Building Terms Glossary

Also: disc RPM compatibility, max RPM rating, wheel speed rating

A safety-critical requirement that every abrasive disc's maximum RPM rating (stamped on the disc) must exceed the angle grinder's no-load RPM. A mismatch — fitting a disc rated 6,650 RPM to a grinder running 8,500 RPM — can cause the disc to shatter explosively. Common beginner mistake when transferring discs between a large 9" grinder (slower) and a small 4.5" grinder (faster). Governed by EN 12413:2007+A1 and HSG17.

Also: roof abutment, wall abutment, side abutment, abutment flashing

Also: site access, vehicular access

The route from the public highway to the application site. Planning officers check access routes on location plans to assess how the site is reached by vehicles and pedestrians. The red line boundary must include the access route.

Also: ANLA 1992, ANLA, Access to Neighbouring Land Act

Permits access to a neighbour's land for basic preservation/repair works only. Does NOT apply to new construction including extensions. A neighbour can legally refuse scaffold access for a new extension and ANLA 1992 provides no remedy — a court Access Order costs £5,000-£7,000 and courts typically side with the refusing neighbour.

Also: acoustic decoupling gap

The counterintuitive principle that mineral wool should NOT fully fill a stud cavity for acoustic insulation. Leaving a gap prevents vibration transfer to plasterboard, improving sound reduction.

Also: acrow props, adjustable steel props, telescopic props, RSJ props

Temporary steel props hired for structural support during beam installation. Set in pairs on timber spreader boards to carry loads while a wall is opened up. Per BS 4074/BS 5507-3, loads up to 35kN; minimum 48-hour mortar cure before removal.

Also: adjoining property owner, affected neighbour

The legal term for the neighbour whose property shares a wall or boundary with the building owner under the Party Wall Act

Also: adjoining premises, neighbouring property

In planning law, an adjoining property is one that shares a boundary with the application site. It does not mean the buildings are physically attached — a detached house with a shared garden fence is an adjoining property. Prior approval neighbour consultation letters are sent to all adjoining owners and occupiers.

Also: construction adjudication, statutory adjudication

A fast, legally binding way to resolve disputes with your builder, where an independent adjudicator makes a decision within 28 days. It’s much quicker and cheaper than going to court.

Also: adjustable spanner, shifter, crescent wrench, Swedish key

A wrench with a movable jaw that adjusts to fit different sizes of nut and bolt. Essential for tightening compression fittings, tap connectors, and general plumbing connections. Keep two sizes: a small one for tight spaces and a larger one for bigger fittings.

Also: company administration, administrator appointed, gone into administration

A formal insolvency process where a company is placed under the control of an administrator to try to rescue it or get a better result for creditors. Work on your project will likely stop while this is sorted out.

Also: Arc Fault Detection Device, arc fault detection device, arc fault protection

A device that detects dangerous arc faults in cables or connections and disconnects the circuit before a fire starts. Mandatory for high-rise and HMOs under BS 7671 Amendment 2; recommended for standard domestic extensions.

Also: sub-base aggregates, fill materials, loose-tipper aggregates, groundwork aggregates

Loose tipper-delivered fill materials used to build up ground levels under foundations and slabs, bed underground drainage, and provide a clean blinding surface for reinforcement. The first deliveries on every extension and the bulk-cost backbone of any groundwork quote.

Also: single agreed surveyor, joint surveyor

A single party wall surveyor appointed by agreement to act for both building owner and adjoining owner, saving 40-60% vs two separate surveyors

Also: AAV, Durgo valve, mini vent

A one-way valve admitting air into the drainage system to prevent siphonage of trap seals, used instead of extending a vent pipe through the roof.

Also: compressor, oilless compressor, oil-free compressor, portable compressor

The required power source for pneumatic nail guns — the tool cannot operate without one. Entry-level oilless compressors cost £80–200 and also power other tools (spray guns, tyre inflators). The compressor requirement affects mobility, setup time, and total purchase cost when choosing between pneumatic and gas-powered nail guns.

Also: air leakage, air-tightness, air permeability rate, q50 result

The rate at which air leaks through a building's envelope at a 50 Pa pressure differential, measured in m³/(h·m²) of envelope area. Approved Document L 2021 sets 8 m³/(h·m²) as the maximum for new dwellings and a 5 m³/(h·m²) notional target. Tested by a registered air-tightness tester using a blower-door fan.

Also: airtightness test, pressurisation test, blower door test

A pressurisation test measuring how quickly air leaks through a building envelope. Required under Part L for extensions over a certain size or with substantial glazing. Expressed as m³/(h.m²) at 50 Pa pressure. A fan pressurises the building and the leakage rate is measured; results must meet the target in the SAP assessment or a default backstop value of 10 m³/(h.m²).

Also: drainage air test, pipe pressure test

A pressure test applied to drainage pipework to check for leaks. The BCO requires a satisfactory air test before drainage runs are backfilled. The pipe system is sealed and pressurised; any pressure drop indicates a leak that must be fixed.

How well sealed a building is against uncontrolled air leakage

Also: air permeable underlay, Roofshield type membrane, SMS membrane, spunbond-meltblown-spunbond underlay

Also: ballast, all-in aggregate, combined aggregate, all-in, concrete ballast

A pre-blended combination of sharp sand and coarse aggregate sold as a single product, used as a shortcut for site-mixing concrete. Common in UK builders merchants. Distinct from sharp sand (fine only) or coarse aggregate (coarse only). A standard 1:5 cement:ballast mix is commonly used for general-purpose concrete.

Also: foil tape, PIR joint tape, insulation tape, Gapotape

Self-adhesive aluminium tape used to seal joints between PIR insulation boards, completing the vapour control layer. Untaped joints reduce effective R-value by 20-30%.

Also: residential amenity, neighbour amenity

In planning law, amenity refers to the quality of life and enjoyment a property provides to its occupants — including access to natural light, privacy, freedom from noise, and not being overlooked or overshadowed. Prior approval assessments are limited to assessing impact on the amenity of adjoining properties.

Also: expansion bolts, through bolts, sleeve anchors

Mechanical expansion anchors for fixing heavy items into masonry and concrete. The bolt expands a sleeve inside the drilled hole when tightened, creating a powerful grip. Used for fixing wall plates, base plates and heavy brackets to blockwork or concrete.

Also: corner beads, plaster beads, stop beads

Metal or PVC strips fixed to external plaster corners to create a straight, protected edge

Also: L brackets, corner brackets, right angle brackets

L-shaped galvanised steel brackets for connecting timber members at right angles. Used extensively in roof construction, stud walls and general framing. Available in light, medium and heavy-duty versions.

Also: 4.5 inch grinder, 9 inch grinder, disc cutter, 115mm grinder, 230mm grinder

A handheld power tool with a spinning disc for cutting and grinding metal, masonry, and tile. Available in 4.5" (115mm) for general use and 9" (230mm) for heavy cutting. Used for cutting steel lintels, chasing walls, and trimming bricks.

Also: AVR, AVT, AVC, AVS, active vibration reduction, active vibration control

A mechanical or electronic isolation system built into professional-grade breakers and power tools to reduce vibration transmitted to the operator's hands. Required by law on all vibrating tools under the Supply of Machinery (Safety) Regulations 1992. Hilti and Makita tools are marketed on their AVR/AVT credentials. Homeowners need to understand this term when comparing hire equipment and understanding why cheaper breakers carry higher HAVS risk.

Also: statement of case, grounds of appeal, appeal grounds

The critical document a homeowner submits when lodging a planning appeal, making a policy-based case addressing each reason for refusal.

Also: validation check, invalid application

The process by which the local planning authority checks that a submitted application is complete and includes all required documents before starting the determination clock.

Also: decision notice, planning decision notice, grant of permission

The formal document granting planning permission, which lists all enforceable conditions. Every condition must be read carefully before starting work, as some require formal discharge before construction begins.

Also: Part H, Building Regs Part H, AD H, Drainage and Waste Disposal

Building regulations governing drainage and waste disposal. Specifies waste pipe gradients (18–90mm fall per metre for 40mm pipes), trap requirements, and drainage connection rules for extensions.

Also: Part J, Combustion Appliances and Fuel Storage Systems, Building Regs Part J

Covers boiler flue siting requirements including minimum distances from windows, boundaries, ground level, and roof openings.

Also: private building control, approved building inspector, Registered Building Control Approver, RBCA, local authority building control, LABC

A private building control body registered to carry out building regulations inspections as an alternative to the local authority. Homeowners can choose between the council or an approved inspector for their building control service.

Also: front apron flashing, window apron flashing, lower lead flashing

The lead detail at the bottom edge of a roof window where it meets the tiles below. Distinct from lead soakers (which run up the sides). The corner junction between soakers and apron flashing is the most common failure point for roof window leaks.

Also: arborist, tree surveyor, ISA arborist

Specialist who produces tree surveys that inform the structural engineer's foundation depth calculation. Required before digging if trees are within 10m of the extension.

Also: chartered architect, RIBA architect

Designs the extension, prepares drawings, and may handle planning applications

Also: ARB, arb.org.uk

The statutory regulator of architects in the UK. Only professionals registered with ARB can legally use the title ‘architect’.

Also: reclamation yard

Yards selling reclaimed building materials including bricks, tiles, timber, and period features

Also: MCIAT, architectural technician

A professional who specialises in the technical design and detailing of buildings. They produce detailed construction drawings and can manage building regulations applications.

Also: door architrave, window architrave, door trim, door moulding

Decorative trim fitted around door and window frames to cover the joint between the frame and the wall. Should match the skirting profile for a consistent look. Available in MDF or softwood.

Also: AONB, National Landscape

Designated landscape areas where permitted development rights are restricted or removed. Renamed to National Landscape in 2023 by the Levelling Up and Regeneration Act but AONB remains in common use and in planning legislation.

A council order that removes specified permitted development rights for particular streets or areas. Separate from conservation area restrictions. Check with your council's planning department whether one applies to your address.

Also: on-construction SAP, as-built Part L calculation, as-built EPC for extension

The final energy calculation produced under the Standard Assessment Procedure by an accredited on-construction SAP assessor (Elmhurst, Stroma, or BRE) after works are complete, confirming Building Regulations Part L compliance for new dwellings and extensions that alter the thermal envelope. Required by Building Control for completion sign-off and provides the data for the Energy Performance Certificate lodged on the EPC Register.

Also: asbestos-containing materials, ACM

Hazardous fibrous mineral used in UK building materials until 1999, strictly prohibited from skips and requiring licensed specialist removal

Also: licensed asbestos contractor, asbestos surveyor, asbestos remediation specialist

HSE-licensed specialist legally required for notifiable asbestos removal work under the Control of Asbestos Regulations 2012

Also: ABI, abi.org.uk

The UK trade association representing insurance companies. Publishes authoritative guidance on when homeowners must notify their insurer (before extension works begin and after completion), how to calculate rebuild cost, and subsidence risks from new extensions.

Also: APL, landscaper.org.uk

The primary UK professional body for landscapers. Provides a member directory homeowners can use to find vetted landscapers. Unlike builders, landscapers have no mandatory certification scheme, making APL membership the main quality benchmark. Provides guidance on written contracts and CDM 2015 responsibilities.