All Glossary Terms — A thru A
All Home Inspection Glossary terms beginning with 'A'
With this post, we complete the first stage of the Home Inspector’s Glossary: eight individual entries devoted entirely to terms beginning with the letter A.
Each post offered a mix of common and overlooked words, all drawn from the language of Home Inspections, Standards, and the Systems that connect them.
This post brings all terms beginning with the letter ‘A’ together in one place — alphabetically arranged and ready for reference.
A/C (Alternating Current)
The standard form of electricity used in residential and commercial buildings throughout North America. In an alternating current system, the flow of electricity reverses direction many times per second — typically 60 times per second (60 Hz) in the U.S. All typical household power — including lighting, outlets, and appliances — runs on A/C.
This is distinct from D/C (Direct Current), which flows in one direction and is commonly found in batteries, electronics, and some solar system components.
A/C
An abbreviation for air conditioner or air conditioning.
Air Conditioner Condenser (Outdoor Unit)
The outdoor component of a split-system air conditioner. It includes a compressor, a fan, a condenser coil, and other components that work together to transfer heat from the indoor air to the outdoors. The refrigerant releases heat in this unit and returns to the indoor evaporator coil to absorb more heat. Often located near the exterior wall of the home, this is commonly referred to as the “AC unit” or “outside unit.”
A/C Disconnect
A locally mounted electrical shutoff device installed near an exterior air conditioning or heat pump unit. It allows technicians to safely service the unit by interrupting power without accessing the main electrical panel. The disconnect may take the form of a pull-out block, a breaker-style switch, or a lever-operated mechanism, and may or may not contain fuses depending on the system design. A disconnect is required by electrical code for all outdoor HVAC equipment, including both split system air conditioners and heat pumps.
Inspector Note: Home inspectors should verify that a permanent, readily accessible disconnect is installed near the outdoor unit, typically within sight and not more than 6 feet away. Missing or damaged disconnects are a defect. Inspectors are not required to open or test the disconnect itself but should note safety concerns such as corrosion, exposed wiring, improper mounting, or blocked access.
ABS (Acrylonitrile Butadiene Styrene)
A rigid black plastic pipe most commonly used for drain, waste, and vent (DWV) systems in residential and commercial plumbing. It is also found in certain exterior drainage and underground applications, such as rigid perforated drain tile. ABS is lightweight, impact-resistant, and typically joined with solvent cement.
Absolute Humidity
The total mass of water vapor present in a given volume of air, expressed in grains per cubic foot or grams per cubic meter. In water damage restoration, absolute humidity is critical for tracking moisture removal and sizing drying equipment. It provides a direct measure of moisture load, unlike relative humidity, which fluctuates with temperature.
While absolute humidity is essential in restoration, HVAC design, and advanced indoor air quality assessments, it is not typically measured or referenced during a standard home inspection. Home inspectors more often rely on relative humidity, which reflects the percentage of moisture in the air relative to its temperature.
Access Panel
A removable or hinged cover that allows access to concealed areas of a structure for the inspection, maintenance, or repair of components — most commonly plumbing, HVAC, or hydronic systems. These panels are typically found in walls, ceilings, floors, or cabinetry. A missing or sealed panel may limit the inspector’s ability to observe components such as a whirlpool tub motor or a shutoff valve.
Inspector Note: Electrical components are generally not intended to be concealed behind building finishes; access to electrical equipment is typically integrated into the equipment itself.
Accessible (Inspector Accessibility)
A condition or location is considered accessible when it can be safely and reasonably reached, entered, or viewed by the inspector without the need to: climb over or move obstacles, including personal property, stored items, or debris; use tools or specialized equipment beyond standard inspection tools (e.g., a ladder, a flashlight, and a screwdriver); expose oneself to risk of injury due to unstable surfaces, unsafe ladders, deteriorated structures, electrical hazards, or the presence of aggressive animals; remove covers, panels, hatches, or fasteners not intended for user removal unless explicitly required by the Standard of Practice.
Inspector Note: The term does not require accessibility for individuals with disabilities, nor does it imply compliance with ADA standards. Accessibility is determined at the time of inspection and may vary based on weather, site conditions, and safety considerations.
Accessible (Code-Specific Accessibility to Systems and Components)
A condition in which systems, equipment, or components are installed so they can be safely and readily reached, operated, serviced, or maintained as required by building codes, safety standards, or manufacturer instructions. Code-specific accessibility typically addresses issues such as clearance distances, unobstructed working spaces, reachable operating controls, and provisions for safe serviceability.
Examples of code-specific accessibility include:
Minimum clear working space in front of electrical panels (e.g., 30" wide by 36" deep).
Service access to HVAC equipment, such as furnaces and air handlers.
Readily reachable locations for circuit breakers, gas shutoff valves, and water shutoff valves.
Accessibility of fire suppression devices and life-safety alarms.
Inspector Note: Code-specific accessibility focuses on safe operation, servicing, and emergency use. It differs from inspector accessibility, which addresses whether the inspector can reasonably and safely access an area or component at the time of the inspection.
Editor’s Note: This post was updated after publication to clarify distinctions between inspector accessibility and code-required accessibility, based on valuable reader feedback.
Accordion Door
A lightweight folding door made of multiple narrow panels connected by hinges, designed to fold repeatedly in a flexible pattern similar to an accordion. Accordion doors are commonly used as room dividers, utility closet covers, or in spaces where a wide opening must be enclosed without the clearance needed for swinging doors.
Inspector Note: Home inspectors should check accordion doors for smooth operation, secure attachment at the track, torn or missing panels, and broken hinges. Accordion doors are typically less durable than bifold or conventional doors and may sag, jam, or separate with age or heavy use.
Acre
A unit of land area equal to 43,560 square feet. While most home inspections focus on the structure and nearby features, understanding lot size may help inspectors anticipate site conditions — especially when wells, septic systems, or outbuildings are located at a distance from the home.
Acrylic
A type of durable plastic (PMMA) used in both clear and molded forms.
Transparent acrylic—sold under brand names like Plexiglas or Lucite—is often used for windows, skylights, and light lenses as a lightweight, shatter-resistant alternative to glass. Opaque or colored acrylic is vacuum-formed to create the visible surfaces of bathtubs, shower bases, whirlpool tubs, and similar fixtures. Inspectors may encounter issues such as cracking, yellowing, flexing, or surface delamination.
Activate
To initiate the operation of a system, appliance, or component using normal operating controls.
This includes switches, thermostats, or valves. Home inspectors may activate systems only when it can be done safely and without the use of specialized procedures, tools, or equipment. Systems that are shut down, decommissioned, or require actions beyond standard controls (such as lighting a pilot or opening a gas valve) are typically not activated during a standard home inspection.
A/C Wiring (Alternating Current)
The type of electrical wiring found in most homes, where the flow of electricity changes direction many times per second.
This kind of power makes it easier to deliver electricity over long distances and is used in nearly all wall outlets and light switches.
Adapter (or Adaptor)
A fitting or device used to connect different sizes, types, or materials in mechanical, plumbing, or electrical systems.
Adapters may be found in piping transitions (e.g., ABS to cast iron), electrical conduit connections (e.g., EMT to FMC), or HVAC ductwork and flexible hose connections. Inspectors often encounter adapters in repair work or upgrades and should look for signs of improper installation, incompatible materials, missing clamps, or unsupported transitions.
Adhesion
The ability of a coating, sealant, or adhesive to bond to the surface or material to which it is applied.
Poor adhesion may result in peeling paint, separated caulking, disbonded tapes, or components no longer held in place—such as trim, panels, or stair treads. While inspectors may not use the word “adhesion” in reports, they often describe the effects of failed adhesion when noting movement, gaps, or detached materials.
Adhesive
A substance used to bond materials together, often in place of mechanical fasteners.
Adhesives may be liquid, paste, or tape-based, and are used in a variety of applications including flooring, wall panels, roofing membranes, vapor barriers, and tile installations. While typically hidden from view, adhesive failure can result in lifting or curling of flooring or roofing materials, delamination of panels, gaps, bubbles, or loose edges in applied surfaces. Adhesive selection and installation method vary based on material type, surface condition, and temperature or humidity exposure.
See also: Caulk, Sealant, Fastener, Laminate, Flooring, Membrane.
Adhesive Failure
The loss of bond between a material and the surface it was applied to.
Often the result of improper preparation, movement, moisture, or aging. Adhesive failure may appear as peeling, lifting, or separation of coatings, sealants, trim, or panels.
This is essentially the opposite of adhesion.
Adjustable Steel Column
A load-bearing vertical support consisting of a telescoping steel tube with a threaded adjustment mechanism.
Commonly used to provide temporary or permanent support for beams and floor structures in basements, crawlspaces, or during structural repairs.
While adjustable steel columns are often mistakenly referred to as "Lally columns," a true Lally column is a fixed-length, concrete-filled steel tube originally manufactured under the Lally name. Lally columns are not adjustable.
Inspector Note: Most adjustable steel columns are not rated for permanent installation unless specifically labeled for such use. Posts designed only for temporary support are typically labeled accordingly. Home inspectors are trained to identify the presence or absence of proper labeling but are not responsible for determining whether a column is suitable for permanent structural support.
See also: Beam, Post.
Adversely Affected
(As found in the ASHI Standard of Practice, 2014 Edition.)
Constituting, contributing to, or affirmatively tending to cause a negative or undesirable impact on a system or component’s ability to perform its intended function or to continue its expected service life.
Aerator
A small fitting attached to the end of a faucet spout that mixes air into the water stream.
Aerators help reduce splashing, improve water flow, and may include a screen to catch debris or reduce sediment.
AFCI (Arc-Fault Circuit Interrupter)
A type of circuit breaker or receptacle designed to detect and interrupt dangerous electrical arcing conditions, which can lead to fires. AFCIs are intended to protect against electrical faults caused by damaged wiring, loose connections, or deteriorated insulation — especially in hidden areas of a home.
Recent editions of the National Electrical Code (NEC) have expanded the list of rooms requiring AFCI protection. However, local jurisdictions vary in adoption and enforcement, so inspectors should stay informed about regional standards.
Related Terms: Circuit Breaker, Receptacle, GFCI, Overcurrent Protection Device, Electrical System
Aggregate
Granular material such as crushed stone, slag, or gravel used in construction for strength, stability, or drainage. Aggregates are common in concrete, asphalt, drainage systems, and roofing. In window wells, they help prevent water accumulation around foundations.
Inspectors often encounter aggregates in roof ballast layers, drainage applications, and landscaping around the home.
Agreement
A written document outlining the terms, conditions, and scope of a home inspection, signed by both the client and the inspector. It typically includes fees, services, exclusions, limitations, and legal disclaimers.
Inspector Note: An agreement does not authorize the inspection — it defines the inspector-client relationship. A signed agreement before the inspection is both best practice and a key risk management tool.
Related Terms: Contract, Scope, Limitation, Exclusion, Disclaimer
AHJ (Authority Having Jurisdiction)
The organization, office, or individual responsible for enforcing codes and standards in a given area. Typically, this could be a building department, electrical inspector, or fire marshal. AHJs have legal authority to approve or reject installations and require corrective actions, even if interpretations vary between jurisdictions.
Inspectors must be aware of local AHJ practices and interpretations of risk, code, or precedent.
Air Balancing
The process of adjusting a heating and cooling (air conditioning) system based on a forced-air furnace and/or central air conditioning to ensure that air is distributed evenly and efficiently throughout a building. Air balancing involves measuring airflow at supply registers and modifying dampers, fan speeds, or duct configurations to achieve proper volume. The goal is to maintain consistent temperatures and comfort levels in all rooms while optimizing system performance and energy efficiency.
Inspector Note: Home inspectors do not perform air balancing but may observe signs of imbalance such as uneven temperatures between rooms, unusually noisy vents, or closed/blocked registers. Poor air balancing may also contribute to indoor air quality issues such as poor humidity and temperature control.
Related Terms: HVAC System, Airflow, Supply Air, Return Air, Static Pressure, Zoning (HVAC)
Air Barrier
A continuous system of materials designed to limit or prevent uncontrolled airflow through a building envelope. Air barriers help improve energy efficiency, reduce moisture migration, and maintain indoor comfort.
Air barriers differ from vapor barriers: air barriers control airflow, while vapor barriers control vapor diffusion.
Examples: Housewraps (Tyvek®), spray-applied sealants, rigid foam sheathing, taped drywall seams.
Related Terms: Air Leakage, Air Infiltration, Vapor Barrier, Building Envelope, Weather Barrier
Air Chamber
A short, vertical air-filled pipe installed in older plumbing systems to help prevent water hammer — sudden pressure surges when water flow is quickly shut off. Modern plumbing codes now favor mechanical water hammer arrestors because traditional air chambers lose effectiveness over time.
Related Terms: Water Hammer Arrestor
Air Duct
A pipe or enclosed passage made of sheet metal, flexible plastic, or fiberglass board that carries heated or cooled air through a forced-air HVAC system. Inspectors should check for disconnected sections, crushed ducts, or missing insulation — all of which can impair system efficiency.
Air Filter
A device installed in an HVAC system to capture airborne particles such as dust, pollen, and lint. Common residential filters include disposable pleated filters and fiberglass throwaway filters. Filter performance is rated using the MERV (Minimum Efficiency Reporting Value) scale.
Inspector Note: Dirty or missing filters can impair HVAC performance and degrade indoor air quality. Filter compartments are typically at the return plenum, air handler, or within wall/ceiling grilles.
Related Terms: MERV Rating, HEPA Filter, Electrostatic Filter, Indoor Air Quality, Air Handler, Return Air
Air Flow
The movement of air through ductwork and registers in a forced-air heating or cooling system. Airflow is typically measured in cubic feet per minute (CFM) and is critical to the proper operation of a central HVAC system. Factors affecting airflow include duct sizing, filter condition, fan speed, damper position, and the overall design of the distribution system.
Inspector Note: Inspectors do not measure airflow as part of a standard home inspection but may note symptoms of restricted airflow, such as weak output from registers, clogged filters, or visibly undersized return ducts. Consistent airflow is essential to occupant comfort and system efficiency.
Related Terms: HVAC System, Air Balancing, Supply Register, Return Register, CFM, Ductwork, Static Pressure
Air Gap
A deliberate, unobstructed space between two components or systems, designed to prevent physical contact, facilitate drainage, ventilation, or prevent contamination.
Common uses include:
Plumbing: A vertical space between a fixture outlet and the flood level rim of a plumbing fixture (such as a sink or dishwasher drain) to prevent backflow into the potable water supply.
Wall Systems: A designed gap between exterior cladding (such as brick veneer) and the wall sheathing to allow drainage and ventilation.
Roof Assemblies: Ventilation spaces beneath roof sheathing or within cathedral ceiling assemblies to prevent moisture accumulation.
Rainscreens and Siding Systems: Intentional air gaps behind cladding to promote drainage and drying.
Windows: The sealed air or gas-filled space between panes in an insulated glazing unit (IGU), though typically called an air space.
Inspector Note: Inspectors should distinguish between air gaps required by design or code and gaps caused by construction defects or damage.
Related Terms: Backflow Prevention, Drainage Plane, Ventilation, Rainscreen
Air Balancing
The process of adjusting airflow within a ducted forced-air heating, ventilation, and air conditioning (HVAC) system to achieve uniform distribution of air to all conditioned spaces.
Proper air balancing improves occupant comfort, system efficiency, and can help prevent issues such as uneven temperatures, drafts, or excessive wear on HVAC components. Balancing may involve adjusting dampers, modifying ducts, or regulating fan speeds.
While formal air balancing typically requires specialized equipment, inspectors may note signs of poor air distribution that suggest balancing deficiencies.
See also: Ductwork, Forced-Air System, HVAC, Register
Air-Dried Lumber
Lumber that has been naturally dried by exposure to air, usually in stacks protected from rain and sun. Unlike kiln-dried (KD) lumber, air-dried lumber reaches an equilibrium moisture content (EMC) of about 12–15% in most U.S. climates and closer to 19% in the more humid southern states. It was commonly used in residential construction prior to the 1960s, before kiln drying became standard in lumberyards nationwide.
Inspectors Note: Air-dried lumber is now rare in new construction and most often found in homes over 50 years old, particularly in regions like the Northeast and Midwest where the median age of housing is higher. Visible signs include surface checking, end splits, and mild warping—often stabilized decades ago. These features are not defects in themselves but remnants of the material’s drying history. Recognizing them helps inspectors explain why certain old-home quirks exist and avoid mischaracterizing them as current issues. Most newer inspectors will rarely see this, unless inspecting historic or unrestored homes.
See also: Kiln-Dried Lumber, Moisture Content, Wood Movement, Checking
Air Handler
A key component of a forced-air HVAC system, the air handler houses the blower fan, evaporator coil, and often other controls or filtration components. It is responsible for circulating conditioned air throughout the ductwork in the home.
Inspectors Note:
• Air handlers are typically found in split-system air conditioners and heat pumps, where they are paired with an outdoor condenser unit. In electric-only systems, the air handler may also include electric resistance heating elements. Unlike a furnace, an air handler does not burn fuel.
• Common installation locations include attics, utility closets, basements, and crawlspaces.
See also: HVAC, Evaporator Coil, Blower, Heat Pump, Condenser Unit, Furnace, Ductwork
Air Infiltration
The uncontrolled flow of outdoor air into a building through cracks, gaps, or openings in the building envelope — including around windows, doors, plumbing penetrations, attic hatches, and framing joints. Air infiltration can lead to energy loss, uneven temperatures, drafts, and reduced comfort.
This is distinct from intentional ventilation, which introduces outdoor air in a controlled way. Air infiltration is most common in older homes or homes with poor air sealing.
Home inspectors may observe signs of air infiltration such as:
• Drafts near windows or baseboards
• Dust patterns along framing or insulation
• Client complaints of inconsistent temperatures
See also: Air Barrier, Blower Door Test, Draft, Energy Efficiency, Weatherstripping
Air Leakage
The uncontrolled movement of air through the building envelope, including both infiltration (air entering) and exfiltration (air escaping) through gaps, cracks, and openings in walls, ceilings, floors, or around penetrations. Unlike intentional ventilation, air leakage occurs unintentionally and can affect a home’s energy efficiency, comfort, and moisture control.
Air leakage is influenced by: Wind pressure, Stack effect (temperature-driven airflow), Mechanical system operation, and the overall tightness of the building envelope.
It is typically measured or evaluated during a blower door test and may leave visible clues, such as dust streaks on insulation, temperature inconsistencies, or drafts near baseboards or outlets.
See also: Air Infiltration, Blower Door Test, Stack Effect, Air Barrier, Weatherstripping
Air Sealing
The process of reducing or eliminating unintended air leakage through the building envelope. Effective air sealing improves energy efficiency, enhances indoor comfort, and helps prevent moisture-related problems by controlling the flow of air between conditioned and unconditioned spaces.
Common air sealing practices target gaps and penetrations around windows, doors, utility openings, attic hatches, and framing joints. Air sealing is distinct from insulation; while insulation resists heat transfer, air sealing controls the movement of air.
Proper air sealing is critical for maintaining energy performance and reducing the risk of condensation, mold growth, and drafts.
See also: Building Envelope, Insulation, Vapor Barrier, Air Barrier
Air Space
A deliberate gap between two building components that allows for drainage, ventilation, or thermal performance. Air spaces are commonly found behind brick veneer (to allow moisture drainage), beneath roof sheathing with radiant barriers (to reduce heat transfer), or between layers in rain screen wall assemblies.
Standard framed wall cavities are not designed to include an air space between insulation and the sheathing—insulation should be in full contact with the surrounding surfaces unless otherwise specified by the wall design.
Airway
A continuous open space that allows air to flow from soffit vents up through the rafter bays to the ridge or roof vents. Airways are typically maintained by installing baffles or ventilation chutes between the roof sheathing and attic insulation.
Proper airways help prevent moisture buildup, extend roof life, and support effective attic ventilation. Blocked or missing airways are a common cause of ice dams, attic condensation, and reduced insulation performance.
Alarm System (Residential)
An electronic system designed to detect and alert occupants to specific hazards or intrusions. Residential alarm systems may include security features (such as motion sensors, door/window contacts, and glass-break detectors), life-safety devices (including smoke alarms and carbon monoxide detectors), or water leak detection. These systems may be standalone or integrated, and some may be monitored remotely.
Author's Note: This definition was written in 2025 and may become outdated as technology continues to evolve. While certain appliances (e.g., sump pumps or ejector pumps) may include alarms, they are typically not considered part of the home’s alarm system.
Alarm systems are increasingly integrated with smart home platforms, voice assistants, and whole-home automation features. Inspectors may encounter systems that blend security, communication, and environmental monitoring into a single interface. They may also encounter remnants of mothballed, hardwired systems—abandoned in favor of interconnected, wireless, and globally aware modern alternatives.
Algae
Simple microorganisms that can grow on surfaces exposed to moisture, shade, and organic debris.
Inspectors notes:
• In residential settings, algae are most commonly seen as dark streaks or discoloration on asphalt shingles, siding, or exterior walls—especially on the north side of a roof or home. Although often mistaken for mold or fungus, algae are biologically distinct. They can affect the appearance of surfaces but typically do not cause structural damage.
• Algae growth on roofing is often cited as cosmetic, though it may contribute to premature aging of shingles in some cases.
Alligatoring
A pattern of cracking that resembles the skin of an alligator, typically seen in aged asphalt or heavily layered exterior paint. It occurs when materials lose flexibility due to age, exposure to sunlight, and the breakdown of oils or binders. In paint, it results from applying new coats over old ones that have lost adhesion or elasticity. In roofing, it appears in old asphalt membranes or coatings as they dry out and become brittle.
Inspector Note: Alligatoring is not typically seen on asphalt shingles, which age differently (granule loss, curling, cracking). When found on roofing, alligatoring may precede more serious deterioration such as open cracks or water intrusion. On painted surfaces, it often results from repeated repainting over failing layers without proper surface prep.
See also: Checking, Crazing, Paint Failure, Roof Covering, Surface Aging
Allowable Span
The maximum horizontal distance that a structural member such as a joist, rafter, or girder can span between two supports without sagging or failing, based on material type, grade, spacing, and load conditions. Allowable spans are determined by building codes and engineering tables. Inspectors typically do not perform span calculations but may note conditions such as visible sagging, over-spanning, or inadequate support when observed during an inspection.
Alteration
A modification or change made to an existing system, component, or structure. Alterations may occur during original construction or at any time afterward. Inspectors evaluate alterations based on current condition, workmanship, and potential impact on the function and safety of the system or structure, regardless of when the change was made.
See also: Installation, Modification, Repair
Alternating Current (AC)
An electrical current that reverses at regularly recurring intervals of time and that has alternately positive and negative values. Electrical power distribution systems in North America supply alternating current at a frequency of 60Hz. This allows for efficient transmission and compatibility with most household appliances, lighting, and HVAC systems. Nearly all household circuits operate on AC unless specific systems (e.g., solar panels, batteries, or electronic devices) convert or generate DC.
Aluminum Wire
An electrical conductor that is used in both residential and commercial wiring. Modern (post 1972) aluminum building wire must conform to the standards for an AA8000 series alloy. Older wiring (especially in multiconductor cables) does not meet that standard and is often a utility grade of aluminum.
Because aluminum is lighter and less expensive than copper but also less conductive and more prone to expansion, contraction, and oxidation, it is generally used for larger wire sizes (e.g., No. 8 AWG and larger) such as feeder cables or service entrances. Single-strand aluminum wiring, primarily installed in homes during the 1960s through 1972, has been linked to a higher risk of overheating and fire when improperly terminated or connected to incompatible devices.
Inspector Note: Home inspectors should pay close attention to any visible aluminum wiring, especially single-strand branch circuits. Signs of past modifications, improper terminations, or mixed metal connections (e.g., aluminum to copper without approved connectors) may warrant further evaluation by a licensed electrician. In modern homes, aluminum wiring is still common in large-gauge circuits such as subpanel feeds or service entrance cables and is considered safe when properly installed and maintained.
See also: Copper-Clad Aluminum, Branch Circuit, Oxidation, Service Entrance, Feeder Cable
Ampacity
The current that a conductor can carry without exceeding the temperature rating of its insulation. Factors affecting ampacity include material, temperature, and size.
The IEEE dictionary defines this term as the current-carrying capacity, expressed in amperes, of a wire or cable under stated thermal conditions.
Example: A 12-gauge copper wire typically has an ampacity of 20 amps under standard conditions.
See also: Conductor, Circuit Breaker, Overcurrent Protection, Electrical Panel, Wire Gauge
Amperage
The amount of electrical current flowing through a circuit, measured in amperes (amps). Amperage represents the volume of electricity moving through conductors and is a key factor in sizing wiring, breakers, and service panels. Excessive amperage beyond the rating of a conductor or device can lead to overheating or fire hazards.
See also: Ampacity, Overcurrent Protection, Electrical Load, Circuit Breaker
Amps (Amperes)
The amount of electrical current at a given voltage. Residential electrical systems are commonly rated in amps, such as a 15-amp circuit for lighting or a 200-amp service panel for the whole home. Amps are a critical value when sizing conductors, circuit breakers, and service capacity.
See also: Amperage, Ampacity, Circuit Breaker, Electrical Panel
Anchor Bolts
Bolts used to secure structural wood members, such as sill plates, to concrete or masonry foundations. In residential construction, anchor bolts are typically embedded in the foundation and fasten the sill plate to prevent lateral or uplift movement. Proper installation includes correct spacing, embedment depth, and visible washers and nuts. Inspectors often note missing bolts, inadequate spacing, or corrosion.
See also: Sill Plate, Foundation, Uplift, Structural Fasteners
Angle Iron
A steel L-shaped support—commonly used as a lintel above window and door openings—to carry the weight of masonry veneer such as brick or stone. The angle iron transfers the load to the adjacent structural framing and must be properly flashed to prevent corrosion and moisture intrusion. Occasionally used as a shelf angle at foundation transitions where masonry overhangs the footing or requires additional support.
Also known as: Lintel, Shelf Angle
See also: Brick Veneer, Masonry Support, Corrosion, Flashing
Angle Stop
A small shutoff valve used to control water flow to individual fixtures such as sinks or toilets. The valve connects to the water supply pipe in the wall or floor and typically turns the flow 90 degrees toward the fixture. Angle stops allow isolation of a fixture without shutting off water to the entire home. Inspectors may note corrosion, leakage, or valves that are stuck or missing.
See also: Shutoff Valve, Supply Line, Fixture Plumbing.
Annealing
A process in which a material is heated and then cooled slowly in order to relieve internal stresses and increase ductility. In glass manufacturing, annealing is performed in a lehr (a long, temperature-controlled kiln) to prevent residual stress that could cause spontaneous breakage. In metals, including copper and aluminum, annealing is used to soften the material after work hardening and improve flexibility.
Inspector Note: While inspectors are not expected to identify annealing processes directly, understanding the difference between annealed and tempered glass is essential. Annealed glass breaks in large, sharp shards, whereas tempered glass fractures into small, granular pieces. Improperly labeled or installed glass in hazardous locations may pose a safety risk. Annealed copper is also more flexible than hard-drawn copper and may be used in different applications (e.g., coiled refrigerant lines).
See also: Tempered Glass, Safety Glazing, Copper Pipe, Float Glass, Work Hardening
Anti-Scald Valve
A plumbing safety device installed in showers or tubs to reduce the risk of sudden hot water temperature increases caused by changes in water pressure or temperature. Anti-scald valves help prevent burns by limiting how hot the water can get during normal use. Most modern fixtures are required to include anti-scald protection. Inspectors may note missing, inoperative, or improperly adjusted valves as a safety concern.
See also: Shower Valve, Temperature Limiting Device, Plumbing Safety.
Anti-Siphon (Valve)
A device designed to prevent contaminated water from being siphoned backward into the clean water supply. Anti-siphon valves are typically installed on exterior hose bibs or irrigation systems to protect against backflow, especially when a garden hose or submerged outlet could introduce pollutants. These valves are a critical safeguard against cross-contamination in residential plumbing systems.
See also: Backflow Prevention, Hose Bibb, Cross-Connection, Check Valve.
Appliance
A household device designed to perform a specific function such as cooking, cleaning, refrigeration, or laundry. Appliances are typically powered by electricity or gas and include equipment like ranges, ovens, dishwashers, clothes washers and dryers, refrigerators, and built-in microwaves. Standalone appliances such as upright or chest freezers may be noted for their presence but are typically not included in the scope of a standard home inspection unless built-in.
See also: Built-In Appliance, Mechanical Systems, Fixture.
Appliance Clearance
The minimum space required between an appliance and surrounding materials or objects. Clearances are typically specified to prevent fire hazards by maintaining separation from combustible materials and to allow adequate access for inspection, maintenance, and servicing. Requirements may be established by the appliance manufacturer, local building codes, or both.
Inspectors should verify that clearances meet safety and serviceability standards but should defer to specific manufacturer instructions or applicable codes for definitive clearance requirements.
See also: Combustible Material, Service Access, Manufacturer’s Instructions
Appliance Connector (Gas Supply)
A flexible gas line used to connect a gas appliance to the building’s gas piping. Appliance connectors are made of corrugated metal tubing, most often stainless steel with a yellow polymer coating. The yellow color is a consistent industry standard for these connectors. In older homes, bare stainless steel or uncoated brass connectors may still be present.
These connectors are:
• Factory-fitted with specialized, non-removable end fittings
• Designed for short, visible runs, typically 3 to 5 feet in length
• Sold in standard increments from 1 to 6 feet, with 6 feet representing the maximum allowable length for indoor use under most model codes
• Intended only for final appliance connections — never as a substitute for building gas distribution piping
Inspector Note: Appliance connectors must not pass through walls, floors, or concealed spaces. They should be fully visible, free of damage, and installed without kinks, improper joints, or excessive bends. Only one appliance connector should be used per appliance; connectors must not be joined together or extended in any way. Inspectors should confirm that the gas shutoff valve is accessible and that any excess connector length has not been looped or hidden behind the appliance.
Do not confuse appliance connectors with CSST (Corrugated Stainless Steel Tubing). While both may have a corrugated appearance and yellow jacket, appliance connectors are limited to short visible runs at appliances and are not bonded, while CSST is a gas distribution product that must be bonded to the electrical system.
See also: CSST, Gas Line, Shutoff Valve, Bonding
Appliance Conversion
The process of modifying a combustion appliance to operate on a different fuel or to meet updated performance standards. Common conversions include changing from oil to natural gas, oil to propane, or propane to natural gas.
Appliance upgrades to more efficient models may also require changes to venting systems due to lower exhaust gas temperatures and the potential for condensation.
Conversions typically require manufacturer-approved kits and proper adjustment of burners, regulators, and controls to ensure safe operation. Inspectors should verify that evidence of proper conversion, such as updated labeling, is present and that venting systems (such as B-vents or chimney liners) are suitable for the converted or upgraded appliance.
Improper appliance conversion can lead to combustion safety hazards, including incomplete combustion and carbon monoxide production.
See also: B-Vent, Chimney Liner, Fuel Type, Combustion Appliance, Condensing Appliance
Appliance Wiring
The visible electrical wiring that supplies power to fixed appliances such as dishwashers, ovens, electric water heaters, HVAC air handlers, and outdoor condensers. While internal appliance wiring is not evaluated during a standard home inspection, the supply wiring may be subject to visual review for safety concerns, including: Improper splices or unsupported connections, Unprotected cable entries, Incorrect use of flexible conduit or armored cable. Inspectors should be cautious around 240V or 208V appliance circuits, as both conductors are energized, increasing the risk of shock during access or maintenance.
See also: 240V, 208V, Circuit Breaker, Flexible Conduit, Disconnect, Overcurrent Protection Device
Appreciation
Recognition for those who take the time to read with care, think deeply, and reach out when something resonates. Appreciation goes a long way when you show it to your customers. :-)
See also: You
Apron (Interior Window Trim)
A horizontal trim board installed directly beneath the interior window sill. The apron gives the window a finished appearance and may be simple or decorative, depending on the casing style. Home inspectors may report missing, damaged, or poorly fitted aprons as part of interior finish observations.
Related Terms: Casing (Window Trim), Interior Trim, Sill (Window)
Apron (Driveway and Street Interface)
The paved section of a residential driveway that lies between the public sidewalk and the street, often including the curb cut. The apron may be concrete or asphalt and is typically considered part of the municipal right-of-way, though maintenance responsibilities may vary. Inspectors may observe cracking, settling, or improper slope contributing to drainage issues.
Related Terms: Driveway, Curb Cut, Right-of-Way, Pavement
Apron (Garage Threshold Area)
The flat, often sloped area of a driveway immediately in front of a garage door. This apron helps guide vehicle entry and may assist in diverting water away from the garage. In some installations, a concrete apron bridges the gap between a sloped driveway and the level garage floor. Inspectors may note spalling, heaving, or inadequate drainage at this transition.
Related Terms: Driveway, Garage Floor, Drainage Slope, Spalling
Arch-Top Window
A window with a curved top edge. Arch-top windows may be fixed or operable and are sometimes described as radius-top, eyebrow, or segmental-arch windows, depending on the shape and depth of the curve.
Inspector Note: The curved profile may require special attention to water management and flashing details, as installation methods and materials can differ from those used for standard rectangular windows.
Related Terms: Eyebrow Window, Radius Window, Extended Leg Half-Round, Flashing, Fenestration
Architect
A licensed design professional who creates building plans and specifications, often working with clients, structural engineers, and code officials to ensure the design meets functional, aesthetic, and regulatory requirements.
Related Terms: Plans, Structural Engineer, Building Permit, Construction Documents
Architectural Shingle
A type of asphalt roofing shingle made with multiple layers of material bonded together to create a thicker, more durable, and dimensional profile. Also called laminated or dimensional shingles, architectural shingles are designed to mimic the appearance of wood shakes or slate while offering improved performance compared to traditional 3-tab shingles. They typically provide greater wind resistance, a longer service life, and enhanced aesthetic value.
Related Terms: Asphalt Shingle, 3-Tab Shingle, Roof Covering, Wind Resistance
Area Well
A recessed enclosure, typically made of corrugated metal, concrete, or plastic, installed around basement or below-grade windows to retain surrounding soil and allow light and ventilation into the space. Area wells are often filled with gravel at the base to promote drainage and reduce water accumulation. Some area wells may include ladder rungs or built-in steps to comply with egress requirements for emergency escape and rescue openings.
Inspector Note: Inspectors should verify that area wells are free of debris, properly drained, and not obstructed. Standing water may lead to window leakage or contribute to basement moisture intrusion. When serving an egress window, the well must meet specific size and clearance requirements. If the well depth exceeds 44 inches, a permanently affixed ladder or steps is required for emergency escape. Protective grates or covers are commonly installed for safety and fall protection, but they must be removable from inside the well without tools and must not obstruct emergency egress.
Related Terms: EE&R Window, Basement Drainage, Window Well Cover, Foundation Wall, Subgrade Moisture Intrusion
Areaway
An excavated, open subsurface space adjacent to a foundation wall, typically used to provide natural light, ventilation, or access to a basement window or door. Areaways may include poured concrete or masonry walls, drains, and full stairways. They are commonly found outside basement egress windows or exterior basement doors.
Inspector Note: Inspectors should evaluate areaways for safety and drainage. Conditions of concern may include missing or unsecured covers, water accumulation, improper slope, or inadequate guardrails and handrails at stairwells.
Related Terms: Area Well, Egress Window, Basement Entry, Drainage, Guardrail
Asbestos
A naturally occurring mineral fiber once widely used in building materials for its fire resistance, strength, and insulating properties. Asbestos may be present in older insulation, flooring, siding, pipe wrap, roofing, and textured wall or ceiling coatings. Inhalation of asbestos fibers can cause serious health conditions, including lung disease and cancer. Materials containing asbestos are considered most hazardous when friable—that is, crumbled, damaged, or deteriorated in a way that allows fibers to become airborne.
Inspector Note: Home inspectors do not test for asbestos but may note the presence of suspect materials and recommend further evaluation by a qualified professional.
Related Terms: Friable, Hazardous Material, Inspection Limitations
Ash Pit
A masonry cavity located below the firebox of a wood-burning fireplace, designed to collect ashes that fall through a small trapdoor or opening in the firebox floor. Ashes accumulate in the ash pit and are periodically removed through a fireplace cleanout door, typically located at the base of the chimney.
Inspector Note: Ash pits are most often found in older masonry fireplaces and may be concealed or unused in modern homes. Inspectors should identify the presence of an ash pit and cleanout access where visible, and may report missing covers, deterioration, or obstruction.
Related Terms: Fireplace Cleanout, Masonry Fireplace, Firebox
Asphalt (Paving Material)
A black, sticky, petroleum-based binder mixed with aggregate to form a flexible pavement surface, commonly used in driveways and roads. Inspectors may report on cracking, potholes, erosion, or improper slope affecting water drainage.
Related Terms: Driveway, Settlement, Surface Drainage
Asphalt Felt (Building Paper)
A moisture-resistant sheet material made from organic or fiberglass mats saturated with asphalt. Traditionally used as underlayment beneath roofing or behind siding to provide a secondary moisture barrier.
Related Terms: Underlayment, Building Wrap, Water-Resistive Barrier
Asphalt Shingles
The most common roofing material used on residential homes in the United States. Asphalt shingles consist of a fiberglass or organic mat coated with asphalt and surfaced with ceramic-coated mineral granules.
There are two main types:
• Three-tab shingles – flat, uniform in appearance
• Architectural shingles – thicker, layered for dimension
Inspector Note: Report signs of aging such as curling, cracking, lifting, or granule loss.
Related Terms: Roof Covering, Flashing, Underlayment
Assembly (Construction)
A combination of materials and components joined together to perform a specific function, such as a wall assembly, roof assembly, or window assembly. The term refers to the full build-up rather than a single product.
Inspector Note: While not formally defined in most home inspection standards, understanding assemblies can clarify discussions about thermal performance, air leakage, and moisture resistance.
Related Terms: Component, Building Envelope, Wall Cavity
Attic Access
An entry point for reaching an attic space, which may be a hatch, pull-down ladder, scuttle, or permanent stairway.
Inspector Note: Home inspectors are not required to enter attics that are not readily accessible or that pose safety risks.
Related Terms: Readily Accessible, Inspection Limitation, Attic Ventilation
Attic Bypass
A gap or opening that allows air from the conditioned interior of the house to leak into the attic space. These bypasses commonly occur around plumbing stacks, recessed lighting, chimney chases, and attic hatches.
Inspector Note: Attic bypasses are a major contributor to heat loss and ice dam formation in cold climates.
Related Terms: Air Leakage, Thermal Envelope, Ice Dam
Attic Fan
A powered fan used to ventilate the attic space by drawing hot air out of the attic and pulling in cooler air through soffit or gable vents.
Inspector Note: Fan operation should be evaluated based on climate, attic ventilation design, and potential for drawing conditioned air from the home.
Related Terms: Ventilation, Soffit Vent, Ridge Vent
Attic Insulation
Insulation installed between ceiling joists or along roof rafters to reduce heat loss or gain through the top of the house. Materials may include fiberglass batts, blown-in cellulose, or spray foam.
Inspector Note: Inconsistent depth, missing areas, or compressed insulation can reduce performance.
Related Terms: R-Value, Thermal Resistance, Unfinished Space
Attic Ventilation
The movement of air through the attic space to remove heat and moisture, typically provided by a combination of intake (soffit) and exhaust (ridge, gable, or roof) vents.
Inspector Note: Poor ventilation can contribute to mold growth, roof deck deterioration, and energy inefficiency.
Related Terms: Ridge Vent, Soffit Vent, Moisture Control
Automatic Safety Control
A device designed and installed to protect a system or component from unsafe conditions by shutting it down or limiting its operation. Examples include pressure relief valves, limit switches, or flame sensors.
Inspector Note: While not always required to test them, inspectors should recognize their presence and note any obvious deficiencies.
Related Terms: Normal Operating Control, Shut Down, Unsafe
Auxiliary Drain Pan
A secondary pan installed beneath air handlers or evaporator coils to catch condensate overflow if the primary drain becomes blocked. Often required in attics or other locations where water leakage could damage interior finishes.
Inspector Note: Rust, standing water, or lack of a secondary drain line can indicate maintenance or installation issues.
Related Terms: Condensate Drain, HVAC, Overflow Protection
Awning Window
A window hinged at the top that opens outward from the bottom, creating an angled panel that resembles an awning when open. Awning windows are typically operated with a crank and are commonly installed in basements, bathrooms, and other areas where ventilation is desired during light rain.
In homes built during the 1950s and 1960s, awning windows were sometimes installed in bedrooms—even on upper floors. These older installations often fail to meet current emergency egress requirements and may pose a significant life-safety risk during a fire.
Related Terms: Hopper Window, Casement Window, Egress Window
Axial Fan
A fan that moves air parallel to the fan’s axis, typically using propeller-style blades. Axial fans are commonly used in exhaust applications such as bathroom ventilation or attic cooling, where moderate air movement with low static pressure is acceptable.
Related Terms: Centrifugal Fan, Ventilation, Exhaust Fan
Axis (Structural or Visual)
In construction or design, an axis refers to an imaginary central line used to organize structural elements, layout symmetry, or align visual components. Inspectors may note structural misalignment or rotation around an axis as signs of settlement or deformation.
Related Terms: Plumb, Out-of-Square, Deflection
Azimuth (Solar Orientation)
The compass direction from which sunlight is coming at a particular time of day. Solar azimuth is an important factor in evaluating passive solar gain, shading strategies, and photovoltaic panel orientation.
Inspector Note: Azimuth is often used in combination with solar altitude to assess sun exposure on building surfaces.
Related Terms: Solar Gain, Overhang, Orientation
That completes the letter A.
The glossary continues with the B group, one post at a time. Once the B entries are complete, a similar full listing will appear here in the Full Glossary section. You can expect the B group to open with terms like Baluster, Band Joist, Baseboard, Batt Insulation, Beam, Bentonite, Bitumen, Bond Beam, and Box Sill.
Feel free to comment or share suggestions as the project evolves. And if you’ve found this glossary helpful, bookmarking this section may be the easiest way to keep it close.