Buildings and Architecture Glossary: P - R

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- P -

Panel, truss: A portion of a truss bounded by a top chord, a bottom chord, and two adjacent vertical members.

Panic hardware: A door latch release mechanism that works automatically if pressed against.

Parapet wall: A wall that projects above surrounding roof areas.

Passive: Working by ambient energy flows rather than by the introduction of energy from outside sources that are under human control.

Pattern staining: Discoloration of a wall or ceiling caused by the variable adhesion of dust to surfaces at different temperatures.

Pediment: The ornamented gable end of a roof in classical architecture.

Performance bond: An insurance policy that guarantees money to finish a construction project if the original con tractor should fail to do so.

Photovoltaic panel: A group of photocells mounted on a roof and wired together to produce electricity from sunlight.

Pile: A foundation element consisting of a long, slender piece of wood, steel, or reinforced concrete driven vertically into the ground.

Pile, end-bearing: A pile that is driven until its lower end rests on firm soil or rock.

Pile, friction: A pile that develops its load-bearing capacity by means of friction between the sides of the pile and the soil.

Pile driver: A heavy, mechanical hammer used to drive piles into the ground.

Portland cement: See Cement, portland.

Post-tensioning: The application of compressive stress to a concrete structural member by means of internal strands of high-strength steel that are stretched to a high tension after the concrete has hardened.

Precast concrete: Concrete that is cast and hardened away from the building site, then put in place in the building as rigid elements.

Precipitation, chemical: Causing constituents of a solution or suspension to fall to the bottom of a container by combining them chemically with compounds that convert them to dense solids.

Principal stress, lines of: Lines drawn to trace the directions of maximum tensile and compressive stresses in a structural member.

Pressure equalization chamber (PEC): An airspace in an external building component that is pressurized by the wind in such a way as to prevent strong air currents from passing through the wall.

Primary treatment of sewage: Anaerobic fermentation of sewage.

Pyrolysis: The heating of materials to reduce them to their constituent inorganic components.

- Q -

Quoins: Square blocks of masonry built into the exterior corners of a building, originally as a means of stabilizing a wall made of weak materials, but now as ornament.

- R -

Radiation: The passage of electromagnetic waves through space or air.

Radiational cooling: The cooling of terrestrial objects by radiating heat from the objects to the night sky.

Radiator: A heating device in which heat from steam or hot water is transferred to the air in a room. The transfer is achieved mainly by convection, not radiation, but the name persists.

Rafter: A slender, sloping beam used repetitively at narrow spacings to support a roof plane.

Rainscreen: The outer layer of a wall that has a pressure equalization chamber and air barrier.

Raised access floor: A floor made up of rigid, square, removable tiles supported a short distance above a structural floor on pedestals, so that pipes, wires, and ducts may run freely beneath to any point in a building.

Recycling: Sending used materials back to factories for reprocessing and reuse rather than discarding them.

Reflectance: The proportion of incident radiation that is turned away by a surface, expressed as a decimal fraction of one.

Regenerative wheel: A rotating mass of metal mesh through which air is blown to transfer heat from the air in one duct to the air in another.

Reglet: A slot into which a flashing or the edge of a roof membrane may be tucked.

Regulator, gas: A device for reducing and controlling the pres sure of gas at the point of use.

Reinforced concrete: Concrete into which steel bars have been cast to resist tensile stresses.

Reinforcement, sound: Strengthening sound in a performance hall by means of reflections from surfaces in the hall.

Relative humidity: See Humidity, relative.

Relay: An electrical switch that is activated by another electric current.

Reservoir: A large container or pond for the storage of water.

Resonator: A hollow chamber that vibrates sympathetically and thereby absorbs sound energy at a given frequency.

Reverberation time: The time it takes for a loud sound to diminish to inaudibility in a performance hall.

Ribbed slab: A concrete spanning element consisting of a thin slab supported by closely spaced, parallel joists.

Ridge: The intersection of two roof slopes in a gable roof.

Rigid frame: A structure in which rigid joints provide lateral stability.

Rise of an arch: The vertical distance from the lowest part of the center line of an arch to the highest.

Rise of a stair: The total vertical dimension between the bottom and top of a stair.

Riser: A vertical planar element between two treads in a stair.

Roof, low-slope: A roof that has too shallow a slope for shingles and must be made waterproof by a continuous membrane.

Roof monitor: See Monitor.

Roof, steep: A roof that can be made waterproof with shingles.

Roof, thatched: A roof that is covered with bundles of reeds, grasses, or leaves.

Run of stair: The total horizontal dimension of a stair, measured from the lowest riser to the highest.

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