Building Terms Glossary

Also: pattress box, metal back box, flush box, dry lining box

Galvanised steel boxes recessed into the wall to house the wiring connections behind socket and switch faceplates. Available in 25mm and 35mm depths. 35mm deep boxes are needed for sockets and dimmers; 25mm is sufficient for most switches. Must be earthed.

Also: closed-cell foam rod, joint backer, sealant backer rod, polyethylene backer rod

Closed-cell polyethylene foam cylinder pushed into a joint or gap before sealant is applied, controlling sealant depth, preventing three-sided adhesion, and reducing the volume of sealant required. Sized 6mm to 50mm diameter for 3mm to 40mm gaps, oversized by ~25% to friction-fit. Specified in NHBC 6.7.3 for joints over 6mm and BS 6213 for sealant in buildings.

Also: BBS, rebar schedule, reinforcement schedule

Document produced by the structural engineer specifying all rebar: type, size, length, shape code (BS 8666), and quantity. Used to order cut-and-bent rebar from fabricators. Reading a BBS is the #1 knowledge gap for homeowners receiving structural drawings.

Also: barge board, verge board, gable board, uPVC bargeboard

The angled board that finishes the sloping edge (verge) of a gable roof, the equivalent of a fascia running up the rake rather than along the eaves. It protects the exposed roof timbers at the gable and gives the verge a clean line. Usually matched to the fascia in uPVC or timber.

Also: BASEC, British Approvals Service for Cables, BASEC mark, BASEC certified

Third-party certification mark for UK electrical cables, administered by the British Approvals Service for Cables. The primary quality signal distinguishing compliant cable from cheap imports.

Also: batten end caps, verge end clips, batten clips, end grain clips

A metal clip that secures the cut end of a tiling batten where driving a nail into the end grain would split the timber or pull out under wind uplift. It is commonly used with dry verge systems to meet BS 5534.

Also: tile gauge, batten spacing, gauge spacing

The centre-to-centre spacing set between roofing battens so each course of tiles or slates laps the course below by the required headlap. It is worked out from the tile or slate length minus the overlap, and determines how many battens and tiles a roof needs.

Also: British Board of Agrement certificate, BBA certification, BBA approval, Agrement certificate

A technical approval certificate issued by the British Board of Agrément (BBA) confirming that a construction product or system has been independently assessed for fitness for purpose. Required by NHBC Standards for certain systems (e.g. GRP waterproofing) on NHBC-registered builds.

Also: Building Cost Information Service, BCIS House Rebuilding Cost Calculator, BCIS online calculator, bcis.co.uk

The Building Cost Information Service, operated by RICS. Provides the standard rebuild cost calculator used by insurers across the UK. ABI explicitly recommends homeowners use the BCIS calculator to estimate rebuild cost before contacting their insurer after renovation.

Also: steel bearing, minimum bearing length, bearing length

The length by which a steel beam overlaps its support (padstone or wall) at each end. Planning Portal specifies 150mm minimum each side; NHBC 6.5 specifies 100mm onto padstone, 200mm for in-line steels. A building control check point.

Also: ground bearing capacity, soil bearing capacity, bearing pressure

The key soil property that determines foundation design. Building control checks actual ground conditions against the assumed bearing capacity on dig day.

Also: bearing stratum, bearing ground, load-bearing strata, suitable bearing strata

The layer of ground strong enough to carry the weight of a building and its foundations. Building control inspects the trench bottom on dig day to confirm the foundations have reached a suitable bearing stratum — typically firm clay, gravel, or rock. If bearing strata are deeper than expected, foundations must be dug deeper or redesigned, adding cost.

Also: power belt sander

A power sanding tool used after planing for surface refinement — the planer removes bulk material, the belt sander smooths and closes the grain to a finish-ready state before painting or staining. Complementary to the electric planer in the timber-finishing sequence.

Also: manhole benching, channel benching, drainage benching

The smooth concrete slope inside an inspection chamber or manhole that channels flow from incoming pipes through the chamber and out the exit pipe. Prevents waste pooling at the base. Building control inspectors check that benching is smooth, correctly shaped to direct flow, and free from steps or lips that could cause blockages.

Also: Benchmark logbook, HHIC commissioning logbook, boiler commissioning logbook, Part L commissioning record

The industry-standard boiler commissioning logbook published by HHIC. Completing it constitutes compliance with Part L of Building Regulations. It documents system flush, inhibitor addition, gas pressure readings, safety device tests, and radiator balancing. Building control may request it at final inspection.

Also: Benchmarx, benchmarx.co.uk

Trade-only kitchen supplier owned by Travis Perkins. Sells kitchen units, worktops, and accessories through trade accounts only. Named alongside Howdens in community comparisons as a trade-only alternative.

Also: pipe bending spring, internal bending spring, external bending spring, pipe spring

A coiled steel spring inserted inside (or placed outside) a copper pipe to prevent kinking during hand-bending. Internal springs suit 12-22mm pipe, external springs suit 6-10mm pipe. A budget-tier alternative to a lever bender for occasional 15mm bends.

Also: fixed aluminium rooflight, structural rooflight, bespoke rooflight, large-format rooflight, aluminium glazed rooflight

Made-to-order large-format fixed aluminium rooflights supplied by specialist glazing companies. Substantially different from standard Velux pivot windows — installed by specialist supplier rather than roofer, cost £10,000-15,000 for large units, 8-16 week lead time. May require 30-minute fire resistance glazing if over escape routes. A documented 30m² kitchen extension in Oxfordshire used two units (3,525×2,380mm and 2,325×2,380mm) via a specialist supplier at £11,748 net total.

Also: British Institute of Fitted Interiors Specialists, bifis.org, BiKBBI, British Institute of Kitchen, Bedroom & Bathroom Installation, bikbbi.org.uk

Government-sanctioned not-for-profit body for fitted interiors specialists, administering the only officially recognised qualification for kitchen fitters (NVQ Level 2 Fitted Interiors). Rebranded from BiKBBI (British Institute of Kitchen, Bedroom & Bathroom Installation) in 2025.

Also: bifold doors, bi-fold door, bi-fold doors, bifolding door

A concertina-style door system that folds back to create a wide opening between the house and garden. Common in kitchen extensions but requires significant structural support (larger lintels, potential cantilever design) due to the wide span.

Also: BOQ, bill of quants

A detailed document listing every material and task needed for your build, with quantities. It lets you compare quotes fairly because all builders are pricing exactly the same work.

Also: Blackwells Maps, blackwells.co.uk

OS-licensed mapping provider used by council planning departments, offering bundle pricing for location and site plans.

Also: arbor bore, blade bore, arbor diameter, spindle bore, bore size

The central hole in a saw blade that fits the saw's spindle. Standard UK mitre saw arbor is 30mm. Evolution saws use a non-standard 25.4mm bore, making them incompatible with most third-party blades without a reducing ring adapter.

Also: lean mix concrete, blinding, C8/10 concrete

Thin layer (50-75mm) of weak concrete (C8/10) poured over excavated ground to provide a clean, level surface for placing reinforcement and DPM. Halves the required reinforcement cover from 75mm to 40mm under Eurocode 2.

Also: Benchmark checklist, boiler commissioning record

The Benchmark scheme commissioning record completed and signed by the installing heating engineer when a new boiler is commissioned. Records the installation, commissioning parameters, and any initial service. Most boiler manufacturers make the Benchmark entry a condition of their extended warranty — an unsigned checklist typically voids years 2 onwards of the warranty, so homeowners should insist on it at handover.

Also: flue terminal, flue outlet, balanced flue

Exhaust pipe carrying combustion gases from boiler to outside. Approved Document J specifies strict minimum distances from windows, doors, and boundaries.

Also: Quooker, hot water tap, 3-in-1 tap, 4-in-1 tap, instant boiling water tap, boiling tap, Zip HydroTap, Quooker tap

A tap that delivers near-instant filtered boiling water via an under-counter tank. Installation requires coordination between three trades: plumber (water supply and waste), electrician (dedicated power socket), and kitchen fitter (undermount clearance). A common scope dispute risk.

Also: brick bolster, brick chisel, masonry bolster

A wide, flat chisel for cutting bricks and blocks by hand. Place it on the brick where you want to cut, strike with a club hammer, and the brick splits along the line. Also useful for chasing out mortar joints and removing old tiles.

Also: bonded floor screed, mechanically keyed screed

Screed mechanically keyed to the structural slab using a bonding agent. Can be as thin as 25-50mm. Requires careful substrate preparation.

Also: bonding coat, undercoat plaster, Thistle Bonding, Thistle BondingCoat

Gypsum-based undercoat plaster applied as a base coat on dense or smooth surfaces (concrete blocks, engineering bricks) that multi-finish plaster would not adhere to directly. Applied 8-11mm thick on walls, 8mm on ceilings. Scratched to provide a key for the finishing coat. Coverage: 2.75m² per 25kg bag at 11mm. BS EN 13279-1 type B4/20/2.

A tinned copper sleeve crimp-fitted to stranded conductor ends before insertion into screw terminals, required under BS 7671 Section 526.9.1.

Also: lead bossing mallet, bossing stick, leadworker's mallet

A boxwood or hardwood mallet used to dress and shape lead sheet around chimney junctions, valleys, and abutments. The head profile (often shaped like a wedge or cylinder) lets the leadworker shrink and stretch lead by working it cold without splitting.

Also: bottle gully trap, yard gully, rainwater gully, bottle trap gully, gully

A trapped surface-water fitting set at ground level that receives a downpipe or yard drainage and connects to the underground drain. A removable bottle-shaped insert traps silt and provides a water seal against drain smells, and is easier to rod and clear than a back-inlet gully. Distinct from an inspection chamber or a channel drain.

Also: scraping the bottom, trench bottom preparation

The process of scraping loose, disturbed, or wet soil from the base of a foundation trench immediately before the BCO inspection and before concrete is poured. If the trench bottom is not clean and firm, the foundation will fail to achieve its designed bearing capacity.

Also: distance from boundary, 2-metre boundary rule

The distance between an extension and the property boundary. Under PD rules, extensions within 2 metres of a boundary are subject to a 3-metre eaves height limit. Side extensions must not project beyond the side wall of the original house facing a highway.

Also: tap connector, flexi tap connector, flexible tap connector, braided tap connector

A short flexible or rigid brass connector joining the isolating valve on a supply pipe to the tail of a tap. Available in straight and angled forms; length typically 300–500mm.

Also: contract breach, repudiatory breach, fundamental breach

When one party to a contract fails to perform their obligations. A homeowner must prove breach of contract to claim damages or terminate a building contract and engage a replacement contractor.

Also: roof felt, breathable membrane, roofing underlay, Tyvek, breather membrane, vapour permeable underlay, roofing felt, Tyvek HD Plus, Tyvek Supro Plus, DuPont Supro Plus

Modern breathable underlay laid over rafters beneath the battens and tiles. Allows water vapour to escape from the roof space while preventing wind-driven rain from entering. Has largely replaced traditional bitumen roofing felt in new construction. Required by current Building Regulations.

Also: jointing iron, mortar jointer, half-round jointer

Hand tool for finishing mortar joints between bricks to a consistent profile

Also: bricklaying trowel, London trowel, Philadelphia trowel

A flat, pointed metal blade on a handle for spreading and shaping mortar when laying bricks and blocks. The primary tool for any bricklaying or blockwork. Choose a size that feels comfortable in your hand.

Also: brickhunter.com

UK brick matching service for sourcing matching bricks for extensions. Useful for older properties where matching existing brickwork is a significant challenge, particularly in conservation areas.

Also: brickie

Lays bricks and blocks to build walls, including cavity walls and foundations above DPC

Also: bridging finance, bridge loan, short-term bridging finance

A short-term, high-cost secured loan marketed to homeowners as an extension funding option. Typically wrong-tool for standard residential extensions — short tenure, high rates, and refinancing risk. The FCA has taken enforcement action against bridging lenders for inappropriate sales to homeowners.

Also: BROOF t4, flat roof fire classification, BS EN 13501-5 BROOF, external fire performance

The top reaction-to-fire classification for roof coverings exposed to an external fire, tested under BS EN 13501-5 using method t4. A BROOF(t4) covering can usually be built close to a boundary without extra fire restrictions under Building Regulations Part B.

Also: BS 5325, BS 8201, BS 8203, screed moisture test standards, hygrometer box method standards

British Standards mandating the hygrometer box method for measuring screed moisture content before flooring is laid. 75% ERH threshold for most finishes, 65% for timber over UFH.

Also: BS 6222, BS 6222-2, kitchen unit performance standard

British Standard covering performance requirements for domestic kitchen units (fitted, peninsular, island units, breakfast bars). A voluntary standard, not a legal requirement, but referenced by kitchen manufacturers as evidence of unit quality.

Also: BS 6576, British Standard 6576, BS6576

Code of Practice for diagnosis of rising damp and installation of chemical DPC systems. Governs drill patterns, injection spacing, dosage, and curing for remedial chemical injection DPC.

Also: BS 6700:2006+A1:2009, Design, installation, testing and maintenance of services supplying water

The foundational British Standard for domestic water pipe sizing using the loading units method. Referenced by CIPHE and CIBSE for pipe sizing calculations.

Also: 18th Edition, IET Wiring Regulations, BS 7671:2018+A2:2022, BS 7671:2018+A3:2024, BS 7671:2018+A4:2026

The primary technical standard governing all UK domestic electrical installation work, covering socket distances, RCD protection, cable burial rules, and voltage drop limits.

Also: BS 8417:2011+A1:2014

British Standard governing preservation of wood. Defines the use class system (UC1-UC4) that determines treatment requirements. The 2024 revision upgraded outdoor deck wall plates/beams from UC3 to UC4.

Also: BS EN 13859-1, EN 13859-1, underlay performance testing standard, W1 classification standard

BS EN 13859-1:2014 defines and sets the test requirements for flexible underlays used beneath the covering of pitched (discontinuous) roofs, including breather membranes and traditional felts. It is the standard a roofing underlay is UKCA or CE marked against.

Also: BS EN 539-2, EN 539-2, clay tile frost resistance test, clay tile freeze-thaw test

BS EN 539-2:2013 sets the test method for the frost resistance of clay roofing tiles laid on pitched (discontinuous) roofs. Tiles are put through repeated freeze-thaw cycles, and for UK conditions the guidance is that they should survive a high number of cycles to count as frost resistant.

Also: BS EN 60669, BS EN 60669-2-1, dimmer switch standard, switch standard

The product standard for domestic switch faceplates. Part 1 covers general requirements; Part 2-1 covers electronic control devices including dimmers.

Also: BS EN 61009, BS EN IEC 61009-1, RCBO standard

The product standard for RCBOs (residual current circuit-breakers with integral overcurrent protection). Compliance with this standard certifies that an RCBO is type-tested and fit for installation.

Also: BS EN 934-3:2009+A1:2012, Admixtures for masonry mortar

European standard governing chemical admixtures for masonry mortar (including air-entraining mortar plasticisers). Specifies definitions, requirements, conformity assessment, and CE marking. Manufacturers must declare dosage, density, and reference mortar performance. Used alongside BS EN 998-2 for conformity of finished mortar.

Also: BSPT, British Standard Pipe Taper, tapered thread, R thread, BSP taper

The thread type on which PTFE tape actually works. PTFE tape seals by compressing between the male and female tapered threads as the fitting is tightened. Most UK domestic valve connections (shower valves, radiator valves, tap tails) are BSPT.

Also: sewer build-over, Class 1 agreement, Class 2 agreement, Class 3 agreement

A mandatory agreement from the local water company when building within 3m of a public sewer or 1m of a public lateral drain. Without it, the water company may demolish the new structure and the building control completion certificate will not be issued.

Also: general builder, building contractor, main contractor

A general building contractor who carries out the physical construction work on an extension or renovation project. Responsible for groundwork, blockwork, roofing, and overall site management.

Also: upfront payment, advance payment, initial payment

The upfront payment made to a builder before work begins, with recommended caps of 10-25% depending on project size.

Also: verbal estimate, rough estimate, ballpark figure

A non-binding, rough figure given by a builder — often verbal — that homeowners frequently mistake for a binding quote.

Also: fixed-price quote, written quotation, itemised quote, tender

A written, itemised, binding commitment to carry out specified work for a stated price.

Also: builder due diligence, credential verification, builder checks

The structured process of verifying a builder's credentials before appointment: trade body membership, Companies House registration, insurance certificates, references, and site visits to completed work.

Also: string line, brick line

A taut string stretched between two points as a guide for keeping brickwork straight and level. Wrapped around line pins or blocks at each end of a wall to guide each course of bricks. Cheap but absolutely essential for bricklaying.

Also: roofing square, combination square, framing square, speed square, rafter square, try square, carpenter's square

A large L-shaped metal square for checking and marking right angles. Essential for ensuring walls meet at 90 degrees, setting out foundations, and marking square cuts on timber and sheet materials.

Also: Travis Perkins, Jewson

Trade-focused merchants stocking bricks, blocks, timber, cement, insulation, and heavy building materials

Also: SI 2024/110, RBCA Regulations 2024, Approved Inspector replacement regulations

Statutory instrument (in force 6 April 2024) replacing Approved Inspectors with Registered Building Control Approvers (RBCAs). Makes it a criminal offence to carry out restricted building control activities without RBI registration. Homeowners choosing private building control must verify their provider is a registered RBCA.

Also: Building Act, BA 1984

The primary enabling Act of Parliament under which the Building Regulations 2010 (SI 2010/2214) and all the Approved Documents are made. The Approved Documents derive their legal status from this Act, not from the regulations themselves. Section 36 of the Act gives local authorities the power to issue enforcement notices. The Building Safety Act 2022 amended several provisions, most notably repealing the old Section 16 'deposit of plans' route from October 2023, replaced by the new building control approval application.

Also: building regulations approval

The process of ensuring construction work complies with building regulations. Involves a separate application, fees (typically £250-550 application plus £330-400 inspection fees), and inspections throughout the build. Can be done by the local authority or a private approved inspector. Completely separate from planning permission.

Also: BCO final certificate, Building control completion certificate, LABC completion certificate, building regs completion certificate, building regs sign-off, building regulations certificate, completion certificate

The statutory certificate issued by the Local Authority Building Control (LABC) or an Approved Inspector on satisfactory final inspection of notifiable works. Confirms the works meet the Building Regulations and is the single most important document for insurance, re-mortgage, and resale — solicitors will ask for it and buyers' surveyors will flag its absence as a defect. Not a competent-person-scheme certificate; it is issued by the building control body itself after the final inspection sign-off.

Also: conditional BC approval, conditions on full plans approval

When a Full Plans application is approved with conditions requiring further information before certain work proceeds. The normal outcome for extensions — distinct from planning conditions.

Also: BC documents, building regulations documents, building control submission pack

The package of technical documents prepared by the architect and structural engineer for a Full Plans building control submission — structural drawings, steelwork calculations, timber specifications, thermal calculations, drainage layout, and written construction specification.

Also: draughtsperson, draughtsman

An unregulated professional who produces building plans and drawings. Unlike architects (ARB-regulated) and architectural technologists (CIAT-regulated), no formal qualifications or professional indemnity insurance are required.

Also: building control officer, BCO

Inspects work at key stages to ensure compliance with building regulations

Also: baseline, setting-out baseline, frontage line

The first straight reference line from which the footprint corners are located during setting out. On an extension this is usually the face of the existing house wall the extension joins, or a known boundary. It is the horizontal control for the set-out, distinct from the level datum (the vertical control). Corners are measured off the building line and then squared with the 3-4-5 check and equal diagonals, which is why 3-4-5 alone does not set out a whole building: you locate corners from a measured baseline first, then prove the angles.

Also: building notice application, building notice submission

The alternative to Full Plans: no detailed drawings required, work can begin 2 days after submission, no formal approval letter issued. Suited to simpler works but not permitted near public sewers or on buildings covered by the Fire Safety Order.

Also: Building Regulations 2010, building regs, the regulations

The body of mandatory standards under the Building Regulations 2010 governing the design and construction of buildings in England and Wales. Compliance is demonstrated against Approved Documents (A through S) and verified by a Building Control body during construction.

Also: The Building Regulations 2010, SI 2010/2214

The primary statutory instrument governing building regulations in England. All the approved documents (Part A, B, C, etc.) flow from this instrument.

Also: Reg 17, Regulation 17 completion certificates, Building Regulations 2010 Reg 17

Provision under the Building Regulations 2010 that mandates the local authority shall issue a completion certificate within 8 weeks of receiving a valid completion notice. The 2012 amendment changed "may give" to "shall give", making issuance mandatory for full plans applications.

Also: boiler notification certificate, gas self-certification notice, building regs gas certificate

Document issued by the Gas Safe Register to the Local Authority, notifying them of a gas installation within 30 days of completion under the competent persons self-certification scheme. Legally distinct from the Gas Safety Certificate and the Building Control Completion Certificate. Its absence can block building control final sign-off.

Also: SI 2023/911, Building Regulations Amendment 2023, October 2023 building regulations changes

Statutory instrument (in force 1 October 2023) introducing the deemed commencement notification requirement (Reg 16(3C)), the 3-year lapse provision for building control approvals, the new duty holder regime, and start notices.

Also: building regs indemnity, BC indemnity insurance, building control indemnity policy

A specialist insurance policy that satisfies mortgage lenders when a property has unauthorised or unsatisfactorily completed building work. Distinct from professional indemnity insurance.

Also: Part A, Approved Document A, AD A, Structure

The statutory requirement covering structural safety of buildings in England and Wales. Approved Document A sets out acceptable methods for meeting Part A: foundation design (type, depth, width, concrete grade), wall and roof structural calculations, stability against disproportionate collapse, and combined dead/imposed/wind loading. For extensions, Part A governs the minimum 1m foundation depth to firm ground, trench fill vs strip foundation rules, and steelwork specifications. Your structural engineer designs to Part A and building control checks against it.

Also: Part B, Approved Document B, AD B, Fire Safety

The part of the Building Regulations covering fire safety: means of escape, fire spread within and between buildings, and access for the fire service. For extensions it governs matters such as escape windows, protected stairways and how close to a boundary certain roof coverings can sit.

Also: Part C, Approved Document C, AD C, Site Preparation

Site preparation and resistance to contaminants and moisture

Also: Part D, Approved Document D, AD D, Building Regs Part D, Toxic Substances

Building regulations covering toxic substances released by building materials. The single substantive requirement (D1) prohibits insulating materials that release formaldehyde gas in concentrations harmful to occupants. Rarely engaged on modern domestic extensions because mainstream insulation products are already compliant, but remains the statutory hook if a non-standard insulating material is proposed.

Also: Part E, Approved Document E, AD E, Resistance to Sound

The part of the Building Regulations covering resistance to the passage of sound, setting sound insulation standards mainly between dwellings and for separating walls and floors. It is most relevant to conversions and new separating elements.

Also: Part F, Approved Document F, AD F, Ventilation

The part of the Building Regulations covering ventilation, setting the background and purge ventilation a habitable space needs to control moisture and air quality. It is closely tied to Part L, because making a building more airtight raises the importance of adequate ventilation.

Also: Part G, Approved Document G, AD G, Sanitation, Hot Water Safety and Water Efficiency

Sanitation, hot water safety and water efficiency

Also: Part H, Approved Document H, AD H, Building Regs Part H, Drainage and Waste Disposal, approved-document-h, H4, Approved Document H4, Part H4

Building regulations governing drainage and waste disposal in England. Specifies waste pipe gradients (18–90mm fall per metre for 40mm pipes), trap requirements, foul drainage construction (granular bedding to BS EN 1610), and the four-step priority hierarchy for surface-water discharge (soakaway, watercourse, surface water sewer, combined sewer). Building control inspects drainage runs and connections against Part H before backfill.

Also: Part J, Approved Document J, AD J, Combustion Appliances and Fuel Storage Systems, Building Regs Part J, approved-document-j

Building regulations covering combustion appliances (boilers, stoves, fires) and fuel storage systems. Sets boiler flue siting requirements including minimum distances from windows, doors, boundaries, ground level, and roof openings; carbon monoxide alarm requirements for solid fuel and biomass installations; hearth, chimney and flue construction; and oil/LPG fuel storage tank separation distances.

Also: Part K, Approved Document K, AD K, Protection from Falling, Collision and Impact

Protection from falling, collision and impact. In England (since April 2013), Part K also absorbed the glazing safety requirements that previously sat in Part N — covering safety glazing in critical locations, opening/cleaning of windows, and impact protection.

Also: Part L, Approved Document L, AD L, Conservation of Fuel and Power

Conservation of fuel and power (energy efficiency)

Also: Part M, Approved Document M, AD M, Access to and Use of Buildings

The part of the Building Regulations covering access to and use of buildings, including level thresholds, door widths and accessible facilities. A new extension should not make a dwelling less accessible than it was before.

Also: Part N, Approved Document N, AD N, Glazing safety in relation to impact

Approved Document N (Glazing — safety in relation to impact, opening and cleaning) was withdrawn in England in April 2013 when its requirements were absorbed into Approved Document K. Wales has not adopted this change: Part N remains a standalone Approved Document in Wales, governing safety glazing in critical locations (below 800mm in walls, in doors, in side panels), the safe opening and cleaning of windows, and impact protection. Homeowners and builders in Wales must refer to AD N rather than AD K for glazing safety requirements.

Also: Part O, Approved Document O, AD O, Building Regs Part O, Overheating

Building regulations introduced in June 2022 limiting summer overheating in new residential buildings in England. Applies primarily to new dwellings and material change of use to residential, not generally to extensions of existing dwellings. Sets two compliance routes: a simplified method based on glazing area, ventilation openings and shading, or a dynamic thermal modelling method (CIBSE TM59). Building control checks Part O at design stage for in-scope projects.

Also: Part P, Approved Document P

The electrical safety section of the Building Regulations for England and Wales. Makes any new circuit, consumer unit replacement, and work in special locations (for example bathrooms and kitchens) notifiable. Compliance must be certified either by a competent-person-scheme registered installer (NICEIC, NAPIT, ELECSA), a third-party certifier, or by direct building control notification before work starts. Non-compliant work becomes a legal issue at sale, mortgage and insurance time, not just a technical breach.

Also: Approved Document Q, Part Q, security in dwellings, security of dwellings

Approved Document Q requires easily accessible windows and doors in new dwellings to meet PAS 24:2016 security standard. Glazing within 400mm of door locks must meet BS EN 356:2000 P1A.

Also: Part R, Approved Document R, AD R, Building Regs Part R, High-Speed Electronic Communications, broadband regs

Building regulations requiring new buildings (and major renovations) to be equipped with in-building physical infrastructure capable of carrying high-speed electronic communications, and a dedicated access point. Applies on a building-by-building basis: typically engaged for new dwellings, and for major renovations involving the building envelope, but not usually for ordinary domestic extensions. Implements the EU Broadband Cost Reduction Directive in England.

Also: Part S, Approved Document S, AD S, Building Regs Part S, Infrastructure for Charging Electric Vehicles, EV charging regs

Building regulations introduced in June 2022 requiring electric vehicle charge points to be installed on most new dwellings, dwellings undergoing major renovation that have associated parking, and new non-residential buildings with parking. For domestic extensions the trigger is whether the work creates a new associated parking space; ordinary rear extensions to an existing house do not normally engage Part S, but garage conversions or driveway works that change parking provision can. England-only.

Also: Part T, Approved Document T, AD T, Building Regs Part T, Toilet Accommodation

Building regulations effective 1 October 2024 governing the provision of toilet accommodation in non-domestic buildings: minimum proportions of universal toilets, separate-sex facilities, and ambulant accessible WCs in new and materially altered non-domestic buildings. Does not apply to dwellings, so out of scope for ordinary domestic extensions. Included in the graph for completeness when the site covers commercial conversions or mixed-use schemes.

Also: BSA 2022, Building Safety Act

Strengthened building safety rules and extended the time limit for claims about defective work on dwellings to 30 years for certain claims.

Also: BSR

Part of the Health and Safety Executive, the Building Safety Regulator oversees the safety and performance of buildings in England. Maintains the register of Registered Building Control Approvers (RBCAs) and regulates the building control profession.

Also: soft sand, bricklaying sand, mortar sand

Fine, smooth sand used for mortar mixes in bricklaying and blockwork. Produces a workable, cohesive mortar that adheres well to masonry units.

Bringing blockwork up to the damp proof course level

Also: home buildings insurance, buildings cover, structural insurance

Insurance covering the fabric of a property (walls, roof, floors, fixed fittings) against damage or destruction. Distinct from contents insurance. A completed extension increases the sum insured for buildings insurance because it increases the rebuild cost. Homeowners must notify their insurer and update their buildings insurance on practical completion of an extension.

Lightweight head protection meeting EN 812. Protects against bumps but not falling objects. Not a substitute for EN 397 hard hats on construction sites.

Also: DPM jointing tape, butyl tape, damp-proof membrane tape, DPM tape, vapour-barrier tape, self-adhesive butyl tape, ClassicBond butyl tape

A self-adhesive double-sided or single-sided tape with a butyl rubber adhesive layer, used to join overlapping sheets of damp-proof membrane (DPM) and to seal membrane to wall, column, or service penetrations. The adhesive flows to conform to surface irregularities, creating a continuous watertight bond. Required at all DPM joints and upstands before concrete oversite or screed is poured. Available in 50mm and 100mm widths.

Also: buyaplan.co.uk

An online service for purchasing Ordnance Survey map extracts required for planning applications, from £8.99.