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Roof Types

Aggregate: (1) crushed stone, crushed slag or water-worn gravel used for surfacing a built-up roof. (2) any granular mineral material.

Alligatoring: the cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator's hide; the cracks may or may not extend through the surfacing bitumen.

Ambient Temperature: temperature of air - - air temperature.

Application Rate: the quantity (mass, volume or thickness) of material applied per unit area

Bitumen: the generic term for an amorphous, semi-solid mixture of complex hydrocarbons derived from any organic source. Asphalt and coal tar are the two used in the roofing industry.

Bituminous: containing or treated with bitumen. Examples: bituminous concrete, bituminous concretes, bituminous felts and fabrics, bituminous pavement.

Bituminous Grout: a mixture of bituminous material and fine sand that will flow into place without mechanical manipulation when heated
Blends:  Mixtures of various colored granules found on the one face of mineral-surfaced roofing.

Blind nailing:  Nails driven in such a way that the heads are not visible.

Blister:  An enclosed raised spot evident on the surface of a building. They are mainly caused by the expansion of trapped air, water vapor, moisture or other gases.

Board Stock Insulation:  A board stock insulation has a core of one of the following materials: APA-rated OSB; asphalt/glass; glass-based; gypsum; mineral wool; perlite; polyisocyanurate/polyurethane; expanded polystyrene foam (EPS); extruded polystyrene foam (XPS); or wood fiber. The material, the number of board stock layers, and the position of the product within the assembly determine whether it will be classified as an insulation, a cover board, or a thermal barrier.
Bond breaker  A layer or coating that is applied to a specific area of a substrate, such that, when a subsequent layer or coating is applied over the bond breaker, it will not bond or adhere in that area.

Boston lap:  A method of finishing the ridge of a shingle course, using overlapping vertical joints.

Bowstring roof:  A roof constructed with curved timber trusses and horizontal tie-beams connected by light diagonal lattices of wood.

Built-up Roof Membrane (BUR): a continuous, semi-flexible roof membrane assembly, consisting of plies of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, generally surfaced with mineral aggregate, bituminous materials, or a granule-surfaced roofing sheet.

Butyl: a rubber like material produced by copolymerizing isobutylene with a small amount of isoprene, Butyl may be manufactured in sheets, or blended with other elastomeric materials to make sealants and adhesives.

Class "A": The highest fire-resistance rating for roofing as per ASTM E-108. Indicates roofing is able to withstand severe exposure to fire originating from sources outside the building.

Class "B": Fire-resistance rating that indicates roofing materials are able to withstand moderate exposure to fire originating from sources outside the building.

Class "C": Fire-resistance rating that indicates roofing materials are able to withstand light exposure to fire originating from sources outside the building.

Concrete: A construction material that consists, in its most common form, of Portland Cement, aggregate (usually gravel and sand) and water. Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration. The water reacts with the cement, which hardens, bonding the other components together and eventually creating a stone-like material.

Condensation: The change of water from vapor to liquid when warm, moisture-laden air comes in contact with a cold surface.

Cool Roofing A cool roof is defined as a roof surface that has both high reflectivity and high emissivity. High reflectivity requires the surfacing material to reflect solar energy away from the surface. High emissivity requires radiating heat energy away from the surface. Roofs undergo significant expansion and contraction as they heat and cool throughout the day. Heat absorbed by the roof can also accelerate degradation by ultraviolet rays and water. A reflective roof can reduce the amount of thermal shock that occurs on the roof surface and prolong the life of the roof.

Energy StarŽ: A registered trademark of the U.S. government. The ENERGY STARŽ Program* represents a voluntary partnership between the federal government and businesses to promote energy efficiency and environmental activities. ENERGY STARŽ labeled roof products are reflective and lower roof surface temperature by up to 100°F., decreasing the amount of heat transferred into a building. ENERGY STARŽ labeled roof products are designed to help save money on utility bills and reduce energy waste.  Reflective roof products can help reduce the "heat island effect," a phenomenon in which cities can be 2 to 8°F. warmer than the surrounding countryside. Such heat islands occur, in large part, because many buildings and paved surfaces are designed with dark materials that absorb heat from the sun. This heat is released at night, causing the air temperature to remain high. The resulting elevated temperature leads to an increased demand for air conditioning in buildings, increased fuel use for vehicle air conditioning, increased levels of smog, and associated increased levels of heat-related and smog-related health problems. Installing reflective roofs helps reduce the heat island effect, decreasing the amount of smog in the air and benefiting the entire community.  *ENERGY STARŽ is a registered trademark of the U.S. government.

Elastomer: a macromolecular material that returns rapidly to its approximate initial dimensions and shape after substantial deformation by a weak stress and the subsequent release of that stress.

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

EPDM: EPDM rubber (ethylene propylene diene Monomer (M-class) rubber),a type of synthetic rubber, is an elastomer which is characterized by wide range of applications.The E refers to Ethylene, P to Propylene, D to diene and M refers to its classification in ASTM standard D-1418. The "M" class includes rubbers having a saturated chain of the polymethylene type. The diene(s) currently used in the manufacture of EPDM rubbers are DCPD (dicyclopentadiene), ENB (ethylidene norbornene) and VNB (vinyl norbornene).

The ethylene content is around 45% to 75%. The higher the ethylene content the higher the loading possibilities of the polymer, better mixing and extrusion. Peroxide curing these polymers give a higher crosslink density compared with their amorphous counterpart. The amorphous polymer are also excellent in processing. This is very much influenced by their molecular structure. The dienes, typically comprising between 2.5 wt% up to 12 wt% of the composition serve as crosslinks when curing with sulfur and resin, with peroxide cures the diene (or third monomer) functions as a coagent, which provide resistance to unwanted tackiness, creep or flow during end use.

Fascia - The vertical board secured to the ends of the rafters under the lower end of the roof to which the guttering is normally fixed - traditionally timber, nowadays usually PVC.

Felt roof - Cold - Normally a two or three layers system for boarded flat roofs using cold applied adhesive. Each layer has traditionally been bitumen based, however high performance polymer based materials are available which offer better performance. Usually for bitumen based materials, the first layer is just nailed to the roof boarding, the middle and top layers are glued with the top layer being covered in protective mineral chippings - should be good for at least 10 years.

Felt roof - Hot - Normally a two or three layers system for boarded flat roofs using hot bitumen or a flame torch. Each layer has traditionally been bitumen based, however high performance polymer based materials are available which offer better performance. Usually for bitumen based materials, all the layers are put down using hot bitumen or a flame torch with the top layer being covered in protective mineral chippings or painted with a solar reflective protective coating.

Flashing - A weather seal, usually lead or zinc, made where part of the roof abuts a vertical surface - one side of the flashing is normally embedded in a joint between two rows of bricks, the other side being shaped to fit onto the roof surface. Plain flashing is where the roof meets the vertical surface horizontally. Stepped flashing is where the roof meets the vertical surface at an angle - the steps in the flashing align with the joints of different courses in the brickwork

Flash Point: The critical temperature at which a material will ignite.

Flashing: Pieces of metal or roll roofing used to prevent seepage of water into a building around any intersection or projection in a roof such as vent pipes, chimneys, adjoining walls, dormers and valleys. Galvanized metal flashing should be minimum 26-gauge. There are 4 main types of flashing used in residential roofing systems:

Valley flashing: This flashing is used in open valleys of the roof. Most often leaks are found in the valley flashings due to flashing that is nailed to tightly to the decking or shingles that are not trimmed far enough off the flashing.

Plumbing vent flashing: Plumbing vent flashing prevents rainwater from running into holes cut for pipes in the roof. This flashing is sold according to the size of the vent pipe and the roof angle. Roofing material is installed over the flashing.

Lead flashing: When working with tile roofs, lead flashing is used. In the case of a plumbing vent flashing, the lead flashing is actually molded to the shape of the tile's surface. Then the top of the lead flashing is covered by the next tile to prevent water from seeping under the flashing.

Step flashing: When a chimney or dormer wall intercepts the slope of the roof, step flashing is used. Step flashing is usually a metal piece that is bent in the middle, so that one end lays on the roof, and the other against the vertical wall of the dormer or chimney.

Flat Roof - A roof which has negligible slope, usually covered in felt, metal, or other material which is impermeable to water.

Gable - The vertical wall at the end of a pitched roof, an inverted 'V'.

Gauge - The measurement between the roof battens for positioning the slates or tiles, the minimum gauge is normally specified by the manufacturer/supplier - although a different meaning, the measurement is the same as the margin.

Hip - A sloping ridge formed by the junction of a pitched roof and a hip end.

Hip board - The board along the line of a hip from the fascia to the ridge of the pitch.

Hip end - A sloping end to a pitched roof which is covered with slates or tiles.

Ice dam: Ice dams occur when snow melts near the ridgelines of warm roofs (roofs without adequate ventilation). As the water runs down the roof to the overhang, it cools and freezes. If the snow continues this melt and freeze process, an ice dam can form that can seep under the shingles, through the decking and into the house. This, of course, can cause serious roof leaks--even in freezing temperatures.   The best prevention to ice dams is a well-ventilated (cool) roof. Additional protection for your roof can be applied with an impermeable ice and water membrane. The membrane is installed on top of the decking, under the roofing material. Temporary prevention of ice dams can also be done through the use of electric cables along the eaves of the roof (where the dams usually form). However, new ice dams can form above the cables and still cause extensive damage. Another emergency solution to ice dams is to fill a sock or nylon with calcium chloride. Lay the stocking vertically across the ice dam. The calcium chloride will melt the ice and release the water so that it can drain outside, and not inside your roof.

ISO Board: Polyisocyanurate Board-a polyurethane foam supplied in board form primarily as an insulation material for the construction industry.

Margin - The exposed area of a slate or tile - usually the minimum is quoted by the manufacturer/supplier and may vary for a given slate/tile depending on slope of the roof and exposure - although a different meaning, the measurement is the same as the gauge..

Mastic: An asphalt-based cement used to bond roofing materials. Also known as flashing cement.

Metal Flashing: see FLASHING; metal flashing is frequently used as through wall flashing, cap flashing, counterflashing or gravel stops.

Material Safety Data Sheet (MSDS): a written description of the chemicals within a product, and pertinent other data including such things as safe handling and emergency procedures.   A MSDS for any Sealoflex product is available by request.

Mechanically-Fastened Membranes: generally used to describe membranes that have been attached at defined intervals to the substrate. Mechanically fastening may be performed with various fasteners and/or other mechanical devices, such as plates or battens.

Metal drip edge: A narrow strip of non-corrodible metal used at the rake and eave to facilitate water runoff.

MIL: Measurement often used to determine thickness of a roofing membrane.    1 mil = .001 inch (1/1000) or 25.400 microns. 1 millimeter approx equal to 40 mils

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

Nail Sickness - Associated with slate roofs when the nails have corroded to such a state that they fail to hold the slates. Usually it starts with one or two displaced slates being observed but, as the whole roof was probably covered at the same time using the same type of nails, the problem is likely to get progressively worse.

Organic felt: An asphalt roofing base material manufactured from cellulose fibers.

Organic shingle: An asphalt shingle reinforced with organic material manufactured from cellulose fibers.

OSD (or OSB) Plywood: OSD plywood (which is also commonly known as OSB or oriented strand board) is produced by binding wood chips together with a mix of glue and resin. The mixture is then cast and baked to produce a plywood-like sheet. Because OSD does not use costly veneers it is as much as half the price of regular plywood.
OSD also tends to have better waterproof characteristics, since the glue and resin make the wood chips impervious to moisture that can seep in between the plies of standard plywood. This means that OSD is the perfect choice for applications such as exterior wall sheathing and roofing.

Percent Elongation: In tensile testing, the increase in the gauge length of a specimen measured at or after fracture of the specimen within the gauge length. This is usually expressed as a percentage of the original gauge length.

Perm: A unit of water vapor transmission, defined as one grain of water vapor per square foot per hour per inch of mercury (Hg) pressure difference (1 inch of mercury = 0.491 psi).

Permeability: The rate of flow of a liquid or gas through a porous material.

Pitch: Also known as "slope", pitch is the measure of how "steep" a roof is. For example, if a roof is "4 in 12", the roof rises 4 inches for every horizontal run of 12 inches. The pitch of the roof is a big factor in determining the kinds of materials that can be used and the longevity of the roof. Usually, a steeper roof (higher pitch) will last longer due to its better drainage capabilities.

Polyvinyl chloride, (IUPAC Poly(chloroethanediyl)) commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups (ethenyls) having one of their hydrogens replaced with a chloride group.Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene  PVC is widely used in construction because it is cheap, durable, and easy to assemble.

Rafter - A vertical, sloping timber used to form the shape of the roof - the side of a truss.

Ridge - The horizontal line at the top of a pitched roof - applies whether there is a sloping roof on both sides 

Ridge board - The horizontal board along the line of the ridge - normally along the top of the rafters or trusses.

Ridge tile - Normally a semicircular or angled tile used to seal the top of pitched roofs (and also hips). Usually the tile is secured by mortar and covers the fixings and top edge of the tiles/slates on both sides.

Roof Slope : Roof slope is the most important factor in roof design. The slope of a roof effects the interior volume of a building, drainage, style, and material used for the roof covering. If water collects on the roof (no or poor drainage), the cause is probably related to the slope. Slope is the angle made by the roof surface plane with the horizontal plane and expressed as the amount of vertical rise for every twelve inch (12") horizontal run. For instance, a roof that rises four inches (4") for every twelve inch (12") horizontal run, is expressed as having a "four in twelve" slope; often written as "4:12." Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also known as the Roof Pitch. Some common roof slopes and the terms that classify them are:
* Flat Roof: 2/12
* Low Slope: 2/12-4/12
* Conventional Slope Roof: 4/12-9/12
* Steep Slope: 9/12 and higher

Sarking - Another name for roofing underfelt.

Sarking board - Used, where appropriate board over the rafters for additional insulation.

Shingle: (1) a small unit of prepared roofing material designed to be installed with similar units in overlapping rows on inclines normally exceeding 25 percent; (2) to cover with shingles; (3) to apply any sheet material in overlapping rows like shingles

Slate - Common sizes are 460x305mm and 610x355mm although other sizes may be available. Slates needs to be laid in a brick like bond with a double lap to avoid water entry around the sides, but even with this required double lap, they tend to be lighter per square meter than both plain and interlocking tiles. Slates do not have locating lugs (nibs) on the back (as do both types of tile) and so each slate needs to be individually positioned and nailed into place on the roofing battens, therefore roofing with slates can be more time consuming than either of the tiles. Usually suitable for pitched roofs with a slope of 23° or greater, larger slates can be used for even lower slopes. Alternatives to natural slate are manmade alternatives, some are lighter, most are cheaper.

Single coverage: Asphalt roofing that provides one layer of roofing material over the deck.

Single Ply: A descriptive term signifying a roof membrane composed of only one layer of material such as EPDM, Hypalon or PVC.

Shore A Hardness: The relative hardness of elastic materials such as rubber or soft plastics can be determined with an instrument called a Shore A durometer. If the indenter completely penetrates the sample, a reading of 0 is obtained, and if no penetration occurs, a reading of 100 results. The reading is dimensionless.

Slope: Soffit - The horizontal board used to seal the space between the back of the fascia and the wall of the building - traditionally timber, or cement board nowadays usually uPVC with air vents.

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

Substrate: the surface upon which the roofing or waterproofing membrane is applies (i.e. the structural deck or insulation).

Tensile Strength The maximum force a material can bear without tearing apart. Roofing membranes should have sufficient tensile strengths to resist the severe stresses caused by internal and external forces imposed on it. Thermal shock, caused by sudden heating or cooling of a membrane, causes stress that a roofing membrane must be able to withstand. The greater the tensile strength of a membrane, the greater resistance it will have to splitting, breaking or tearing.

Tiles - interlocking - Traditionally made from concrete with a profile allowing the tiles to overlap each other side to side, so giving much better protection from the ingress of water. Typically 380x230mm with an effective width of 200mm (i.e. 30mm overlap). They are normally laid in straight lines up the roof with a single lap. They tend to be heavier per square meter than slate but lighter than plain tiles. Locating lugs (nibs) on the back are used to mount then on the roofing battens. Usually suitable for pitched roofs with a slope of 23° or greater.

Tiles - plain - Traditionally made from clay, generally about 265x165. Need to be laid in a brick like bond with a double lap to avoid water entry around the sides, due to the required double lap, they tend to be heavier per square meter than both slate and interlocking tiles. Locating lugs (nibs) on the back are used to mount then on the roofing battens. Usually suitable for pitched roofs with a slope of 35° or greater.

Tingle - A small strip of lead, zinc or copper, nailed to the batten under a displaced slate, the slate is then replaced and the bottom of the tingle is bent up over the bottom edge of the slate and back onto the front surface to hold it in place. 

Truss - Normally, factory made roof frame.

Underfelt - A layer of material between the back of the slate/tiles and the roof frame providing slight insulation and an extra waterproof barrier for any moisture. Traditionally made from bitumen with a strong woven base but this is liable to become brittle with age and rot where exposed to sunlight, modern alternatives are generally lighter and more durable.

Valley - The internal angle formed where adjacent pitched roofs meet. Traditionally zinc or lead sheeting was used on site to create a water channel downwards, nowadays pre-shaped valley channels are available.