Building Terms Glossary

Also: 110V, 110 volt site power, site voltage, CTE transformer, centre-tapped earth transformer

UK professional tool hire companies predominantly supply tools at 110V (centre-tapped earth transformer) rather than 240V domestic supply, as a site safety measure that limits shock voltage to 55V. Homeowners hiring a breaker without a 110V step-down transformer cannot use hire-grade 110V tools. A genuine friction point: 'no 110V converter = friction with hire'.

Also: roof valley

Where two roof slopes meet, requiring weatherproofing

Also: VE, value optimisation

The practice of substituting equivalent performance at lower cost when a budget category is trending over. For example, using radiators instead of underfloor heating, or standard tiles instead of large-format porcelain.

Also: VCL, vapour barrier, vapour check

A membrane or sealed layer that restricts the passage of water vapour through a building element. PIR foil facing acts as a VCL only when all joints are taped with foil tape.

Also: variation order

A change to the agreed scope of work, usually with cost implications

Also: VAT threshold, £90,000 VAT threshold, mandatory VAT registration threshold

Builders earning above a certain turnover (currently £90,000) must register for VAT and add 20% to their invoices. A builder not charging VAT isn’t necessarily dodgy — they may simply be below the threshold.

Also: VAT record, VAT column, construction VAT records

The practice of maintaining a dedicated VAT column in a cost tracker, recording VAT paid per line item. Creates a VAT-ready record and helps verify that VAT-registered builders invoice correctly.

A German certification mark indicating tools are tested to IEC 60900 for 1,000V AC use on live circuits. Relevant to wire strippers and voltage tester leads.

Also: VELUX, Velux UK, velux.co.uk, Velux GGL, Velux GGU, Velux Certified Installer

Market-dominant branded roof window manufacturer in the UK. Their size code system (CK02, FK04, MK06, etc.) is the de facto industry standard. Their underfelt collar, flashing kit, and installation system are specifically referenced in DuPont's Tyvek technical manual. Offer a Velux Certified Installer programme.

The planned approach to providing fresh air while maintaining energy efficiency

Also: vertical damp proof course, abutment DPC

A strip of DPC material fixed vertically where the new extension wall abuts the existing house wall, sealed with mastic, to prevent moisture transferring between old and new masonry.

Also: voltage drop limit, 5% voltage drop, Reg 525.1

BS 7671 Reg 525.1 limits voltage drop to 5% of supply voltage for power circuits over the full circuit length, directly relevant to long cable runs to kitchen islands.

Also: non-contact voltage tester, NCV tester, voltage pen, volt stick

A pen-shaped device that detects live electrical cables without touching bare conductors. Hold it near a cable or socket and it beeps or lights up if voltage is present. A critical safety tool — always test before working near electrics.