Building Terms Glossary

Also: boiler copper pipe rule, 1m copper rule

Industry-standard requirement that at least 1 metre of copper pipe must be used between a boiler and any push-fit plastic connection.

Also: straight edge, feather edge, aluminium straight edge, plastering feather edge

A rigid 2-metre aluminium tool used to check the flatness of walls and floors against NHBC Chapter 9.1 tolerances. Measures surface flatness (±3mm in 2m for walls, ±5mm in 2m for floors). Distinct from a spirit level, which measures level not flatness.

Also: 3-4-5 triangle, builders triangle method, 6-8-10 method

Pythagorean method for checking right angles on site using measurements of 3, 4, and 5 units (or multiples)

Also: machine grading, MGS, machine graded structural timber, strength graded timber, visually graded timber, visual grading

Also: magnet.co.uk, Magnet

Major UK kitchen retailer offering a free home measure service. Good mid-range kitchen supplier with declining showroom presence.

Also: magnetic level, magnetic torpedo level

A spirit level with a magnetic base that grips onto metal pipes, angle irons, and steel frames without needing to be held. Used by plumbers for checking pipe falls and by electricians for aligning metal conduit.

Also: magnetic filter, boiler filter, Magnaclean, Fernox TF1, system filter

A filter fitted on the central heating return pipe to capture ferrous debris (sludge, magnetite) before it enters the boiler heat exchanger. Often a boiler warranty condition. Costs £120-250. Omission is a common commissioning defect flagged in NHBC Part 8.

A two-storey flat with its own entrance. Like flats, PD rights for extensions do not apply to maisonettes — planning permission is required for any extension.

Also: manhole move, inspection chamber relocation, sewer access chamber relocation

A bench-mounted tool that scores and snaps ceramic and porcelain tiles along a straight line. Quick and clean for straight cuts on standard tiles. Not suitable for curved cuts or very thick porcelain.

Also: mapserve.co.uk

OS-licensed mapping platform used by architects and endorsed by Ordnance Survey for planning application maps.

Also: pin gauge, spur gauge, wheel marking gauge, wheel gauge, panel gauge

A tool for scribing a line parallel to an edge at a set distance. Used for marking timber for cutting, setting consistent margins, and transferring measurements. A simple but precise tool for repetitive marking tasks.

Also: thermally broken block, insulating block, Marmox Thermoblock, thermal bridge block

Thermally broken masonry block (lambda 0.27 W/mK vs 1.13 for dense concrete block) used at wall junctions to interrupt thermal bridges where extension walls meet the existing house structure.

Also: painter's tape, decorator's tape

Low-tack tape used to protect surfaces adjacent to painting areas — window frames, floor edges, ceiling lines, switches and sockets. Using standard adhesive tape instead of low-tack masking tape can damage surfaces when removed.

Bricks, blocks, sand, cement and mortar products used in wall construction and structural masonry work.

Also: exterior paint, outdoor wall paint, weathershield

Durable, weather-resistant paint formulated for exterior masonry surfaces including render, pebbledash and concrete. Available in smooth and textured finishes. Good quality masonry paint lasts 10-15 years between recoats. Apply to dry surfaces only; spring/summer is ideal.

Also: material planning considerations, planning material considerations

The legal framework for what a planning inspector or officer may and may not take into account when making a decision.

Also: commencement of development, starting development

The specific legal definition of what constitutes starting a planning permission, critical for the 3-year validity window.

Also: materials description, external materials statement

A required document for prior approval submissions describing external materials and confirming visual similarity to the existing house.

Also: MCB lock-off device, circuit breaker lockout, MCB lockout, breaker lock

A mechanical clip that fits over a miniature circuit breaker (MCB) in the OFF position and accepts a padlock, physically preventing re-energisation during dead work. Required by Electricity at Work Regulations 1989 Reg 13. Insulating tape is not an adequate substitute.

Also: trip curve, B curve MCB, C curve MCB, D curve MCB, Type B MCB, Type C MCB

The characteristic defining how quickly an MCB trips at different levels of overcurrent. Type B (3-5x rated current) is the domestic standard; Type C (5-10x) for motors and fluorescent lighting; Type D (10-20x) for heavy industrial.

Also: circuit breakers, circuit breaker, MCB, trip switch, fuse

Automatic switches that trip to disconnect a circuit when current exceeds the rated value (6A for lighting, 32A for ring mains, etc.). Fit into the consumer unit on a DIN rail. Protect against overload and short circuit but not earth faults (that is the RCD's job).

Also: MDF board, medium density fibreboard, MR MDF, moisture resistant MDF

Smooth, dense engineered board available in 12mm and 18mm thicknesses. Excellent for internal finishing work, shelving and painted surfaces. Not suitable for wet areas unless moisture-resistant grade is used. Produces fine dust when cut; always wear a mask. Standard sheet size 2440x1220mm.

Also: site survey, architectural survey

An accurate measurement of your existing property, usually done with a laser, that your architect needs before they can start drawing plans. This is typically one of the first things you’ll pay for.

Precision tools for measuring distances, checking levels, and marking positions. Accurate measurement is the foundation of quality construction work.

Also: ADR, alternative dispute resolution, RICS mediation, building dispute mediation

A voluntary, non-binding process where a neutral third party facilitates negotiation between disputing parties. Any agreement reached becomes binding. Government-cited research shows 70% of mediation cases resolve without going to court. Courts increasingly expect parties to have attempted mediation before issuing proceedings.

Also: methyl ethyl ketone peroxide, Butanox M50, GRP hardener, fibreglass catalyst, catalyst hardener

Also: roof underlay tape, membrane sealing tape, breather membrane tape, lap tape, self-adhesive roofing tape

Also: A142 mesh, fabric reinforcement A142, steel mesh A142, 6mm mesh

Light-duty welded steel mesh used to reinforce ground floor concrete slabs. A142 is the lightest standard mesh and is sufficient for most domestic floor slabs.

Also: A193 mesh, fabric reinforcement A193, steel mesh A193, 7mm mesh

Medium-duty welded steel mesh for floor slabs requiring greater reinforcement, such as where ground conditions are poor or spans are longer.

Also: A252 mesh, fabric reinforcement A252, steel mesh A252, 8mm mesh

Heavy-duty welded steel mesh for reinforced slabs, raft foundations and areas subject to heavier loads. Typically specified by the structural engineer.

Also: gas meter housing, electricity meter housing, semi-recessed meter box, external meter box

The housing installed in the external wall of the extension to receive the gas or electricity meter. Must be installed by the builder during wall construction before scaffolding comes down.

Also: piece rate, bricklayer meterage, per-thousand rate, price per 1,000 bricks

A payment structure where bricklayers are paid per 1,000 bricks or blocks laid rather than a day rate. This creates weather-related disputes because bricklayers on meterage rates lose money in bad weather and may refuse to attend site.

Also: Rockwool, Knauf insulation, glass wool, loft insulation, stone wool insulation, Rockwool RWA45, Knauf Earthwool

Flexible mineral fibre insulation in rolls or slabs. Used between timber studs, joists and rafters. Good acoustic properties as well as thermal. Cheaper than PIR but requires greater thickness for equivalent thermal performance. Common brands include Rockwool and Knauf.

Also: excavator, 1.5T digger, 3T digger, tracked excavator

The primary piece of plant used to excavate foundation trenches. Hire cost typically £125-250/day self-drive. Groundworkers bring their own or hire one.

Also: minimum pitch, minimum tile pitch, minimum pitch for tiles

Also: mist coat primer, diluted emulsion

A diluted coat of non-vinyl matt emulsion (typically 70:30 paint to water) applied as the first coat on new plaster. Allows the paint to soak into the porous plaster surface and create a bond. Using vinyl or undiluted paint instead causes peeling. Must be applied before any topcoats.

Also: Mitre Mate, mitre adhesive

Two-part cyanoacrylate adhesive and activator spray for instant-bonding mitre joints in skirting and architrave. Prevents joints opening as timber shrinks. Mitre Mate is the most common UK brand.

An angled joint (typically 45 degrees) where two pieces of trim meet at a corner. Used at the top corners of architrave and at external corners of skirting. Internal skirting corners use a scribed joint instead.

Also: chop saw, drop saw

A bench-mounted power saw with a pivoting circular blade for precise crosscuts, mitres, bevels, and compound angles. Used for skirting boards, architrave, roof timbers, and flooring. Available as basic compound, sliding compound, and double-bevel sliding variants.

Also: chop saw stand, saw stand, universal mitre saw stand

A folding stand that raises a mitre saw to working height with roller supports for long workpieces. Enables accurate cutting of full-length skirting and architrave boards. Typically £60–130.

Also: plaster mixer, mixing whisk, paddle mixer attachment

Drill attachment for mixing plaster, mortar, or render in a bucket

Also: MCOL, mcol.gov.uk, online court claim

The online portal for filing civil money claims against individuals or businesses in England and Wales without using paper forms. Available at gov.uk/make-court-claim-for-money.

Also: moneyhelper.org.uk, Money and Pensions Service, MaPS

A free government-backed service offering impartial guidance on borrowing, budgeting, and financing home improvements.

Also: wet bedding, wet ridge, cement-bedded ridge, bedded ridge, mortar bed fixing

Also: mortar snots, cavity droppings, mortar bridges

Lumps of mortar that fall into the cavity during bricklaying and accumulate on wall ties or the DPC, creating moisture bridges. Building control inspects for this at the DPC stage.

Also: joint profile, pointing profile, bucket handle joint, flush joint, weather-struck joint, recessed joint

The finished shape of a mortar joint between bricks, affecting weather resistance and appearance

Also: plasticiser, liquid plasticiser, mortar additive

Liquid additive mixed into blockwork mortar to improve workability without increasing the water:cement ratio. An alternative to hydrated lime in above-DPC mortar mixes. Sold in 5-litre bottles; a small amount goes a long way.

Also: mortise gauge, double-pin gauge, double marking gauge

A marking gauge with two independently adjustable pins for scribing both sides of a mortise or tenon shoulder in a single pass. Essential for joinery involving mortise-and-tenon joints.

Also: Meter Point Administration Number, electricity supply number, supply number

The 21-digit number uniquely identifying an electricity supply point, found on the electricity bill and required for DNO meter relocation applications.

Also: Meter Point Reference Number, gas supply number

The 10-digit number uniquely identifying a gas supply point, found on the gas bill and required for GDN meter relocation applications.

Also: multi-finish, skim coat, finish plaster, Thistle Multi

Versatile finishing plaster applied as a thin (2-3mm) skim coat over plasterboard or bonding plaster to create a smooth, paint-ready surface. The most commonly used finishing plaster in domestic work. Setting time approximately 90 minutes. Coverage: 10m² per 25kg bag at 2mm. BS EN 13279-1 type B1/20/2.

Also: digital multimeter, DMM

An electronic instrument for measuring voltage, current, and resistance in electrical circuits. Used for testing circuits are correctly wired, checking continuity, and diagnosing faults. Digital multimeters are easier to read than analogue.

Also: scaffold cycle, scaffold restrike, two-phase scaffolding

The often-underplanned reality that an extension may need scaffolding erected and struck multiple times — typically once for structural walls and again for the roof phase, weeks apart. Each cycle incurs full erection and striking costs. A typical kitchen extension example: scaffold up for brickwork, struck, then re-erected weeks later for roof fitting.

Also: mushroomed head, spalled chisel head

Dangerous deformation of a chisel or punch head caused by repeated hammer strikes, creating sharp metal splinters that can fly off

Also: Mechanical Ventilation with Heat Recovery, heat recovery ventilation, MVHR system, whole-house ventilation

A whole-house ventilation system that extracts stale air from wet rooms and recovers heat to warm incoming fresh air. Increasingly required under Part F where high airtightness levels make natural ventilation insufficient.

Also: MVHR commissioning report, ventilation commissioning certificate, mechanical ventilation commissioning sheet

Document required by building control at final inspection when MVHR is installed. Confirms the ventilation system has been commissioned to Part F flow rate requirements. Often forgotten by homeowners, delaying the completion certificate.

Also: mybuilder.com

Online platform for finding and vetting tradespeople including structural engineers. Homeowners can post jobs, receive quotes, and read reviews.