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Roofing 101

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A

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

1. 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. 2. An asphalt composition used for pavements and as waterproof cement.

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.

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Attic

The open space between the underside of the roof sheathing and the upper side of the ceiling directly below the roof.

B

Base Sheet

A heavy sheet of felt sometimes used as the first ply in built-up roofing.

Base Flashing

1. That portion of the flashing that 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.

2. 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 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 -vapor 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 vapor 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.

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C

Cant Strip

A beveled 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 beveled 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 cutout. 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 nails heads used to fasten the roofing to nail able decks. Also referred to as blind nailing.

Condensation

The change from water vapor to liquid water, resulting from a drop in temperature of an air vapor mixture.

Conductor

A pipe for conveying rainwater 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 sidewalls 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.

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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 rainwater 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.

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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 rainwater. 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.

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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 fibers unsaturated, saturated, or saturated and coated with asphalt or coal-tar pitch

Felt, Asbestos

Felt made from asbestos fibers, 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 fiber, 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 fiber 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 fiber, 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.

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 meter above the roof.

Fire-resistant

Material that is resistant to catching on fire when exposed to open flame or flaming ashes.

Fish mouthing

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. Fish mouthing 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.

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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 rainwater from the roof to a downspout.

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H

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.

Head lap

The overlapping of shingles or roofing felt at their top edge. Roofing felt should be head lapped 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.

I

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 rainwater from exiting the roof, and the water backs up under the shingles instead.

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J

Jack

A flanged metal sleeve used as part of the flashing around small items that penetrate a roof.

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K

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.

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L

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.

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M

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 pre-cast slab decks when mopping is kept back from the joints it is referred to as strip mopping.

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N

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-nail able 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.

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O

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.

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P

Parapet

A low wall along the edge of and surrounding a roof deck. It is generally an extension of exterior building walls and firewalls that usually extend about a meter 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.

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Q

R

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 counter flashing 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 colored 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 colored 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 rainwater 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 fibers, glass fibers, 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, vapor 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.

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S

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 un-surfaced strip along a sheet or roll roofing which forms the under portion 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 roofline. Also whenever the roof shingles must butt up against the wall or chimney and the shingles transverse from the eaves to the ridge.

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T

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.

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U

V

Valley

The horizontal line formed along the depressed angle at the bottom of two inclined roof surfaces.

Vapor barrier

A material that prevents the passage of water or water vapor 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 airflow.

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.

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W

Water Vapor

Moisture existing as a gas in air. Warm air can hold more water vapor than cold air. Water vapor in the air creates a pressure much like any other gas. Cold air has a relatively low vapor pressure, but warm air with larger amounts of water vapor has a greater pressure. The difference in pressures cause the vapor to do strange things such as penetrating building materials in the direction from high to low vapor 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.

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Roofing 101

you should know the basics

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