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Stone, slag or river rock that comes in a variety of sizes. Used as ballast and / or UV protection for certain roof
systems, BUR, EPDM etc.

Alligatoring
A characteristic in asphalt which occurs during aging. Exposed asphalt inherently over time loses volatile oils, in
conjuction with oxidation caused by UV exposure (solar radiation) creates a pattern of cracks. These cracks
resemble alligator hide.
Apron 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 roof.
Architectural Shingle
A laminated asphalt shingle that provides a dimensional appearance.
Asphalt
a dark bituminous substance that is found in natural beds and is also obtained as a residue in petroleum refining
and that consists chiefly of hydrocarbons. Asphalt is used in many different roofing products, including but not
limited to, shingles, underlayments, emulsions etc.
Asphalt Shingle
A shingle manufactured by coating a reinforcing material (felt or fibrous glass mat) with asphalt and having mineral
granules on the side exposed to the weather (see shingle)
ASTM
American Society for Testing and Materials
Ballast
Various materials used to protect roof systems from UV rays, or to prevent blow off of systems which are not fully
adhered. River rock, brick, pavers etc.
Back Nailing
Installation of nails in roof felts (to the deck) under the overlaps along with hot mopping to precent slippage during
process.
Base Sheet (Ply)
An asphalt saturated or coated felt, installed as the first layer (ply) with 4" laps in a built up roof (BUR) system.
Base Flashing
A portion of the flashing attached to or resting on the deck used to direct the flow of water onto the roof covering
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
Blister / Blistering
An enclosed bubble (under the surface). Can be caused by different reasons, for example, expansion of trapped
air and water - vapour or moisture or other gases. Some blisters will expand during rising outside temperatures,
this also causes the plies of roofing material to seperate from each other or from the deck. Blueberry blisters are
smaller in size and are more common on unprotected roof systems (smooth modified or BUR without coating or
aggregate)
Blocking (aka Racking)
A method of applying shingles in vertical rows from the eave to the ridge, rather than horizontally from rake to
opposing rake. This is not a recommended method of installation, some shingle manufacturers will not warranty
this.
BUR / Built Up Roof
Layers, or plies of roofing felt, bonded together with hot bitumen (see bitumen and asphalt), typically finished with a
flood coat of hot bitumen and a protective coating or aggregate (rock etc)
Cant Strip
A bevelled material used at the intersection of a roof deck with vertical structural detail (parapet wall). Used to
support roofing membrane used to form a base wall flashing in order to prevent breakage of materal (felts,
modified, membrane etc). Made of various materials including bevelled wood, insulation, grout or concrete etc.
Cap Sheet
A granulated surface bitumen material commonly used as the top ply of a built up roof system (BUR). Use of
aggregate for UV protection is not necessary when a cap sheet is installed.
Cladding
Material used as the exterior wall enclosure of a building
Class "A"
Refers to the highest of fire- resistant ratings in regards to roofing materials per ASTM E-108. A Class "A" rating
indicates the material is able to withstand severe exposure to fire originating from outside the building in which the
material is installed and will not support a flame on it's own.
Closed Cut Valley
A method of valley application in which shingles from one side of the valley extedn across the valley while shingles
from the other side are trimmed back either in the middle of the valley or off center.
Coal Tar
A dark brown to black colored, semi-solid hydrocarbon produced by the distillation of coal. Coal tar pitch is further
refined to conform to certain roofing grade specifications;

Coal Tar Pitch:
A coal tar used as the waterproofing agent in dead-level or low-slope built up roof membranes and membrane
waterproffing systems, conforming to ASTM Specification D 450 Type I

Coal tar waterproofing pitch:
A coal tar used as the dampproofing or waterproofing agent in below-grade structures, conforming to ASTM
Specification D 450 Type II

Coal Tar Bitumen:
A proprietary trade name for TypeIII coal tar used as the dampproofing or waterproofing agent in dead-level or low
slope built up roof membranes and mambrane waterproofing systems, conforming to ASTM D 450 Type III
Cold Roof Assembly
a rof assembly in which the insulation is located below the deck, and not typically in contact with the deck, allowing
for ventilation space. The temperature of the roof assembly remains close to the outside air temperature.
Composition Shingle
An asphalt shingle roof, non specific to the design. (see further shingle definitions)
Composite board roof insulation
Rigid board insulation generally comprised of perlite or wood fiberboard factory bonded to polyisocyanurate or
polystyrene.
Compounded Thermoplastics
A category of roofing membranes made by blending thermoplastic resins with plasticizers, various modifiers,
stabilizers, flame retardants, UV absorbers, fungicides and other proprietary substances alloyed with proprietary
organic polymers
Condense
To make denser or more compact, as when a material (water vapor etc) changes from it's gas phase to it's liquid
phase
Condensation
The conversion of water vapor or other gas to liquid phase as the temperature drops; the act or process of
condensing
Coping
The covering piece on top of a wall exposed to the weather, usually made of metal, masonry, or stone and sloped
to carry off water
Copolymer
The product of polymerization of two or more substances, as two different isomers, together
Core Sample
(1) a smaple taken from a low-slope roof system for the purpose of obtaining information about it's construction.
 Typically core sample analysis can reveal the type of materials used, the number of plies, thiickness and condition
of insulation (if present) and the type of deck material used as the substrate for the system.
(2) in regards to an SPF roof system, core samples are used to obtain both quantitative and qualitative information
(thickness of the foam, thicness and adhesion of the coationg, thickness of installation passes, and adheasion
between each pass and to the substrate.
Cornice
The decorative horizontal molding or projected roof overhang
Counter batten
Vertical wood strips installed ona sloped roofs over which horizontal batens are secured. The primary roof covering
is attached or secured to these horizontal battens (tile, slate, aluminum shingles etc)
Counterflashing
Metal or elastomeric sheeting, secured on or into a way, curb, pipe, rooftop unit or other surface, to cover and
protect the upper edge of base flashing and it's fasteners.
Course
A term used for a row of roofing material , and/or one layer of a series materials.
CPA
Copolymer alloy
Cricket
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.
Curb (curbing)
A raised member used to support roof penetration fixtures, skylights, mechanical equipment (HVAC) hatches etc, above the roof
surface, also a low raised roof perimeter.
Cure
A process whereby a material is caused to form permanent molecular linkages by exposure to chemicals, heat, pressure,
weathering. Cure time is the time required for a material to reach it's resiliant long term characteristics. Cured, is also used in
reference to the time frame a material has been exposed to weather, and will eventually lose it's resiliant qualities.
Dead level
Absolutely no slope
Deck
A structural component of a roof. The deck supports the design, dead, and live loads, including the weight of the roof system, and
additional live loads (ie snow etc.) as set forth (requred by) in building codes. The seck also provides the substrate to which the
roofing or waterproofing system is applied to the structural surface of a building. Decks can be non combustible, metal, concrete,
gypsum, or combustible, wood, plywood, osb etc.
Degradation (degraded)
A change in the chemical structure, physical properties or appearance of a material from natural or artificial exposure, (UV,
moisture, heat, freezing, wind etc)
Delamination
Separation of the laminated layers of a component
Dimensional Shingle
a shingle that is textured, or laminate to produce a three dimensional effect **See architectural shingle**
Dormer
A structural projection from a sloping roof, typically housing a window, or a ventilation fixture
Downspout
A vertical pipe, or conduit used to facilitate runoff water from a scupper, or gutter of a building to a lower roof level, to the ground,
or a storm drain system.
Drip Edge
Metal flashing, or other overhanging component with an outward projecting lower edge, used to control the direction of dripping
water and help protect underlying building components (fascia etc)


Eave
The lower edge of sloped roof, extending past the wall.
Eave Vent
Protected openings along roof perimeter (edge) used as the intake part of a ventilation systems, to disapate heat and moisture.
Elasticity
The flexibility property of returning to an initial for or state following deformation (streching, pulling, compression etc)
Elastomeric Coating
A coating that is capable of being streched at least twice it's orginal length (100% elongation) and returning to it's original
dimensions when pressure is released.
Elongation
The extension of a material (streching) beyond it's original state.
Emulsion
A mixture of bitumen (asphalt) and water, with uniform dispersion of the bitumen or water glbules, usually stabilized by an
emulsifying agent or system.
End Lap
The distance of the overlap where one ply, or piece extends beyond the end of the immediatly adjacent underlying ply / piece.
EPDM
(Ethylene Propylene Diene Monomer) A material used for low slope roof installations. Typically black in color, although some
manufacturers have introduced white sheets.
Epoxy
A class of synthetic, thermosetting resins that produce though, hard, chemical-resistant coatings and adhesives.
Ethylene Interpolymers (EIP)
Thermoplastic compounds generally based on PVC polymers from which single ply roofing membranes can be formulated
Exhaust ventilation
Aire that is vented, / exhasted from the roof cavity or attic space. Typically through vents installed near the ridge of a sloped roof.
Expansion Joint
A structural separation between two building elements that allows free movement between the elements without damage to the
roofing system.
Eyebrow
A dormer, typically small, whose roof line is arched, (curved) resembling the arch of an eyebrow.


Fabric
A woven cloth or material of organic or inorganic filaments, threads, or yarns used for reinforcement in certain membranes,
flashings, and roof systems.
Fascia
On a sloped roof, the fasica board is nailed to the end of the rafters, sometimes supporting a gutter, on low sloped roofs it is
typically a border around the perimeter.
Felt
A flexible sheet of interlocking fibers with a binder, or through moisture or heat process. Typically manufactured from wood pulp
and vegetable fibers (organic) glass fibers, or polyester fibers. Used as an underlayment in some roof systems (shingle systems for
example)
Field Seam
A splice or seam made in the field, where overlapping sheets are joined together using sealing / joining method particular to the
roof system.
Fishmouth
A half cylindrical shaped opening or void in a lapped edge or seam. Typically caused by wrinkling or shifting of ply sheets during
installation. Shingle fishmouths occur at the cut edge.
Flashing
components used to weatherproof or seal roof system edges at perimeters, penetrations, walls, expansion joints, drains and other
areas where the roofing material is interrupted or ends.
Fleece
Mats or felts composed of fibers, sometimes used as a membrane backer for fully adhered installations.
Flood Coat
Surfacing layer of bitumen (asphalt) on a built up roof installation.
Gable
The vertical triangular portion of the end of a building with a double sloped roof
Galvanize
To coat steel or iron with zinc for corrosion resistance
Guage
A metal thickness measurement.
Granule
Opaque, natural or synthetically colored aggregate commonly used to surface roofing materials, shingles cap sheets, etc.
Gravel Stop
A flanged device typically metal, designed to prevent loose gravel (aggregate) from washing off the roof. Also serves as a
continuous finished edge.
Gussett
Typically used at the bottom of a valley, a flat metal piece, wider thant the valley to help prevent debris build up at the base of the
valley.
Hand Tabbing
Spot applying adhesive (asphalt based) to underside of shingles for extra securement and wind resistance.
Heat Seaming
AKA heat welding, the process of joining thermo plastic membranes by heating and then applying pressure to join materials
together.
Hip
The inclined external angle formed by the intersection of two sloping roof planes.
HVAC
Heating, Ventilating and air conditioning equipment.


Ice Dam
Ice formed at the transition from a warm to a cold roof surface. Typically formed at the over hang (eave). Snow melts down from
the warm area of the roof, over attic space, to the eave where the temperature is the same as the ambiant temperature, where it
freezes. Ice and water will then back up under roofing materials and can result in a leak.
Impact Resistance
Resistance to fracture under sudden application of force. For example, shingle manufacturers are producing impact resistant
shingles for hail prone areas.
Impregnate
In regards to roofing materials; completely surround fibers in a felt or mat with bitumen. Spaces between the fibers are partially or
completely filled without a continuous coating of bitumen on the surface.
Infrared Thermography
The process of displaying variations of apparent temperatures over the surface of a roof by measuring the viariations in infrared
radiance.
Inorganic
composed of materials other than hydrocarbons and their derivatives, matter that is not of plant or organic origin.
Insulation
Materials designed to reduce the flow of heat, either entering or exiting a building.
Intake Ventilation
Fresh air drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.
Interlayment
a felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather and water shedding
characteristics of the primary roof materials in times of wind driven precipitation. This method is typically used in wood shake
installations.
Interlocking Shingles
These are individual shingles that mechanically attach to each other. This provides additional wind resistance as they do not rely
soley on sealing strips.
Isolation Sheet
Refer to Slip Sheet
Joist
Timbers, metal, or wood beams that are arranged parallel to each other, spanning from wall to wall, supporting a floor, ceiling or
the roof of a building / structure.
Laminate
To join layers of materials together. The process of joing layers of materials together utilizing ahesive / adhesion.
Laminated Shingles
Refer to Dimensional or Archtectural shingles
Liquid Applied
The application of bitumous cements, adhesives, coatings, applied at ambient or slightly above ambien temperatures (cold applied)
Live Loads
Temporary in nature loads that the roof structure must be designed to support as set forth in govt building codes. Generally
dynamic or environmental (installation equipment, snow, rain, ice, service personel etc)
Loose Laid
Referring to a ballasted roof system whereas membrane is attached to the substrate only at the edges and the penetrations of the
roof. Ballast is required as there are no field attachments along the roof with the exception of penetrations.
Low Slope Roof
A roof with a pitch (slope) lower or lesser than 3:12 (14 degrees). Typically these roofs have membrane (single ply, EPDM,
modified bitumen) roof systems installed as shingles are not meant to be waterproof, but to shed water.
Low temperature flexibility
The ability of roofing material to flex, resist cracking when subjected to low temperatures. Particularly important on roofs where
there may be anticipated foot traffic during winter months for maintenance.


Mansard
A decorative addition, steep slope usually with shingles or metal on the perimeter of a building. A mansard roof is this portion of a
roof, which terminates into a flat roof at it's highest point.
Mastic
An adhesive material (cementing agent) used to facilitate holding waterprofing membrane in place on a roof surface.
Mat
Thin layer of woven, knitted, or non woven fiber used as a reinforcement in roofing materials. (shingles, membranes)
MSDS (Material Safety Data Sheets
A written description of chemicals and other pertinent data in a roofing material. Including safe handling and emergency
procedures. It is the responsibility of the manufacturer to produce an MSDS to comply with OSHA regulations.
Mechanically Fastened
Referring to membrane (single ply) installations, describing the process of attaching the membrane at strategic points to the
substrate (screws and plates etc)
Membrane
A flexible / pliable roofing material which excludes water (waterproofing sheet)
Metal Roof Panel
an interlocking metal sheet, with an installed exposure of approx. 3 square feet.
Metal Roof Shingle
Interlocking metal component, with an installed exposure of less than 3 feet.
Mil
A unit of measurement. One mil is equal to .001 inches, 25.4 micrometers. Used to indicate the thickness of a roofing material,
typically membrane.
Mildew
Growth produced on organic matter or living plants by fungi.
Millimeter
A unit of measurement, equalling .03937 inches.
Mineral Surfaced Roofing
Roofing material with a surface (top) of granules (embedded). Mineral surfaced sheet, commonly referred to as "rolled roofing", a
class B material typically used on out buildings.
Model Codes
Commonly referred to as "building codes", are standards or codes established to provide uniformity in regulations in regards to
construction. These codes are set forth by local govt entities.
Modified Bitumen
A roofing material used on low slope roofs. a bitumen modified by adding one or more polymers (atactic polypropylene, butadiene
styrene etc.). Sheet forms are typically reinforced with various types of mats or films, also surfaced with films (smooth modified) or
mineral granules (granulated modified)
Moisture Relief Vent
AKA Anti condensation vent, a device installed through roofing membrane to vent moisture vapor pressure from within the system.
Moisture Scan
A process utilizing a device (infrared, capacitance etc) to detect the presence of moisture within a roofing system.
Monolithic / Monoform
A roofing system formed from or comprised of a single material, hence seamless.
Monomer
Low molecular weight substance, consisting of molecules capable of reacting with like or unlike molecules to form a polymer.
Mopping
Application of a hot bitumen with a mop applicator to the substrate or plies of membrane
Nailer
Lumber and or plywood material (incl osb) secured to the deck, or walls, that provides
a receiving medium for the fasteners used to mechanically attach single ply
membranes, or flashing.
Net Free Vent Area
Area open to unrestricted air flow. Commonly used as a measuring unit of sorts, to
measure vent performance. (eg; area of the opening of vent, minus the area displaced
by the screening material)
Night Seal / Night Tie In
The method of temporarily sealing an existing membrane edge to the newly installed
membrane edge, while roof installation is underway, but halted by nightfall. This
method is used to protect structure from possible water until roof installation can
resume.
Non Traffic Bearing
A roof system that will not withstand foot traffic without reinforcement / protection
(walk tread etc)
Nonwoven Fabric
A roofing related textile structure processed by bonding or interlocking fibers. This is
accomplished by use of chemicals, thermal, solvent or mechanical processes.
NRCA
National Roofing Contractors Association
Open Valley
A type of material installation in the valley (steep slope roofs) where both sides of the
valley are trimmed, and metal installed (exposed) in the valley
Organic
Composed of hydrocarbons or derivatives, or of plant or animal design.
Overflow Drainage
A component in a roof drainage system. This component is to safeguard the roof
structure in the event primary drains are blocked, or partially blocked, thus there is a
large collection of water on the roof. (scuppers, overflow interior drains)
Parapet Wall
The portion of the perimeter wall that extends above the roof level.
Pass
Refers to one layer of roofing material applied, typically in regards to spray materials.
(SPF, emulsion etc)
Pedestal
A base, or support for roof top components, HVAC units, pipes, pavers etc.

Penetration
Any fixture construction that passes through the roof surface (HVAC, pipes, conduits
etc)
Perlite
Aggregate used in insulating concrete and preformed insulation boards
Pipe Boot
Prefabricated flashing unit used to flash around pipe penetrations.
Pitch Pan / Pitch Container
Flanged open bottomed fixture made of sheet metal (or other) placed around a roof
penetration, filled with sealants to seal the area around penetrations.
Plasticizer
Material incorporated (mixed) in a material increasing it's ease of flexibility or
warkability.
Pliability
Property of a roofing material to be flexible or moldable.
Ply
A layer of felt or sheet in a BUR (built up roof) system.
Polymer
Macromolecular material formed by chemical combination of monomers
Polyvinyl Chloride / PVC
Synthetic Thermoplastic polymer processed from vinylchloride. The flexibility or
rigidity of PVC is contingent upon the use of plasticizers, stabilzers, fillers and other
modifiers. EG, used in pipes for plumbing (rigid form) single ply membranes (flexible
form)
Pond (ponding)
On a roof surface, an area that is incompletely drained.
Primer
Solvent based, liquid applied bitumen, typically used to approve adhesion of bitumen
based roofing materials, applied to the substrate.
PVC Polyvinyl Cloride

R-Value
A term used to describe the thermal resistance of insulation, see THERMAL resistance.
Racking
A method of asphalt shingle installation where courses are aplied vertically up the roof. This is not a recommended installation
method.
Rafter
A structural component installed from ridge (high point) to eave, designed to support the roof deck, roof system and live loads.
Rake
The sloped edge of a roof, directional of rafter.
Rake Starter
Bleeder Strip - Starter Strip. Used along the rake edges in an asphalt shingle installation.
Re-cover
Installation of new roofing materials over existing roof system.
Reflectivity
The ability of a roofing material to reflect light instead of absorbing and the heat.
Release Tape / Strip
Plastic or paper film or strip applied to self sealing shingles to prevent them from sticking toether in the packaging. This strip need
NOT be removed during installation.
Ridge
Highest point of the roof, where two slopes come together.
Ridge Cap
The roofing material specifically purposed / manufactured for installation on the ridge.
Ridge Vent
Contiuous ventilation along the ridge of the roof utilizing specifically manufactured vent components.
Roof Cement
See asphalt roof cement.
Roof Covering
The outer most exterior layer of roof assembly.
Roof Jack
A bracket used to support toe boards on sloped roofs, these are for saftey and convenience during roof installation.
Roof Slope (pitch)
The rate of vertical rise to horizontal length. 4:12 = four inch vertical rise per 12 inch horizontal lentch
Roof System
All components included in the installation of a roof.
Rubber
Quite possibly the most mis-used term when referring to low slope or flat roof materials.
Run
The horizontal dimension of a roof slope.
Saddle
See Cricket
Saturated Felt
A felt material that has been immersed in hot asphalt (bitumen). The materail remains porous, used as underlayment for various
roof systems.
SBS
Styrene Butadien Styrene.
Scrim
A woven or nonwoven fabric of continuous strands of material. This is used as a reinforcement for strengthening membranes.
Scupper
A secondary (back up) drainaige device, through a wall or parapet wall.
Self Adhering Membrane
A roofing membrane manufactured to self adhere to the substrate and underlying material by removal of a film or paper.
Shingle
A small unit designed for installation with like units, overlapping rows, for installation on slopedroofs. Typically steeper sloped than
3:12. Ther term "Shingle" also refers to the act of installing shingles
Shrinkage
A decrease in one or more dimensions of an object or material. In regards to roofing, some materials will, over time, shrink, and
begin pulling away from parapet walls / perimeters.
Single Ply Membrane
Roofing Membranes that are field applied using just one layer of single ply. Often thermoset or thermoplastic.
Skirt Flashing
Metal counterflashing used under a mechanical unit, or skylight. Used to cover an protect the upper edege of a base flashing enad
it's fasteners.
Slate
A hard brittle rock consisting mainly of clay minerals. Used on steep sloped roofs.
Slip Sheet
A sheet material (kraft paper, plyester scrim, polyethylene etc) placed betweent to components of a roof system. It's purpose is to
ensure no adhesion occures between them and to protect one or more component.


Snow Guard
A series of devices attached to a roof in a pattern used to prevent snow sliding from the roof in a sheet onto the ground. These are
used on steep sloped roofs and metal roofs.
Snow Load
The live load due to the weight of snow (see live load)
Soffit
The undersurface of any exterior overhanging section of a roof eave.
Soffit Vent
Intake vents installed unobstructed at the eave to facilitate circulation of air along the underside of decking to exhaust vents located
at the ridge or near the ridge.
SPF
Spray Polyurethate Foam, formed by spraying two components "A" and "B" that forms a fully adhered insulating membrane.
SPF Compound
A term used to describe the raw materials used to make polyurethane foam (Isocynate and resin)
Square
A unit of measurement used for roof areas. One square = 100 square feet.
Standing Seam
A type of seam between adjacent sheets of metal material which are manipulated and then interlocked.
Starter Course
The first course of roofing material, installed at the lower most edge.
Steep Slope Roof
A roof with a pitch, or slope greater than 3:12 - 14 degrees
Step Flashing
Individual pieces of sheet metal material used to flash around chimneys, dormers, walls.
Strapping
A method of installing roof felts parallel with the slope of the roof.
Surfacing
The top layer of a roof covering specifically in place to protect the underlying material from direct exposure to UV or weather
(granules etc)
Tar
A brown or black bituminous material liquid or semi solid in consistency.
Tear Strength
the maximum force require to tear a roofing material
Tensile Strength
The strenth of a material under tension as distinct from torsion, compression or shear.
Thermal Expansion
The increase in the dimension or volume of a body due to temperature variations.
Thermal Insulation
A material used to reduce the flow of heat.
Thermoplastic
A material that softens when heated and hardens when cooled, used in roofing single ply membranes.
Thermoplastic Olefin Membrane (TPO)
A blend of polypropylene and ethylene propylene plymers, flame retardants and other proprietary substanes for desired physical
properties. TPO may or may not be reinforced.
Tie In
The transition from one roof system to another type roof system. Typically where a steep sloped roof, terminates and joins with a
low slope roof, the tie in is the junction between the two roofing materials.
Tongue and Groove
One of the oldest types of wood used as roof decking. The sides are convex and concave, joining and aligning each other to form
deck.
Traffic Bearing
In roofing, a membrane or area of roofing system forumlated to withstand foot traffic. (Walk Tread for maintenance workers /
HVAC)


UL
Underwriters Laboratories Inc. A testing facility, which certifies roofing and other materials have met certain criteria.
Ultraviolet / UV
Invisible light radiation, adjacent ot the violet end of the visible spectrum with wavelengths from about 200 to 400 nanometres
Underlayment
An asphalt saturated felt, or other sheet type material installed between the roof deck and other roofing materials. Underlayments
are also a second line of defense in shedding water on steep sloped roofs.
Valley
The area (internal angle) formed by the intersection of two sloping roof planes.

				
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