Aggregrate: (1) crushed stone, crushed slag
or water worn gravel used for surfacing a built-up roof; (2)
any granular mineral material.
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.
Application Rate: the quantity
(mass, volume or thickness) of material applied per unit area.
Area Divider: a raised,
double wood member attached to a properly flashed wood base
plate that is anchored to the roof deck. It is used to relieve
thermal stresses in a roof system where no expansion joints
have been provided.
Asbestos: a group of natural,
fibrous, impure silicate materials.
Asphalt: a dark brown to
black cementitious material in which the predominating constituents
are bitumens, which occur in nature or are obtained in petroleum
Asphalt, Air Blown: an
asphalt produced by blowing air through molten asphalt at
an elevated temperature to raise its softening point and modify
Asphalt Felt: an asphalt-saturated
felt or an asphalt-coated felt.
Asphalt Mastic: a mixture
of asphaltic material and graded mineral aggregate that can
be poured when heated but requires mechanical manipulation
to apply when cold.
Asphalt, Steam Blown: an
asphalt produced by blowing steam through molten asphalt to
modify its properties.
Asphaltene: a high molecular
weight hydrocarbon fraction precipitated from asphalt by a
designated paraffinic naphthasolvent at a specified temperature
and solvent-asphalt ratio.
Asphaltic Roof Fill: a
blend of asphalt and pearlite aggregate typically installed
at precise drainage slopes.
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Backnailing: the practice
of blind-nailing roofing felts to a substrate in addition
to hot-mopping to prevent slippage.
Base Ply: the lowermost
ply of roofing material in a roof membrane assembly.
Base Sheet: a saturated
or coated felt placed as the first ply in some multi-ply built-up
Bitumen: (1) a class of
amorphous, black or dark colored, (solid, semi-solid or viscous)
cementitious substances, natural or manufactured, composed
principally of high molecular weight hydrocarbons, soluble
in carbon disulfide, and found in asphalts, tars, pitches
and asphaltites; (2) a generic term used to denote any material
composed principally of bitumen.
or treated with bitumen. Examples: bituminous concrete, bituminous
felts and fabrics, bituminous pavement.
Bituminous Emulsion: (1)
a suspension of minute globules of bituminous material in
water or in an aqueous solution; (2) a suspension of minute
globules of water or an aqueous solution in a liquid bituminous
material (invert emulsion).
Bituminous Grout: a mixture
of bituminous material and fine sand that will flow into place
without mechanical manipulation when heated.
Blackberry: a small bubble
or blister in the flood coating of a gravel-surfaced roof
Blind Nailing: the practice
of nailing the back portion of a roofing ply in a manner that
the fasteners are not exposed to the weather in the finished
Blister: an enclosed pocket
of air mixed with water or solvent vapor, trapped between
impermeable layers of felt, or between the felt and substrate.
Blocking: wood built into
a roofing system above the deck and below the membrane and
flashing to stiffen the deck around an opening, act as a stop
for insulation, or to serve as a nailer for attachment of
the membrane or flashing.
Bond: the adhesive and
cohesive forces holding two roofing components in intimate
Brooming: embedding a ply
of roofing material by using a broom to smooth out the ply
and ensure contact with the adhesive under the ply.
British Thermal Unit (BTU): the
heat energy required to raise the temperature of 1 pound of
water 1 degree Fahrenheit.
Built-Up Roof Membrane: 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
surface with mineral aggregate, bituminous materials, or a
granule-surfaced roofing sheet.
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Cant Strip: a beveled strip
used under flashing to modify the angle at the point where
the roofing or waterproofing membrane meets any vertical element.
Capillarity: the action
by which the surface of a liquid (where it is in contact with
a solid) is elevated or depressed, depending upon the relative
attraction of the molecules of the liquid for each other and
for those of the solid.
Cap Sheet: a granule-surfaced
coated sheet used as the top ply of a built-up roof membrane
Caulking: a composition
of vehicle and pigment, used at ambient temperatures for filling
joints, that remains plastic for an extended time after application.
Coal Tar: a dark brown
to black, semi-solid hydrocarbon obtained as residue from
the partial evaporation or distillation of coal tar.
Coal-Tar Felts: a felt
that has been saturated with refined coal tar.
Coated Sheet Felts: (1)
an asphalt felt that has been coated on both sides with harder,
more viscous asphalt; (2) a glass fiber felt that has been
simultaneously impregnated and coated with asphalt on both
a continuous, semi-flexible roof membrane, consisting of plies
of felts, mats or fabrics that are laminated on a roof with
alternate layers of cold-applied roof cement and surfaced
with a cold-applied coating.
Condensation: the conversion
of water vapor or other gas to liquid as the temperature drops
or the atmospheric pressure rises.
Coping: the covering piece
on top of a wall exposed to the weather, usually sloped to
metal or elastomeric sheeting secured on or into a wall, curb,
pipe, rooftop unit or other surface, to cover and protect
the upper edge of a base flashing and its associated fasteners.
Course: (1) the term used
for each application of material that forms the waterproofing
system or the flashing; (2) one layer of a series of materials
applied to a surface (i.e., a five-course wall flashing is
composed of three applications of mastic with one ply of felt
sandwiched between each layer of mastic).
Coverage: the surface area
continuously covered by a specific quantity of a particular
Crack: a separation or
fracture occurring in a roof membrane or roof deck, generally
caused by thermal induced stress or substrate movement.
Creep: the permanent deformation
of a roofing material or roof system caused by the movement
of the roof membrane that results from continuous thermal
stress or loading.
Cricket: a relatively small,
elevated area of a roof constructed to divert water around
a chimney, curb or other projection.
bitumen used in cold process roofing adhesives, flashing cements
and roof coatings.
Cutoff: a detail designed
to prevent lateral water movement into the insulation where
the membrane terminates at the end of a day's work, or used
to isolate sections of the roofing system. It is usually removed
before the continuation of the work.
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of a surface or structure to resist the passage of water in
the absence of hydorstatic pressure.
Dead Level: absolutely
horizontal, or zero slope.
Dead Loads: non-moving
rooftop loads, such as mechanical equipment, air conditioning
units, and the roof deck itself.
Deck: the structural surface
to which the roofing or waterproofing system is applied.
of the plies in a roof membrane system or separation of laminated
layers of insulation.
Dew Point: the temperature
at which water vapor starts to condense in cooling air at
the existing atmospheric pressure and vapor content.
Double-Pour: the process
of applying two layers of aggregate and bitumen to a built-up
Drain: a device that allows
for the flow of water from a roof area.
Dropback: a reduction in
the softening point of bitumen that occurs when bitumen is
heated in the absence of air.
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Edge Sheets: felt strips
that are cut to widths narrower than the standard width of
the full felt roll, used to start the felt shingling pattern
at a roof edge.
Edge Stripping: application
of felt strips cut to narrower widths than the normal felt
roll width to cover a joint between flashing and built-up
Edge Venting: the practice
of providing regularly spaced protected openings along a roof
perimeter to relieve moisture vapor pressure.
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: a rubber like
synthetic polymer that will stretch when pulled and will return
quickly to its original shape when released.
Embedment: (1) the process
of pressing a felt, aggregate, fabric, mat, or panel uniformly
and completely into hot bitumen or adhesive; (2) the process
of pressing granules into coating in the manufacture of factory
Emulsion: the intimate
dispersion of an organic material and water achieved by using
a chemical or clay emulsifying agent.
Envelope: a continuous
membrane edge seal formed at the perimeter and at penetrations
by folding the base sheet or ply over the plies above and
securing it to the top of the membrane. The envelope prevents
bitumen seepage from the edge of the membrane.
Equilibrium Moisture: (1)
the moisture content of a material stabilized at a given temperature
and relative humidity, expressed as percent moisture by weight;
(2) the typical moisture content of a material in any given
Equiviscous Temperature (EVT): the
temperature at which the viscosity is 75 centipoise for asphalt
and 25 centipoise for coal tar products; the recommended temperature
plus or minus 25º F at the time of application.
Expansion Joint: a structural
separation between two building elements that allows free
movement between the elements without damage to the roofing
or waterproofing system.
Exposure: (1) the traverse
dimension of a roofing element not overlapped by an adjacent
element in any roof system. The exposure of any ply in a membrane
may be computed by dividing the felt width minus 2 inches
by the number of shingled plies; thus, the exposure of 36
inch-wide felt in a shingled, four-ply membrane should be
8 1/2 inches; (2) the time during which a portion of a roofing
element is exposed to the weather.
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Fabric: a woven cloth of
organic or inorganic filaments, threads or yarns.
Factory Mutual (FM): an
organization that classifies roof assemblies for their fire
characteristics and wind uplift resistance for insurance companies
in the United States.
Factory Square: 108 square
feet of roofing material.
Felt: a flexible sheet
manufactured by the interlocking of fibers through a combination
of mechanical work, moisture and heat. Felts are manufactured
principally from vegetable fibers (organic felts), asbestos
fibers (asbestos felts) or glass fibers (glass fiber felts);
other fibers may be present in each type.
Felt Layer: a machine used
for applying bitumen and built-up roofing felts.
Felt Mill Ream: the mass
in pounds of 480 square feet of dry, unsaturated felt; also
termed "point weight".
Fine Mineral Surfacing:
water-insoluble, inorganic material, more than 50 percent
of which passes the no. 35 sieve, used on the surface of roofing.
Fishmouth: (1) a half-cylindrical
or half-conical opening formed by an edge wrinkle; (2) in
shingles, a half-conical opening formed at a cut edge.
Flashing: the system used
to seal membrane edges at walls, expansion joints, drains,
gravel stops, and other places where the membrane is interrupted
or terminated. Base flashing covers the edge of the membrane.
Cap flashing or counterflashing shields the upper edges of
the base flashing.
Flashing cement: a trowelable
mixture of cutback bitumen and mineral stabilizers, including
asbestos or other inorganic fibers.
Flood Coat: the top layer
of bitumen into which the aggregate is embedded on an aggregate-surfaced
built up roof.
Fluid Applied: an elastomeric
material, fluid at ambient temperature, that dries or cures
after application to form a continuous membrane. Such systems
normally do not incorporate reinforcement.
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Glass Felt: glass fibers
bonded into a sheet with resin and suitable for impregnation
in the manufacture of bituminous waterproofing materials,
roof membranes, and shingles.
Glass Mat: a thin mat composed
of glass fibers with or without a binder.
Glaze Coat: (1) the top
layer of asphalt in a smooth surfaced built-up roof assembly;
(2) a thin protective coating of bitumen applied to the lower
plies or top ply of a built-up roof membrane when application
of additional felts or the flood coat and aggregate surfacing
Gravel: course, granular
aggregate, with pieces larger than sand grains, resulting
from the natural erosion of rock.
Gravel Spot: a flanged
device, frequently metallic, designed to provide a continuous
finished edge for roofing material and to prevent loose aggregate
from washing off of the roof.
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Headlap: the minimum distance,
measured at 90 degrees to the eaves along the face of a shingle
or felt, from the upper edge of the shingle or felt to the
nearest exposed surface.
Holiday: an area where
a liquid-applied material is missing.
"Hot Stuff" or "Hot":
the roofer's term for hot bitumen.
absorbing and retaining atmospheric moisture.
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Ice Dam: a mass of ice
formed at the transition from a warm to a cold roof surface,
frequently formed by refreezing melt-water at the overhang
of a steep roof, causing ice and water to back up under roofing
Incline: the slope of a
roof expressed either in percent or in the number of vertical
units of rise per horizontal unit of run.
Inorganic: being or composed
of matter other than hydrocarbons and their derivatives, or
matter that is not of plant or animal origin.
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Job-Average Basis: a technique
for determining the average dimensions or quantities of materials,
by analysis of roof test cuts. The technique requires a minimum
of three test cuts per roof area, plus one cut for each additional
10,000 square feet of roof area. Job-average basis is computed
by dividing the sum of all measurements taken by the number
of measurements taken. The results would describe the job-average
for the quantity or dimension. It's generally not considered
a good idea to evaluate roofs on this basis as sample size
is small relative to job size. The NCRA recommends competent
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Knot: an imperfection or
non-homogeneity in materials used in fabric construction,
the presence of which causes surface irregularities.
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Live Loads: moving roof
installation equipment, wind, snow, ice or rain.
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Membrane: a flexible or
semi-flexible roof covering or waterproofing layer, whose
primary function is the exclusion of water.
Mesh: the square opening
of a sieve.
Metal Flashing: Metal flashing
is frequently used as through-wall flashing, cap flashing,
counterflashing or gravel stops.
Mineral Fiber Felt: a felt
with mineral wood as its principal component.
Mineral Granules: opaque,
natural, or synthetically colored aggregate commonly used
to surface cap sheets, granule-surfaced sheets, and roofing
Mineral Stabilizer: a fine,
water-insoluble inorganic material, used in a mixture with
solid or semi-solid bituminous materials.
built-up roofing materials whose top ply consists of a granule-surfaced
Mineral-Surfaced Sheet: a
felt that is coated on one or both sides with asphalt and
surfaced with mineral granules.
Modified Bitumen: are composite
sheets consisting of a copolymer modified bitumen often reinforced
and sometimes surfaced with various types of films, foils
Mole Run: a meandering
ridge in a roof membrane not associated with insulation or
Mop-and-Flop: an application
procedure in which roofing elements (insulation boards, felt
plies, cap sheets, etc.) are initially placed upside down
adjacent to their ultimate locations, are coated with adhesive,
and are then turned over and applied to the substrate.
Mopping: the application
of hot bitumen with a mop or mechanical applicator to the
substrate or to the felts of a built-up roof membrane.
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NRCA: National Roofing
Contractor Association. Professional trade group for the roofing
Neoprene: a synthetic rubber
(polychloroprene) used in liquid-applied and sheet-applied
elastomeric roof membranes or flashings.
Nineteen-Inch Selvage: a
prepared roofing sheet with a 17-inch granule surfaced exposure
and a nongranule-surfaced 19-inch selvage edge. This material
is sometimes referred to as SIS or as Wide Selvage Asphalt
Roll Roofing Material Surfaced with Mineral Granules.
Ninety-Pound: a prepared
organic felt roll roofing with a granule surfaced exposure
that has a mass of approximately 90 pounds per 100 square
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Organic: being or composed
of hydrocarbons or their derivatives, or matter of plant or
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Parapet Wall: that part
of any wall entirely above the roof.
Perlite: an aggregate used in lightweight
insulating concrete and in preformed perlitic insulation boards,
formed by heating and expanding siliceous volcanic glass.
Perm: a unit of water vapor
transmission defined as 1 grain of water vapor per square
foot per hour per inch of mercury pressure difference (1 inch
of mercury = 0.49 psi).
Permeance: an index of
a material's resistance to water vapor transmission.
Phased Application: the
installation of a roof system or water-proofing system during
two or more separate time intervals.
Picture Framing: a rectangular
pattern of ridges in a roof membrane over insulation or deck
Pitch Pocket: a flange,
open-bottomed, metal container placed around columns or other
roof penetrations that is filled with hot bitumen or flashing
cement to seal the joint. The use of pitch pockets is not
recommended by NRCA.
Plastomeric: a plastic-like
polymer consisting of any of various complex organic compounds
produced by polymerization which are capable of being molded,
extruded or cast into various shapes or films. Generally they
are thermo plastic in nature, i.e., they will soften when
heated and harden when cooled.
Ply: a layer of felt in
a built-up roof membrane system. A four-ply membrane system
has four plies of felt.
Pond: a roof surface that
is incompletely drained.
Positive Drainage: the
drainage condition in which consideration has been made for
all loading deflections of the deck, and additional roof slope
has been provided to ensure drainage of the roof area within
48 hours of rainfall.
Primer: a thin, liquid
bitumen applied to a surface to improve the adhesion of subsequent
applications of bitumen.
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Rake: the slope edge of
a roof at the first or last rafter.
Re-covering: the process
of covering an existing roofing system with a new roofing
Re-entrant Corner: an inside
corner of a surface, producing stress concentrations in the
roofing or waterproofing membrane.
Reglet: a groove in a wall
or other surface adjoining a roof surface for use in the attachment
Reinforced Membrane: a
roofing or waterproofing membrane reinforced with felts, mats,
fabrics or chopped fibers.
Relative Humidity: the
ratio of the weight of moisture in a given volume of air-vapor
mixture to the saturated (maximum) weight of water vapor at
the same temperature, expressed as a percentage. For example,
if the weight of the moist air is 1 pound and if the air could
hold 2 pounds of water vapor at a given temperature, the relative
humidity (RH) is 50 percent.
Replacement: the practice
of removing an existing roof system and replacing it with
a new roofing system.
Re-roofing: the process
of re-covering or replacing an existing roofing system.
Ridging: an upward, tenting
displacement of a roof membrane frequently occurring over
insulation joints, deck joints and base sheet edges.
Roll Roofing: smooth-surfaced
or mineral-surfaced coated felts.
Roof Assembly: an assembly
of interacting roof components (including the roof deck) designed
to weatherproof and, normally, to insulate a building's top
Roofer: the trade name
for the workman who applies roofing material.
Roof System: a system of
interacting roof components (not including the roof deck)
designed to weather proof and, normally, to insulate a building's
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Saddle: a small structure
that helps channel surface water to drains, frequently located
in a valley, and often contracted like a small hip roof or
like a pyramid with a diamond shape base.
Saturated Felt: a felt
that has been partially saturated with low softening point
Screen: an apparatus with
circular apertures from separating sizes of materials.
Scuttle: a hatch that provides
access to the roof from the interior of the building.
Seal: (1) a narrow closure
strip made of bituminous materials; (2) to secure a roof from
the entry of moisture.
Sealant: a mixture of polymers,
fillers, and pigments used to fill and seal joints where moderate
movement is expected; it cures to a resilient solid.
Selvage: an edge or edging
that differs from the main part of (1) a fabric, or (2) granule-surfaced
roll roofing material.
Selvage Joint: a lapped
joint designed for mineral-surfaced cap sheets. The mineral
surfacing is omitted over a small portion of the longitudinal
edge of the sheet below in order to obtain better adhesion
of the lapped sheet surface with the bituminous adhesive.
Shark Fin: an upward-curled
felt side lap or end lap.
Shingle: (1) a small unit
of prepared roofing material designed for installation 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.
Shingling: (1) the procedure
of laying parallel felts so that one longitudinal edge of
each felt overlaps and the other longitudinal edge underlaps,
the adjacent felt. Normally, felts are shingled on a slope
so that the water flows over rather than against each lap;
(2) the application of shingles to a sloped roof.
Sieve: an apparatus with
apertures for separating sizes of material.
Slag: a hard, air-cooled
aggregate that is left as a residue from blast furnaces, used
as a surfacing aggregate.
Slippage: relative lateral
movement of adjacent components of a built-up membrane. It
occurs mainly in roofing membranes on a slope, sometimes exposing
the lower lies or even the base sheet to the weather.
Smooth-Surfaced Roof: a
built-up roof membrane surfaced with a layer of hot-mopped
asphalt, cold-applied asphalt clay emulsion, cold-applied,
asphalt cutback, or sometimes with an unmopped inorganic felt.
Softening Point: the temperature
at which bitumen becomes soft enough to flow, as determined
by an arbitrary, closely defined method.
Softening Point Drift: a
change in the softening point of bitumen during storage or
Solid Mopping: a continuous
mopping of a surface, leaving no unmopped areas.
Split: a membrane tear
resulting from tensile strength.
Spot Mopping: a mopping
pattern in which hot bitumen is applied in roughly circular
areas, leaving a grid of unmopped, perpendicular bands on
Sprinkle Mopping: a random
mopping pattern in which heated bitumen beads are strewn onto
the substrate with a brush or mop.
Spudding: the process of
removing the roofing aggregate and most of the bituminous
top coating by scraping and chipping.
Square: the term used to
describe 100 square feet of roof area.
Stack Vent: a vertical
outlet in a built-up roof system designed to relieve the pressure
exerted by moisture vapor between the roof membrane and the
vapor retarder or deck.
Strip Mopping: a mopping
pattern in which hot bitumen is applied in parallel bands.
Stripping or Strip-Flashing:
(1) the technique of sealing a joint between metal and the
built-up roof membrane with one or two plies of felt or fabric
and hot-applied or cold-applied bitumen; (2) the technique
of taping joints between insulation boards or deck panels.
Substrate: the surface
upon which the roofing or waterproofing membrane is applied
(i.e., the structural deck or insulation).
Sump: an intentional depression
around a drain.
Superimposed Loads: loads
that are added to existing loads. For example, a large stack
of insulation boards placed on top of a structural steel deck.
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Tapered Edge Strip: a tapered
insulation strip used to (1) elevate the roof at the perimeter
and at curbs that extend through a roof; (2) provide a gradual
transition from one layer of insulation to another.
Tar: a brown or black bituminous
material, liquid or semi-solid in consistency, in which the
predominating constituents are bitumens obtained as condensates
in the processing of coal, petroleum, oil shale, wood, or
other organic materials.
Test Cut: a sample of the
roof membrane that is cut from a roof membrane to: (a) determine
the weight of the average interply bitumen moppings; (b) diagnose
the condition of the exiting membrane (e.g., to detect leaks
Thermal Conductance (C):
a unit of heat flow that is used for specific thicknesses
of material or for materials of combination construction,
such as laminated insulation.
Thermal Conductivity (k):
the heat energy that will be transmitted by conduction through
one square foot of one inch thick homogeneous material in
one hour when there is a difference of one degree Fahrenheit
perpendicularly across the two surfaces of the material.
Thermal Insulation: a material
applied to reduce the flow of heat.
Thermal Resistance (R):
an index of a material's resistance to heat flow; it is the
reciprocal of thermal conductivity (k) or thermal conductance
Thermal Shock: the stress-producing
phenomenon resulting from sudden temperature changes in a
roof membrane when, for example, a rain shower follows brilliant
a water-resistant membrane or material assembly extending
through a wall and its cavities, positioned to direct water
entering the top of the wall to the exterior.
Tuck Pointing: (1) troweling
mortar into a joint after masonry units are laid; (2) final
treatment of joints in cut stonework. Mortar or a putty-like
filler is forced into the joint after the stone is set.
Underwriters Laboratories (UL):
an organization that classifies roof assemblies for their
fire characteristics and wind uplift resistance.
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Vapor Migration: the movement
of water vapor from a region of high vapor pressure to a region
of lower vapor pressure.
Vapor Retarder: a material
designed to restrict the passage of water vapor through a
roof or wall.
Vent: an opening designed
to convey water vapor or other gases from inside a building
or a building component to the atmosphere, thereby relieving
Vermiculite: an aggregate
used in lightweight insulating concrete, formed by the heating
and consequent expansion of a micaceous mineral.
of a surface or structure to prevent the passage of water
under hydrostatic pressure.
Wythe: a masonry wall,
one masonry unit, a minimum of two inches thick.
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