UK DIY and building glossary
Plain-English definitions of the terms in UK DIY, building and energy projects, with the calculator or guide that uses each one.
A
- Approved Documents
The guidance that goes with the Building Regulations in England. Each one covers a part, such as K for stairs and falls, J for combustion appliances and P for electrical safety. Other parts of the UK have their own versions.
See: Stair Calculator (UK): Rise, Going and Building Regulations
B
- Ballast
All-in aggregate: a mix of sand and gravel used with cement to make concrete. It is sold loose by the tonne or in bulk bags.
- BTU
A unit of heat, still used for radiators and boilers. One watt is 3.412 BTU per hour, so a 2,000 watt radiator gives out about 6,824 BTU an hour.
See: Radiator Size Calculator (UK, Watts and BTU) · What Size Radiator Do I Need? Watts and BTU for Each Room (UK)
- Building control
The local authority department or approved inspector that checks that building work meets the Building Regulations. Work such as new stairs, structural changes and many electrical and heating jobs needs approval.
See: Stair Calculator (UK): Rise, Going and Building Regulations
C
- Cavity wall
A wall built as two leaves with a gap between them. The gap can be filled with insulation, which cuts the heat lost through the wall. The leaves are held together by wall ties, at least 2.5 to every square metre.
See: Loft Insulation Calculator (UK) · Wall Tie Calculator (UK): How Many Ties and How Long · How Many Wall Ties Do I Need? Spacing and Length (UK)
- Combi boiler
A boiler that heats the hot water as you use it, so it needs no hot water cylinder. Its output is set mostly by the hot water it must provide at once, which is why a house needing 7 kW for heating may have a 24 kW combi.
See: Boiler Size Calculator (UK): What kW Boiler Do I Need? · What Size Boiler Do I Need? kW for a Combi or System Boiler (UK)
- Consumer unit
The electrical panel (the fuse box) in a UK home. It holds the main switch, the RCDs and the circuit breakers (MCBs) for each circuit.
D
- DPC and DPM
A damp-proof course (DPC) is a layer in a wall, about 150 mm above the ground, that stops damp rising. A damp-proof membrane (DPM) is a sheet under a concrete floor or screed that stops moisture coming up from the ground.
F
- Fall (drain or gutter)
The slope that lets water run along a pipe or gutter. A fall of 1 in 80 drops 12.5 mm in each metre, so a drain of 15 m falls about 188 mm. Gutters need at least 1 in 600.
See: Drain Fall Calculator (UK): Gradient, Pipe and Bed · Guttering Calculator (UK): Lengths, Brackets and Downpipes · Drain Fall and Gradient: How Much Fall Does a Drain Need? (UK) · How Much Guttering Do I Need? Lengths, Brackets and Fall (UK)
G
- Gas Safe
The register of engineers who are allowed by law to work on gas appliances, such as boilers and gas fires, in Great Britain. Always check the engineer's card.
- Geotextile
A woven or felt-like membrane laid under gravel, paving or a retaining wall. It stops the stone sinking into the soil below and lets water through, and it is sold by the roll (often called weed membrane or filter fabric).
- Going
The depth of a stair tread, measured from the front edge of one tread to the front edge of the next. For a private stair it must be at least 220 mm.
See: Stair Calculator (UK): Rise, Going and Building Regulations · Staircase Regulations UK: Rise, Going, Pitch and Number of Steps
- Grit sand (sharp sand)
Coarse sand with angular grains, used for the bedding layer under paving and block paving and in concrete. Soft (building) sand is finer and is used for mortar and plaster.
H
- Hardcore
Broken brick, stone or concrete, compacted in a layer under a slab, a path or a shed base. It is sold by the tonne or the bulk bag, and is topped with a finer layer such as MOT Type 1 or sharp sand.
- HETAS
The official body for solid fuel heating in the UK. Stoves and wood burners should be installed by a HETAS-registered installer, or with approval from building control.
See: Wood Burner Size Calculator (UK): What kW Stove Do I Need? · What Size Wood Burner Do I Need? Room Size to kW Chart (UK)
J
- Joist tape
Self-adhesive tape stuck to the top of decking joists before the boards go on. It keeps water out of the timber where screws go in, which makes the frame last years longer.
K
- kWh and pence per kWh
A kilowatt-hour is the unit of energy on an electricity or gas bill. The unit rate is the price in pence for each kWh, and the cost of an appliance is its kilowatts times the hours it runs times the unit rate.
See: Electricity Cost Calculator (UK) · How Much Does It Cost to Run Common Appliances? UK Table
- kWp (kilowatt peak)
The rating of a solar panel system: the number of panels times the watts of each. In the UK each kWp makes about 850 to 1,050 kWh a year on a south-facing roof.
See: Solar Panel Calculator (UK): Output, Savings and Payback · How Many Solar Panels Do I Need? UK Output, Savings and Payback
L
- Lintel
A beam over a door or window opening that carries the wall above it. It can be concrete, steel or timber.
M
- MCS
The Microgeneration Certification Scheme, which certifies installers and products for solar panels, heat pumps and other small renewable systems. Installations usually have to be MCS certified to receive export payments or a grant.
See: Solar Panel Calculator (UK): Output, Savings and Payback · Heat Pump Calculator (UK): Size and Running Cost vs a Gas Boiler
- MOT Type 1
A crushed stone sub-base material that compacts hard, used under paving, driveways and artificial grass. It weighs about 2.2 tonnes per cubic metre once compacted.
See: Paving Slab Calculator (UK) · Artificial Grass Calculator (UK): Roll, Sub-base and Sand
P
- Part J
The part of the Building Regulations that covers combustion appliances such as stoves and boilers, including the air supply and the flue. A stove over 5 kW in an older house needs a permanent air vent.
See: Wood Burner Size Calculator (UK): What kW Stove Do I Need?
- Part K
The part of the Building Regulations that covers stairs, ramps and guarding. For a private stair it sets a maximum rise of 220 mm, a minimum going of 220 mm and a maximum pitch of 42 degrees.
See: Stair Calculator (UK): Rise, Going and Building Regulations · Staircase Regulations UK: Rise, Going, Pitch and Number of Steps
- Permitted development
Rights to make some changes to a home without a planning application, within limits. Solar panels, small outbuildings and some extensions can fall under it, but there are exceptions, for example for listed buildings.
See: Solar Panel Calculator (UK): Output, Savings and Payback
- Pitch line
An imaginary line through the front edges of the treads of a stair. The handrail height and the headroom are measured from it.
See: Stair Calculator (UK): Rise, Going and Building Regulations
- Plasterboard
Boards of gypsum between sheets of paper, used to line walls and ceilings. The standard sheet is 2,400 by 1,200 mm, 9.5 or 12.5 mm thick.
R
- RCD (residual current device)
A device that cuts the power in a fraction of a second when it detects a leak of current to earth, such as through a person. A 30 milliamp RCD protects the sockets and circuits in a home.
- Ring main
A circuit for sockets that runs in a loop from the consumer unit, round the rooms and back, on a 32 amp breaker. Each socket can be fed from both directions.
S
- SCOP and COP
The coefficient of performance of a heat pump: the heat produced for each unit of electricity. The SCOP is the seasonal figure over a whole year. A SCOP of 3 means 3 kWh of heat for every 1 kWh of electricity.
See: Heat Pump Calculator (UK): Size and Running Cost vs a Gas Boiler · What Size Heat Pump Do I Need? UK kW Chart and Running Cost
- Screed
A thin layer of sand and cement, or a flowing screed, laid over a concrete base or insulation to give a smooth, level floor for tiles or flooring. It is usually 50 to 75 mm thick.
- Smart Export Guarantee (SEG)
A scheme under which energy suppliers pay you for the electricity from your solar panels that you export to the grid. Each supplier sets its own rate per kWh.
See: Solar Panel Calculator (UK): Output, Savings and Payback
- Smoke control area
An area, usually in a town or city, where you may burn only authorised smokeless fuels or use an exempt appliance. Many wood burners are DEFRA-exempt, which means they may be used in one.
See: Wood Burner Size Calculator (UK): What kW Stove Do I Need?
- Sub-base
The compacted layer of stone under paving, block paving, a drive or artificial grass. MOT Type 1 is the usual material, laid 100 to 150 mm deep for a patio and drive.
See: Block Paving Calculator (UK) · Artificial Grass Calculator (UK): Roll, Sub-base and Sand
- System boiler
A boiler that heats a hot water cylinder as well as the radiators. It is sized for the heating load, and suits a home with more than one bathroom.
T
- Tonne
A metric tonne is 1,000 kilograms. Sand, gravel and MOT Type 1 are sold by the tonne, in bulk bags of about 0.8 tonnes or loose.
U
- U-value
A measure of how fast heat passes through a wall, a roof or a window, in watts per square metre per degree. A lower U-value means better insulation. The thickness of insulation to reach a target is the extra resistance (1 divided by the U-value) multiplied by the conductivity of the insulation.
See: Loft Insulation Calculator (UK) · Insulation Thickness Calculator (UK): Thickness for a Target U-Value · How Thick Should Insulation Be? Thickness for a Target U-Value
W
- Wacker plate (plate compactor)
A petrol or electric machine with a vibrating steel plate that packs sub-base or sand down hard and flat. A compacted base under paving or a shed stops the surface sinking later. It can be hired by the day.
- Water butt
A barrel for collecting rainwater from a downpipe. Every millimetre of rain on a square metre of roof is a litre, so a garage roof of 20 m² collects about 160 litres in a 10 mm shower.
See: Water Butt Calculator (UK): How Much Rain Can I Collect? · How Big a Water Butt Do I Need? Roof Area, Rainfall and Litres (UK)
Δ
- ΔT50
The standard rating of a radiator, taken with the water in it 50°C above the room temperature (a flow of about 75°C). A radiator on a heat pump gives out less than its ΔT50 output, so it needs to be larger.
See: Radiator Size Calculator (UK, Watts and BTU) · What Size Radiator Do I Need? Watts and BTU for Each Room (UK)
This glossary uses metric units and UK terms. Not in the UK? See the US glossary