Building Terms Glossary

Also: frosted glass, privacy glass, opaque glazing

Non-transparent glazing required under permitted development for upper-floor side windows, which must be obscure-glazed and non-opening unless the sill is 1.7m+ above floor level.

Also: Office of Gas and Electricity Markets, ofgem.gov.uk

UK energy regulator that sets rules energy suppliers must follow, including smart meter restoration standards and meter relocation charge regulation.

Also: Bolt & Nut, Fixings Warehouse

Online suppliers specialising in screws, bolts, wall plugs, anchors, and specialist fixings

Also: Online Insulation Sales, Trade Insulations, Insulation Superstore, National Insulation Supplies

Online specialist insulation retailers offering 20-70% savings over builders' merchants and DIY retailers. Key channel for PIR, mineral wool, and EPS products.

Also: Toolstation, Screwfix

Trade counters and online stores specialising in tools, fixings, electrical, and plumbing supplies

Also: dumpy level, automatic level, auto level

A precision optical instrument mounted on a tripod for establishing level points across a site. Used with a staff (graduated measuring rod) to check foundation levels, set drainage falls, and ensure floor slabs are flat. Requires a second person to hold the staff.

Also: pendulum action, orbital setting, elliptical stroke, 3D cutting

A saw feature that moves the blade in an ellipse rather than straight back-and-forth. Settings 0–3: 0=off for metal and laminate; 1=low for nail-embedded wood; 2–3=high for fast demolition cuts in softwood.

Also: OS

The national mapping agency. OS map extracts are required for planning applications (site plan and location plan) and typically cost around £30-35.

Also: OS map, site plan, location plan, block plan, planning map, planning application map

Scaled OS map extracts required for the site plan and location plan in a planning application. Typically cost around £30-35 and must be at specified scales (usually 1:1250 site plan and 1:2500 location plan).

The house as it stood on 1 July 1948, or when first built if later. Permitted development limits are measured against the original house, meaning previous extensions by former owners count against your PD allowance.

Also: OSB3, sterling board, strand board, oriented strand board, SterlingOSB

Engineered wood panel made from compressed wood strands. Available in 11mm and 18mm thicknesses. OSB3 grade is moisture-resistant and suitable for structural use. Cheaper than plywood but not suitable for direct tiling or where a smooth finish is needed. Standard sheet size 2440x1220mm.

Also: OIS, OIS blade fitting, universal blade fitting, OIS adapter

The older blade attachment standard for oscillating multi-tools, used by budget brands. Most aftermarket blades are OIS-compatible. OIS tools cannot accept Starlock blades without an adapter.

Also: multi-cutter, multi-tool, oscillating tool, Multimaster, OMT

A compact power tool with an oscillating blade for precision cutting, sanding, and scraping in tight spaces. Invaluable for trimming door frames for new flooring, cutting out plasterboard, and removing grout or sealant.

Also: oscillating arc angle, swing angle, arc angle, degree of oscillation

The arc degree of an oscillating multi-tool's blade movement (1.6°–4.0°). Higher angle = faster, more aggressive cut. Lower angle = more precise, less vibration. Fein: 4.0°, Milwaukee/Makita: 3.6°, DeWalt DCS356N: 1.6°.

Also: OPM, strokes per minute oscillating, oscillation speed, variable speed oscillating

The speed specification for oscillating multi-tools (10,000–22,000 OPM). Variable speed is critical: low OPM for grout removal (avoids blade burning), high OPM for wood cutting.

Specialist power tools for grinding, breaking, compacting, mixing, nailing, heating, planing, and routing. Many of these are hire items for one-off jobs rather than purchases.

Also: garden building, shed

A separate structure in the garden such as a shed, workshop, or summer house. Outbuildings with foundations can trigger party wall obligations if within 3-6 metres of proposed excavation.

Also: sketch plans, concept drawings, initial drawings

Rough initial sketches your architect produces to explore layout options before committing to detailed plans. These help you agree the overall approach before spending money on full drawings.

Also: garden tap, external tap, hose tap, bib tap

An external tap provision that must be roughed in at first fix — the cold supply pipe is run through the external wall before insulation and plasterboard seal it. Requires a double check valve inside the building and an isolation valve upstream under the Water Fittings Regulations.

Also: sense of enclosure, dominant impact

A material planning consideration where a proposed development is so close or so large relative to a neighbouring property that it creates a sense of enclosure or dominance.

When the digger excavates deeper or wider than specification, common on all foundation projects. Budget 5-10% extra concrete to account for it.

Also: loss of privacy, privacy impact

A material planning consideration where a proposed development allows views into a neighbour's habitable rooms or private garden.

A material planning consideration where a proposed development casts shadow over a neighbouring property, reducing daylight to habitable rooms or gardens.

Also: oversite preparation, oversite slab, floor slab preparation

The prepared base layer for the ground floor of an extension — typically hardcore fill, sand blinding, and a concrete slab. A distinct building control inspection stage between foundations and drainage.

Also: Certificate A, Certificate B

A mandatory declaration included with every planning application confirming the ownership status of the application site.