» Backer board A fi ber-reinforced cement board or glass-mat-faced gypsum board used as a base for thin-set tile applications.
» Backer rod A fl exible, compressible strip of plastic foam inserted into a joint to limit the depth to which sealant can penetrate.
» Backfi ll Earth or earthen material used to fi ll the excavation around a foundation; the act of fi lling around a foundation.
Backup, backup wall A vertical plane of masonry, concrete, or wood framing used to support a thin facing such as a single wythe of brickwork.
» Backup bar A small rectangular strip of steel applied beneath a joint to provide a solid base for beginning a weld between two steel structural members.
» Ballast A heavy material installed over a roof membrane to prevent wind uplift and shield the membrane from sunlight.
» Balloon frame A wooden building frame composed of closely spaced members nominally 2 inches (51 mm) thick, in which the wall members are single pieces that run from
the sill to the top plates at the eave.
» Baluster A small vertical member that serves to fi ll the opening between a handrail and a stair or floor.
» Band joist A wooden joist running perpendicular to the primary direction of the joists in a fl oor and closing off the floor platform at the outside face of the building.
» Bar A small rolled steel shape, usually round or rectangular in cross section; a rolled steel shape used for reinforcing concrete.
» Barrel shell A scalloped roof structure of reinforced concrete that spans in one direction as a barrel vault and in the other as a folded plate.
» Barrel vault A segment of a cylindrical surface that spans as an arch.
» Barrier wall An exterior wall of a building whose watertightness depends on its freedom from passages through the wall.
» Basalt A very dense and durable igneous rock, usually dark gray in color; classified by ASTM C119 in the Granite group.
» Baseboard A strip of fi nish material placed at the junction of a fl oor and a wall to create a neat intersection and to protect the wall against damage from feet, furniture, and fl
oor-cleaning equipment.
Base-coat plaster One or more preparatory plaster coats that provide a flat, solid surface suitable for the application of the final finish coat plaster. See also Scratch coat and
Brown coat.
» Base fl ashing The flashing at the edges of a low-slope roof membrane that turns up against the adjacent face of a parapet or wall, and frequently overlapped by a counterf
lashing.
» Base isolator A device at foundation level that diminishes the transmission of seismic motions to a building.
» Baseplate A steel plate inserted between a column and a foundation to spread the concentrated load of the column across a larger area of the foundation.
» Basic oxygen process A steel-making process in which a stream of pure oxygen is introduced into a batch of molten iron so as to remove excess carbon and other impurities.
» Batten A strip of wood or metal used to cover the crack between two adjoining boards or panels.
» Batten-seam A seam in a sheet metal roof that encloses a wood batten.
Batter board Boards mounted on stakes outside the excavation area of a building, used to preserve locations for string lines marking the corners of the building foundation.
» Bay A rectangular area of a building defined by four adjacent columns; a portion of a building that projects from a facade.
» Bead A narrow line of weld metal or sealant; a strip of metal or wood used to hold a sheet of glass in place; a narrow, convex molding profi le, a metal edge or corner
accessory for plaster.
» Beam A straight structural member that acts primarily to resist nonaxial loads.
» Beam blank See Bloom.
» Bearing A point at which one building element rests upon another.
» Bearing block A piece of wood fastened to a column to provide support for a beam or girder.
» Bearing pad A block of plastic or synthetic rubber used to cushion the point at which one precast concrete element rests upon another.
» Bearing wall A wall that supports floors or roofs.
» Bed See Casting bed.
» Bed joint The horizontal layer of mortar beneath a masonry unit.
» Bedrock A solid stratum of rock.
» Bending moment The combination of tension and compression forces that cause a beam or other structural member to bend. See also Moment.
» Bending stressA compressive or tensile stress resulting from the application of a nonaxial force to a structural member.
» Bent A plane of framing consisting of beams and columns joined together, often with rigid joints.
» Bentonite clay An absorptive colloidal clay that swells to several times its dry volume when saturated with water; the primary ingredient in bentonite waterproofing.
» Bessemer process An early method of steel manufacturing in which air was blown into a vessel of molten iron to burn out impurities.
» Bevel An end or edge that is cut at an angle other than a right angle.
» Bevel siding Wood cladding boards that taper in cross section.
» Billet A large cylinder or rectangular solid of material.
» BIM See Building information modeling.
» Birdsmouth cut An angled notch cut into a rafter to allow the rafter to seat securely on the top plate of a wall.
» Bite The depth to which the edge of a piece of glass is held by its frame.
» Bitumen A tarry mixture of hydrocarbons, such as asphalt or coal tar.
» Bituminous roof membrane A low-slope roof membrane made from bituminous materials, either a built-up roof membrane or a modifi ed bitumen roof membrane.
» Blast furnace slag A hydraulic cementitious material formed as a byproduct of iron manufacture, used in mortar and concrete mixtures; also called slag cement.
» Blast-resistant glazing Window, storefront, or curtainwall systems designed for resistance to the force of explosive blasts.
» Bleed water In freshly placed concrete, water that rises to the top surface of the concrete as the solid cement and aggregate particles settle.
» Blended hydraulic cement Hydraulic cement made from a mixture of cementitious materials such as portland cement, other hydraulic cements, and pozzolans for the purpose
of altering one or more properties of the cement or reducing the energy required in the cement manufacturing process.
» Blind nailing Attaching boards to a frame, sheathing, or subfl ooring with toe nails driven through the edge of each piece so as to be completely concealed by the adjoining
piece.
» Blind-side waterproofing An impervious layer or coating on the outside of a foundation wall that, for reasons of inaccessibility, was installed before the wall was constructed.
» Blocking Pieces of wood inserted tightly between joists, studs, or rafters in a building frame to stabilize the structure, inhibit the passage of fi re, provide a nailing surface for fi
nish materials, or retain insulation.
» Bloom A rectangular solid of steel formed from an ingot as an intermediate step in creating rolled steel structural shapes.
» Blooming mill A set of rollers used to transform an ingot into a bloom.
» Bluestone A sandstone that is gray to blue-gray in color and splits readily into thin slabs; classifi ed by ASTM C119 in the Quartz-Based Stone group.
» Board foot A unit of lumber volume, a rectangular solid nominally 12 square inches in cross-sectional area and 1 foot long.
» Board siding Wood cladding made up of boards, as differentiated from shingles or manufactured wood panels.
» Bolster A long chair used to support reinforcing bars in a
concrete slab.
» Bolt A fastener consisting of a cylindrical metal body with a head at one end and a helical thread at the other, intended to be inserted through holes in adjoining pieces of
material and closed with a threaded nut.
» Bond In masonry, the adhesive force between mortar and masonry units, or the pattern in which masonry units are laid to tie two or more wythes together into a structural unit.
In reinforced concrete, the adhesion between the surface of a reinforcing bar and the surrounding concrete.
» Bond breaker A strip of material to which sealant does not adhere.
» Bonded posttensioning A system of prestressing in which the tendons are grouted after stressing so as to bond them to the surrounding concrete.
Bonded terrazzo Terrazzo flooring whose underbed is poured directly upon the structural floor.
» Bottom bar A reinforcing bar that lies close to the bottom of a beam or slab.
» Bottom plate See Sole plate.
» Bound water In wood, the water held within the cellulose of the cell walls.
See also Free water. Box beam A bending member of metal or plywood whose cross section resembles a closed rectangular box.
» Box girder A major spanning member of concrete or steel whose cross section is a hollow rectangle or trapezoid.
» Box nail A nail with a more slender shank than a common nail, used for fastening framing members in wood light frame construction.
Braced frame A structural building frame strengthened against lateral forces with diagonal members.
» Bracing Diagonal members, either temporary or permanent, installed to stabilize a structure against lateral loads.
» Brad A small fi nish nail.
» Brake A machine used to form lengths of sheet metal into bent shapes.
» Brazing A process that uses molten, nonferrous metal to join two pieces of metal. The brazing metal is melted at a temperature below that of the metals being joined, so that,
unlike in welding, the joined metals remain in a solid state throughout the process.
Breather mat A wiry plastic matting placed within a roof or wall assembly to create a space for drainage and ventilation.
Bridging Bracing or blocking installed between steel or wood joists at midspan to stabilize them against buckling and, in some cases, to permit adjacent joists to share loads.
» British thermal unit (BTU) The quantity of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit.
» Broom fi nish A skid-resistant texture imparted to an uncured concrete surface by dragging a stiff-bristled broom across it.
» Brown coat The second of two basecoat plaster applications in a three-coat plaster.
» Brownstone A brownish or reddish sandstone; classifi ed by ASTM C119 in the Quartz-Based Stone group.
» BTU See British thermal unit.
» Buckling Structure failure by gross lateral deflection of a slender element under compressive stress, such as the sideward buckling of a long, slender column or the upper
edge of a long, thin fl oor joist.
» Building brick Brick used for concealed masonry work where appearance is not a concern.
» Building code A set of regulations intended to ensure a minimum standard of health and safety in buildings.
Building enclosure The parts of the building, principally its walls, roofs, and fenestration, that separate the interior of the building from the exterior, and that must effectively
control the fl ow of heat, air, and moisture; also called the thermal envelope or the building envelope.
» Building envelope See Building enclosure.
» Building felt See Asphalt-saturated felt.
» Building information modeling (BIM) The computerized three-dimensional modeling of building systems, with the linking of model components to a database of properties
and relationships.
» Building paper A water-resistive, asphaltsaturated paper used similarly to asphaltsaturated felt, to provide a protective layer in an exterior wall assembly.
Building separation joint A plane along which a building is divided into separate structures that may move independently of one another. Built-up roof (BUR) A multi-ply roof
membrane, made from layers of asphaltsaturated felt or other fabric, bonded together with bitumen.
» Bull fl oat A long-handled tool used for the initial fl oating of a freshly poured concrete slab. See also Darby.
» Buoyant uplift The force of water or liqufi ed soil that tends to raise a building foundation out of the ground.
» BUR See Built-up roof.
» Butt The thicker end, such as the lower edge of a wood shingle or the lower end of a tree trunk; a joint between squareedged pieces; a weld between squareedged pieces of
metal that lie in the same plane; a type of door hinge that attaches to the edge of the door.
» Butt-joint glazing A type of glass installation in which the vertical joints between lights of glass do not meet at a mullion, but are made weathertight with a sealant.
» Button head A smooth, convex bolt head with no provision for engaging a wrench.
» Buttress A structural device of masonry or concrete that resists the diagonal forces from an arch or vault.
» Butyl rubber A synthetic rubber compound.
