½ Bathroom (half bath): a bathroom with a sink and a toilet; also called a powder room.
¾ Bathroom: a bathroom with a sink, toilet, and a shower. AAV: see Air Admittance Valve (AAV).
Aerator: a device that introduces air into a water stream; usually attached to the outlet of sink and lavatory faucets.
Adapter: a fitting that allows connection of different pipe types or different pipe sizes. AFUE: see Annual Fuel Utilization Efficiency (AFUE).
Air barrier: any material or combination of materials that prevents the flow of air from unconditioned areas into the thermal envelope.
Air Admittance Valve (AAV): an air pressure operated one-way valve used in place of an at-mospheric plumbing vent; this device is different from a check (cheater) vent which contains a spring loaded gasket and is not approved for use in site-built houses.
Air conditioning: this term, broadly defined, includes heating, cooling, humidification, de-humidification, ventilation, and air filtration. Air conditioning, as the term is typically used in residential construction, refers to the cooling, dehumidification, ventilation, and air filtration functions.
Air conditioning system (central): a system that includes an air handler or a furnace, an evaporator coil, and a condenser unit that cools a house by removing heat from the house and moving the heat outside. See also Heat pump and Split (air conditioning) system.
Air gap: the vertical distance between a water supply discharge, such as a faucet, and the flood rim level of a fixture such as a sink; an air gap is one method of preventing a cross-connection between the water supply and drainage systems.
Air handler: the inside unit of a heat pump containing a fan, evaporator coil, and associated control and operating parts; air handler is sometimes used to describe a fuel-fired forced air furnace.
Ampacity: the maximum current that a conductor or device may carry continuously without exceeding its temperature rating.
Annual Fuel Utilization Efficiency (AFUE): a ratio of heat generated by a heating system versus the energy used; the minimum AFUE for most gas furnaces is 80 meaning that the furnace converts 80% of the fuel to heat and 20% is lost through the vent or by other means.
Appliance, plumbing: an appliance connected to the plumbing system that uses energy to perform its function, such as a clothes washing machine, dishwashing machine, food-waste disposer, or a water heater.
Arm, shower: the generally horizontal pipe that connects the shower riser to the shower head; usually curves down at about a 30° angle near the shower head.
Attic: a usually uninhabitable space above the ceiling of the highest habitable area and below the roof framing. Also called a crawl space in some markets.
AWG: the abbreviation for American Wire Gauge, a system for identifying the diameter of electrical wires; larger numbers identify smaller diameter wires; #14 (pronounced number 14 or 14 gauge) is the smallest wire used in house wiring, and 4/0 (pronounced four-oh) is usually the largest.
Axial force (load): the vertical force acting on a structural member such as a column or a beam, which places the member under compression at the loading point.
Backflow: the flow of a contaminate from an unintended source into the potable water supply system from an unintended source. See Backpressure and Backsiphonage.
Backflow preventer: a device or other means used to prevent backflow into the water supply system.
Backpressure: an uncommon condition that can occur when the pressure at a point outside the water supply system is greater than the water supply pressure. Example: the weight of water in a swimming pool located above the water supply system pipes can create enough pressure to force water back into the water supply pipes.
Backsiphonage: an uncommon condition that can occur when there is negative pressure in the water supply or distribution pipes; contaminants can be sucked into the pipes. Back-siphonage usually occurs because of a sudden loss of water pressure combined with rapid drainage of the water supply pipes.
Backwater valve: a device installed in the building drain pipe to prevent the flow of sewage from a public sewer into the house. A backwater valve is recommended when plumbing fixtures in a house are located below the nearest upstream manhole cover of the public sewer.
Balcony: an outdoor platform that is located at the second story or above. A balcony may be supported by posts, or it may be cantilevered.
Barrier, access (child): a fence, wall, house wall, or similar structure that is designed to limit access to the pool or spa area by unauthorized persons, especially children. A natural barrier such as a large body of water, a hill, or a cliff may also serve as a barrier, with approval.
Basement (cellar): a story that is partially or completely below grade; often has a ceiling height of 7 feet or more, but sometimes less in older houses.
Basement (daylight basement, walk out basement): a basement that has a door to the exterior.
Basement wall: a wall with at least (≥) 50% of its area below grade (covered by earth on the outside) and encloses conditioned space.
Beam (girder): a structural member that carries loads from other members such as joists, rafters, and other beams.
Bed molding: a thin decorative molding that covers the seam between the soffit and the frieze and between interior walls and ceilings; also used for shadow boxes and for other decorative purposes.
Bend: a fitting that changes the direction of flow in drainage pipes. Bends are identified by the angle of the direction change either by a fraction or by the number of degrees of the direction change. Common bends include: 90° (¼ bend), 60° (1/6 bend) 45° (⅛ bend), and 22½° (1/16 bend). The fraction describes how much of a 360° circle that the bend angle sweeps. See Elbow and Sweep.
Bonding: the process of connecting, both physically and electrically, metal components of the electrical system that are not intended to carry electrical current to provide a low resistance return path to the circuit breaker or fuse to clear ground faults; bonding is an electrical safety system.
Boot (HVAC distribution system): sheet metal formed into a rectangle or circle that connects an air duct to a grille or a register.
Boot (flashing): the flashing surrounding a roof penetration such as a plumbing vent or a fuel-burning appliance vent; also called a roof jack.
Bow (bowed): a condition where a structural member is curved along its long axis.
Branch circuit: conductors that begin at a circuit breaker or fuse and serve one or more outlets.
Branch circuit, multiwire: a branch circuit in which two energized conductors share one neutral conductor; examples can include clothes dryers, ranges and other cooking appliances, and split-wire receptacle circuits; 240 volt water heaters and condensers for air conditioners and heat pumps are not usually multiwire branch circuits.
Braced wall: see Shear wall.
Branch drain (fixture branch): a pipe that receives material from two or more fixture drains or from other branch drains; branch drains are usually horizontal pipes that may have some vertical sections; a branch drain usually flows into a stack or into the building drain.
Brazing (silver soldering): a method of joining metal pipe and fittings (usually copper) by fusing them together with an alloy made mostly from sliver at a temperature above 800° F; makes a stronger connection than soldering. See Soldering (sweating).
British thermal unit (Btu): the amount of heat required to increase the temperature of 1 pound of water by 1° Fahrenheit; this is a common description of the size or cooling capacity of an air conditioning system. See Ton (of refrigeration).
Building drain: usually the lowest drainage pipe in the house; it extends 30 inches from the house exterior wall where it connects to the building sewer. See Sewer (building).
Building thermal envelope: the conditioned (heated and cooled) area of the building. The envelope boundary between conditioned and unconditioned space includes walls, ceilings, floors, basement walls and slab-on-grade foundations. The thermal envelope may include the attic and the crawl space if these areas are designed and built as conditioned space.
Bulkhead door: a horizontal or inclined door that provides access to an area under the house or to a storage area such as a cellar; sometimes referred to by the brand name Bilco.
Bus (buss, busbar): the heavy, rigid metal part of a panelboard on which circuit breakers or fuses are mounted; sometimes used to describe metal terminals to which the neutral and equipment grounding conductors (EGCs) are connected.
Cable (electrical): two or more conductors encased in sheathing; examples include non-metallic sheathed cable (often referred to by the brand name Romex) and armored cable (often referred to by the brand name BX).
Cantilever: a structural member (such as a floor joist) that extends horizontally beyond the vertical support (usually a wall) and has no other posts or supports.
Ceiling joist: a horizontal structural member that forms the ceiling of a room below an attic.
Ceiling, vaulted: a ceiling that extends at an angle above the top of a full-height wall; the ceiling finish (drywall) is usually attached directly to the rafters.
Ceiling, tray (or trey): a horizontal ceiling raised above the top of a full-height wall; the ceiling is often raised in one or two risers and decorated with crown molding or bed molding.
Chimney: a generally vertical structure containing one or more flues that conducts combustion products from a fuel-burning appliance to a point outside the house; chimneys are constructed using masonry and metal pipes.
Chimney cap (crown): the water-tight component at the top of a chimney; a masonry chimney cap should be made using concrete, metal, or stone; a factory-built chimney cap (pan) is usually made using metal.
Chimney connector: a component that conducts combustion products from a fuel-burning appliance to a chimney. See Vent connector.
Cinder block: a concrete masonry unit made using coal ash or other residue of combustion. Cinder blocks are less common in modern residential construction. Cinder blocks may contain corrosive materials. See Concrete masonry unit (CMU).
Circuit breaker: see Overcurrent protection device (OPD).
Cleanout (ash dump): an opening in a fireplace hearth into which ashes may be swept into pit below.
Cleanout (plumbing): an accessible opening in drainage pipes that allows clearing of block-ages; a cleanout may be a fitting with a covered opening, or it may be a removable trap or a fixture such as a toilet.
CMU: see Concrete masonry unit (CMU).
Collar (duct): a round sheet metal ring that connects a duct to a plenum or to a trunk duct.
Collar tie: a horizontal member (usually a 1×4 or a 2×4) installed in the upper third of the attic between two rafters to help tie rafters together at the ridge.
Column: a generic term describing a structural member designed to support a concentrated vertical load. A column is usually a tall and relatively narrow component. Also called a post, especially when used with decks. See Pier and Pile.
Commode: a regional term primarily used in the South and Southeast; see Toilet.
Compression: The force that crushes or shortens a structural member. A beam under a vertical load is under compression on the top. See Tension force (load).
Compression fitting: a method of connecting water supply pipes and valves using a compression ring (ferrule) and a compression nut; commonly used to connect small size pipes and tubes to fixture shutoff valves and appliances such as ice makers.
Compressor: part of an air conditioning or heat pump condenser unit; this device compresses the gas refrigerant into superheated gas, and provides the energy to move the refrigerant through the system.
Concrete masonry unit (CMU): a usually rectangular block made from concrete, aggregate, and water and intended for installation with other blocks to form walls and other structures. See Cinder block.
Condensate: water that condenses into liquid when heat is removed from the air flowing over the evaporator coil; this water must be disposed of in an appropriate manner; significant amounts of water can be produced in humid environments. Condensate is also produced when heat is removed from combustion gasses in the heat exchanger of a high efficiency furnace or boiler.
Condenser (coils): part of an air conditioning or heat pump condenser unit; these are the tubes (coils) around the perimeter of the condenser unit.
Condenser (unit): the outside unit of a split air conditioning or heat pump system consisting of a compressor, condenser coils, a fan, and associated control and operating parts.
Condominium: a form of real property ownership in which the owner holds 100% ownership of a dwelling unit and shares ownership of the common elements. Condominium does not describe a type of building.
Conductor: a material, such as copper or aluminum, that permits electricity to flow with low resistance; wires are conductors.
Cooktop: a cooking appliance installed in an opening in a countertop.
Coping: the material at the edge of a concrete pool that covers the bond beam. Coping is not required; the deck may be installed up to the edge of the water.
Corbel: the outward horizontal projection of a masonry course beyond the course below; corbelling changes the shape of a chimney, usually for aesthetic reasons. Compare Racking (back).
Cornice: the usually decorative exterior trim where the rafters and wall meet. Cornice usually encloses the eaves. Cornice often consists of the fascia, soffit, and bed molding.
Cornice return: the continuation of the cornice in a different direction, such as at a gable end.
Corrugated Stainless Steel Tubing (CSST): a flexible tube that is used to convey fuel gas.
Coupling: a plumbing fitting that allows two pipes to be connected in a straight line.
Crawl space: an accessible area within the foundation walls below the first habitable story, usually having a soil floor, and a small distance between the soil and the floor joists. Also used to describe an attic in some markets.
Creep: See Deformed.
Creosote: a flammable byproduct of improperly burning wood, such as burning wet wood, and burning wood without adequate combustion air.
Cricket (saddle): a small gable-shaped projection that is installed on the high side of where the roof intersects a chimney that is more than 30 inches wide parallel to the ridge; a cricket diverts water around the chimney.
Cross-connection: a connection between the water supply pipes and a potential contaminate source, such as the DWV pipes, that could allow contaminated water to flow from the contaminate source into the water supply pipes. A cross-connection can be intentional, such as the fill valve in a toilet tank. A cross-connection can be unintentional, such as a hand-held shower head hanging below the flood rim level of a bathtub. See Backflow.
Crown (camber): a condition where a board or beam is curved along the long axis. See Bow (bowed). Most dimensional lumber joists have a natural crown which should be installed with the high side vertical. Manufactured beams have a camber built into the beam. The crown or camber installed with the high side vertical usually becomes straight when a load is applied.
Crown molding: a decorative molding that covers the seam between the soffit and the frieze and between interior walls and ceilings; usually wider and more ornate than bed molding.
CSST: see Corrugated Stainless Steel Tubing (CSST).
Culvert: a below ground passage that allows water to flow, usually through a large diameter metal or concrete pipe. In residential construction, a culvert may be located at the end of a driveway to permit water to flow in a swale under the driveway.
Cup (cupped): a condition in which a board is curved along the face of the board.
Current: the amount of electricity in a circuit; (similar to water gallons per minute; water flow in a pipe); unit of measure is the Ampere (Amp); expressed as I in Ohm’s Law and Watt’s Law equations.
Damper (barometric): a device used to control draft in an oil-fired appliance vent connector when using a masonry chimney as a vent; the damper is a round metal plate that is mounted on two hinges. It opens and closes based on the pressure in the vent connector.
Damper (fireplace): an operable metal plate that opens to allow combustion gasses to flow into a chimney, and closes to restrict outside air entry into the house when the fireplace is not being used.
Damper (HVAC duct system): a plate or louvers installed in a duct system that permits control of how much air flows in a duct; a damper may be controlled manually or it may be controlled by a motor. Motor controlled dampers are one method of installing a zoned system where one HVAC system is controlled by two or more thermostats.
Dead front cover: a panel that is removed to gain access to the energized components inside an electrical enclosure; the dead front cover is usually behind a door that must be swung or lifted in order to gain access to the dead front cover.
Deadman: a buried component, such as a railroad tie or landscape timber, that serves as an anchor to keep a retaining wall from rotating; a deadman is connected to the retaining wall using a tieback.
Deck: an outdoor recreational area that is usually, but not always, attached to the house. A deck is supported by posts. A deck is usually not covered. See Balcony and Patio.
Deflect (deflection): a condition where a structural member bends from its normal shape or position, such as when a joist bends under a load. Deflect implies a temporary condition wherein the member will return to its normal shape or position when the load is removed.
Deformed (deformation): a condition where a structural member changes shape or dimension from its normal shape or dimension. Permanent deformation occurs when the member will not return to its normal shape or dimension when the load is removed. Permanent deformation is called creep.
Developed length: the length of a pipe measured along the pipe including all fittings. For pipes that convey material under pressure (water pipes and gas pipes), an amount is sometimes added to the developed length of the physical pipe to account for pressure loss caused by friction at the fittings.
Dew point (temperature): the temperature at which water vapor in the air may condense into liquid water. A higher dew point temperature indicates that the air contains more water vapor.
Direct exhaust appliance: a fuel-burning appliance that obtains combustion air from inside the house and expels combustion products outside the house. These are usually high efficiency appliances with a sealed combustion chamber. Some appliances can be configured in the field as a direct vent appliance or a direct exhaust appliance. Also called a non-direct vented appliance.
Direct vent appliance: a fuel-burning appliance that obtains combustion air from outside the house and expels combustion products outside the house. These are usually high efficiency appliances with a sealed combustion chamber.
Dishwashing machine (dishwasher): a plumbing appliance that is used to clean eating and cooking utensils.
Disposall (Disposal): See Food-waste disposer (disposal).
Diverter: (1) a valve in a bathtub spout that directs water from the spout to the shower riser. (2) Any valve that directs water flow from one pipe to other pipes, such as a valve in a shower that directs water from the shower head to body spray heads.
Dormer: a projection above a sloped roof that usually contains a window. A dormer usually has two sidewalls and a gable roof, but it may have any style roof.
Downdraft exhaust (vent): a fan located under a cooktop which pulls the cooking odors and moisture down and exhausts them to the outdoors through a duct located under the floor or in the foundation. A downdraft exhaust is sometimes used when a cooktop is located in an island, a peninsula, or other space where installing a hood is impractical or expensive.
Draft (forced): a method of expelling combustion gasses from gas-fired and oil-fired appliances that uses a fan (blower) to force the gasses through the vent under pressure; also referred to as positive pressure draft. Forced draft fans are installed at the beginning of the vent system, usually inside the appliance. Forced draft vents must be sealed to prevent combustion gasses from escaping through the vent.
Draft (induced): (1) the process of using negative pressure created by a fan to pull combustion gasses through a heat exchanger; draft inducers do not place combustion gasses in a chimney or vent under positive pressure; most medium efficiency gas furnaces are induced draft appliances. (2) the process of using negative pressure created by a fan to pull combustion gasses through a vent; this vent system may be used when the vent system for a natural draft appliance cannot be installed to operate using the stack effect; mechanical draft inducers are installed at the vent termination.
Draft (mechanical): a vent system that uses an electrically powered fan to assist in expelling combustion gasses through a chimney or vent; mechanical draft may be forced draft (positive pressure) or induced draft (negative pressure).
Draft (natural): the tendency of combustion gasses to rise in a chimney or vent due to the gasses being hotter and at a lower pressure than the surrounding gasses (also known as the stack effect); fireplaces and most gas-fired and oil-fired appliances rely on natural draft to expel combustion gasses.
Drain, waste, and vent pipes (DWV): see DWV system.
Drain (soil) pipe: a pipe that conveys feces and urine. Contrast Waste pipe.
Drainage pipe: a generic term that refers to a drain pipe or a waste pipe.
Drainage (storm water): a system intended to capture water and direct it away from the house and ultimately off the property. A drainage system may include components such as gutters and downspouts, swales, underground drains, and grading.
Driveway: a private road that is intended for vehicle use between a public road and a building.
Duct (branch): a duct that runs between a trunk duct or a plenum and one supply or return boot.
Duct (stack): a (usually) sheet metal duct that runs in a wall cavity; it terminates in a stack head instead of a boot. See Boot and Stack head.
Duct (trunk): a large duct that serves multiple branch ducts.
DWV system: an abbreviation used to describe the plumbing drain, waste, and vent pipes and associated fittings and fixtures.
Eaves: the extension of the rafters beyond the exterior wall of the building. See Cornice. EGC: see Grounding conductor, equipment (EGC).
EIFS: an acronym for Exterior Insulation and Finish System, a type of wall covering that looks like stucco. EIFS is not stucco and should not be described as such.
Elbow: a water supply fitting that changes the direction of flow in pipes. Elbows are identified by the number of degrees of the direction change. Common elbows include: 90°, 45°, and 22½°. Elbow is frequently used when discussing DWV fittings, but bend is the more technically correct term for DWV fittings. See Bend.
Enclosure (electrical): a case or a cabinet intended to prevent accidental contact with energized parts; a panelboard is housed inside an enclosure.
Energy recovery ventilator (ERV): a whole house mechanical ventilation system that transfers heat and moisture between the incoming ventilation air and the outgoing exhaust air. Compare Heat recovery ventilator (HRV).
Equipment Grounding Conductor (EGC): see Grounding conductor, equipment. ERV: see Energy Recovery Ventilator (ERV).
Evaporator coil: part of an air conditioning or heat pump system; this device is located in the air handler of a heat pump or is attached to a furnace after the combustion chamber; an evaporator coil should not be located before a furnace combustion chamber because the moist air from the evaporator coil will damage the furnace.
Evaporative (swamp) cooler: a type of cooling system that reduces air temperature by pulling air through media soaked with water; these systems were once common in dry climates in the west, but have usually been replaced by a central air conditioning system.
Exhaust: air removed from a specific location by mechanical means; examples include bath-room exhaust fans, kitchen exhaust fans, and clothes dryers.
Exhaust hood (vent): an appliance that is installed above a range or cooktop to remove or filter cooking odors and moisture. An exhaust hood should be ducted to the outdoors; however, an exception allows for a hood that recirculates the exhaust back into the house if an operable window exists in the kitchen area or if the house is served by a system such as an ERV or HRV. See Downdraft exhaust (vent).
Extruded Polystyrene (XPS): a type of insulation that is manufactured in sheets.
Fascia (eaves): vertical trim at the end of the eaves, usually part of the cornice.
Faucet: a type of valve that allows water to flow through the air from an outlet. See Fixture, supply.
Feeder conductors: conductors from the service equipment or from a panelboard that supply electricity to another panelboard such as a subpanel.
Fenestration: openings in the wall and roof of a house such as windows, doors, and skylights.
Firebox: the firebox of a fireplace consists of the hearth and the walls from the hearth to the throat of the fireplace. See Hearth.
Fireplace: an opening at the base of a chimney in which a solid-fuel such as wood may be burned.
Fitting: a part that allows two or more pipes to be joined together; commonly used to describe components that connect plumbing pipes.
Fixture drain (trap arm): a pipe that conveys material from a fixture trap to another drainage pipe.
Fixture, drainage: a receptacle (such as a floor drain, bathtub, or sink) or a device (such as a toilet) that receives water from the water supply system and discharges the water and other material into the drainage pipes.
Fixture, supply: a device (such as a faucet or hose bibb) from which water flows in the plumbing system. The term fixture is often used to describe a supply fixture, a drainage fixture, or both.
Flared fitting: a method of connecting annealed copper water supply tubing and gas tubing and their associated valves by enlarging the end of the tube and securing the tube on a flare fitting using a nut.
Flood rim level: the highest level water can rise in a drainage fixture before the water flows out from the fixture to an unintended area such as the floor or the countertop.
Floor drain: a plumbing fixture recessed in a floor; floor drains in houses are usually located in the basement and receive water from sources such an as air conditioning condensate drain.
Flue: this term most accurately describes a generally vertical passageway inside a chimney; a chimney has at least one flue and may have several flues. See Vent (combustion).
Food-waste disposer (disposal): a plumbing appliance that is used to grind and dispose of soft food waste matter into the plumbing system. This appliance is often called a disposal based on a brand name Disposall. Brand names should not be used to describe systems and components. This appliance is sometimes called a garbarator in Canada.
Footing (footer): the part of a foundation that transmits loads directly to the soil, usually made from concrete in modern houses.
Frieze: vertical trim that connects or covers the top course of wall covering with the bottom of the cornice. A frieze board usually hides the termination of wall covering such as brick or stone.
Functional drainage: when the water drainage rate from the fixture is approximately equal to the maximum water flow rate into the fixture; water should not be able to reach the flood rim level of the fixture when the drain is fully open.
Functional flow: a water flow rate at a water supply fixture (in gallons per minute, (gpm)) that is equal to the minimum recommended flow rate at the fixture supply pipe (with no fixture attached), or to the maximum recommended flow rate at the fixture, whichever is less. Examples: bathtub, 4 gpm:, sink or lavatory, 2.2 gpm; shower, 2.5 gpm: hose bibb, 5 gpm.
Fuse: see Overcurrent protection device (OPD).
GEC: see Grounding electrode conductor (GEC).
Girder: see Beam (girder).
Grade: the elevation or level of the ground outside the house.
Grading: the act of moving soil or other material to form a desired elevation on the property. The term is often used in conjunction with drainage to describe shaping land to affect water flow.
Gray water: liquid waste from lavatories, bathtubs, showers, clothes washers, and laundry trays. Gray water may be processed and recycled to flush toilets and for landscape irrigation. Gray water recycling may not be allowed in some jurisdictions or there may be different regulations.
Grille: a cover with louvers or perforations that are not adjustable and may not be closed; a grille usually covers a return air opening, but may cover a supply air opening.
Grounded: a conductor that is intentionally connected to ground; this describes what is often called the neutral conductor.
Grounding: providing an intentional connection to the earth; grounding provides an alternate path for current to return to its source; in an electrical power system, the source is the utility’s transformer and ultimately the power plant. See Grounding electrode and Grounding electrode conductor (GEC).
Grounding conductor, equipment (EGC): a bare or green insulated conductor that provides a ground fault current path (a bonding connection) for equipment with metal cases and parts; these have been installed in most house branch circuit wiring since around 1960.
Grounding electrode: metal that is in direct contact with the earth and serves as the electrical system grounding connection; examples include copper rods, galvanized steel pipes, water service pipes and well pipes, and reinforcing steel encased in the footings.
Grounding electrode conductor (GEC): a conductor that runs between the grounding electrode and an accessible point downstream from where the grounded service entrance conductor connects to the service drop or lateral; the GEC connection is usually at the service equipment.
Ground fault: an event that occurs when metal that should not conduct electricity, such as a metal water pipe, becomes energized; if the metal is properly bonded, current flow should increase in the circuit and trip the circuit breaker or fuse.
Ground fault circuit interrupter (GFCI): a circuit breaker or receptacle that detects a ground fault by monitoring the imbalance in current flow between the energized and neutral conductors and stops current flow (opens the circuit) when a ground fault is detected.
Ground snow load: the estimated weight of accumulated snow on a surface; used when determining rafter span distance and fastening requirements for ceiling joists to rafters and ceiling joists to each other. Also used when determining cantilevered floor joist and deck floor joist span distance.
Grout (masonry): mortar with a high water content and a fluid-like consistency; used to fill the cores of masonry such as CMUs.
Header: a beam above an opening in a wall such as a door or a window.
Hearth: the floor of a fireplace upon which the fire burns. See Firebox.
Hearth extension: the area directly in front and at the sides of a fireplace opening; it is intended to provide a safe, noncombustible, place for embers to land when they escape from the hearth.
Heat pump: a heating and air conditioning system that removes heat from a house in cooling mode and moves heat from outside the house to inside the house in heating mode. See Air handler and Condenser (unit).
Heat recovery ventilator (HRV): a whole house mechanical ventilation system that transfers heat between the incoming ventilation air and the outgoing exhaust air. See Energy recovery ventilator (ERV).
Heat seasonal performance factor (HSPF): a measure of the efficiency of a heat pump in heating mode; obtained by dividing the heating output of a system over a heating season by the electric energy used; HSPF ratings range between about seven and ten.
High loop: a backflow prevention method that helps prevent the flow of contaminated water from the plumbing waste system into a dishwasher. A high loop involves securing the dishwasher drain tube as high as possible in the kitchen sink base cabinet.
Hose bibb (bib): a plumbing supply fixture designed for attachment of a garden hose. See Spigot.
HRV: see Heat Recovery Ventilator.
HSFP: see Heat seasonal performance factor (HSPF).
Hub (bell): the enlarged part of a pipe or fitting that accepts insertion of a pipe; cast iron pipes usually have a hub that accepts the spigot end of the pipe.
Humidity, relative: the amount of water vapor that is actually in the air compared to the amount of water vapor that could exist in the air at a given air temperature, expressed as a percentage. More moisture can exist in warm air than in cold air, so raising the air temperature while keeping the water vapor constant reduces relative humidity. Conversely, lowering the air temperature and keeping the water vapor content constant increases relative humidity.
HVAC: an abbreviation meaning heating, ventilation, and air conditioning; this is a common abbreviation used to describe cooling and heating systems.
Hydronic heating: a heating system that circulates hot liquid or steam through pipes; the pipes may be installed in the floor or may serve radiators or similar devices.
Joist: a horizontal structural member that supports a floor or ceiling.
Joules Law: a formula for calculating heat in an electrical circuit expressed as Heat = Current2 X Resistance X Time.
Keyway: a slot or groove used to secure concrete or masonry walls to each other that are built at different times. A keyway is cut into the footing during finishing to help keep concrete or masonry walls from sliding off the footing.
Kicker: a piece of lumber, usually a 2×4, that is connected to a rafter and to a ceiling joist to reduce rafter thrust that could move the wall on which the rafter bears. A kicker serves the same function as a rafter tie. See Rafter tie.
Knockouts: stamped openings in an electrical enclosure where conduit or cable clamps are installed in order to secure conductors or cables. See Tabs (twistouts).
Landscape (garden) block: a manufactured solid concrete block used to construct a landscape wall.
Landscape wall: a short height structure (usually 2 feet or less) that holds soil or fill on one side and keeps it from moving beyond the wall; a short height retaining wall.
Latent load: the amount of heat energy that an air conditioning system must remove from the air inside a home because of water vapor in the air; contributors to latent load include people breathing, activities such as cooking and bathing, and air infiltration from the outside; latent load is usually less in a desert location than in a coastal location. See Sensible load.
Laundry tray: a deep sink usually located in a laundry area; more commonly called a deep sink or a laundry sink.
Lavatory: a sink located in a bathroom.
Line set (refrigerant): the tubes in which refrigerant flows between the condenser and the evaporator coil in an air conditioning and heat pump; the line set consists of the liquid line and the suction line.
Lintel (angle iron): a horizontal structural component that carries the load from above. Lintels are used in masonry construction over openings such as windows and doors. Lintels are usually made from L-shaped steel, but may be made from steel reinforced concrete or wood.
Lintel (fireplace): a noncombustible material, usually iron or steel, that supports stone or masonry, and is installed above the fireplace opening.
Liquid line (tube): part of the refrigerant line set; the smaller, usually an uninsulated copper tube.
Load center: see Panel (panelboard, load center).
Load (dead): the downward force on a structure imposed by the building materials and by permanently attached fixtures such as HVAC equipment.
Load (live): the downward force on a structure imposed by occupants and their belongings. Live load does not include environmental loads such as wind and earthquakes.
Lug: a connection point where conductors are inserted and secured; examples include the connection points on panelboards for service entrance and feeder conductors, on terminal bars for neutral and EGCs, and on circuit breakers for branch circuit conductors.
Manifold (plumbing): several fittings spaced close together to which branch pipes or tubes are connected; can be a manufactured device or field-assembled; used to distribute water or gas to individual fixtures or appliances or to a group of fixtures or appliances; common uses include PEX water distribution systems and CSST gas distribution systems.
Mainfold (vent connector): a type of vent connector in which two or more vent connectors are joined together before being connected to the vent.
Mantel: the decorative facing around a firebox opening; it may consist of a horizontal shelf above the firebox opening and vertical trim at the sides of the firebox opening. The vertical trim is sometimes called the legs.
Mass wall: above-grade walls made from concrete masonry units, concrete, insulated concrete forms, masonry cavity, brick (structural, not veneer), adobe, compressed earth block, rammed earth, and solid timber logs.
Microwave oven (microwave): a cooking appliance that uses high frequency electromagnetic radiation to heat food; microwaves installed above ranges and cooktops usually have a built-in exhaust fan and light. A microwave may include a convection oven.
Offset (chimney): a change in the direction of a chimney or flue from vertical.
Ohm’s Law and Watt’s Law: expressions of the relationship between current, voltage, power, and resistance; expressed as Power = Volts X Amps and Resistance = Volts/Amps.
OPD: see Overcurrent protection device (OPD).
Outlet: a place where current is taken for use; examples include receptacles, light fixtures, and connections at electric appliances such as water heaters.
Oven: an enclosed cooking appliance intended for baking and broiling food. An oven may be mounted in a cabinet (a wall oven), or it may be part of a range.
Oven (convection): an enclosed cooking appliance intended for baking and broiling food. Cooking speed is enhanced by using a fan to circulate air inside the oven.
Overcurrent protection device (OPD): a fuse or a circuit breaker; overcurrent protection devices interrupt the flow of electricity when a set current flow is exceeded (an overload), or when a short circuit fault is detected; these devices prevent conductors and devices from overheating and causing fires.
Package (air conditioning) system: an air conditioning system or heat pump in which an evaporator coil and fan are contained in one cabinet; package units are usually located outside on the ground or on the roof, but may be located inside.
Panel (panelboard, load center): the equipment on which circuit breakers or fuses are mount-ed; panels include associated terminal bars; a panelboard is contained in an enclosure; the first and usually the largest panel is often referred to as the main panel or the service panel; there are, however, no generally accepted terms to identify panels.
Parapet wall: the section of a wall that is above the roof; often seen where a low slope roof is installed; also seen as an extension of a firewall in multi-family dwellings.
Patio: a flat outdoor recreational area adjacent to a house, usually but not always on grade.
Permeability: the ability or property of a material to resist or allow the diffusion of water vapor through the material. Permeability (perms) is expressed as a number greater than zero. For example, glass is a very low permeability material and fiberglass batt insulation is a high permeability material.
PEX: Cross-linked polyethylene, a type of water distribution pipe and water service pipe.
Pier: a column designed to support a concentrated vertical load, often installed above ground, but may be installed below ground.
Pilaster: a column that supports a concentrated vertical load. A pilaster may be on the interior or the exterior of a building, and may be taller and more decorative than a pier.
Pile: a column installed in the ground that is designed to support a concentrated vertical load. A pile is part of the foundation of a house, and is usually found where the soil has poor load-bearing capacity or is unstable.
Pipe, water service: the pipe beginning at the water meter or at the well head and ending at the main water shutoff valve.
Pipes, water distribution: pipes beginning at the main water shutoff valve that convey potable water to fixtures and appliances in the house.
Pitch (of a roof): the ratio of the total vertical height of a roof to the total horizontal distance that the roof covers. For example, if the total height of the roof from the top plate to the ridge is 12 feet and the total horizontal distance between the ridge and the edge of the eaves is 24 feet, the roof has a ½ pitch. See Slope (of a roof).
Plenum: an enclosed space through which air flows in an air conditioning system; a plenum supplies air to or receives air from branch ducts; a plenum is usually installed on the supply and return side of a furnace and air handler; a distribution plenum is a plenum that receives air from a duct and distributes the air to branch ducts.
Plumb cut: a vertical cut of a rafter at the ridge or at a hip and valley rafter; also the vertical cut of a stair stringer at its support.
Porch: an outdoor area that is attached to the house. Porches are usually covered, which is a way to distinguish a porch from a deck.
Potable water: water that is safe to drink; taste and visual appeal are not considerations.
Power: a measure of the work performed by electricity; unit of measure is the Watt.
Press-connect fitting: a proprietary method of connecting copper water supply tubes and valves that uses specially designed fittings and a crimping tool to seal the fitting; sometimes called a compression fitting.
Pump: a device that moves water through the circulation system. A pool pump consists of three parts, a basket strainer, a pump, and an electric motor that provides the mechanical energy to move the water through the pump.
Purlin: a brace installed near the midpoint of a rafter that transmits the rafter load to a load-bearing wall, and allows the rafter to span a greater distance. A purlin consists of a purlin that is at least as wide as the rafter and a purlin brace that is at least a 2×4 and bears on a load-bearing wall. Purlin braces should be installed at least every 4 feet.
Push-connect (push-fit) fitting: a proprietary method of connecting water supply tubes that allows the tube to be pushed into the fitting, securing the tube without the use of solder, washers, nuts, or similar components (e. g., Sharkbite, Probite).
Raceway: enclosed metallic or nonmetallic components designed and listed for holding conductors or cables between points in the electricity distribution system of the house; examples include various types of conduit and tubing.
Rack (racking): the distortion or movement of a structure or its components; usually caused by wind or seismic loads.
Racking (back): the horizontal placement of a masonry course inward from the course below; racking is usually done to narrow the width of a chimney above the fireplace. Contrast Corbel.
Radiant cooling: a cooling system that circulates cool liquid through pipes; pipes are often installed in the ceiling, but may be installed in the floor; these system only address the sensible load, so they are not recommended for high humidity environments; these systems are uncommon in houses, but are sometimes encountered in adobe houses. Contrast Hydronic heating.
Rafter: an inclined roof structural member that supports the roof sheathing and roof covering.
Rafter (common): an inclined roof structural member that runs between the ridge and the top plate.
Rafter (fill-in): a dimensional lumber rafter used with trusses and I-joist rafters to construct parts of the roof system where trusses and I-joists are not practical.
Rafter (hip): an ascending rafter formed at the intersection of two hip roof sections. Hip rafters may need to be supported at a ridge board by a brace to a load-bearing wall.
Rafter (jack): a rafter that runs between a hip or valley rafter and the ridge, or between two rafters. Rafters that run between a hip rafter and the ridge are hip jack rafters and rafters that run between a valley rafter and the ridge are valley jack rafters. Rafters that run between valley and hip rafters are cripple jack rafters.
Rafter (valley): a descending rafter formed by the intersection of two roofs. Valley rafters are load-bearing members. Valley rafters may need to be supported at a ridge board by a brace to a load-bearing wall.
Rafter tail: the part of a rafter that extends past the exterior wall top and forms part of the eaves.
Rafter tie: a horizontal member running between rafters on opposite sides of the roof when ceiling joists run perpendicular to the rafters. Rafter ties act like ceiling joists to keep the rafters from pushing the walls out.
Rain cap: a cover over a chimney flue that protects from water entry into the flue, often combined with a spark arrestor; rain caps are not required. See Spark arrestor.
Range: a cooking appliance that combines a cooktop and an oven into one cabinet.
Rangetop: a cooking appliance that is similar to a cooktop, but is usually heavier and larger with commercial-type features. Rangetops usually use gas as the fuel.
Receptor, shower: a term sometimes used to describe a shower pan.
Receptacle: an outlet designed to accept a plug that supplies electricity to an appliance.
Resistance: the property of a material to allow or restrict the flow of electricity; materials with low resistance are conductors and materials with high resistance are insulators; unit of measure is the Ohm.
Refrigerant (coolant): the substance that flows through an air conditioning and heat pump system liquid and suction tubes; this substances was Freon (R-22) in older systems, but because of its negative environmental effects Freon has been phased out of production; the current refrigerant is R-410A.
Register: a cover with louvers or perforations that are adjustable or with a damper that may be opened and closed; a register usually covers a supply air opening. Contrast Grille.
Retaining wall: a structure that holds soil or other fill on one side and keeps it from moving beyond the wall; usually applied to walls more than 2 feet tall.
Ridge: the top horizontal board or beam of a roof. Most roofs use a ridge board that is a place to fasten rafters and does not provide structural support. Roofs supporting vaulted ceilings should usually have a ridge beam designed to provide structural support. Ridge boards and ridge beams should be deep enough so that the entire plumb cut of the rafter bears on the ridge.
Riser: (1) a vertical plumbing pipe that extends one story or more; (2) a vertical plumbing pipe that connects a valve to a water faucet. Examples: a shower riser connects the shower valve to the arm that supports the shower spray head, a fixture riser connects the shutoff valves to the faucet.
Rotate (rotation): a condition where a structural member moves laterally from its normal position relative to vertical, such as when a foundation wall moves inward due to pressure from soil.
Rumford fireplace: a fireplace with a tall opening and a shallow hearth that is designed to reflect more heat into the room; these fireplaces are most likely to be found in houses built in the first half of the 19th century, but may be found in any house; these fireplaces have different hearth and firebox dimensions compared to traditional masonry fireplaces.
R-value: the ability or property of a material to slow heat transfer. A higher R-value number equals a higher ability to slow heat transfer. R-value is expressed as a number greater than zero. R-value is used to compare the insulation value of materials.
Schedule 40 and Schedule 80 pipe: this refers to the thickness of pipe walls. Schedule 40 pipe has a thinner wall than Schedule 80 pipe. Schedule 40 pipe is more commonly used. Both have the same outside diameter; Schedule 80 pipe has a smaller internal diameter.
Schrader valves: valves at a condenser unit where technicians attach a gauge set to measure pressures in the refrigerant lines; similar to valves on automobile tires.
Seasonal energy efficiency ratio (SEER): see SEER.
Seat cut: the horizontal rafter cut at a wall top or a valley. Also the horizontal cut at the end of a stairway stringer.
SEER (seasonal energy efficiency ratio): a measure of the efficiency of a cooling system and a measure of the efficiency of a heat pump in cooling mode; obtained by dividing the cooling output of a system over a cooling season by the electric energy used; the minimum allowed SEER is currently 14 for most of the United States, and the maximum available is around 20; older systems may have SEERs of 10 or less. These ratings may be different in some states.
Sensible load: the amount of heat energy that an air conditioning system must remove from the air inside a home because of the temperature of the air, contributors to sensible load include heat gain through walls and ceilings, solar heat gain through windows, equipment operation such as ovens and lights; sensible load is usually greater in a southern location than in a northern location. Contrast Latent load.
Septic tank: a vessel that receives sewage from the building sewer pipe, allows the solids to settle and decompose, and allows the liquid to drain off into drain (leach) field. Septic tanks are usually made from concrete, but some are made from corrosion-resistant metal and from plastic.
Service drop and service lateral: the conductors between the transformer belonging to the utility and the house; a service drop is above-ground and a service lateral is below ground.
Service entrance conductors: the conductors between the service drop or the service lateral and the service equipment.
Service equipment: the circuit breakers, switches, or fuses that shut off power to the house; all power should be shut off using six or fewer circuit breakers, switches, or fuses; often called the main shutoff or main disconnect.
Service point: the place where the service drop or service lateral conductors end and the house service entrance conductors begin; this is usually at the drip loops for service drops; the service point for service laterals is more difficult to distinguish, but is often at the meter.
Sewage: liquid and solids in drainage or sewer pipes that contains animal or vegetable matter or any other impurities.
Sewage disposal system, (individual/private): an on-site system that disposes of sewage from a house. A modern system usually consists of a septic tank and drain field, but mechanical systems (such as mound systems) are also available. See Septic tank.
Sewage ejector pump: a pump that drains a sump filled with sewage and pumps the sewage into the building drain. Contrast Sump pump.
Sewer (building): a pipe that conveys sewage from the building drain to the public sewer or private sewage disposal system; begins 30 inches beyond the house exterior walls where it connects to the building drain; sometimes called the sewer lateral. See Building drain.
Sewer (public): a system that conveys sewage from houses to a central treatment plant, usually owned and operated by a local government.
Shear: the deformation of a structural member (such as a beam) in which parallel planes slide relative to each other.
Shear wall: a wall designed not to change shape (rack) under loads such as wind and earth-quake; also called a braced wall. See Rack (racking).
Sheathing: (1) the material covering the top of the rafters; (2) the material covering the top of the floor joists, also called the subfloor; (3) the material covering the exterior wall structural components.
Single phase electrical service: electrical service consisting of two energized 120 volt conductors and one grounded conductor; this is by far the most common residential electrical service.
Short circuit: this event occurs when current flows between conductors in an unintended manner, such as between the hot and neutral conductors.
Slip joint: a plumbing drainage connection, usually at a sink trap, that is secured by a gasket under a nut, and can be removed by hand or with a tool such as pliers; slip joints must be accessible.
Slope (of a roof): the number of inches that a roof increases in height (rise) for every 12 inches of horizontal distance (run). The slope is usually expressed as 4/12 or 4:12 where the first number is the rise and the second number is always 12, the run. The terms pitch and slope are sometimes used as synonyms. This is not technically correct. See Pitch (of a roof).
Smoke chamber: the area between a masonry fireplace throat and the flue; it helps direct the combustion gasses toward the flue.
Soffit (eaves): the horizontal trim that covers the rafters, usually part of the cornice.
Solar heat gain coefficient (SHGC): a measure of the amount of solar radiation that passes through a window. A lower SHGC means that less solar radiation passes through a window.
Soldering (sweating): a method of joining metal pipe and fittings (usually copper) by fusing them together with an alloy made mostly from tin at a temperature below 800° F. See Brazing (silver soldering).
Span: the horizontal distance between structural supports. Overspan is an informal term that refers to a joist or a rafter that is longer than allowed between structural supports. Rafter span is measured horizontally, not along the length of the rafter.
Spark arrestor: a screen around the perimeter of a chimney flue termination that helps keep hot embers from escaping and causing a fire, often combined with a rain cap; spark arrestors are required in some areas that are prone to wildfires. See Rain cap.
Spigot: (1) the unenlarged end of a pipe that is inserted into a hub; (2) a hose bibb.
Split (air conditioning) system: an air conditioning system or heat pump in which an evaporator coil and fan are located inside, and a condenser unit is located outside; this is the most common type of air conditioning system.
Square (squared): a condition that occurs when intersecting walls form a 90° angle. Squared walls can be determined by measuring and applying the formula A2 + B2 = C2 to the right triangle formed by the walls.
Stack: a vertical drainage pipe or vent pipe that extends more than one story.
Stack vent: an extension of a drainage stack that serves as the vent for the stack and fixtures connected to the stack.
Stack effect: the tendency of warmer, more boyant air to rise by displacing cooler air. The stack effect allows natural draft to occur in vents and chimneys and affects air flows inside buildings.
Stack head (HVAC distribution system): sheet metal formed into a rectangle or circle that connects a stack duct to a grille or a register. See Boot and Duct (stack).
Standpipe: (1) a pipe used to receive liquid waste from a fixture or appliance, usually a clothes washing machine; (2) a system of pipes and fire department connections intended to provide water for fighting fires; fire fighting standpipes are found in commercial and industrial buildings.
Stoop: a small platform that serves as a landing on the exterior side of a door.
Stove: a device that uses an energy source to produce heat. In modern usage, the term stove sometimes refers to a range when used to describe a cooking appliance. The term is also used to describe a space heating appliance such as a wood-burning stove.
Street bend (elbow): a bend with a hub on one end and a spigot on the other end.
Stud: (1) a grade of lumber used in wall construction rated below #2 grade and approximately equal to #3 grade; (2) a vertical structural member in a wall.
Stud (cripple): a less than full height vertical structural member usually found under windows and in partial height walls.
Stud (jack): a less than full height vertical structural member placed under a header to provide bearing support for the header.
Stud (king): a full height vertical structural member placed on the sides of a header.
Subdrain: a drain pipe located below the building drain; usually occurs when basement plumbing is located below the building drain; the sewage is pumped up to the building drain by a sewage ejector pump. See Sewage ejector pump.
Subpanel: a panelboard that receives power from an upstream panelboard, usually the main panelboard; also called a downstream or a distribution panel; however, there are no generally accepted terms to identify panels.
Suction line (tube): part of the refrigerant line set; the larger, insulated copper tube. See Line set (refrigerant).
Sump (crock): a vessel or pit that receives sewage, waste, storm water, or ground water from around the house foundation; a sump is installed below a level where it could drain by gravity, therefore it must be drained by a pump.
Sump pump: a pump that drains a sump filled by storm water or by ground water from around the house foundation. Contrast Sewage ejector pump.
Surcharge (earth): earth located above the top of a retaining wall.
Sweep: a DWV fitting with a 90° direction change; the term is more commonly used when referring to cast iron DWV fittings. A sweep may be a long sweep or a short sweep. A long sweep has a larger curve radius than a short sweep. A long sweep may be used in all direction changes whereas there are limits on how a short sweep may be used.
Swale: a depression or channel in the soil intended to direct water in a particular direction.
Tabs (twistouts): rectangular metal pieces on the dead front cover that are removed before installing a circuit breaker; tabs must be replaced by a filler plate if a tab has been removed and no circuit breakers is installed. See Knockouts.
Tailpiece (also tail piece): a vertical pipe installed between a sink outlet and trap, or between a sink outlet and a fitting that runs to a trap.
Tension force (load): The force that pulls or stretches a structural member. A beam under a vertical load is under tension on the bottom. Contrast Compression.
Terminal bars: metal bars associated with a panelboard on which neutral and equipment grounding conductors are mounted; called a neutral bar when neutral conductors or neutral and equipment grounding conductors are connected; called a ground bar if only equipment grounding conductors are connected.
Thermal expansion: the tendency of water to expand in volume when heated; 50 gallons can expand by ½ gallon or more when heated to about 115° Fahrenheit.
Thermal expansion tank: an enclosed vessel containing air that absorbs the water which has expanded when heated in a storage-type water heater or a hot water boiler.
Three phase electrical service: electrical service consisting of three energized conductors and one grounded conductor; this service type is mostly for commercial and industrial buildings.
Throat: the opening between a fireplace hearth and the smoke chamber. See Damper (fire-place).
Tieback: a device used to resist the lateral force on a retaining wall. See Deadman.
Toilet (commode, water closet, WC): a plumbing fixture that receives human excrement and discharges it into the drain pipes.
Ton (of refrigeration): a measure of the size or cooling capacity of an air conditioning system equal to 12,000 Btu per hour; a 3 ton air conditioning system has a cooling capacity of 36,000 Btu. See Brittish thermal unit (Btu).
Townhouse: a single family attached dwelling with all of the following: (1) three or more dwellings in one building, (2) dwelling extends from the foundation to the roof, (3) a yard or public way on at least two sides. A townhouse is a type of building, not a form of real property ownership.
Trap: a component that maintains a water seal to prevent sewer gas from entering the house; a trap may be a separate fitting or it may be integrated into a fixture such as a toilet.
Trap arm: see Fixture drain.
Trap primer: a device or pipe that conveys water to a trap to maintain the water seal; usually associated with floor drains because these fixtures often do not receive enough water to maintain the trap water seal.
Urea-Formaldehyde Foam (UFFI): a type of spray foam insulation.
U-value (factor): the ability or property of a material to allow heat transfer. U-value is the inverse of R-value (R-value = 1/U-value). U-value is expressed as a number greater than zero. A larger number equals a higher rate of heat transfer and a lower R-value. U-value is primarily used in residential construction to compare the thermal performance of fenestration. For example, metal such as aluminum has a high U-value; this is why higher quality aluminum windows have a thermal break in the frame to slow heat transfer.
Valve: a device used to activate and deactivate the flow of a liquid or gas; some valves can control the flow rate of the liquid or gas.
Valve, full open (full flow): a valve that has minimal resistance to water flow when open; ball and gate valves are the most common examples in houses.
Valve, quick closing: a valve that closes rapidly to stop the flow of water; typically found on clothes washing and dishwashing machines. Quick closing valves can cause water hammer.
Valve, service (main shutoff): the valve that activates and deactivates the water flow to the water distribution pipes.
Vapor barrier: a technically questionable term often used when the term vapor retarder is intended. Class I vapor retarders are effectively vapor barriers, but the term vapor retarder is preferred.
Vapor diffusion: the process by which water vapor passes through a permeable material from an area of greater vapor pressure to an area of lower vapor pressure.
Vapor drive: a condition that occurs when heat and vapor pressure cause increased vapor diffusion. One example is when water vapor diffuses through permeable building materials from heated interior areas in the winter. Another example is when solar radiation heats wet bricks forcing water vapor through permeable building materials in the summer. Vapor drive is usually less of a factor than vapor flow by convection through openings in the building envelope.
Vapor retarder: a material that restricts the flow of water vapor. A Class I vapor retarder is rated at 0.1 perms or less. Polyethylene sheeting is an example. A Class II vapor retarder is rated at between 0.1 and 1.0 perms. Kraft paper used as the facing on some batt insulation is an example. A Class III vapor retarder is rated at between 1.0 and 10.0 perms. Latex and oil paints are examples.
Veneer: a decorative surface applied over the exterior walls of a house. The term is usually applied to wall coverings such as brick and natural stone.
Vent, branch: a vent pipe that connects two or more individual vents to a vent stack or stack vent.
Vent (combustion): the final vertical component in a vent system; this term most accurately describes manufactured products such as metal pipes.
Vent connector: a component that conducts combustion products from a fuel-burning appliance to a vent; vent connectors are single-wall or double-wall metal pipes.
Vent, pipe (plumbing): a pipe that conveys air.
Vent, plumbing: a pipe system that conveys air to help equalize pressure in the drain and waste pipes. The vent system protects the trap water seal from siphoning and blowout.
Vent stack: a vertical plumbing vent that extends more than one story.
Vent system: a passageway that conducts combustion products from a fuel-burning appliance to a point outside the house; the vent system begins at the appliance draft hood or flue collar and ends outside the house; the vent system consists of a vent or chimney and a vent connector, if one is used.
Ventilation (building): the process of supplying outside air to a house or removing inside air from a house by natural or mechanical means; ventilation can be random and uncontrolled (air leaks), or it can be designed and controlled (outside air ducts, heat recovery ventilators, energy recovery ventilators).
Vertical pipe (plumbing): a pipe that is 45° or more relative to horizontal.
Voltage: the pressure of electricity in a circuit; similar to water pressure in a pipe; unit of measure is the Volt.
WC: see Toilet.
Walkway: a private path on private property that is intended for pedestrian use.
Wall covering (cladding): a non-load-bearing material or assembly that is applied over the exterior walls of a house.
Waste: liquid in drainage pipes that does not contain feces or urine. Waste pipe: a drainage pipe that does not convey feces or urine.
Water closet (WC): see Toilet.
Water hammer: a thumping or banging noise caused by the sudden stopping of water flow. Water hammer can damage pipes and fixtures.
Water hammer arrestor: a device that absorbs the hydraulic shock caused by the sudden stopping of water flow, usually installed near clothes washing machine and dishwasher water supply connections.
Water flow rate: the amount of water that comes from a plumbing fixture, usually measured in gallons per minute. Water flow is a function of the pipe type, pipe internal diameter, pipe length, and the number of elbows between the water source and the fixture. Increasing the water pressure past the point where a pipe is full will not increase the water flow rate, but it may burst the pipe.
Water pressure: the amount of force that water exerts on the walls of a pipe, usually expressed in pounds per square inch (psi). The minimum water pressure is 40 psi and the maximum pressure is 80 psi. Water pressure exceeding 80 psi should be reduced by installing a water pressure regulator in the water service pipe.
Water pressure regulator: a usually bell-shaped device installed on the water service pipe near where the pipe enters the house and downstream from the water shutoff valve of the house; it is adjustable and reduces water pressure.
Water (weather)-resistive barrier (WRB): a material that resists penetration of liquid water; usually describes materials such as asphalt-impregnated building paper (e. g., #15 felt) and house wraps.
Watt’s Law: see Ohm’s Law and Watt’s Law. WC: see Toilet.
Wiring methods: cables and raceways approved for distributing electricity from the service point to panelboards and outlets; examples include armored cable, nonmetallic sheathed cable, and various types of conduit and tubing.
WRB: see Water (weather)-resistive barrier (WRB).
Wythe (withe): (1) a course of masonry (usually brick) that separates flues in a masonry chimney; (2) a vertical masonry wall that is one masonry unit thick. A typical brick veneer wall is one wythe thick.
XPS: see Extruded Polystyrene (XPS).