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Glossary of Home Inspection Report Terms

Having trouble understanding a term in your home inspection report? These are all of the terms we use in our home inspection reports so you can better understand them. In addition, we have linked to helpful articles that explain the topics in greater detail. The keywords are organized in alphabetical order so you can quickly find the term you are looking for.


Abbreviation for air conditioner and air conditioning.


Acronym for acrylonitrile butadiene styrene; rigid black plastic pipe used only for drain lines.


Acronym for Arc-fault circuit interrupter: A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected. Learn more.


Corrugated Stainless Steel Tubing (CSST) is a type of conduit used for natural gas heating in homes. It was introduced in the United States in 1988. CSST consists of a continuous, flexible stainless-steel pipe with an exterior PVC covering. The piping is produced in coils that are air-tested for leaks.

Bus Bar

Electrical distribution made of conductive metal that both ground and conduct electricity.

Back-Flow Device

A faucet aerator (or tap aerator) is often found at the tip of modern indoor water faucets. Aerators can simply be screwed onto the faucet head, creating a non-splashing stream and often delivering a mixture of water and air.

Automatic Pressure Reverse

Safety feature to reverse the garage door when an object is encountered.

Air Gap

Air gap (drainage): The unobstructed vertical distance through the free atmosphere between the outlet of the waste pipe and the flood-level rim of the receptacle into which the waste pipe is discharged.


Copper (wiring).


Cellulose insulation: Ground-up newspaper that is treated with fire-retardant.

Cloth Wiring

Cloth wiring refers to electrical wiring that is insulated with a cloth. This type of wiring was common in the 1950s-1970s before plastic insulation became the standard. Today, cloth wiring is considered a fire hazard.

Combustion Air

The ductwork installed to bring fresh outside air to the furnace and/or hot water heater. Normally, two separate supplies of air are brought in: one high and one low.

Condensate Line

A plumbing line used to route moisture collected by the HVAC system that exits at the exterior of the building.




In modern plumbing, a drain-waste-vent (or DWV) is part of a system that removes sewage and greywater from a building and regulates air pressure in the waste-system pipes, facilitating flow. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped section of pipe that always contains water. All fixtures must contain traps to prevent sewer gases from leaking into the house. Through traps, all fixtures are connected to waste lines, which in turn take the waste to a soil stack, or soil vent pipe. At the building drain system’s lowest point, the drain-waste vent is attached, and rises (usually inside a wall) to and out of the roof. Waste is removed from the building through the building drain and taken to a sewage line, which leads to a septic system or a public sewer.

Electrical Disconnect

An electrical device used to ensure that the system can be turned on and off for servicing.


Ducts are conduits or passages used in heating, ventilation, and air conditioning to deliver and remove air.

Drip Loop

The whole purpose is to let water pile up at the bottom and drip off. Learn More.

Drip Edge

Drip edge is a metal flashing applied to the edges of a roof deck before the roofing material is applied. The metal may be galvanized steel, aluminum (painted or not), copper and possibly others.

Drain Pan

A means to collect condensate and/or water and directing it to the exterior of the building.

Double Tap

A double tap occurs when two conductors are connected under one screw inside a panel board. Most circuit breakers do not support double tapping, although some manufacturers, such as like Cutler Hammer, make hardware specially designed for this purpose.

Double tapping is a defect when it is used on incompatible devices. If the conductors come loose, they cause overheating and electrical arcing, and the risk of fire is also present. A double tap can be accommodated by installing a new circuit board compatible with double tapping. It is also possible to add another circuit breaker or install a tandem breaker to the existing breaker box.

Learn More.


Exterior insulation and finishing system (EIFS) is a type of building exterior wall cladding system that provides exterior walls with an insulated finished surface and waterproofing in an integrated composite material system. For more information please visit


The eaves are the edges of the roof which overhang the face of a wall and, normally, project beyond the side of a building.

Electronic Eye

The photo-eye consists of two sensors, one on either side of the garage door, about 6- inches above the floor.

Expansion Tank

An expansion tank or expansion vessel is a small tank used to protect closed (not open to atmospheric pressure) water heating systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibility cushions shock caused by water hammer and absorbs excess water pressure caused by thermal expansion.


A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test.

Package Unit

A package unit is the all-in-one heating and cooling system for homes that don’t have a lot of room indoors for either a furnace and coil or an air handler. Package units will contain all of their parts in one outdoor unit that sits on either the roof or to the side of a building.


PEX stands for cross-linked polyethylene. It is a type of plastic tubing made from high-density polyethylene. Learn More.

Knob and Tube

Knob-and-tube wiring was an early standardized method of electrical wiring in buildings from about 1880 to the 1940s. The system is considered obsolete and can be a safety hazard. Learn More.


A framework, typically consisting of rafters, posts, and struts, supporting a roof, floor, or other structure.


Ice or frost build-up due lack of system airflow.


What is the purpose of a high loop? A high loop prevents wastewater back-flowing from your sink to your dishwasher. Learn More.

Heat Pump

An HVAC system that transfers hot and cold air into the structure by using thermal energy.


Heat recovery ventilation, also known as HRV, mechanical ventilation heat recovery, or MVHR, is an energy recovery ventilation system using equipment known as a heat recovery ventilator, heat exchanger, air exchanger, or air-to-air heat exchanger which employs a counter-flow heat exchanger (countercurrent heat exchange) between the inbound and outbound air flow.[1] HRV provides fresh air and improved climate control, while also saving energy by reducing heating (and cooling) requirements.

Hardie Board

Hardie Board siding is a durable siding product that is made of cement, sand, and cellulose fibers.


The heating, ventilation, and cooling system(s).


The early stage of mold-like bacteria and/or fungi.


A special device that is intended for the protection of personnel by de-energizing a circuit, capable of opening the circuit when even a small amount of current is flowing through the grounding system. Learn More.


Modern construction standards require “fire separation” (sometimes called a “firewall”) in an attached garage to separate the garage from living space and/or an attic.


This foundation involves wood posts or concrete piers set into the ground that bear the weight of the building.


WDO stands for “wood-destroying organism.”

Vapor Barrier

A vapor barrier slows or prevents the evaporation of ground moisture into the crawl space air.

Valley Flashing

Sheet metal or other material used to line a valley in a roof to direct rainwater off the roof.


The internal angle formed by the junction of two sloping sides of a roof.

Tension Spring(s)

Your windows use spring balances to help you raise and lower the window sash and keep the sash in a raised position.

Temperature Differential

The temperature differential is just a fancy way of saying that we measure the temperature of the air going into the return vs the measure of the air as it comes out at the registers.


Predominantly constructed masonry footings with masonry walls, they rise above the ground level to provide a raised platform for placing the building sub-floor.

Sheathed Non-Metallic

The non-metallic (NM) designation refers to the outer sheathing that bundles individual wires together like a cable.

Secondary Float Switch

A condensate overflow switch that detects rising water in the HVAC system and shut off the system to prevent overflow and water damage.

Roof Flashing

Roof flashing is a thin material, usually galvanized steel, that professional roofers use to direct water away from critical areas of the roof, wherever the roof plane meets a vertical surface like a wall or a dormer.

Refrigerant Dryer

A mechanical device used to remove condensation from the refrigerant line.


Air-distribution box attached directly to the supply and return side of the air handler.