Standards and regulations
Short explainers for the standards and regulations our calculators cite. Each links to the official source: check it, not our summary.
Approved Document A (structure)
What Approved Document A covers for small buildings, wall ties and lintels in England, and how our brickwork calculators use it.
Approved Document F (ventilation)
What Approved Document F says about extract ventilation in kitchens, bathrooms and utility rooms, and how our fan calculator uses it.
Approved Document G (hot water safety)
What Approved Document G says about unvented hot water systems and who may fit them, and how our cylinder calculator uses it.
Approved Document H (drainage)
What Approved Document H covers for drains, soakaways and gutters in England, and how our drainage calculators use it.
Approved Document K (stairs and guarding)
What Approved Document K says about stair rise, going, pitch and the 100 mm sphere rule, and how our stair calculators use it.
Approved Document L (conservation of fuel and power)
What Part L sets for U-values in England, how Wales, Scotland and Northern Ireland differ, and how our U-value calculators use it.
Approved Document M (access)
What Approved Document M says about ramp gradients, goings and landings in England, and how our ramp calculator uses it.
Approved Document P (electrical safety)
What Part P means for electrical work at home in England and Wales, when to use a registered electrician, and how other nations differ.
BRE Digest 365 (soakaway design)
How BRE Digest 365 sizes a soakaway from a percolation test and storm rainfall, and how our soakaway calculators follow it.
BS 3882 (topsoil)
What BS 3882 says about topsoil grades, what to ask your supplier, and how our topsoil calculator refers to it.
BS 5534 (slating and tiling)
What BS 5534 covers for pitched roofs: headlap, gauge, battens and fixings, and how our roofing calculators use it.
BS 7533 (paving)
What BS 7533 covers for flags and block paving, from laying course to jointing, and how our paving calculators refer to it.
BS 7671 (the IET Wiring Regulations)
What BS 7671, the IET Wiring Regulations, covers, what changed with Amendment 4 (2026) and how our electrical calculators use it.
BS 8204 (screeds)
What BS 8204 covers for floor screeds: types, thickness and drying, and how our screed calculators refer to it.
BS 8500 (concrete)
What BS 8500 covers for specifying concrete, why mix ratios aren't strength classes, and how our concrete calculators refer to it.
BS 8515 (rainwater harvesting)
How BS 8515's simplified method sizes a rainwater harvesting tank from roof area, rainfall and demand, as our calculator does.
BS EN 1264 (underfloor heating)
What BS EN 1264 says about underfloor heating output and floor surface temperature, and how our UFH calculator uses it.
BS EN 12831 and CIBSE DHDG (heat loss)
How BS EN 12831 and the CIBSE Domestic Heating Design Guide calculate room heat loss, and how our heat loss calculator simplifies it.
BS EN 442 (radiators)
How BS EN 442 rates radiators at ΔT50, why output falls at lower flow temperatures, and how our radiator calculators correct for it.
BS EN ISO 13788 (condensation)
How BS EN ISO 13788 assesses surface condensation and mould risk, and what our condensation calculator does and doesn't cover.
BS EN ISO 6946 (U-values)
How BS EN ISO 6946 calculates U-values from layer thickness and conductivity, including bridged layers, as our calculators do.
HSE EH40 (workplace exposure limits)
What EH40 sets as the workplace exposure limit for respirable crystalline silica and how our silica calculator uses it.
The IET On-Site Guide
What the IET On-Site Guide is, how electricians use it with BS 7671, and which of our calculators refer to it.
MCS MIS 3005-D (heat pump design)
What the MCS heat pump design standard requires for sizing, and why our calculator is a planning tool, not an MCS survey.
Control of Noise at Work Regulations 2005
The lower and upper action values and the limit for daily noise exposure, and how our noise calculator uses them.
SHW clause 803 (Type 1 sub-base)
What Specification for Highway Works clause 803 means for Type 1 sub-base and how our MOT Type 1 calculator refers to it.
Control of Vibration at Work Regulations 2005
The hand-arm vibration action and limit values, HSE's points system, and how our HAV calculator uses them.