Building Terms Glossary

Also: prove dead procedure, lock-off procedure, ALIVE procedure

The formal procedure for confirming a circuit is dead before working on it. Governed by HSE GS38 and the Electricity at Work Regulations 1989.

Personal protective equipment (PPE) for working safely on a construction site. Non-negotiable — even on a small extension project. Building control inspectors may refuse to inspect if PPE is not being worn on site.

Also: safety goggles, safety specs, protective eyewear

Eye protection against flying debris, dust, and splashes. Essential when cutting, drilling, grinding, or chiselling. Choose wrap-around styles for better protection. Anti-fog lenses are worth the small extra cost.

Also: toughened glass, laminated glass, safety glass, Part K glazing, impact-safe glazing, Part K glazing zones

Toughened or laminated glass required by Part K in critical locations: wall panels up to 800mm from floor, door glazing up to 1500mm from floor, and door side panels.

Also: blinding layer, blinding sand, sand blinding layer

A 50mm layer of sharp sand placed over compacted hardcore before the DPM is laid. Levels sharp aggregate edges that would otherwise puncture the damp proof membrane. LABC guidance lists sand blinding as a specific inspection check item at the oversite stage.

Also: traditional screed, hand-mixed screed, bonded screed mix, 4:1 screed

Traditional screed mixed 4:1 on site, laid by hand. Costs 50-100% less than liquid anhydrite screed but requires compaction and has slower drying times (1 day per mm to 50mm).

Also: abrasive paper, sanding block, sanding sheets, 120-grit, 180-grit, 240-grit

Abrasive paper used between paint coats and for sanding filled nail holes and filler in skirting/architrave before painting. NHBC Ch. 9.5 requires surfaces to be smooth and free from defects before painting. 120-grit for initial sanding, 180–240 for between-coat work.

Also: SAP calc, Standard Assessment Procedure, energy assessment, Part L compliance report

Standard Assessment Procedure energy calculation required to demonstrate Part L compliance for extension projects, into which window U-values feed.

Also: SAP energy assessor, on-construction SAP assessor, OCDEA

Qualified energy assessor who produces the as-built SAP (Standard Assessment Procedure) calculation required for Building Regulations Part L compliance. The as-built SAP is submitted to Building Control alongside an Energy Performance Certificate for new dwellings and extensions that alter the thermal envelope. On-construction assessors are accredited via Elmhurst, Stroma, or BRE schemes.

Also: circular saw kickback, blade kickback

The primary injury mechanism for circular saws: the blade binds in a cut and the saw violently kicks back toward the operator. Caused by supporting both sides of a cut, a dull blade, or too-deep blade setting.

Power saws for cutting timber, sheet materials, metal, and plastic. Different saw types are designed for different cuts and materials.

Also: scaffold loading class, scaffold design load

Classification of scaffolding by load-bearing capacity: light/inspection (0.75 kN/m²), general purpose (2 kN/m²), and heavy duty (3.0 kN/m²). Different trades require different ratings — roofers unloading tiles need heavy duty; bricklayers need general purpose. Specifying the wrong duty rating creates a safety risk.

Also: scaffolding permit, highway scaffolding permit, scaffold licence

Licence issued by the local highway authority under Highways Act 1980 s.169 permitting scaffolding to occupy or oversail a public pavement or road. Processing time is 2-4 weeks and must be in place before scaffold goes up. Rear garden extensions typically do not need one; front-of-house extensions almost always do. Typical cost £80-£300.

Also: scaffold level, working lift, working platform level

A horizontal level of scaffolding from which work is carried out. Single-storey extensions typically require one lift at approximately 2-2.3m; two-storey extensions require multiple lifts at 4-5m and 7-8m. The number of lifts directly determines the scaffolding cost and appears in contractor quotes.

Also: pre-strike inspection, roof walk before scaffold comes down

The critical homeowner action of personally inspecting all roof junctions, flashings, tile/window details, guttering, and ridge capping while scaffold is still standing. A common real-world mistake: the tile/window junction failure discovered only after scaffold came down, requiring expensive remediation (lead specialist plus expanding foam at £250).

Also: scaffolding overrun rate, weekly hire extension charge

The additional weekly charge applied when a scaffold hire period runs beyond the agreed duration, typically 10-20% of the original weekly hire rate. Scaffolding companies have a commercial incentive to leave scaffold in place. Homeowners should negotiate a fixed-hire-period contract and withhold final payment until scaffold is removed on the agreed date.

Erects and dismantles scaffolding for safe access to height

Provides scaffolding erection, hire, and dismantling services

Also: no-work-under-scaffold rule, scaffold timing for utility relocation

Gas and electricity network operators will not carry out meter relocation work while scaffolding is present on the property, creating a critical sequencing constraint.

Companies providing scaffolding erection, weekly hire, and dismantling for construction access

Also: SoC, condition survey, pre-works condition survey

A photographic and written record of the state of a neighbour's property before building work begins, protecting both parties from post-build disputes

Also: scope of works schedule, works schedule

A detailed list of the work to be done, forming part of the building contract. Defines scope and obligations — what the builder is contracted to do. Distinct from a construction programme, which tracks time not scope.

Also: backing coat, render coat, sand and cement render

A preliminary sand/cement or gypsum backing coat applied to dense blockwork or engineering brick walls before the finishing skim plaster. The surface is scratched with a comb to provide a key for the next coat. Required where bonding plaster alone cannot prepare the surface.

Also: screed contractor, liquid screed contractor

Specialist contractor who installs liquid screed using pump equipment, particularly for underfloor heating systems.

Laying a smooth, level surface over a floor before final flooring

Also: screed products, floor screed

The levelling layer poured over the slab and underfloor heating pipes before the final floor finish is laid. Two main products, traditional sand-and-cement and liquid anhydrite, with very different drying times, costs, and UFH performance.

Also: scribe, scribing to wall, scribing timber, back cut

The technique of tracing the irregular profile of one surface (typically a wall or floor) onto a piece of timber or panel, then cutting to that line so the piece fits flush against the uneven surface. Used for kitchen end panels, skirting boards, and worktops.

Also: jointing tape, plasterboard tape, self-adhesive scrim, fibreglass mesh tape

Self-adhesive fibreglass mesh tape applied over plasterboard joints before skimming or jointing to prevent cracks along board edges. Essential for tapered-edge board joints. Also used to reinforce internal corners.

Also: equivalent air layer thickness, water vapour resistance metric, Sd, vapour diffusion-equivalent air layer

Also: demolition hammer, kango, jackhammer, concrete breaker, electric breaker

A heavy-duty electric hammer for breaking up concrete, masonry, and hard ground. Used for demolishing existing structures, breaking out foundations, and removing floor screed. Usually hired rather than bought.

Also: SDS+ drill, rotary hammer drill

A hammer drill that uses SDS+ chuck system for drilling into masonry, concrete, and brick. The hammer action makes it vastly more effective than a combi drill for hard materials. Essential for any extension project involving blockwork or concrete.

Also: caulking gun, mastic gun, cartridge gun

Hand tool for applying silicone sealant around sinks, hob cutouts, and worktop joints.

Also: EPDM roller, membrane roller, hand roller, wallpaper seam roller

A small hand roller used to press down wallpaper seams and edges for a flat, invisible join. Also used more broadly to apply pressure to flexible membranes — for example rolling EPDM flat roof membrane or laminating veneer edges.

The stage where services are completed after plastering (faceplates, radiators, sanitaryware)

Also: Section 106 notice, s.106 WIA notice, right to connect notice, connection notice

A formal notice served on the water company at least 21 days before making a new connection to a public sewer, under Section 106 of the Water Industry Act 1991. The water company cannot refuse the connection outright but can impose conditions on how it is made. The connection fee is typically £350-600. Connecting without serving notice is a criminal offence. Distinct from a build-over agreement, which covers building near the sewer rather than connecting to it.

Also: s.36 notice, building regulations enforcement notice, section 36 Building Act

An enforcement notice served under Section 36 of the Building Act 1984 by a local authority requiring the removal or alteration of work that contravenes building regulations. The ultimate sanction for non-compliant building work.

Also: 3m rule, 6m rule, 45-degree foundation rule, Section 6 notice

Provisions of Section 6 of the Party Wall Act covering excavation near neighbouring foundations — the 3m and 6m trigger zones that catch most rear extensions

Also: Section 75, s75 protection, credit card protection, Section 75 Consumer Credit Act

A legal right under the Consumer Credit Act that makes your credit card company jointly liable for purchases over £100. If you pay a deposit by credit card and the builder goes bust, you can claim the money back from your card provider.

Also: floor leveller, floor compound, latex screed

Pourable cementitious compound that self-levels to create a smooth, flat floor surface suitable for tiling, vinyl or laminate. Applied over concrete floor slabs to correct minor undulations. Surface must be primed with SBR or proprietary primer first (not PVA). Requires manual spreading and spiked roller despite the name.

Also: semi

A house that shares one wall with an adjoining property. Under the Larger Home Extension scheme, single-storey rear extensions can extend up to 6 metres (compared to 8m for detached). Party wall considerations typically apply.

Also: separate system, separate sewer, dual drainage system

A drainage system with distinct pipes for foul water (to treatment works) and surface water (to watercourse, soakaway, or surface water sewer). Required by Approved Document H5 for new extension drainage where separate public sewers exist in the road. Cross-connecting foul to surface water in a separate system is a prosecutable pollution offence.

Also: single sequential trigger, SST, single actuation trigger, contact trigger, bump trigger, bump fire

The trigger mechanism on a nail gun that requires the nose to be pressed AND the trigger pulled in sequence for each individual shot. OSHA and safety research confirm that nail gun injury risk doubles when using a contact (bump) trigger versus a sequential trigger. Contact triggers fire whenever the trigger is held and the nose touches a surface, causing accidental double-fires and injuries. The single most important safety setting check before using a hire gun.

Also: Section 185 diversion, public sewer diversion, sewer rerouting

The process of permanently rerouting a public sewer that runs directly through a proposed extension footprint, under Section 185 of the Water Industry Act 1991. The water company carries out or approves the diversion. Costs £3,000-10,000+ depending on length and complexity, and takes 8-16 weeks to arrange and complete. Distinct from a build-over agreement, which allows building near or over (not through) the sewer.

Also: public sewer map, drainage map, statutory sewer records

The map of public sewers maintained by water authorities. If a proposed extension is near or over a drain shown on the sewer map, the Full Plans route becomes mandatory.

Also: Design and Construction Guidance, DCG, Sewers for Adoption 7th edition

The industry standard design and construction guide for drainage and sewers. Although technically a guidance document rather than legislation, it is treated as the reference standard by water companies and building control for drainage design, pipe bedding specifications, and construction standards.

Also: XPS shadow line, LED shadow line, shadow cut line, blade shadow guide, DeWalt XPS

An LED-projected shadow that shows the exact blade cut position on a mitre saw. Superior to laser guides — no calibration needed, automatically adjusts when the blade is changed, shows actual kerf width.

Also: concreting sand, grit sand, coarse sand

Coarse, angular sand used in concrete mixes and for floor screeds. Not suitable for bricklaying mortar due to its rough texture.

Also: combination shave hook, triangular scraper, paint scraper hook, shavehook

A scraping tool with a shaped blade — typically triangular, pear-shaped, or combination — used to remove softened paint from mouldings, architraves, and curved surfaces where a flat scraper cannot reach. Used in combination with a heat gun. The combination shave hook (multiple blade profiles on one tool) is the most useful type for general DIY.

Also: natural wool insulation, wool insulation, Thermafleece, Isolena

Natural fibre insulation alternative to mineral wool with lambda 0.035-0.040 W/mK. Better vapour permeability and moisture buffering than synthetic alternatives but carries a 2-3x cost premium.

Also: plasterboard, boards

Plasterboard and specialist board products used for wall and ceiling linings, fire protection, moisture resistance and tile backing.

Also: silicosis risk, engineered stone health risk, crystalline silica dust, RCS

Health risk from cutting engineered stone worktops. HSE published new simplified guidance in January 2025 requiring water suppression or M-class extraction and FFP3 masks. Australia banned engineered stone fabrication in 2024. Eight UK silicosis cases linked to artificial stone cutting were identified in August 2024. Risk is to installers/cutters, not homeowners in daily use.

Also: bathroom sealant, kitchen sealant, sanitary silicone

Flexible waterproof sealant applied from a cartridge using a sealant gun. Used at junctions between tiles and baths/showers, around sinks, worktops and window frames. Choose anti-mould formulations for wet areas. Available in white, clear, black and various colours.

Also: matching materials, materials condition

A PD condition requiring that extension materials are of a similar appearance to the existing house. Subjectively interpreted by each local planning authority with no definitive national standard.

Also: rear extension, single storey extension, back extension

A ground-floor extension built at the rear of a house. The most common type of home extension and the primary subject of permitted development rules under Schedule 2, Part 1, Class A of the GPDO 2015.

Also: Dekton worktop, ultra-compact surface worktop, porcelain worktop

Emerging premium worktop category (Dekton, Neolith). Made by compressing natural minerals at extreme heat. Extremely hard and heat-resistant. £350-700/lm installed. Requires professional templating.

Also: site visit, site survey, site investigation

A physical inspection of the property by a professional before calculations begin. Confirms ground conditions, existing structure, cavity widths, and access constraints.

Also: site record, daily site log, weekly site diary, construction diary

A daily log of what happens on site, including weather, who was working, deliveries, and any problems. Keep your own record — it’s invaluable evidence if there’s ever a dispute about delays or defects.

Also: ground investigation, soil investigation, site survey

A survey of ground conditions at the building site to determine soil type, bearing capacity, water table level, and presence of contamination or made ground. May be required by building control as a condition of approval before foundations are designed.

Also: site coverings, weather protection, tarpaulins, site protection materials

Sacrificial materials used to keep an open extension shell weathertight, protect partial roofs from rain, and cover finished joinery and floors during the messy second-fix trades. Cheap insurance against tens of thousands of pounds of weather damage to part-built work.

Also: hand-mixed concrete, DIY concrete, on-site mixing

The practice of batching concrete on site using a mixer, as an alternative to ordering ready-mix. Appropriate below approximately 2m³; ready-mix is preferable above that threshold. Trade-offs include cost, quality consistency, and labour time — 5m³ site-mixed requires approximately 100–125 mixer loads and 8–12 hours of labour.

Also: local skip companies

Companies providing skips in various sizes for construction waste removal and disposal

Provides skips for waste removal and disposal from construction sites

Also: road skip permit, highway skip permit, skip licence, skip road licence

Local authority licence required to place a skip on a public highway, typically costing £20-£75 per week

Also: skirting, MDF skirting, softwood skirting

Trim fitted at the junction of walls and floors. Available in MDF (cheaper, smooth, easy to paint) or softwood (more traditional). Common profiles include torus, ogee, bullnose and chamfered. Matching existing skirting in the rest of the house is important for a seamless finish.

Also: lump hammer (heavy), demo hammer

A heavy manual striking tool used as a cheaper alternative or follow-up tool to an SDS breaker. Community consensus: adequate for finishing cracked concrete after a breaker has done the primary breaking, but insufficient as a primary tool on slabs thicker than 100mm. Distinct from a lump hammer (smaller, one-handed).

Also: inline sliding door, patio sliding door, slider, inline patio door, lift-and-slide door

Sliding doors slide on a track behind a fixed panel, offering cleaner sightlines (20-35mm) and better thermal performance than bifolds, but with a smaller opening percentage (50-66%).

Also: small claims track, small claims, county court small claims, SCT

The civil court track in England and Wales for claims up to £10,000. Designed to be used without legal representation. Issue fees range from £35 to £455 depending on claim value (2025-2026 scale). Hearings are informal; timeframes typically 3-9 months for contested cases.

Also: Ring doorbell, Nest doorbell, video doorbell, wired doorbell

Video doorbells (Ring, Nest) that require a low-voltage transformer wired by the electrician. Homeowners often assume these are battery-only but wired versions need electrical work.

Also: smart meter mode loss, SMETS2 relocation

When a smart meter is relocated, it may lose smart mode connectivity. New Ofgem rules from February 2026 impose a 90-day limit and £40 compensation for suppliers who fail to fix smart meter mode issues.

Also: Hive thermostat, Nest thermostat, Google Nest, wireless thermostat

Programmable heating controls (Hive, Nest, Google Nest) that require transformer wiring by an electrician — not a simple plug-and-play device in older boiler systems. One of the most common second fix extras.

Also: fire detection system, smoke detector, Grade D2 Category LD3, interlinked smoke alarms, BS 5839-6 alarm system

The fire detection system required under Part B and Approved Document B for dwelling extensions. Typically Grade D2 Category LD3: mains-powered interlinked smoke alarms on each storey of the escape route, complying with BS 5839-6.

Identifying and documenting defects or incomplete work before final sign-off

Also: planer snipe, end gouge, planer end dip

A planer defect where the blade takes a deeper cut at the start or end of a pass, leaving a shallow gouge in the timber surface. Caused by incorrect pressure distribution — the operator must apply front-handle pressure at the start, even pressure in the middle, and shift to rear-handle pressure at the finish. A named technique issue that beginners encounter with electric planers.

Also: SNR, Single Number Rating

EU/UK measure of noise attenuation for hearing protectors. HSE recommends derating by 4 dB for real-world performance.

Also: surface water soakaway

An underground structure that disperses surface water into surrounding soil

Also: storm cell, soakaway cell, plastic soakaway module, infiltration crate, stormwater crate, EcoBloc

Modular polypropylene plastic cubes stacked to form an underground soakaway chamber. Wrapped in geotextile membrane to prevent soil ingress while allowing water to permeate out into the surrounding soil. More durable, compact, and easier to install than traditional rubble-filled soakaways. Multiple units stacked to achieve the required storage volume based on the roof area draining to them.

Also: plug sockets, power sockets, electrical sockets, double socket, single socket

Decorative front plates for electrical sockets, available in single and double configurations. Standard white plastic is cheapest; brushed chrome, stainless steel and matt black finishes are available at higher cost. Choose a consistent style throughout the extension.

Also: plug-in socket tester, socket outlet tester, wiring tester

A plug-in indicator device that tests for common wiring faults in 13A sockets: live-neutral reverse, live-earth reverse, missing earth, missing neutral. Simpler than a multimeter for basic socket checks after second-fix wiring.

The boards under the roof overhang (soffit) and at the roof edge (fascia)

Also: water softener bypass, bypass valve, softener bypass pipework

A section of pipework with isolating valves allowing a water softener to be bypassed for maintenance without shutting off the household water supply. Legally required under Water Fittings Regulations Schedule 2.26(1). Must be installed at first fix — retrofitting in a finished kitchen requires cutting into finished walls.

Also: SVP, soil vent pipe, 110mm drain pipe, soil stack

110mm diameter PVC pipe for connecting toilets and carrying foul waste to the main drain. Also acts as the soil vent pipe (SVP) which must extend above the roofline to ventilate the drainage system. Push-fit ring-seal joints. Building control will inspect the drainage layout.

Also: SVP, soil stack, waste stack

The main vertical waste pipe that carries foul water from bathrooms and kitchens to the underground drainage. Its position and direction constrain kitchen sink and island placement. Verify SVP direction before finalising layout — redesigning after discovery is expensive.

Also: property solicitor, conveyancing solicitor

A legal professional who can handle property matters, party wall disputes, boundary issues, and conveyancing

Also: Corian worktop, Hi-Macs worktop, Staron worktop, acrylic worktop

Acrylic-based worktop (Corian, Hi-Macs, Staron). Seamless joins, non-porous, repairable. Can be moulded into integral drainer and sink. Less heat-resistant than stone. £300-500/lm installed.

Also: timber worktop, wooden worktop, oak worktop, beech worktop, hardwood worktop, oak block worktop

Natural timber worktop (oak, walnut, iroko) at £150-350/lm supply-only. Beautiful and can be sanded and refinished. Requires regular oiling (annually minimum). Affected by moisture — not ideal near sinks without diligent maintenance.

Also: whole-bed method, full-bed adhesive, solid bedding, full coverage adhesive

Tile adhesive application technique achieving 100% contact between tile and substrate, eliminating voids. Required by BS 5385-1:2018 for tiles exceeding 14 kg/m². Critical over UFH — voids cause tile cracking as trapped air expands with heat.

Also: solvent cement fittings, glued waste fittings

Rigid plastic fittings joined with solvent cement to create permanent, leak-free connections for waste pipes. Should always be used for concealed waste pipe runs.

Also: waste pipe, solvent weld pipe, ABS pipe

Rigid plastic waste pipes in 32mm (basin waste) and 40mm (bath/shower/kitchen sink waste) diameters. Joined using solvent cement for a permanent, leak-free connection. Must be installed with correct fall (gradient) for waste to flow properly.

Also: bifold door fabricator, roof lantern supplier, glazing fabricator, bespoke glazing company, bifold door company

A supplier of made-to-order glass and glazing products such as roof lanterns, bi-fold door glass, and structural glazing for extensions.

Also: Toolnut, Classic Hand Tools, Axminster Tools

Specialist retailers stocking premium and mid-range hand tools (Veritas, Joseph Marples, Tite-Mark, Crown) not available at Screwfix or Toolstation

Also: spec creep, scope creep

The informal, uncontrolled process of upgrading materials or adding items mid-build without formally tracking the cost impact.

Also: spec document, project specification, tender specification, written spec

A written document detailing exactly what materials, standards and methods your builder must use, from the type of bricks to how the plastering should be finished. It removes ambiguity and protects you if there’s a dispute about quality.

Also: 600mm level, 1200mm level, 1800mm level, box beam level, Stabila level, I-beam level

A straight bar with bubble vials for checking surfaces are perfectly horizontal (level) or vertical (plumb). You will need multiple lengths: 600mm for kitchen units, 1200mm for general use, and 1800mm for walls and door frames.

Also: spirit level calibration test, 180 degree level test

A practical technique for verifying a spirit level is accurate: place the level on a surface, mark the bubble position, rotate 180 degrees horizontally, and check the bubble reads the same. Cheap or damaged levels fail this test.

Also: plastering sponge float, rubber sponge float

Float with a sponge face for dampening and smoothing plaster during finishing

Also: mortar stand, plaster stand

Flat board on a stand used to hold mixed plaster or mortar at a comfortable working height

Also: milestone payment, progress payment

A payment structure where builders are paid at defined milestones (foundations, walls to roof, roof watertight, first fix, second fix, final/retention) rather than upfront or on completion.

Also: Starlock, Starlock Plus, Starlock Max, StarlockMax, StarlockPlus, Starlock blade interface

The dominant oscillating multi-tool blade system (Bosch/Fein, 2016+). Three tiers: Standard, Plus, Max — backward-compatible upward only. Starlock accessories fit OIS tools; OIS accessories do NOT fit Starlock tools.

Also: 8-week rule, 13-week rule, planning guarantee

The fixed timeframe (8 weeks for non-major, 13 weeks for major applications) within which a local planning authority must determine an application.

Also: deflection gap, lintel deflection gap, bifold head clearance gap, flap trim, edging strip

A visible gap above bifold door frames caused by steel lintel deflection under load. Manufacturers typically require max 5mm deflection. The standard solution is a flap trim or edging strip. Measuring before full structural loading causes incorrect door orders.

Also: fabrication, steel manufacture, beam fabrication

The manufacturing process where a steel fabricator cuts, welds, and finishes structural beams to the exact dimensions in the structural engineer's drawings. Changes after fabrication starts mean paying twice.

Also: steel fabrication company, steelwork fabricator

A specialist manufacturer who cuts, welds, and finishes structural steel beams to the exact dimensions specified by the structural engineer. Lead times of 1-4 weeks depending on complexity.

Also: safety boots

Boots with a protective steel or composite toecap and puncture-resistant sole. Essential on any construction site to protect against dropped materials, standing on nails, and heavy objects. Must meet EN ISO 20345 S3 standard for construction work.

Also: DPC stepping, stepped damp proof course

On sloping ground, the DPC must step down in brick-course increments to maintain 150mm clearance above ground level at every point, with minimum 100mm laps at each step.

Also: granite fabricator, quartz fabricator, stone worktop company, worktop fabricator

A specialist trade that templates, fabricates, and installs stone and quartz worktops. Visits site after kitchen units are fitted to create templates, fabricates off-site (typically 5-10 working days), then returns to install. Separate engagement from the kitchen fitter.

Also: worktop template, templating appointment, worktop survey, stone templating

The process where a fabricator visits after all kitchen units are fitted and fixed to take exact measurements for stone or composite worktops. Templating takes 1-3 hours, followed by 2-4 weeks fabrication before installation. Sinks and hobs must be on-site before templating. Stone worktops cannot be ordered as cut-to-size before units are installed.

Also: stop end tile, ridge stop end, gable stop end, ridge end cap

Also: isolating valves, gate valves, service valves, stopcock

Valves that allow the water supply to be turned off for maintenance or emergency. Available in 15mm and 22mm sizes for different pipe runs. Every appliance and fixture should have its own isolating valve so it can be serviced without shutting off the entire supply.

Also: rubber strap wrench, filter strap wrench

A wrench that uses a fabric or rubber strap instead of serrated jaws to grip round objects without marking them. The correct alternative to a pipe wrench when working on chrome, polished, or soft-finish surfaces such as chrome trap bottles and decorative tap bodies.

Also: traditional strip, strip footing

One of the two most common domestic foundation types, involving a concrete strip at the base of a trench with blockwork built up from it.

Also: saw stroke, blade throw, stroke

The distance a reciprocating saw blade travels on each cycle (22–32mm). Longer stroke = faster, more aggressive cuts. The key performance spec — commonly confused with SPM (strokes per minute), which is less important.

Also: structural calcs

Engineering calculations determining load paths, beam sizes, and foundation requirements

Produces structural calculations and specifies beam sizes, foundations, and load paths

Also: ply, shuttering ply, WBP plywood, CE2+ plywood, exterior plywood

18mm structural-grade plywood suitable for floor decking, roof sheathing, structural bracing and formwork. WBP (weather and boil proof) grade required for any external or moisture-exposed applications. Standard sheet size 2440x1220mm.

Also: steels, RSJ, rolled steel joist, RSJs, steel beam, universal beam, UB

Steel beams used to support loads in building construction, including lintels, ridge beams, and support frames for openings in walls.

Also: sub-board, secondary consumer unit, distribution board, extension board

A secondary electrical distribution board fed from the main consumer unit, housing its own MCBs or RCBOs for extension circuits. Used when the main unit is full or voltage drop on long cable runs requires a local distribution point.

Also: ground subsidence, foundation subsidence

Downward movement of the ground beneath a building caused by soil shrinkage (typically clay in dry weather), tree root extraction, or undermining. Distinct from normal settlement. Indicators include diagonal cracks wider at top than bottom, cracks visible on both internal and external faces, and sticky doors and windows.

Also: additional bonding, earth bonding, equipotential bonding, cross-bonding

An additional earth conductor (typically 10mm² green/yellow cable) connecting metallic services to the earth terminal. Required under BS 7671 when new gas or water services enter an extension.

Also: SGSA 1982, Supply of Goods and Services Act

Requires tradespeople to carry out work with reasonable care and skill, within a reasonable time, and at a reasonable price if no price was agreed.

Also: water pressure test, hydraulic pressure test, above-ground pipe test, plumbing pressure test, BS EN 12056 pressure test

Pressure test of above-ground water supply and sanitary pipework before walls are closed, confirming watertight joints. Protocol: 38mm water gauge for 3 minutes per BS EN 12056. Distinct from drainage air test. A building control hold point before plasterboard and screed.

Also: SR1, SR2, SR3, screed flatness class, floor flatness tolerance

BS 8204 classification system for screed flatness. SR1 (max 3mm gap under 2m straightedge) required for tiles; SR2 (5mm) for general use; SR3 (10mm) for utility areas.

Also: rainwater, surface water drainage, stormwater, surface water run-off

Rainwater collected from roofs, driveways, and other impermeable surfaces that must be managed separately from foul drainage. A new extension adds impermeable area (roof, patio) and creates a new surface water management requirement. The SuDS discharge hierarchy governs how it must be disposed of.

Also: SPD, surge protector, Type 2 SPD, surge protection

An electronic device fitted in or alongside the consumer unit that limits voltage spikes from lightning and switching events. BS 7671 Amendment 2 made SPDs the default requirement for new consumer unit installations.

Also: SPD, Type 2 SPD, surge protector, consumer unit SPD

A protective device fitted inside or alongside the consumer unit that limits voltage spikes from lightning and switching events. BS 7671 Amendment 2 made SPDs the default requirement for new consumer unit installations.

Also: SuDS, sustainable drainage, SuDS hierarchy, discharge hierarchy, Schedule 3 SuDS

An approach to managing surface water that prioritises infiltration and reuse over direct sewer discharge. The national SuDS standards (refreshed June 2025) set a strict discharge hierarchy: rainwater reuse first, then infiltration to ground (soakaway), then discharge to a watercourse, then surface water sewer, then combined sewer as an absolute last resort. Underpinned by Schedule 3 of the Flood and Water Management Act 2010.

Also: steel wire armoured cable, armoured cable, armoured electrical cable, buried outdoor cable

Steel wire armoured cable required for buried outdoor electrical circuits. Can be buried without additional conduit because the steel wire armour provides mechanical protection against digging damage.

Also: light switches, dimmer switches, switch plates

Decorative front plates for light switches, available in 1-gang, 2-gang and 3-gang configurations. Same finish ranges as socket faceplates. Dimmer versions available for compatible lighting. Two-way switching requires specific wiring for hall/landing and room entry points.

Also: sealed system boiler, system boiler with unvented cylinder

Alternative to combi boiler using a separate hot water cylinder. Delivers consistent pressure across multiple outlets simultaneously.

Also: power flush, chemical flush, system inhibitor, heating inhibitor, Fernox F1, Sentinel X100, BS 7593 flush

Before a heating system is commissioned, all flux residues and swarf from new pipework must be flushed out and a corrosion inhibitor added — a legal requirement under BS 7593 and a condition of most boiler manufacturers' warranties.