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Building Regulations calculators
Check your design against the numbers. Free tools for overheating, ventilation, stairs and more, with the source behind every result.
All calculators
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Overheating: simplified method
Glazing limits and minimum free area for new homes, by location risk, orientation and cross-ventilation.
Open calculatorExtension glazing allowance
The 25% rule: how much window, rooflight and glazed door area a home extension can have.
Open calculatorVentilation and trickle vents
Whole-dwelling rate, extract rates, background ventilators and purge openings for a home under the 2021 edition.
Open calculatorStair geometry
Risers, rise, going, pitch, the 2R+G rule and headroom from your floor-to-floor height.
Open calculatorNationally Described Space Standard
Minimum gross internal area, storage and bedroom sizes by bedrooms, bedspaces and storeys.
Open calculatorWater efficiency (110 litres)
The Appendix A calculator: litres per person per day from fittings, against the 125 or 110 l/p/d target.
Open calculatorOccupancy, exits and escape widths
Occupant capacity from floor space factors, then number of exits, exit widths and travel distance by purpose group.
Open calculatorHigher-risk building and height triggers
Is it a higher-risk building under the Building Safety Act, and which height-based fire measures apply to a block of flats.
Open calculatorUrban Greening Factor
London Plan Policy G5 score from surface types and areas, against the 0.4 residential or 0.3 commercial target.
Open calculatorRamp gradient
Maximum gradient for a ramp flight and the shortest going for a given rise, with landings and the lift and steps triggers.
Open calculatorEV charge points
Charge points and cable routes for new and renovated buildings under Regulations 44D to 44H.
Open calculatorHouseholder extension (permitted development)
Check a rear or side extension against the Class A limits, including the larger home extension route.
Open calculatorSpace separation for houses
Unprotected area allowed on an elevation by distance to the relevant boundary, using Method 1 or Table 11.1.
Open calculatorGutters and outlets
Effective roof area from pitch, then the half-round gutter and outlet size it needs.
Open calculatorDrainage field area
Floor area of a drainage field for a septic tank from the percolation test result.
Open calculatorAir supply for appliances
Permanent ventilation for open-flued stoves, boilers and fires by fuel, output and airtightness.
Open calculatorLimiting U-values check
Check walls, roofs, floors, windows and doors against the limiting fabric values in Tables 4.1 and 4.2.
Open calculatorEscape stair capacity
People a stair can carry for simultaneous evacuation (Table 3.2) or the width needed for phased evacuation.
Open calculatorFire resistance periods
Minimum period of fire resistance for the structure by purpose group, sprinklers and height of the top storey.
Open calculatorLondon residential standards
Cycle parking, private outdoor space and play space for a London housing scheme.
Open calculatorM4(2) and M4(3) dimensions
Check door widths, corridors, approach route and turning space against the accessible and wheelchair dwelling categories.
Open calculatorSound testing count
How many pre-completion sound test sets a scheme needs, by group and construction type.
Open calculatorCIL estimate
Borough and Mayoral CIL on net new floorspace, using the borough's charging schedule.
View statusA design aid, not legal advice. Checked against the Building Regulations 2010 for England; confirm with building control.