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

A 30-minute fire resistance rating for internal doors. Covers the entire doorset assembly (door leaf, frame, intumescent strips, and ironmongery), not just the door. Required by Approved Document B for loft conversion escape routes, integral garage doors, flat entrance doors, and HMO internal doors.

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.

Also: CERTASS

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: 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, finished floor level, FFL, floor level datum

The final height of the completed floor surface, accounting for screed, insulation, underlay/adhesive, and floor covering thickness. Must be agreed before construction begins to ensure the extension floor aligns with the existing house floor. A common and expensive defect when not planned upfront.

Also: FFL, floor level, floor datum

The final floor surface height after all layers (slab, insulation, screed, tiles/flooring) are installed. All kitchen dimensions — worktop height (900mm), window sill (1020mm), base unit height (720mm) — are measured from FFL, not the raw slab. 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: kiln skin, tile vitrification layer, hard outer layer

The stage where services (electrics, plumbing, heating) are installed before plastering

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: 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: 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-and-cement screed, liquid 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: boiler flow temperature, heating system flow temperature, 55°C flow temperature limit

The temperature at which hot water leaves the boiler. ADL 2021 mandates a maximum 55°C for all new wet heating systems. UFH runs efficiently at 35-55°C, making it naturally compliant.

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: 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

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: 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.