Building Terms Glossary

Also: pipe chase, chasing, chased channel, cable chase, masonry chase

Channel cut into masonry to conceal pipes and cables within the wall. Approved Document A imposes strict depth limits: vertical chases max one-third of single leaf wall thickness, horizontal chases max one-sixth. Central to both first fix plumbing and first fix electrics.

Also: timber wall plate, roof wall plate

A treated timber member bedded in mortar on top of the blockwork inner leaf, to which rafters, trusses, and ceiling joists are fixed. Holding-down straps secure the wall plate to the blockwork at 2m centres — a BCO check point.

Also: rawlplugs, plastic plugs, expansion plugs

Plastic expansion plugs inserted into drilled holes in masonry to accept screws. Available in 6mm (red), 8mm (yellow) and 10mm (brown) sizes. The drill bit and plug size must match, and the screw gauge must suit the plug. Getting this right is fundamental and something most guides never explain properly.

Also: wall starter, stainless steel starter, channel starter bar, helical starter

A mechanical fixing system for connecting a new extension wall to an existing house wall, replacing the traditional method of toothing out alternate bricks. Faster to install but does not give as clean a finish where brickwork is exposed.

Also: wall ties, cavity wall tie, masonry tie

Stainless steel or galvanised metal connector embedded in the mortar joints of both leaves of a cavity wall, transferring lateral load and stabilising the outer leaf. Spacing and embedment depths are set by NHBC 6.1 and BS EN 845-1; typical spec is 2.5 ties per square metre at 450mm vertical and 900mm horizontal centres, with closer spacing at openings.

Also: cavity wall ties, brick ties

Metal ties embedded in mortar joints that connect the inner and outer leaves of a cavity wall, providing structural stability. Building control inspectors check that wall ties are at correct centres and properly embedded.

Also: warm deck roof

Flat roof construction where insulation sits above the structural deck, keeping the structure warm. Preferred modern approach. Requires 120mm+ PIR for Part L 2021 compliance.

Also: food waste disposer, insinkerator, garbage disposal

An under-sink electrical appliance that grinds food waste. Requires a dedicated 13A switched socket or switched FCU inside the under-sink cabinet as a first fix provision.

Also: WEEE Regulations, WEEE Directive, WEEE

Prohibits electrical appliances from general waste skips due to hazardous materials including lead and mercury

Also: waste pipe gradient, waste pipe slope, drain fall

The gradient at which waste pipes must be installed. Approved Document H specifies 18-90mm/m for 40mm pipe, with a maximum 3m run before an AAV is needed.

Also: P-trap, bottle trap, S-trap, sink trap

U-shaped or bottle-shaped fittings installed below sinks, basins, baths and showers. They hold a small amount of water that acts as a seal to prevent drain smells entering the room. P-traps for wall waste exits, S-traps for floor waste exits, bottle traps where space is limited.

Also: Thames Water, Anglian Water, Severn Trent, Yorkshire Water, Southern Water, United Utilities, Wessex Water, South West Water, Welsh Water

Regional water and sewerage company that homeowners must contact for a build-over agreement when building within 3m of a public sewer. Thames Water Class 1 costs £130, processed in 21 days. Cannot build over shared manholes.

Also: 2011 sewer transfer, private sewer adoption 2011, October 2011 sewer transfer

Also: WIA 1991, Water Industry Act 1991 Section 185, Water Industry Act 1991 Section 106

Section 185 is the statutory basis under which developers with a land interest can request a sewer diversion when an extension is sited over or near a public sewer.

Also: water tube level, hose level, Roman level

A low-tech levelling device using two clear tubes connected by a hose filled with water. Because water finds its own level, it transfers levels around obstacles where optical levels cannot achieve line-of-sight.

Also: salt-based water softener, ion exchange softener, water conditioner

A unit that removes limescale-causing minerals from mains water using ion exchange. Requires plumbing into the cold water supply before the kitchen run, typically under the sink or in a utility room. Unit £500–£1,200, installation £150–£400. Must be specified at first-fix plumbing stage.

Also: Water Fittings Regulations, Water Regulations 1999, WRAS regulations

Primary legislation governing all plumbing fittings and installation in England and Wales. Requires fittings to prevent waste, misuse, and contamination.

Also: Water Quality Regulations 2000, drinking water quality regulations

Sets maximum permissible sodium concentration in drinking water (200mg/l). Basis for the requirement to maintain an unsoftened drinking water tap when a water softener is installed, particularly relevant in hard water areas where softened water may exceed this limit.

Also: drain water test, hydraulic test

The follow-up drainage test triggered by a failed air test. Per BS EN 1610: fill the system and allow 120 minutes for absorption, then monitor water loss over 30 minutes — acceptable loss is 0.15 L/m² for pipelines or 0.20 L/m² including manholes. A failed air test does not condemn the drain; the water test verifies leak severity and location.

Also: watertight shell, windtight and weathertight, building shell, weathertight stage

The construction milestone at which the structure has walls, roof, and all openings sealed against rain and wind. Once achieved, internal trades can work regardless of weather. A key programme milestone that triggers a stage payment and enables parallel internal work.

Also: weep hole, open perpend, cavity vent, perpend weep vent

Small plastic insert placed in the perpend (vertical mortar joint) below a cavity tray to allow water that has entered the cavity to drain back outside. Required at maximum 900mm centres per Approved Document C.

Also: weep hole

Small openings left in perpendicular mortar joints above window and door openings to allow water collected by cavity trays to drain outward. NHBC requires a minimum of two per opening, spaced no more than 450mm apart.

Also: shop vac, industrial vacuum, Class M vacuum, dust extractor, workshop vacuum, M-class vacuum

A Class M industrial vacuum that connects to power tool dust ports to capture fine sawdust not caught by onboard bags. HSE-recommended for indoor mitre saw and power tool use under COSHH.

Also: trustedtraders.which.co.uk

Consumer organisation Which? operates a vetting scheme for tradespeople including builders, with background checks and consumer-verified reviews.

Also: glazier, window fitter, fenestration installer, window company

Specialist trade that surveys, manufactures, delivers, and installs window and door frames and glazed units as a packaged supply-and-fit service.

Also: door reveal, reveal, window lining, reveal depth

Internal recess between the window frame and the internal wall face, finished with timber packing and plaster by the builder after window installation.

Also: sill height, kitchen window sill height

The height of the window sill from finished floor level. Kitchen extension windows should specify 1020mm from FFL, not 900mm. A sill at 900mm (worktop height) creates conflicts with appliances and tiling. Must be specified to the builder before windows are ordered.

Also: automatic wire stripper, T&E stripper, cable stripper

A tool for cleanly removing the insulation from electrical cable without damaging the copper conductor inside. Adjustable types can be set to the exact cable diameter. Essential for preparing cables for connection to sockets, switches, and consumer units.

Also: bevel-edge chisel, paring chisel, bench chisel

A hand tool with a bevelled steel blade used for paring and shaping timber. Used as companion tool to a router for hinge recessing — routers leave rounded corners in hinge recesses that must be squared with a chisel before the hinge will seat flat. Also used for general timber joinery throughout second fix and kitchen installation. Distinct from a bolster chisel (masonry use).

Also: MDF dust risk, hardwood dust WEL, wood dust WEL, softwood dust WEL, timber dust health risk

Wood dust is a respiratory sensitiser causing occupational asthma; hardwood dust is a nasal carcinogen. HSE WELs: hardwood 3 mg/m³, softwood 5 mg/m³. MDF dust also contains formaldehyde. Requires FFP2/FFP3 protection when sawing.

Fills nail holes, screw heads, edge imperfections, and surface defects in timber and MDF before painting. Available in tubs (interior) and tubes (exterior). Sand smooth after drying.

Also: chipboard screws, multi-purpose screws, yellow screws

General-purpose screws for fixing timber to timber. Available in various gauges (3.5mm to 6mm) and lengths (25mm to 150mm). Sold in boxes of 100-1000. Pozi drive (PZ2) is the most common head type. Choose stainless steel or coated screws for external use.

Also: WAH Regs 2005, SI 2005/735

The primary legislation governing all scaffolding erection and use in the UK. Mandates guardrails (min 950mm), toe boards, intermediate rails, formal inspection records every 7 days, and that only competent persons erect, alter, or dismantle scaffold.

Also: rigger gloves

General-purpose gloves for handling rough materials, timber, bricks, and metal. Protect against cuts, splinters, and abrasion. Rigger-style leather gloves are the most common on UK building sites. Keep several pairs as they wear out quickly.

Also: kitchen work triangle, cooking triangle

The spatial relationship between hob, sink, and fridge. Each leg should be 1.2–2.7m with a total perimeter no more than 7m. The primary layout planning principle for decades, now complemented by the zones approach for open-plan kitchens.

Also: worktop connecting bolts, worktop joint fasteners, draw bolts

Specialist bolts that pull worktop sections tightly together at joints.

Also: worktopexpress.co.uk

Online worktop supplier highly recommended on MoneySavingExpert forums. Stocks laminate, solid wood, and quartz worktops for direct purchase by homeowners.

Also: worktop template jig, worktop joint jig, kitchen worktop jig, Unika worktop jig

Metal template clamped to worktop to guide a router for cutting bolt channels and matching joint profiles.

Also: stone worktop template, quartz worktop template appointment, granite templating

Process where a stone/quartz worktop fabricator visits site to create an exact template, with 1-2 week fabrication lead time after the appointment.

Also: kitchen worktops, kitchen countertops, work surfaces

Kitchen work surfaces in quartz, granite, sintered stone, solid surface, solid wood and laminate. Supply-only prices range from £80/lm for laminate to £700/lm installed for premium sintered stone. Stone and solid-surface worktops require professional templating once units are fitted, with 2-4 week fabrication lead times that must be planned into the build schedule.

Also: crowbar, pry bar, pinch bar, swan neck bar

A heavy steel bar with a curved claw end for prying apart timber, removing nails, and demolition work. Invaluable when stripping out old kitchens, removing door frames, and taking up floorboards.

Also: wrenkitchens.com, Wren

The largest kitchen retailer in the UK. Offers step-by-step video measuring guides and an online kitchen planner. Near-permanent sale pricing model — compare actual prices, not advertised discounts.

Also: written reps

The dominant planning appeal procedure covering 91% of householder appeals. All evidence is submitted in writing with no verbal hearing.