Building Terms Glossary

Also: full face visor, grinding visor, face visor

A full-face protective shield worn over the eyes and face during angle grinding, cutting, and other operations where high-velocity sparks, metal fragments, or disc debris can travel toward the operator. RoSPA data cites 5,400 angle grinder injuries per year in the UK with the head and face as the most common injury site. Safety glasses alone do not provide adequate protection for grinding or cutting operations.

Also: house bricks, face bricks

Bricks selected for their appearance, used on visible external walls. Matching existing brickwork on extensions is critical and can be the biggest challenge. Price varies enormously depending on style, colour and whether reclaimed bricks are needed for matching.

Also: FAKRO, Fakro UK, fakro.co.uk, RoofLITE, Fakro FT series, Fakro BBA certified

Main alternative to Velux in the UK pitched roof window market. BBA-certified, typically 10-15% cheaper than Velux. Parent company of RoofLITE brand. Less familiar to UK roofers than Velux but quality equivalent.

Also: MCOB, FCA MCOB Sourcebook, Mortgage Conduct of Business

The FCA regulatory sourcebook governing mortgage and home finance lending in the UK. MCOB 11 (Responsible Lending) contains the affordability rules that apply when homeowners seek a further advance or remortgage for extension funding. Brokers, advisers, and lenders arranging regulated mortgage contracts must comply.

Also: PS25/11, FCA PS25-11, Mortgage Rule Review 2025

FCA Policy Statement PS25/11, in force from 22 July 2025, made targeted simplifications to remortgaging rules and term-reduction processes. Did NOT change core affordability assessments for new or additional borrowing — the MCOB 11.6.18R stress test remains intact.

Also: FD20, FD 20, 20-minute fire door

The BS 476-22 label for a doorset that holds back fire for 20 minutes. Approved Document B Table C1 (item 11b) gives E 20 (FD 20) as the minimum for doors forming part of the enclosure to a protected stairway in a single family dwellinghouse. FD20 doors are no longer commonly tested or certified, so suppliers sell FD30 doorsets, which exceed the minimum (FIS, May 2022). From 2 September 2029 the Approved Document drops the FD labels and states the same minimum as 20 minutes.

Also: FD30 doorset, fire-rated internal door, certified fire door

A fire-resisting internal doorset: leaf, certified frame, intumescent strips, cold smoke seals and marked ironmongery. Approved Document B's minimum for a dwellinghouse stair-enclosure door is FD20/E20; FD30 is the grade usually bought and the one many councils specify, while FD30S (with smoke seals) is required for a house-to-integral-garage door. FD30 refers to the whole installed assembly, not just the leaf.

Also: FD30, 30-minute fire door, fire door rating

A 30-minute fire-resistance rating for an internal doorset (leaf, frame, intumescent strips and ironmongery), tested to BS 476-22 or BS EN 1634-1. In a dwellinghouse, Approved Document B's minimum for a door in the enclosure to a protected stairway is FD20/E20, not FD30; FD30 is the grade most commonly bought and the one many councils specify. FD30S, with cold smoke seals, is required for a house-to-integral-garage door. Fire doors in flats and HMOs are a separate, stricter regime.

Also: FMB, fmb.org.uk

UK trade association providing cost guides, regional labour rates, and a Find a Builder directory for homeowners.

Also: lap panel, featheredge panel, closeboard panel, garden fence panel, fence board panel

Prefabricated fencing section used for boundary reinstatement after construction damage. Types include budget lap panels and more durable closeboard panels. Cost: £40-150/m depending on type and height.

Also: timber fence post, concrete fence post, metal fence spike, post spike, fence post spike

Vertical support post for fence panels. Available in UC4 pressure-treated timber (for ground contact) or concrete. Must be correctly specified to resist rot and provide structural support for the fence panel.

Fenestration Self-Assessment Scheme for window/door replacement

Also: Fenestration Self-Assessment Scheme

UK competent person scheme operator for window and door installations. Runs the self-certification process for Building Regulations compliance on replacement windows and doors: FENSA-registered installers issue the FENSA certificate directly to the homeowner, avoiding a separate Building Control application. Solicitors and buyers' surveyors routinely ask for the FENSA certificate on resale.

Also: end panel, kitchen panel, filler strip, plinth board

The boards that finish a kitchen installation: end panels cover exposed carcass sides, filler panels bridge the gap between the last unit and the wall, and plinths cover the adjustable-leg space at the base. All are typically ordered from the kitchen supplier in the matching door finish.

Also: final exit door, exit to open air

The end of an escape route that gives direct access to a street, passageway, walkway or open space, sited so people move away from the building and are no longer in danger from fire or smoke. Approved Document B Appendix A notes that windows are not acceptable as final exits. In a house it is normally the front or back door, and a loft conversion's protected stairway must lead to one.

Also: independent financial adviser, IFA, financial advisor

FCA-regulated professional who provides regulated advice on broader financial planning decisions that intersect with extension financing — pensions, protection insurance, inheritance tax, and large secured borrowing. Independent advisers (IFAs) source across the whole market; restricted advisers represent a single firm or panel.

Also: FCA, fca.org.uk

The UK financial services regulator. Publishes the Mortgage Conduct of Business (MCOB) sourcebook governing further advances and remortgages, takes enforcement action against inappropriate sales of bridging finance to homeowners, and operates the Financial Services Register where homeowners can verify that a mortgage broker, financial adviser, or equity release adviser is authorised.

Also: FOS, Financial Ombudsman, ombudsman.org.uk

A free, independent service for settling disputes between consumers and financial businesses, including complaints about construction finance or insurance products.

Also: FFH, FFL, Finish Floor Height, finished floor level, floor datum, floor level, floor level datum

The final floor surface height after all layers (slab, insulation, screed, tiles/flooring) are installed. All kitchen dimensions are measured from FFL, not the raw slab: worktop height (900mm), window sill (1020mm), base unit height (720mm). The extension FFL must match the existing house FFL, and this must be established at foundation stage using an optical level.

Also: decorating materials, plastering materials

Plaster, compounds, adhesives, sealants, paints and decorating materials used in the final finishing stages of construction.

Also: alarm commissioning certificate, design, installation and commissioning certificate, fire alarm certificate

The certificate Approved Document B Volume 1 (para 1.14) says should be provided for a fire detection and alarm system, because systems must be properly designed, installed and maintained. A homeowner should ask the loft company or electrician for it at handover and keep it with the building control completion certificate.

Also: fire doors, fire-resisting door, fire doorset, fire resisting doorset, fire-rated door, fire rated door

A complete doorset (leaf, frame, seals, hinges and ironmongery) tested to resist fire for a stated period. On a loft conversion that creates a new storey above 4.5m, Approved Document B Volume 1 (para 2.21) calls for fire-resisting doors and partitions on the full escape route, including upgrading existing doors where necessary. The stated minimum for the door is E 20; FD30 doorsets are what suppliers commonly sell.

Also: REI, REI 30, R 30, loadbearing capacity, integrity and insulation, fire resistance period

How long an element keeps performing in a standard fire test, in minutes. R is loadbearing capacity (it keeps holding weight), E is integrity (it stops flames and hot gas passing through) and I is insulation (the far face stays cool enough). A floor needs all three, so REI 30 means 30 minutes on all three; a steel beam only carries load, so the letter that matters for it is R. Approved Document B states the performance required, not the method.

Also: kiln skin, tile vitrification layer, hard outer layer

The hard, dense outer layer formed on a clay tile during firing in the kiln. It gives the tile its weather and frost resistance; once the fire skin is lost or breached, for example at a cut edge, water reaches the softer body and the tile starts to delaminate.

Also: fire strategy drawing, fire safety strategy, escape strategy

The plan for how people escape and how the building resists fire, normally shown on a drawing: the protected route from the loft to the final exit, which doors and partitions are fire-resisting, where alarms go, and how any open-plan area is handled. For a loft conversion the loft company or designer prepares it and building control agrees it before work starts, which is why the homeowner should ask to see it before signing.

Also: fire-rated glass, fire rated glazing, fire-resisting glass

Glass that is part of a tested fire door or screen and holds back flame for the stated period, unlike ordinary or toughened glass. Approved Document B Appendix A defines a fire doorset as the frame, leaf, essential hardware, edge seals and glazing, so a glazed door onto a protected stair needs glazing that is part of the tested assembly. Table B3 also limits uninsulated glazing in the enclosure to a protected stairway.

Also: fixed ladder access to loft, fixed ladder

A non-retractable ladder with fixed handrails on both sides. Approved Document K para 1.32 allows it only for access in a loft conversion containing one habitable room, and only where there is not enough space without altering the existing space for a stair that meets the dwelling guidance. A loft reached only by a fixed ladder usually will not count as a bedroom when selling.

Also: lump sum contract, fixed-price building contract

A contract where the builder agrees to complete the work for a set price, so you know your costs upfront. Any unexpected expenses are the builder’s problem unless you change what you’ve asked for.

Also: fasteners

Screws, bolts, anchors, brackets and mechanical fasteners used to connect, secure and support building components.

Weatherproofing strips (usually lead) where a roof meets a wall or other surface

Also: apartment

A self-contained dwelling within a larger building. PD rights for extensions apply only to houses, not flats. If you live in a flat, you need planning permission for any extension.

Also: flat-pack units, self-assembly kitchen, knock-down kitchen, pre-assembled kitchen, rigid kitchen units

Kitchen units supplied disassembled for on-site assembly (e.g. IKEA). Compared to rigid pre-assembled units (e.g. Howdens, DIY Kitchens). Flat-pack is cheaper but takes longer to install and may be less structurally rigid. Rigid units are quicker to fit and generally more durable.

Also: flexi duct, corrugated duct, flexible extraction hose

Flexible ducting for extraction runs. The ribbed interior creates turbulence and reduces airflow by approximately 25m³/h per metre. Should only be used for short transition sections (max 300mm), not as a substitute for rigid ducting throughout a run.

Also: flitch plate, flitched beam, timber and steel beam

A beam made by bolting a steel plate between two timber sections, so it carries more load than the timber alone while staying thin enough to hide in a floor. Surrey Building Control guidance lists it as one of the beam types that can support loft floor joists, alongside solid timber, glulam and steel. Whether a flitch, a plain steel beam or timber is used is the structural engineer's call.

Also: schedule float, programme float, free float, total float, slack

The amount of time a non-critical-path task can be delayed without delaying the overall project completion date. Understanding float allows homeowners to distinguish delays that cascade into project overrun from those that can be absorbed.

Also: float and butter method, back-buttering, buttering the back, double-sided adhesive application

Adhesive application technique required by BS 5385-1:2018 for large-format and heavy tiles: adhesive combed onto the substrate (floating) AND applied to the tile back (buttering) to achieve solid bedding and full coverage.

Also: FRA, flood risk assessment (planning)

A report assessing flood risk to and from a development, required with a planning application in some cases, for example where the site is in a higher flood-risk zone. Councils list the triggers on their local validation checklists.

Also: floor construction layers, floor depth calculation, floor level build-up, floor zone

The stacked layers from structural slab to finished floor surface: slab + insulation (70-150mm PIR) + edge strip + UFH pipe + screed (65mm) + adhesive + tiles. Adds 100-170mm to finished floor level. Must be planned at foundation stage to avoid threshold and step height problems.

Also: tog rating for flooring, m2K/W floor covering, floor thermal resistance limit, UFH floor covering limit

The thermal resistance of a floor covering measured in m²K/W (equivalent to tog/10). The critical metric for UFH compatibility. The Future Homes Standard limit is 0.15 m²K/W. Tiles and LVT are well within this; engineered wood (0.10–0.12) is marginal; thick carpet with underlay typically fails. Determines which flooring materials are suitable over UFH.

Also: screed, sand-cement screed

The levelling layer poured over the concrete slab before final flooring. Any services for a kitchen island (waste pipes, water supply, power cables) must be routed through conduit in the screed before it is poured. Once set, there is no retrofit route without breaking up the concrete.

Also: floor finishes, floor coverings

The final floor finish laid over screed or existing substrate, tiles, LVT, engineered wood, laminate, plus the adhesives, trims and levelling aids that hold it all together and make the transitions look right.

Also: floor layer

Installs flooring including tiles, vinyl, laminate, engineered wood, and carpet

Also: floor underlay, laminate underlay, engineered wood underlay, LVT underlay, acoustic underlay, thermal underlay, foam underlay, rubber underlay, cork underlay

A thin cushioning layer laid between the subfloor and a floating floor covering to provide acoustic dampening, thermal insulation, and a level surface. Type depends on the floor finish and substrate: foam or cork for laminate and engineered wood; specific thin-profile or self-adhesive types for LVT; UFH-compatible types must have a tog rating below 0.15 m²K/W. Incompatible underlay is the most common cause of voided floor warranties.

Also: boiler flow temperature, heating system flow temperature, 55°C flow temperature limit, design flow temperature

The temperature at which hot water leaves the boiler or heat pump. Approved Document L 2021 (para 5.10) asks for a newly installed or fully replaced wet heating system to be sized to run at a maximum flow temperature of 55°C or lower, or the lowest temperature that still meets the home's heating needs where that is not feasible. Underfloor heating runs well at 35-55°C.

Also: water risk category, backflow risk category, fluid risk category

Classification of water-using appliances by contamination risk under the Water Fittings Regulations (categories 1–5). Category 3 (outside taps, garden hoses) requires a double check valve; Category 2 (water softeners) requires a single check valve. Determines what backflow prevention device is legally required.

Also: discharge of conditions, condition discharge

The process of submitting evidence to the council (material samples, drainage details, landscape plans) to satisfy planning conditions before starting construction or completing specific stages. Missing a pre-commencement condition can invalidate the entire planning permission.

Also: shuttering, formwork boards, trench boards, concrete shuttering

Timber boards and stakes used to form the edges of concrete pours, holding the wet concrete in shape until it sets. Can often be reclaimed and reused after the pour.

Also: foul drainage, waste water, foul water drainage, sewage

Waste water from kitchens, bathrooms, and WCs that contains organic matter and must be routed to the foul sewer for treatment. Distinct from surface water (rainwater). Cross-connecting foul water into a surface water drain is a notifiable pollution offence that the water company can prosecute.

Also: window fixings, door frame fixings, frame screws

Long screws with integral plugs designed for fixing window and door frames directly through the frame into masonry. Available in various lengths (typically 80-150mm). Provide a secure, adjustable fixing that allows the frame to be plumbed and levelled before final tightening.

Also: plastic packers, window packers, horseshoe packers, shims

Thin plastic shims, often horseshoe-shaped and sold in mixed thicknesses from 1mm to 10mm, slid behind a door lining or window frame at each fixing point. They fill the gap to the wall so the frame stays straight and plumb when the screw is tightened, instead of being pulled into a bow.

Also: mastic sealant, building mastic, pointing mastic, low-modulus sealant, acrylic frame sealant

Acrylic or low-modulus sealant used to seal the vertical DPC at the junction between new and existing walls, and to weatherproof DPC at external corners. Distinct from silicone sealant used in kitchens and bathrooms.

Also: full plans, full plans submission, pre-site approval full plans, application for building control approval with full plans

One of the two main building control application routes. Requires detailed drawings, specifications, and calculations submitted before work starts. Approval is valid for 3 years. Mandatory for work near public sewers, fire safety order buildings, or private streets.

Also: mortgage further advance, additional borrowing on mortgage

A UK mortgage product where a homeowner borrows additional funds from their existing lender on a separate sub-account, typically at a rate that differs from the main mortgage. Distinct from a full remortgage and often the preferred route when the borrower is mid-way through a fixed-rate deal with early repayment charges remaining.

Also: FCU, fused spur, switched fused spur, switched fused connection unit

A wiring accessory providing a fused, switched hardwired connection for fixed appliances where local isolation is required but a standard plug socket would be inaccessible behind an appliance.

Also: FHS, Future Homes and Buildings Standards, FHBS

Upcoming update to Building Regulations requiring new homes in England to be built to higher thermal performance from December 2026. Tightens roof U-values from 0.15 to 0.13 W/m²K and floor from 0.18 to 0.13 W/m²K for new thermal elements.