Building Technical Terms Explained 

Abs— A type of black plastic pipe commonly used for waste water lines.

Aggregate— Crushed rock or stone.

Air chamber— A vertical, air filled pipe that prevents water hammer by absorbing pressure when water is shut off at a faucet or valve.

Air-conditioner condenser— The outside fan unit of the air conditioning system. The condenser discharges heat to the building exterior.

Alligatoring— Coarse checking pattern on the surface of a material. Typically caused by ageing, exposure to sun and/or loss of volatiles.

Ampacity— Refers to the how much current a wire can safely carry. For example, a 12-gauge electrical copper wire can safely carry up to 20 amps.

Asphalt— A bituminous material employed in roofing and road paving materials because of its waterproofing ability.

Backfill— The replacement of excavated earth into a trench or pit.

Backflow— A reverse flow of water or other liquids into the water supply pipes, caused by negative pressure in the pipes

Ballast— A transformer that steps up the voltage in a florescent lamp.

Balusters— Vertical members in a railing used between a top rail and bottom rail or the stair treads. Sometimes referred to as pickets or spindles.

Base sheet— Bottom layer of built-up roofing.

Batt— A section of fiberglass or rock-wool insulation.

Bay window— Any window space projecting outward from the walls of a building, either square or polygonal in plan.

Beam— A structural member transversely supporting a load. A structural member carrying building loads (weight) from one support to another. Sometimes called a girder.

Bearing wall— A wall that supports any vertical load in addition to its own weight.

Bird’s-mouth cut — A cutout in a rafter where it crosses the top plate of the wall providing a bearing surface for nailing. Also called a heel cut.

Bitumen— Term commonly applied to various mixtures of naturally occurring solid or liquid hydrocarbons, excluding coal. These substances are described as bituminous. Asphalt is a bitumen. See Asphalt.

Blocking— Small wood pieces to brace framing members or to provide a nailing base for gypsum board or paneling.

Board and batten — A method of siding in which the joints between vertically placed boards or plywood are covered by narrow strips of wood.

Bottom chord— The lower or bottom horizontal member of a truss.

Brick tie— Metal strips or wires that are inserted into the mortar joints of the brick veneer. Ties hold the veneer wall to the backer wall behind it.

Brick veneer— A vertical facing of brick used to clad a building. Brick veneer is not a load-bearing component.

Building paper— A general term for papers, felts and similar sheet materials used in buildings without reference to their properties or uses. Generally comes in long rolls.

Built-up roof— A roofing composed of three to five layers of asphalt felt laminated with coal tar, pitch or asphalt. The top is finished with crushed slag or gravel. Generally used on flat or low-pitched roofs.

Butt joint— The junction where the ends of building materials meet. To place materials end-to-end or end-to-edge without overlapping.

Cant strip — A triangular shaped piece of lumber used at the junction of a flat deck and a wall to prevent cracking of the roofing which is applied over it.

Cantilever— Any part of a structure that projects beyond its main support and is balanced on it.

Cap flashing— The flashing covering over a horizontal surface to prevent water from migrating behind the base flashing.

Cap sheet — The top layer in modified bitumen roofing.

Casement window — A window with hinges on one of the vertical sides and swings open like a door.

Ceiling joist— One of a series of parallel framing members used to support ceiling loads and supported in turn by larger beams, girders or bearing walls. Can also be roof joists.

Cement— The grey powder that is the “glue” in concrete. Portland cement. Also, any adhesive.

Certificate of Occupancy— Certificate is issued by the local municipality and is required before anyone can occupy and live within the building. It is issued only after the local municipality has made all inspections and all monies and fees have been paid.

Cfm (cubic feet per minute)— A rating that expresses the amount of air a blower or fan can move. The volume of air (measured in cubic feet) that can pass through an opening in one minute.

Chase — A framed enclosed space around a flue pipe or a channel in a wall, or through a ceiling for something to lie in or pass through.

Checking— Cracks that appear with age in many large timber members. The cracks run parallel to the grain of the wood. At first superficial, but in time may penetrate entirely through the member and compromise its integrity.

Cleanout— An opening providing access to a drain line. Closed with a threaded plug.

Closed-cut valley— A method of valley treatment in which shingles from one side of the valley extend across the valley, while shingles from the other side are trimmed 2 inches from the valley centerline. The valley flashing is not exposed.

Collar tie— Nominal one- or two-inch-thick members connecting opposite roof rafters. They serve to stiffen the roof structure.

Column— A vertical structural compression member that supports loads acting in the direction of its longitudinal axis.

Combustion air and ventilation air— The ductwork installed to bring fresh, outside air to the furnace or boiler room. Normally two separate supplies of air are brought in: one high for ventilation and one low for combustion.

Compressor — A mechanical device that pressurizes a gas in order to turn it into a liquid, thereby allowing heat to be removed or added. A compressor is the main component of conventional heat pumps and air conditioners. In an air conditioning system, the compressor normally sits outside and has a large fan (to remove heat).

Concrete board or cement board — A panel made out of concrete and fiberglass, usually used as a tile backing material.

Condensate drain line— The pipe that runs from the air conditioning cooling coil to the exterior or internal building drain, to drain away condensation.

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

Condensing unit— The outdoor component of a cooling system. It includes a compressor and condensing coil designed to give off heat.

Conduit, electrical— A pipe, usually metal, in which wire is installed. The pipe serves to protect the wire.

Control joint — Tooled, straight grooves made on concrete floors or structures to “control” where the concrete should crack (as a result of shrinkage).

Cooling load — The amount of cooling required to keep a building at a specified temperature during the summer, usually 25° C, based on a design outside temperature.

Corbel— To build out one or more courses of brick or stone from the face of a wall. This may be decorative, or serve to support a structural component.

Counterflashing— A metal flashing usually used to cover another flashing and prevent moisture entry.

Course— A row of shingles or roll roofing running the length of the roof. Parallel layers of building materials such as bricks, or siding laid up horizontally.

Cpvc— See pvc.

Crawlspace— A shallow space below a building, normally enclosed by the foundation walls.

Cricket— A saddle-shaped, peaked construction connecting a sloping roof plane with a wall or chimney. Designed to encourage water drainage away from the chimney or wall joint.

Culvert— Round, corrugated drain pipe (normally 15 or 18 inches in diameter) installed beneath a driveway and parallel to and near the street.

Cupping— A type of warping that causes boards or shingles to curl up at their edges. Typically caused by uneven drying or loss of volatiles.

Curb— The short elevation of a supporting element above the deck of a roof. Normally a box (on the roof) on which a skylight or piece of mechanical equipment is attached.

Curtain wall— An exterior building wall that is supported entirely by the building structure, rather than being self-supporting or load-bearing.

Damper— A metal “door” placed within the ductwork, typically. Used to control flow of air, etc., in the ductwork.

Damp-proofing— The black, tar-like material applied to the exterior of a foundation wall. Used to minimize moisture penetration into the wall.

Deck— The surface, installed over the supporting framing members, to which the roofing is applied.

Dedicated circuit— An electrical circuit that serves only one appliance or a series of electric heaters or smoke detectors.

Dew point — Temperature at which a vapor begins to deposit as a liquid. Applies especially to water in the atmosphere.

Disconnect— A large electrical on-off switch.

Diverter valve— A device that changes the direction of water flow from one faucet to another.

Dormer— A box-like projection from the sloping plane of a roof that frames a window.

Double-hung window— A window with two vertically sliding sashes, both of which can move up and down.

Downspout— A pipe for draining water from roof gutters. Also called a leader.

Drain tile— A perforated, corrugated plastic pipe laid at the bottom of the foundation wall and used to drain excess water away from the foundation. It prevents ground water from seeping through the foundation wall. Sometimes called perimeter drain.

Drip—A groove in the underside of a sill or drip cap to cause water to drop off on the outer edge instead of drawing back and running down the face of the building.

Ducts— Usually round or rectangular metal pipes installed for distributing warm or cold air from the heating and air-conditioning equipment.

Eaves protection— Additional layer of roofing material applied at the eaves to help prevent damage from water backup (typically caused by ice damming).

Eifs—Exterior Insulation Finish System. An exterior cladding system that employs a relatively thin acrylic stucco coating over insulation panels. (Pronounced “ee-fus”)

Elbow— A plumbing or electrical fitting that lets you change directions in runs of pipe or conduit.

Evaporator coil— The part of a cooling system that absorbs heat from air passing through it. The evaporator coil is found within the ductwork.

Expansion joint— A joint that allows for building material expansion and contraction caused by temperature changes.

Exposed aggregate finish— A method of finishing concrete which washes the cement/sand mixture off the top layer of the aggregate — usually gravel. Often used with precast concrete exterior wall finishes.

Exposure— The portion of the roofing or wall cladding material exposed to the weather after installation.

Fascia— a vertical member attached to the ends of the roof structure and often the backing of the gutter.

Felt— Fibrous material saturated with asphalt and used as an underlayment or part of a built-up roofing system.

Finger joint— A manufacturing process of interlocking two shorter pieces of wood end to end to create a longer piece of dimensional lumber or molding. Often used in jambs and casings and are normally painted (instead of stained).

Fire stop— A solid, tight closure of a concealed space, placed to prevent the spread of fire and smoke through such a space. Includes stuffing wire and pipe holes in the fire separations.

Flashing— (1) Sheet metal or flexible membrane pieces fitted to the joint of any roof intersection, penetration or projection (chimneys, copings, dormers, valleys, vent pipes, etc.) to prevent water leakage. (2) The building component used to connect portions of a roof, deck, or siding material to another surface such as a chimney, wall, or vent pipe. Often made out of various metals, rubber or tar and is mostly intended to prevent water entry.

Flatwork— Common word for concrete floors, driveways, patios and sidewalks.

Flue— The space or passage in a chimney through which smoke, gas, or fumes ascend.

Fluorescent lighting— A fluorescent lamp is a gas-filled glass tube with a phosphor coating on the inside. Gas inside the tube is ionized by electricity which causes the phosphor coating to glow. Normally with two pins that extend from each end.

Footing — A widened, below-ground base of a foundation wall or a poured concrete, below-ground, base used to support foundations or piers.

Forced air heating— a common form of heating with natural gas, propane, oil or electricity as a fuel. Air is heated through a heat exchanger and distributed through a set of metal ducts.

Form— Temporary structure erected to contain concrete during placing and initial hardening.

Foundation— The supporting portion of a structure below the first floor construction, or below grade, including the footings.

Framing— The structural wood, steel or concrete elements of the building.

Framing, balloon— A system of framing a building in which all vertical structural elements of the bearing walls consist of single pieces extending from the top of the foundation sill plate to the roof plate and to which all floor joists are fastened.

Frost line— The depth of frost penetration in soil and/or the depth at which the earth will freeze and swell. This depth varies in different parts of the country.

Furring— Strips of wood or metal applied to a wall or other surface to even it and normally to serve as a fastening base for finish material.

Gable— A sidewall, typically triangular, that is formed by two sloping roof planes.

Gable roof— A type of roof with sloping planes of the same pitch on each side of the ridge. Has a gable at each end.

Gasket— A device used to seal joints against leaks.

Gfi or gfci or Ground Fault Current Interrupter — A electrical device used to prevent injury in locations where one might be in contact with a grounded surface and an electrical appliance. Most gfis are located in a receptacle or circuit breaker and can be identified by the presence of a “test” and a “reset” button.

Glued laminated beam (glulam)— A structural beam composed of wood laminations. The laminations are pressure-bonded with adhesives.

Granules— Crushed rock coated with ceramic material, applied to the exposed surface of asphalt roofing products to add color and reduce ultraviolet degradation. Copper compounds added to these help make them algae resistant.

Groundwater— Water from a subsurface water source.

Grout— Mortar made of such consistency (by adding water) that it will flow into the joints and cavities of the masonry work and fill them solid.

Gusset— A flat metal, wood, plywood or similar type member used to provide a connection at the intersection of wood members. Most commonly used at joints of wood trusses. They are fastened by nails, screws, bolts, or adhesives.

Gutter— The trough that channels water from the eaves to the downspouts.

H-beam — A steel beam with a cross section resembling the letter H.

H-clip— Small metal clips formed like an H that fits at the joints of two plywood (or wafer board) sheets to stiffen the joint. Normally used on the roof sheeting.

Header— A beam placed perpendicular to joists and to which joists are attached in framing for around an opening.

Hearth— The fireproof area directly in front of a fireplace. The inner or outer floor of a fireplace, usually made of brick, tile, or stone.

Heat pump— A device that uses compression and decompression of gas to heat and/or cool a building.

Heating load— The amount of heating required to keep a building at a specified temperature during the winter, based on an outside design temperature.

Hip— The external angle formed by the meeting of two sloping sides of a roof.

Honeycombs— The appearance concrete makes when aggregate in the concrete is visible and where there are void areas in the concrete.

Hose bib — An exterior water faucet.

Hot wire— The wire that carries electrical energy to a receptacle or other device-in contrast to a neutral, which carries electricity away again. Normally the black wire.

Hvac— An abbreviation for Heat, Ventilation, and Air Conditioning.

I-beam— A steel beam with a cross section resembling the letter I.

Ice damming— The buildup of ice and water at the eaves of a sloped roof. Melting snow on the roof refreezes at the roof overhang, causing the damming. Buildings with inadequate attic insulation or ventilation or with large roof projections beyond the exterior walls are more pronto to ice damming.

Irrigation— Lawn sprinkler system.

Jack post— A type of structural support made of metal, which can be raised or lowered through a series of pins and a screw to meet the height required. Typically used as a replacement for an old supporting member in a building.

Joist— One of a series of parallel beams, usually two inches in thickness, used to support floor and ceiling loads, and supported in turn by larger beams, girders, or bearing walls.

Joist hanger — A metal U-shaped item used to support the end of a floor joist and attached with hardened nails to another bearing joist or beam.

Knob-and-tube wiring— A common form of electrical wiring used before the Second World War. When in good condition it may still be functional for low amperage use such as smaller light fixtures.

Lath— A building material of narrow wood, metal, gypsum, or insulating board that is fastened to the frame of a building to act as a base for plaster, shingles, or tiles.

Lattice— An open framework of crisscrossed wood or metal strips that form regular, patterned spaces.

Leader— See Downspout.

Ledger— The wood or metal members attached to a beam, studding, or wall used to support joist or rafter ends.

Lintel — A horizontal structural member that supports the load over an opening such as a door or window.

Load-bearing wall— A wall supporting its own weight and some other structural elements of the building such as the roof and floor structures.

Louvre — A vented opening into a room that has a series of horizontal slats and arranged to permit ventilation but to exclude rain, snow, light, insects, or other living creatures.

Mansard roof — A roof with two sloping planes of different pitch on each of its four sides. The lower plane is steeper than the upper, and may be almost vertical.

Masonry— Stone, brick, concrete, hollow-tile, concrete block, or other similar building units or materials. Normally bonded together with mortar to form a wall.

Modified bitumen roof — A roof covering that is typically composed of a factory-fabricated composite sheet consisting of a copolymer-modified bitumen, often reinforced with polyester and/or fiberglass, and installed in one or more plies. The membrane is commonly surfaced with field-applied coatings, factory-applied granules or metal foil. The roofing system may incorporate rigid insulation.

Mortise— A slot cut into a board, plank, or timber, usually edgewise, to receive the tenon (or tongue) of another board, plank, or timber to form a joint.

Mullion— A vertical divider in the frame between windows, doors, or other openings.

Neutral wire— Usually color-coded white, this wire carries electricity from a load back to the service panel.

Newel post— The large starting post to which the end of a stair guard railing or balustrade is fastened.

Nosing — The projecting edge of a molding or drip or the front edge of a stair tread.

On center — The measurement of spacing for studs, rafters, and joists in a building from the center of one member to the center of the next.

Open valley— Method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. Valley flashing is exposed.

Open web steel joist — One of a series of parallel beams, used to support floor and roof loads, and supported in turn by larger beams, girders or bearing walls. Consists of horizontal top and bottom chords, with diagonal and/or vertical web members connecting the chords together.

Oriented Strand Board or osb— A manufactured 4-foot-by-8-foot wood panel made out of one- to two-inch wood chips and glue. Often used as a substitute for plywood.

P-trap— Curved, U-section of drain pipe that holds a water seal to prevent sewer gasses from entering a building through a fixtures’ drain pipe.

Parapet— The portion of an exterior wall that extends above the edge of a roof.

Parging— A thin layer of cement placed over masonry units.

Partition— A wall that subdivides spaces within any story of a building or room.

Paver— Materials (commonly masonry) laid down to make a firm, even surface on the exterior.

Performance bond— An amount of money (usually 10 percent of the total price of a job) that a contractor must put on deposit with a governmental agency as an insurance policy that guarantees the contractors’ proper and timely completion of a project or job.

Perimeter drain— Typically 4-inch perforated plastic pipe around the perimeter (either inside or outside) of a foundation wall (before backfill) that collects and diverts ground water away from the foundation.

Pilot light — A small, continuous flame (in a boiler, or furnace) that ignites gas or oil burners when needed.

Pitch— (1) The degree of roof incline expressed as the ratio of the rise, in feet, to the span, in feet. (2) A thick, oily substance commonly obtained from tar, used to seal out water at joints and seams. Pitch is produced from distilling coal tar, wood tar, or petroleum.

Pitch pocket— A container, usually formed of sheet metal, around supporting connections with roof-mounted equipment. Filling the container with pitch, or better yet, plastic roof cement, helps seal out water even when vibration is present. A pitch pocket is not the preferred method of flashing a roof penetration.

Plan view — Drawing of a structure with the view from overhead, looking down.

Plate— Normally a horizontal member within a framed structure, such as: (1) sill plate — a horizontal member anchored to a concrete or masonry wall; (2) Sole plate — bottom horizontal member of a frame wall; or (3) top plate — top horizontal member of a frame wall supporting ceiling joists, rafters, or other members.

Plenum— The main supply air or return air duct leading from a heating or cooling unit.

Plumbing stack— A plumbing vent pipe that penetrates the roof.

Ply— A term to denote the number of layers of roofing felt, veneer in plywood, or layers in built-up materials, in any finished piece of such material.

Point load— A point where a bearing/structural weight is concentrated and transferred to another structural member or component.

Portland cement — Cement made by heating clay and crushed limestone into a brick and then grinding to a pulverized powder state.

Post — a vertical framing member usually designed to carry a beam.

Post-and-beam— A basic building method that uses just a few hefty posts and beams to support an entire structure. Contrasts with stud framing.

Power vent— A vent that includes a fan to speed up air flow.

Pressure relief valve — A safety device mounted on a water heater or boiler. The relief valve is designed to release any high pressure in the vessel and thus prevent tank explosions.

Pressure-treated wood — Lumber that has been saturated with a preservative to resist rot.

Pvc or cpvc — (Polyvinyl choride) A type of white or light gray plastic pipe sometimes used for water supply lines and waste pipe.

Quarry tile— A man-made or machine-made clay tile used to finish a floor or wall. Generally 6 inches by 6 inches by ¼-inch thick .

R value — A measure of insulation’s resistance to heat flow. The higher the R value the more effective the insulation.

Rafter— (1) The framing member that directly supports the roof sheathing. A rafter usually follows the angle of the roof, and may be a part of a roof truss. (2) The supporting framing member immediately beneath the deck, sloping from the ridge to the wall plate.

Rafter, hip— A rafter that forms the intersection of an external roof angle.

Rafter, valley— A rafter that forms the intersection of an internal roof angle.

Rake edge— The overhang of an inclined roof plane beyond the vertical wall below it.

Rebar— Reinforcing bar. Ribbed steel bars installed in concrete structures designed to strengthen concrete. Comes in various thicknesses and strength grades. May be epoxy coated to enhance rust resistance.

Refrigerant — A substance that remains a gas at low temperatures and pressure and can be used to transfer heat. Freon is an example.

Register— A grille placed over a supply air or return air duct.

Reglaze— To replace a broken window.

Reinforcing— Steel rods or metal fabric placed in concrete slabs, beams, or columns to increase their strength.

Relief valve— A device designed to open if it detects excess temperature or pressure. Commonly found on water heating or steam producing systems.

Resilient flooring— A durable floor cover that has the ability to resume its original shape.

Retaining wall— A structure that holds back a slope or elevation of land and prevents erosion.

Ridge— The horizontal line at the junction of the top edges of two sloping roof surfaces.

Riser— A vertical member between two stair treads.

Roll roofing — Asphalt roofing products manufactured in roll form.

Romex— A name brand of nonmetallic sheathed electrical cable that is used for indoor wiring.

Roof deck— The surface, installed over the supporting framing members, to which the roofing is applied.

Roof sheathing— The wood panels or sheet material fastened to the roof rafters or trusses on which the shingle or other roof covering is laid.

Roof valley— The “V” created where two sloping roofs meet.

Roofing membrane— The layer or layers of waterproofing products that cover the roof deck.

Run, stair— The horizontal distance of a stair tread from the nosing to the riser.

Saddle— Two sloping surfaces meeting in a horizontal ridge, used between the back side of a chimney, or other vertical surface, and a sloping roof. Used to divert water around the chimney or vertical surface.

Sanitary sewer — A sewer system designed for the collection of waste water from the bathroom, kitchen and laundry drains, and is usually not designed to handle storm water.

Sash— The frame that holds the glass in a window, often the movable part of the window.

Saturated felt — A felt that is impregnated with tar or asphalt.

Scratch coat— The first coat of plaster, which is scratched to form a bond for a second coat.

Scupper — (1) An opening for drainage in a wall, curb or parapet. (2) The drain above a downspout or in a flat roof, usually connected to the downspout.

Sealer — A finishing material, either clear or pigmented, that is usually applied directly over raw wood or concrete for the purpose of sealing the wood or concrete surface.

Seasoning— Drying and removing moisture from green wood in order to improve its usability.

Service equipment— Main control gear at the electrical service entrance, such as circuit breakers, switches, and fuses.

Service lateral — Underground power supply line.

Shake— A wood roofing material, normally cedar or redwood. Produced by splitting a block of the wood along the grain line. Modern shakes are sometimes machine sawn on one side.

Sheathing — (1) Sheets or panels used as roof deck material. (2) Panels that lie between the studs and the siding of a structure.

Short circuit— A situation that occurs when hot and neutral wires come in contact with each other. Fuses and circuit breakers protect against fire that could result from a short.

Sill — (1) The two-by-four or two-by-six wood plate framing member that lays flat against and bolted to the foundation wall (with anchor bolts) and upon which the floor joists are installed. (2) The member forming the lower side of an opening, as a door sill or window sill.

Skylight — A more or less horizontal window located on the roof of a building.

Slab-on-grade — A type of foundation with a concrete floor which is placed directly on the soil. In warm climates, the edge of the slab is usually thicker and acts as the footing for the walls. In cold climates, the slab is independent of the perimeter foundation walls.

Sleeper — Usually, a wood member that serves to support equipment.

Soffit — (1)The finished underside of the eaves. (2) A small ceiling-like space, often out of doors, such as the underside of a roof overhang.

Solid waste pump — A pump used to ‘lift’ waste water to a gravity sanitary sewer line. Usually used in basements and other locations which are situated below the level of the city sewer.

Spalling— The cracking and breaking away of the surface of a material.

Span— The clear distance that a framing member carries a load without support (between structural supports).

Splash block — A pad placed under the lower end of a downspout to divert the water from the downspout away from the building. Usually made out of concrete or fiberglass.

Stair stringer — Supporting member for stair treads. Can be a notched plank or a steel member.

Starter strip— Asphalt roofing applied at the eaves that provides protection by filling in the spaces under the cutouts and joints of the first course of shingles.

Step flashing — Flashing application method used where a vertical surface meets a sloping roof plane.

Storey — That part of a building between any floor or between the floor and roof.

Storm collar — A metal flashing used to seal around a penetration in a roof.

Storm sewer — A sewer system designed to collect storm water, separate from the waste water system.

Storm window— An extra window usually placed outside of an existing one, as additional protection against cold weather, or damage.

Stucco — An outside plaster finish made with Portland cement as its base.

Stud— One of a series of slender wood or metal vertical structural members placed as supporting elements in walls and partitions.

Stud framing — A building method that distributes structural loads to each of a series of relatively lightweight studs. Contrasts with post-and-beam.

Sump — Pit or large plastic bucket/barrel inside a basement, designed to collect ground water (storm water) from a perimeter drain system.

Sump pump — A submersible pump in a sump pit that pumps any excess ground water to the storm sewer.

Suspended ceiling— A ceiling system supported by hanging it from the overhead structural framing.

Tempered— Strengthened. Tempered glass will not shatter nor create shards, but will “pelletize” like an automobile window. Required in tub and shower enclosures, for example.

Termites— Insects that superficially resemble ants in size, general appearance, and habit of living in colonies; hence, they are frequently called “white ants.” Subterranean termites establish themselves in buildings not by being carried in with lumber, but by entering from ground nests after the building has been constructed. If unmolested, they eat out the woodwork, leaving a shell of sound wood to conceal their activities, and damage may proceed so far as to cause collapse of parts of a structure before discovery.

Terra cotta— A ceramic material molded into masonry units.

Threshold — The bottom metal, concrete, or wood plate of an exterior door frame. They may be adjustable to keep a tight fit with the door slab.

Toenailing— To drive a nail in at a slant. Method used to secure floor joists to the plate. Not acceptable for securing joists flush to a header or beam.

Tongue-and-groove— A joint made by a tongue (a rib on one edge of a board) that fits into a corresponding groove in the edge of another board to make a tight flush joint. Typically, the subfloor plywood is tongue-and-groove.

Top chord— The upper or top member of a truss.

Trap — A plumbing fitting that holds water to prevent air, gas, and vermin from entering into a building.

Tread— The walking surface board in a stairway on which the foot is placed.

Treated lumber — A wood product which has been impregnated with chemicals to reduce damage from wood rot or insects. Often used for the portions of a structure which is likely to be in ongoing contact with soil and water. Wood may also be treated with a fire retardant.

Truss— An engineered and manufactured roof support member with “zig-zag” framing members. Does the same job as a rafter but is designed to have a longer span than a rafter

Tube-and-knob wiring — See knob-and-tube wiring.

Uffi — Urea Formaldehyde Foam Insulation, a foam insulation blown into existing walls. (Pronounced “you-fee”)

Ultraviolet degradation— A reduction in certain performance limits caused by exposure to ultraviolet light.

Underlayment — (1) A one-quarter-inch material placed over the subfloor plywood sheathing and under finish coverings, such as vinyl flooring, to provide a smooth, even surface. (2) A secondary roofing layer that is waterproof or water-resistant, installed on the roof deck and beneath shingles or other roof-finishing layer.

Uv rays— Ultraviolet rays from the sun.

Valley— The inward angle formed by two intersecting, sloping roof planes. Since it naturally becomes a water channel, additional attention to waterproofing it is desirable.

Vapor barrier — A building product installed on exterior walls and ceilings under the drywall and on the warm side of the insulation. It is used to retard the movement of water vapor into walls and prevent condensation within them. Normally, polyethylene plastic sheeting is used.

Vent — A pipe or duct allowing the flow of air and gases to the outside. In a plumbing system, the vent is necessary to allow sewer gases to escape to the exterior

Vermiculite— A mineral closely related to mica, with the faculty of expanding on heating to form lightweight material with insulation quality. Used as bulk insulation and also as aggregate in insulating and acoustical plaster and in insulating concrete floors. Some had an asbestos content.

Water closet— A toilet.

Weather stripping — Narrow sections of thin metal or other material installed to prevent the infiltration of air and moisture around windows and doors.

Weep holes — Small holes in exterior wall cladding systems that allow moisture to escape and air pressure equalization in the cavity space drained by the weep hole.

Wythe— (rhymes with “tithe” or “scythe”) A vertical layer of masonry that is one masonry unit thick.

Zone— The section of a building that is served by one heating or cooling loop because it has noticeably distinct heating or cooling needs. Also, the section of property that will be watered from a lawn sprinkler system.

Zone valve — A device, usually placed near the heater or cooler, which controls the flow of water or steam to parts of the building; it is controlled by a zone thermostat