GUIDES

Part G water efficiency guides

Plain-English guides for builders, architects, developers and self-builders on the water efficiency calculation for new homes, and on commercial water calculations.

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OVERVIEW

At a glance

Part G of the Building Regulations limits how much water a new home is expected to use, and Building Control will ask for a water efficiency calculation to prove it. These guides explain the rules in plain English: which limit applies, how the calculation works, what to submit and what to do if a home fails. They are written for builders, architects, developers and self-builders, and every worked figure uses the same Approved Document G method as our free calculator.

01 / GUIDES

What each guide covers

Part G water calculations explained: The starting point: what a water efficiency calculation is, which projects need one and how the result is expressed in litres per person per day.
110 vs 125 litres: which target applies?: How to tell from your planning permission whether the standard 125 litre limit or the optional 110 litre requirement applies, with worked examples.
How to get a failed calculation to pass: The Appendix A factors for each fitting, which changes save the most water, and a worked example taking a home from 117.1 to 100.5 litres.
What to submit to Building Control: What surveyors check, the five-day notice under Regulation 37, plot-by-plot reports and what to do when fittings change on site.
Conversions and change of use: When barn, office, shop and flat conversions need a water calculation, and the common problems with existing fittings.
Greywater and rainwater in Part G: How reuse systems and water softeners are counted, which standards apply and when a reuse system is worth it.
Commercial water efficiency calculations: For offices, schools, retail and mixed-use schemes, where water use is assessed through BREEAM Wat 01 rather than Part G.

GUIDES & TOOLS

All guides and tools

THE BASICSPart G water calculations explainedWhat the calculation is, who needs one and how the 125 and 110 litre limits work.Read guide → TARGETS110 vs 125 litres: which target applies?How to tell from your planning permission which limit you need to meet.Read guide → FIXING A FAILHow to get a failed calculation to passThe fittings that move the result most, with worked figures.Read guide → SUBMISSIONWhat to submit to Building ControlWhat surveyors check, when it is due and what to do if fittings change.Read guide → CONVERSIONSConversions and change of useBarns, offices, shops and flat conversions: when a calculation is needed.Read guide → WATER REUSEGreywater and rainwater in Part GHow reuse systems and water softeners are counted in the calculation.Read guide → COMMERCIALCommercial water efficiency calculationsOffices, schools, retail and mixed-use schemes, including BREEAM Wat 01.Find out more → FREE TOOLWater efficiency calculatorCheck a new home against 125 or 110 litres per person per day in minutes.Open calculator → REPORTSBuilding Control report pricingFree to calculate. Reports from £20 + VAT, £10 + VAT for each extra plot.See pricing →

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