Building Terms Glossary

Also: T-shank, T-shank jigsaw blade, universal shank, Bosch T-shank

The universal jigsaw blade standard used by all major manufacturers. Enables tool-free blade changes. Replaced the older U-shank system. All modern jigsaw blades (Bosch T101B, T101BR, etc.) use T-shank fitting.

Waterproofing below-ground walls and floors to prevent water ingress

Also: 5m tape measure, 8m tape measure, Class I tape measure, measuring tape, retractable tape measure, Stanley FatMax

A retractable measuring tape marked in millimetres and metres. A 5m tape covers most interior work; an 8m tape is better for measuring rooms and external dimensions. Buy one with a strong lock mechanism and a wide blade that stays rigid when extended.

Also: Class I tape measure, Class II tape measure, EC Class I, EC Class II

The EC Measuring Instruments Directive classifies tape measures as Class I (±0.3mm at 2m) or Class II (±0.7mm at 2m, widening to ±2.3mm at 10m). For extension work where a 5mm error could mean a kitchen unit does not fit, Class I accuracy matters.

Also: loose hook, floating hook, sliding hook

Design feature where the hook at the end of a tape measure slides slightly to compensate for its own thickness, ensuring accurate inside and outside measurements

Also: tungsten carbide tipped blade, carbide tipped blade, carbide saw blade, TCT circular saw blade, TCT mitre saw blade

Tungsten Carbide Tipped blade — the standard blade type for circular and mitre saws. Carbide tips stay sharp far longer than steel. Tooth count (TPI) determines cut quality: 24T for ripping timber, 40-60T for clean cuts on skirting and architrave.

Also: tungsten carbide tipped planer blade, carbide planer blade, TCT planer knife, TCT blade 82mm

Tungsten Carbide Tipped planer blades — last approximately 20x longer than HSS blades and are the industry-standard choice for site work, hardwood, MDF, and chipboard. The correct choice for any timber containing adhesive or abrasive material. Available in reversible double-edged format which effectively doubles service life. Priced at £7.99–£16.47 for a 2-pack (2026).

Also: grain tearout, splintering, chipping, end grain splintering, wood tearout

The specific defect that occurs when a planer blade lifts and tears wood fibres rather than slicing them cleanly. Caused by planing against grain direction, using excessive depth, blunt blades, or wrong technique at end grain corners. The primary quality defect beginners encounter when planing doors or timber surfaces. Can be avoided by reading grain direction, using shallow depth of cut, and correct end-grain technique.

Also: TPI, blade TPI, saw blade TPI, tooth count per inch

The primary blade selection specification: low TPI (6–10) for fast rough cuts in softwood; mid TPI (10–20) for clean cuts in hardwood and MDF; high TPI (20+) for laminate. Applies to jigsaws, reciprocating saws, and hand saws.

Also: kitchen pod hire, portable kitchen unit, temporary kitchen hire

A self-contained kitchen unit delivered to the driveway, fitted with oven, hob, fridge-freezer, and sometimes a washing machine — an alternative to a DIY temporary kitchen setup during long builds

Also: temporarykitchenpod.co.uk

UK temporary kitchen pod hire company offering units with 4-ring gas hob, double oven, refrigerator, and optional washing machine

Also: temporary support, dead shoring, dead shores, propping

The process of installing acro props and strongboys to support the structure above a load-bearing wall before it is opened up for steel beam installation. Props may need to remain in place for days or weeks.

Also: EPDM termination bar, membrane termination bar, aluminium termination bar

Also: terrace, mid-terrace, end-terrace

A house that shares walls with properties on both sides. Under the Larger Home Extension scheme, single-storey rear extensions can extend up to 6 metres. Party wall considerations apply on both sides.

Also: thermally broken frame, thermal barrier

Structural barrier within an aluminium window or door frame that prevents heat conduction through the metal, required by NHBC Standards to prevent cold bridging and condensation.

Also: cold bridging

Where heat passes through a building element faster than surrounding materials, causing cold spots

Also: thermal performance, U-value calculations, SAP calculations

Calculations demonstrating that a building extension meets the thermal performance requirements of Building Regulations Part L, including U-values for walls, roof, floor, and windows.

Also: thermal envelope, 25% re-roofing threshold, renovation threshold

Also: thermal expansion, thermal cycling, differential expansion, thermal fatigue

Also: TMV, blending valve, mixing valve, UFH mixing valve, low-loss header

Required when connecting UFH to an existing gas boiler producing water above 55°C. Blends high-temperature boiler water with cooler return water to deliver safe 35-55°C flow to UFH loops.

Also: TRV, thermostatic valve

Self-regulating valve on radiators that controls room temperature by adjusting hot water flow. Building regulations require TRVs on most radiators.

Also: third surveyor arbitration, party wall arbitrator

A surveyor nominated to arbitrate if two appointed party wall surveyors cannot agree, adding £2,000-5,000 if actively appointed

Also: 3m tail rule, meter tail distance, consumer unit distance limit

The practical constraint that the consumer unit must be within 3 metres of the electricity meter. When a meter is relocated, the consumer unit may also need to move.

Also: patio drainage, door sill drainage, bifold drainage channel, threshold fall, sill fall, 1:60 patio fall

Correct threshold drainage requires the patio to slope away from the house with a drainage channel at the threshold. Wrong sill fall direction is the most common cause of post-installation water ingress. Part C compliance requirement.

Also: through-coloured tile, through-body colour, integral colour

Also: binding wire, rebar tie wire, tying wire, annealed wire

17 gauge annealed steel wire used to bind rebar intersections and mesh overlaps. 9-13 kg needed per tonne of rebar. Costs £6-8 per 8kg coil.

Also: flexible tile adhesive, wall tile adhesive, floor tile adhesive, rapid set adhesive

Cement-based adhesive for fixing ceramic, porcelain and natural stone tiles to walls and floors. Flexible adhesive is essential on floors, heated floors, plywood substrates and large-format tiles. Rapid-set versions allow grouting the same day. White adhesive for translucent tiles; grey for everything else.

Also: tile levelling clips, tile spacers and levelling clips, Rubi tile levelling system, wedge levelling system, lippage control system, tile spacers

Plastic clips and wedges used to hold adjacent tiles at the same height during adhesive set, eliminating lippage. Essential for large-format tiles (60×60cm and above).

Also: roof tile profile, tile shape, tile design

Also: Topps Tiles, Tile Mountain, Porcelain Superstore, Tile.co.uk, Direct Tile Warehouse, Target Tiles, Hyperion Tiles

Suppliers of floor and wall tiles. Trade accounts offer 15–25% off retail prices — the real project saved ~£967 (£3,933 vs ~£4,900 retail) by ordering through the tiler's trade account.

Also: floor tiler

Lays wall and floor tiles in kitchens, bathrooms, and other areas

Structural and non-structural timber products including framing timber, sheet materials, and finishing timbers used throughout a construction project.

Also: timber conditioning, acclimatising timber

Allowing timber to adjust to the moisture content of its installation environment before fixing. Typically 24-48 hours for interior trim (skirting, architrave). Prevents warping, shrinkage, and joint opening after installation.

Also: truss clips, restraint straps, framing anchors, hold-down straps

Galvanised steel straps, clips and plates used to tie structural timber elements together and restrain them against wind uplift. Restraint straps connect the roof structure to the walls, and truss clips connect individual trusses to the wall plate. Building control will specifically check these are installed.

Stamp on structural timber showing strength class (C16/C24), grading body, species, moisture condition (KD = kiln dried), and CE marking. Building control inspectors check these on every structural timber member. Missing or illegible stamps can cause work to be rejected.

Specialist suppliers of structural and finishing timber, sheet materials, and treated wood

Also: use class, timber use class, UC rating

The UC1-UC4 classification system (BS 8417/BS EN 335) that determines what level of preservative treatment timber needs based on its moisture exposure. UC1 is interior dry, UC2 is interior with wetting risk (wall plates), UC3 is external above ground, UC4 is ground contact. The single most important thing to understand when buying treated timber.

Also: time of the essence notice, making time of the essence

A legal term meaning the completion date in your contract is a strict deadline, not a rough target. If this clause is included and the builder misses the date, you can claim compensation or terminate the contract.

Also: aviation snips, metal shears, compound snips

Heavy-duty shears for cutting thin sheet metal, roof flashing, metal stud framing, wire mesh, and ventilation ducting. Compound-action (aviation) snips come in straight, left-cut, and right-cut variants for different curve directions.

Also: tingle, line tingle

Small metal plates used to support a builder's line on long runs to prevent sagging

Also: power tool consumables, blade consumables, fuel cells, replacement blades

Recurring power-tool running costs that quote-writers tend to ignore — gas fuel cells for cordless nailers and replacement planer blades. Small unit prices but meaningful over the course of a build.

Also: topseal.co.uk, Topseal GRP

Also: screened topsoil, garden topsoil, BS3882 topsoil

Upper layer of fertile growing medium required for turfing or planting. Construction machinery compacts subsoil and removes topsoil; new topsoil must be brought in at 100-150mm depth over any area to be turfed or planted. Cost: £45-135/m³.

Also: lime torching, mortar torching, internal tile bedding

Also: boat level, pocket level, mini spirit level

A compact 230-250mm spirit level with three vials (horizontal, vertical, 45-degree) that fits in a tool belt. Preferred by electricians and plumbers during first-fix work in tight spaces.

Also: DMPO 2015, Development Management Procedure Order

The specific statutory instrument that sets the 8-week determination target for non-major applications, 13-week for major, and the framework for neighbour consultation.

Also: GPDO 2015, GPDO, General Permitted Development Order

The specific statutory instrument that defines all permitted development rights for houses in England, including Schedule 2, Part 1, Class A (single-storey rear extensions) and the prior approval route for larger extensions.

Also: TCPA 1990, TCPA

The primary legislation enabling planning appeals in England. Section 78 gives householders the right to appeal a refusal to the Planning Inspectorate.

Also: trade account holder, Howdens trade account, builders merchant trade account

An account with a builders merchant or kitchen supplier that is only available to trade professionals, not homeowners. Explains why homeowners cannot buy direct from Howdens or Benchmarx.

Also: trade account supplier, trade-only kitchen supplier, Howdens model

A supplier model where homeowners cannot order directly — they must use a tradesperson who holds a trade account with the supplier. Howdens and Benchmarx are the primary examples in the kitchen context. Creates a sequencing dependency: the homeowner must appoint a fitter before they can even get a price.

Also: Local Trading Standards, Trading Standards Service, Citizens Advice consumer helpline

The local authority service that enforces consumer protection law. Contact them if a builder or supplier has been misleading, aggressive, or dishonest.

Also: threshold strip, floor trim, door threshold, T-bar trim, ramp strip, joining strip, floor transition profile

A metal, wood, or plastic profile that covers the join between two different floor finishes or accommodates a height difference at the threshold. Must be planned before flooring is laid, not after. Critical at the junction between extension floor and existing house floor.

Also: tanalised timber, pressure treated timber, green timber, Tanalith E treated timber, VPI treated timber

Timber pressure-treated with preservative (typically tanalith) to resist rot and insect attack. Essential for any timber in contact with or close to the ground, external use, or within 150mm of a DPC. Has a distinctive green tint when new.

Also: TPO, tree preservation orders, protected tree rules

A legal designation by the local planning authority protecting specific trees. Cutting roots, raising or lowering ground levels around a TPO-protected tree requires written LA consent before work begins. Penalties are unlimited. Homeowners must check for TPOs before any landscaping excavation near mature trees.

Also: trenchfill, deep trench fill, trench fill

The modern preferred method for most UK domestic extensions where the trench is filled almost entirely with concrete, eliminating below-ground blockwork.

Also: rammer, jumping jack, compaction rammer, wacker rammer

A compaction tool that uses impact force rather than vibration, suited to narrow trenches and confined drainage backfill where a plate compactor cannot fit. The correct tool for trench backfill around drainage pipes. Available from the same hire companies as plate compactors. Distinct from a plate compactor (vibration-based, suited to open areas) and a roller.

Also: trench support, battering, shoring

Required for safety when foundation trenches exceed 1.2m depth, adding significant cost and time.

Also: Trend, trend-uk.com, Trend router bits, Trend jigs

The dominant UK router bit and jig manufacturer. Market leader in UK router cutters. Their jigs (KWJ worktop jig series, Butt Hinge Template, Concealed Hinge Jig) and bit sets are the primary products recommended for UK homeowners. Products stocked at Screwfix and Toolstation. Trend T4EK (1/4" collet) and T7EK (1/2" collet) are the two most referenced UK router models.

Also: test pit, exploratory pit

An exploratory excavation to inspect soil type, depth to bearing stratum, and contamination before foundation design.

Also: background ventilator, trickle ventilator

A small continuous ventilation slot in a window or door frame, required under Approved Document F to provide background ventilation to habitable rooms. The BCO checks new windows include trickle vents or equivalent ventilation.

Also: trustmark.org.uk

Government-endorsed quality scheme for tradespeople in the UK, covering a wide range of trades including builders.

Also: 1.5mm T&E, lighting cable, 1.5mm twin and earth

1.5mm² twin-and-earth flat cable used for lighting circuits. Contains live (brown), neutral (blue) and earth (bare copper, sleeved green/yellow at terminations). Sold in 100m drums. Must be run in accordance with BS 7671 wiring regulations.

Also: 10mm T&E, 10mm twin and earth, 10mm cooker cable, 10mm shower cable

Heavy-duty electrical cable required for large induction hobs over 7.4kW that need a 40A breaker. More expensive than standard 6mm² cooker cable and must be specified before first fix.

Also: 2.5mm T&E, ring main cable, socket cable, 2.5mm twin and earth

2.5mm² twin-and-earth flat cable used for socket ring mains and radial circuits. The standard cable for power sockets throughout the extension. Sold in 100m drums.

Also: 4mm twin and earth, 4mm² cable, 4mm² twin-and-earth, 4mm T&E

Cable specified for kitchen island socket circuits where the run exceeds approximately 15m, to stay within BS 7671 Reg 525.1 voltage drop limits. Sits between standard 2.5mm² socket cable and 6mm² cooker cable.

Also: 6mm T&E, cooker cable, shower cable, 6mm twin and earth

6mm² twin-and-earth cable for high-power circuits: cookers, electric showers and electric hobs. Thicker and stiffer than smaller cables, requiring larger back boxes and more careful routing. Sold in 50m drums.

Also: two-pole tester, contact voltage indicator, approved voltage indicator, AVI, self-proving tester

A contact tester that measures voltage by touching conductors directly. Tests all conductor combinations (L-E, L-N, N-E). Under HSE GS38, only a two-pole tester complying with BS EN 61243-3 is acceptable for proving a circuit dead.

Also: 2-way switching, two-way switch circuit, staircase switching, landing switching

A wiring arrangement allowing a single light to be controlled from two switch positions (e.g. top and bottom of stairs). Requires specific cabling (three-core-and-earth strapper cable between switches).

Also: Type A, Type AC RCD, Type B RCD, RCD type classification, Type A RCBO

The classification system for RCDs and RCBOs based on what type of electrical fault they can detect. Type AC detects only sinusoidal AC leakage; Type A detects AC and pulsating DC (mandatory minimum for domestic socket circuits since BS 7671 Amendment 2).