first
shingle do not show.
Blisters, structural
The more evident and more serious blisters are structural blisters. They occur in many forms of
deformation and are not confined to the exposed surface. They are caused mainly by the
expansion of trapped air and water -vapour or moisture or other gases. Air and moisture trapped
within the construction tend to expand during a rise in air temperature or from the heat of the
sun, and this expansion causes the plies of the roofing to separate and bulge the roof surface in a
balloon effect. The blisters are spongy to the touch, and may occur between any of the layers of
roofing felt, or between membrane and deck, or membrane and insulation.
Block method
The method of applying shingles in vertical rows from eave to peak rather than in horizontal
rows from rake to rake. This method makes shading more noticeable and can lead to improper
fastening. It is not a recommended method. Also called straight up method.
Blueberry
A term sometimes used to describe weather blisters. These are small surface blisters, which can
be seen in large numbers over the entire roof area, more predominant during warm weather
where roofs are exposed directly to the sun, and which are a result of natural weathering of the
surface bitumen. Volatiles and water vapour in the bitumen tend to be driven off by heat, and
when the gases are trapped they form small blisters. This type of blistering usually does not
cause any failure during the normal life of the roof. Also sometimes called pimpling, pin
blistering and bitumen bubbling.
Bond
Adherence between plies of felt, or between felts and other elements of roof systems, which use
bitumen or other materials as the cementing agent.
Breather
A type of roof vent consisting of a hooded flanged pipe 2" to 8" in diameter, penetrating the
roofing membrane to allow escape of moisture from insulation.
Buckling
Warping or wrinkling of the roof membrane.
Built-up Roofing
A built-up roofing consists of plies or layers of roofing felt bonded together on site with hot
bitumen. A protective surface coating of gravel or slag is sometimes embedded in a heavy top
coating of hot bitumen. It is laid down to conform to the roof deck, and to protect all angles
formed by the roof deck with projecting surfaces, and forms a single-unit flexible waterproofed
membrane fastened to the deck by cementing and nailing. The simple principle on flat roofs is to
turn the membrane up to form a skirting or base flashing on the vertical surfaces, making a large
watertight tray. The only outlets from this tray are the roof drains to dispose of water.
Cant Strip
A bevelled support used at the intersection of the roof deck with vertical surfaces so that bends in
the roofing membrane to form base flashings can be made without breaking the felts. They may
be a bevelled strip of wood or insulation and in some cases cement grout or lightweight concrete.
Cantilever
A self supporting projection without external bracing in which a beam or series of beams is
supported by a downward force behind a fulcrum.
Cap Flashing
That portion of the flashing built into a vertical surface to prevent the flow of water behind the
base flashing. The cap flashing overlaps and caps off the top of the base flashing.
Caulk
Fill in a joint with mastic or cement.
Cement Asphaltic Plastic
A mixture of asphalt, solvent and mineral stabilizer used for example to adhere flashings or to
fill pan flashings.
Clawing
The downward curving of the butt portion of the shingle. This creates a hump along the leading
edge and a widening of the cut-out. The bulge thus created is susceptible to substantial damage
by wind action, hail and ice. Clawing is part of the normal aging process of shingles and is a sign
of long service.
Closed valley
A valley where the flashing is covered by shingles.
Coal Tar Pitch
A bituminous material produced by distilling crude tar residue derived from the cooking of coal.
It is used as the waterproofing material for tar and gravel built-up roofing.
Collar
A metal cap flashing around a vent pipe projecting above a roof deck.
Concealed nailing
Application of roll roofing in such a manner as to conceal or cover all nail heads used to fasten
the roofing to nailable decks. Also referred to as blind nailing.
Condensation
The change from water vapour to liquid water, resulting from a drop in temperature of an air
vapour mixture.
Conductor
A pipe for conveying rain water from a roof gutter to a drain, or from a roof drain to a storm
drain.
Coping
The cap or highest covering course of a wall, usually overhanging the wall and having a sloping
top to carry off water.
Cornice
Projection at the top of a wall. Term applied to a construction under the eaves where the roof and
side walls meet. The top course, or courses of a wall when treated as a projecting crowning
member.
Counter flashing
Strips of metal, roofing, or fabric inserted and securely anchored to the reglet or attached to a
vertical surface above the plane of the roof and turned down over the face flashing to protect the
base flashing.
Course
Row of shingles that can run horizontally, diagonally or vertically and sometimes termed the run
of the shingle.
Cracking
After long exposure, a fissure or fissure pattern appearing on the shingle or roofing due to
weathering of the asphalt.
Crazing
Surface deterioration of a shingle by the formation of a pattern of fine hairline cracks.
Cutout
The slot between shingle tabs to create the distinctive 2 or 3 tab appearance.
Curb
A wall of wood or masonry built above the level of the roof, surrounding a roof opening such as
for installation of roof fans or other equipment, and at expansion joints in the roof deck.
Cut off
A piece of roofing membrane consisting of one or more layers of felt used to seal the edges of
insulation at the end of a day's work, or to separate the insulation into multiple areas so that, in
case of a roof leak, any damage would be isolated to the cut-off section surrounding or adjacent
to the leak.
Cut Back
A solution of bitumen in a volatile solvent. Cut backs are used as primers, cold application
cementing agents, and damp roofing coatings.
Dead load
The total weight of all installed materials and the constant weight of a roof used to compute the
strength of all supporting framing members.
Deck
The structural roof to the top surface of which a roof covering system is applied. Some forty or
more roof deck types are currently in use in the construction industry.
Dormer
A separate smaller roofed structure that projects from a sloping roof to provide more space
below the roof and to accommodate a vertical window.
Double pour
The application of the top coating of bitumen and the gravel surfacing of a built-up roofing in
two separate applications, used on dead level roofs, particularly when the roof is designed for
flooding with water. This is accomplished by embedding a quantity of gravel in a first top pour
of bitumen and later repeating the operation with additional gravel embedded in a second pour of
bitumen.
Downspout
A pipe for conveying rain water from a roof gutter to a drain, or from a roof drain to a storm
drain.
Drip edge
A modified L-shaped flashing used along the eaves and rakes. The drip edge directs runoff water
into the gutters of air and away from the fascia.
Eave
The horizontal roof overhang that extends outward and is not directly over the exterior walls or
the building's interior.
Eaves Trough
A gutter at the eaves of a roof for carrying off rain water. It may be of wood or metal attached to
the eaves, or a built-in part of the eaves design usually lined with metal.
Ell
An extension of a building at right angles to its length.
Emulsified Asphalt
Straight run asphalt liquefied by clay emulsifiers and water. Finely divided dust-like particles of
asphalt are kept in suspension in a cold but unsolidified state. Cementing action by solidification
takes place when the water in the emulsion evaporates. Asphalt dispersed in water.
End Lap
The amount of overlap at the end of a ply on the application of roll roofing felts for built-up
roofing.
Expansion joint
A planned, controlled joint placed between two roof surfaces or between two sections of a built-
up roof. The expansion joint allows the roof to expand without physical damage to the roof or the
building.
Exposure
That portion of a shingle that is exposed to the weather. Exposure is usually measured from the
butt of one shingle to the butt of the next overlaying shingles.
Face nailing
Nailing with the nails placed in the exposed area or face of the shingle.
Fascia
A wood trim board used to hide the cut ends of the roof's rafters and sheathing. Fascia is either
one by or two by lumber. The gutter system is usually nailed to the fascia.
Felt
A very general term used to describe roll roofing materials, consisting of a mat of organic or
inorganic fibres unsaturated, saturated, or saturated and coated with asphalt or coal-tar pitch.
Felt, Asbestos
Felt made from asbestos fibres, impregnated or impregnated and coated with asphalt.
Felt, Asphalt Saturated
Any type of felt that has been impregnated or saturated with asphalt. Sometimes referred to as
merely asphalt felt, which can also mean felt impregnated and coated with asphalt.
Felt, Coated
Bitumen saturated felt that has been coated on one or both sides with bitumen by further
processing. Coated felt may be used as base sheets, in some types of built-up roofing, and with
mineral surfacing added as cap sheets and shingles.
Felt, Glass
A non-woven mat of flexible glass fibre, formed by spreading fibrous material over a screen and
pressing it together to form a sheet. For use in built-up roofing applications the glass fibre mat is
impregnated with asphalt.
Felt, No. 15
Asphalt or coal-tar saturated felt weighing approximately 15 pounds per 100 square feet.
Felt, Perforated
Asphalt saturated felt perforated with small holes, which allow trapped air to escape during
laying, and bitumen to enter to form a well-bonded membrane.
Felt, Rag
A type of heavy paper made principally from wood fibre, wood flour, waste paper and a small
percentage of rag. It was formerly made principally of rag when first used in the manufacture of
roofing materials. Rag felt is saturated or saturated and coated with bitumen to produce a variety
of roofing felts, and prepared roofing.
Felt, Tar Saturated
Felt impregnated or saturated with coal-tar pitch.
Fill
Lightweight concrete placed on a level roof deck in varying thickness' to build slopes to the roof
drains, Also referred to as screeding.
Fire wall
Any wall built for the purpose of restricting the spread of fire in a building. Such walls of solid
masonry or concrete usually divide a building from the foundations to about a metre above the
roof.
Fire-resistant
Material that is resistant to catching on fire when exposed to open flame or flaming ashes.
Fishmouthing
The raising of a portion of the butt edge (lower edge) of a shingle. This curved short section
tapers back into the shingle. Usually, only the front part of the shingle is affected. At the end of
the exposure, the shingle will be perfectly flat. Fishmouthing is often the result of moisture
absorption followed by moisture evacuation in the shingle.
Flashing, Eaves
Treatment of the edge of a roof with felt and/or metal.
Flashing block
A specially designed masonry block having a slot or opening into which the top edge of the roof
flashing can be inserted and anchored. Also known as raggle block.
Flashing
Metal strips used to form a watertight seal between the items butted up against the shingles.
Flashing is used along walls, chimneys, and dormers. Metal is usually 28 gauge galvanized sheet
metal, but may be lead, copper , tin or aluminum.
Gable
The triangular end of an exterior wall from the level of the eaves to the ridge of a double-sloped
roof.
Gambrel Roof
A type of roof which has its slope broken by an obtuse angle, so that the lower slope is steeper
than the upper slope. A double sloped roof having two pitches.
Glaze Coat
A mopping of bitumen on exposed felts to protect them from the weather pending completion of
the job.
Gravel stop
A gravel guard used at the rakes and eaves of a built-up gravel coated roof.
Gutter
Trough at the eaves of a roof to convey rain water from the roof to a downspout.
Header
The beam into which the common joists are fitted when framing around a roof opening. The
headers are placed so as to fit between two long beams or trimmers to support the joist ends.
Headlap
The overlapping of shingles or roofing felt at their top edge. Roofing felt should be headlapped
by a minimum of 2 in.
Hip Roof
A roof which rises by inclined planes from all four sides of a building. The line where two
adjacent sloping sides of a roof meet is called the hip. Also called a cottage roof.
Horizontal application
The application of roll roofing parallel to the eaves.
Ice dam
A build-up of ice at the eaves drainage area or in the valley of a sloping roof. An ice dam is very
harmful since it prevents melting snow or rain water from exiting the roof, and the water backs
up under the shingles instead.
Jack
A flanged metal sleeve used as part of the flashing around small items that penetrate a roof.
Kettle Temperature
The temperature to which bitumen is heated in the kettle. The maximum recommended kettle
temperature varies with the type of bitumen, but generally must never be greater than 400ºF for
coal tar pitch and 450ºF. for asphalt.
Lap Cement
A cut back asphalt used for cementing the laps of roll roofing.
Lean-to-roof
The sloping roof of a room having its rafters or supports pitched against and leaning on the
adjoining wall of a building.
Live Load
The total weight of all installed equipment and materials and all variable weight (such as snow,
ice and people) that will move across a surface. Used to compound the strength of all supporting
framing members.
Lock Shingles
Designed with a mechanical locking feature to provide effective wind resistance.
Membrane
A saturated cotton or burlap fabric used for certain built-up roofing applications. Also used to
describe the combination of felts and layers of bitumen forming a single flexible unit and
waterproofing system of a built-up roof covering.
Mill Deck
A type of wood roof deck constructed from wood planks placed on edge vertically, and spiked or
nailed together.
Mopping
A layer of hot bitumen mopped between layers of roofing felt. Also the act of spreading molten
bitumen.
Mopping, Full
The application of bitumen by mopping in such a manner that the surface being mopped is
entirely coated with a reasonably uniform coating.
Mopping, Spot
Application of bitumen by mopping in spots, during the placing of certain portions of some built-
up roofing systems. Staggered, roughly circular spots of bitumen in a fairly regular pattern to
secure felts to certain types of roof decks.
Mopping, Strip
The application of bitumen by mopping in a strip pattern. On certain types of precast slab decks
when mopping is kept back from the joints it is referred to as strip mopping.
Nailing Strips
Strips of wood placed at the eaves of all types of roof decks except wood, and at the tops of
masonry expansion or ventilation curbs for the attachment of flashing. On slopes in excess of 3-
inches to the foot on non-nailable decks it is sometimes necessary to embed nailing strips in the
deck to provide for anchoring of the roof to the deck to prevent sliding. Also simply called
nailers.
Open valley
A valley where the flashing is exposed to the weather.
Overhang
That portion of roofing extending beyond the deck. As related to the roof structure, that part of
the roof structure which extends beyond the exterior walls of a building.
Parapet
A low wall along the edge of and surrounding a roof deck. It is generally an extension of exterior
building walls and fire walls that usually extend about a metre or less above the roof.
Penetration
A measure of the viscosity of a bitumen.
Pitch
Height from the joist to ridge divided by rafter length, which translates to rise in inches per
horizontal foot or ratio of pitch. Ratio is any portion up to full pitch (24" in 12").
Pitch Pan or Pocket
Usually a rectangular flanged metal collar placed around metal supports that project above a roof
deck. The pitch pan is placed on top of the roofing felts, and the flanges stripped in with
additional felts. Plastic roof cement is placed around the metal support in the bottom of the pan,
and it is then filled to the top with bitumen. Also mastic pan.
Ply
A single layer or thickness of roofing material. Built-up roofs are described as three , four ply,
etc., according to the number of layers of felt used to build up the membrane.
Ponding
The collecting of water in shallow ponds on the top surface of roofing. Certain roofs are
designed for the ponding of water to a shallow depth over the whole surface of the roof deck, to
aid in summer cooling and as fire protection.
Pour Coat
The top coating of bitumen on a built-up roof. The final pouring of hot bitumen into which the
gravel or slag surface dressing is embedded.
Primer
A cut back asphalt coating of thin consistency used on concrete or metal preparatory to applying
a built-up roof.
Purlin
Boards laid from gable to gable on which the common rafters sit.
Rafters
The lumber supports that make up the roof structure. Usually 2" x 12" lumber. The roof
sheathing is nailed to the rafters.
Raggle or raglet
A horizontal slot or opening left in a parapet or other masonry wall into which the top edge of
flashing can be anchored. In unit masonry this is usually achieved by inserting a 2" deep wood
strip in a horizontal joint during construction and later removing this strip. For concrete work it
may be achieved by attaching a wood strip or a patented metal form to the concrete forms before
pouring.
Reglet
A groove in the vertical wall adjacent to a roof surface, above the top of base flashing into which
the metal counterflashing is placed and rigidly held in place; it is either formed in concrete or
consists of a metal insert, or a "reglet block" of masonry.
Ridge
The horizontal line where two opposite sloping sides of a roof join at the highest point of the
roof, hip, or dormer. On double sloped gable roofs sometimes called the comb.
Ridge cap
Formed shingles, shake or tile, used to cover the ridge of a building.
Roll Roofing
Any roofing material which comes from the dealer in rolls. More specifically it applies to
mineral surfaced asphalt, or composition roofing.
Roll Roofing-Granule Surfaced
Roll-roofing asphalt-coated on both sides, and finished on one side with natural or synthetic
coloured mineral granules. Also called mineral surfaced.
Roll Roofing-Smooth Surfaced
A type of roll-roofing which is asphalt-coated on both sides with either a smooth or veined
surface, finished with talc, mica, or other fine mineral particles.
Roll Roofing-Wide Selvage
Asphalt-coated roll-roofing finished with natural or synthetic coloured mineral granules for only
a part of its width, usually for 17-inches, and sometimes referred to as 19-inch selvage.
Sometimes also referred to as split sheet mineral surfaced felt.
Roof Drain
The termination or fitting at the roof of an interior drain or leader for draining rain water from
nominally flat roofs. The fitting itself usually consists of a base with or without a sump, a clamp
ring and gravel stop, and a basket strainer to prevent debris clogging the drain. The base is
sometimes fastened to the leader with an expansion sleeved fitting. Some roofers dispense with
the specially engineered roof drains, and use instead a flanged copper pipe stripped into the
roofing felts with the end projecting loosely inside the leader.
Roof Insulation
Any medium or low density material used as a part of the roofing system to reduce heat loss
through the roof. A variety of insulation materials are being used including wood fibres, glass
fibres, cork, plastics, and poured lightweight fills.
Roof span
Distance from outer wall to opposing outer wall of a building covered with a roof.
Roofing system
The waterproof roof covering, roof insulation, vapour barrier (if used) and roof deck as an entity.
Run
The horizontal distance between the face of a wall and the ridge of the roof, being half the span
for a symmetrical gable roof. Sometimes, though incorrectly, used to denote the slope distance
from the eave to the ridge.
Scupper
An outlet in the wall of a building or a parapet wall for drainage of overflow water from a floor
or roof directly to the outside. Special scupper drains connected to internal drains are also
sometimes installed at roof and wall junctions.
Self-healing
A term used in reference to bitumen which melts with the heat from the sun's rays, and seals over
cracks that earlier formed in the bitumen from other causes.
Selvage
The unsurfaced strip along a sheet or roll roofing which forms the underportion at the lap in the
application of the roof covering.
Side Lap
The horizontal distance one shingle overlaps adjacent shingle in the same course; also the
horizontal distance one sheet of roofing overlaps adjacent sheet.
Single Coverage
Method of applying roof shingles to provide only one complete layer of roof protection. Many
special shingles for re-roofing are designed for single coverage for reasons of economy and
flexibility.
Sky Dome
Dome shaped plastic cover for a curved opening in a roof to admit light to the interior.
Sky Light
Glazed opening in a roof to admit light.
Soffit
A board or sheet that extends from the fascia to the buildings siding and hides the bottom of an
overhang. Soffit can be made from wood, vinyl plastic, sheet steel, aluminum, and other
materials. Soffit may or may not contain ventilation slots depending of the attic venting system
used.
Soil Stack
The main vertical pipe which receives waste matter from all plumbing fixtures. The vent stack to
the roof frequently is incorrectly referred to as the soil stack.
Starter Course
The first course of shingles installed on a roof, starting at the lower left edge of the eave.
Step flashing
Metal shingles or plates used in a stair-step pattern under regular shingles. Step flashing is the
recommended flashing whenever a wall or chimney is above the roof line. Also whenever the
roof shingles must butt up against the wall or chimney and the shingles transverse from the eaves
to the ridge.
Tab
Weather exposure surface of a shingle between the cutouts.
Tabbing
Method of applying high strength adhesives to shingles for wind resistance.
Trimmers
A beam that receives the end of a header.
Truss
A combination of members such as beams, bars and ties, usually arranged in triangular units, to
form a rigid framework for supporting loads over relatively long spans as in wide span roof
construction.
Tuck pointing
Mason term used for describing the act of placing mortar into a joint with the use of a pointed
trowel. Usually done during a repair of an item like a chimney.
Valley
The horizontal line formed along the depressed angle at the bottom of two inclined roof surfaces.
Vapour barrier
A material that prevents the passage of water or water vapour through it. Vinyl, plastic,
aluminum foil, Kraft paper, asphalt felt, asbestos felt and a laminated combination of these
materials are considered vapor barrier materials.
Vent sleeves
Sheet metal flanged collars placed around vent pipes for the purpose of sealing-off the roofing
around the vent pipe openings.
Vent
An outlet for air; vent pipe in a plumbing system; a ventilating duct.
Vent pipe or Vent
A vertical pipe providing an escape for foul gases from a sanitary fixture. For a number of
fixtures the vent pipes lead into a larger vertical pipe to the outside through the roof called a vent
stack.
Ventilators
Devices installed on the roof for the purpose of ventilating the interior of the building.
Frequently combined with motorized fan equipment mounted on the roof, to provide positive air
flow.
Viscosity
The internal frictional resistance offered by a fluid to change of shape or to the relative motion or
flow of its parts. Viscous materials are glutinous, adhesive and sticky.
Water Vapour
Moisture existing as a gas in air. Warm air can hold more water vapour than cold air. Water
vapour in the air creates a pressure much like any other gas. Cold air has a relatively low vapour
pressure, but warm air with larger amounts of water vapour has a greater pressure. The
difference in pressures cause the vapour to do strange things such as penetrating building
materials in the direction from high to low vapour pressure.
Wrinkle
A slight ridge caused by folding, rumpling or creasing. In roofing usually refers to the common
"wrinkle" pattern that forms over the joints of insulation in insulated roof systems. See also
buckling.
