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Building Regulations Part G


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What is Part G of the building regulations?

The Part G Building Regulations (also known as Approved Document G) gives detailed guidance on how to meet the building regulations for a dwelling’s water system, including its cold water supply, water efficiency, hot water supply, sanitary areas, water efficiency and usage, washing facilities and waste water pipes. The Part G Building Regulations water supply pipe rules also cover installation, when a water efficiency calculation is needed, and state the extra safety measures needed for new or replacement hot water systems. 


Part G also gives detailed advice on how to meet the building regulations for water pipes in floors, walls and supply pipes, covering materials, measurements and workmanship. Part G building regs applies to most extensions, renovations, conversions and all new building projects.


Part G Building Regs is split into 7 main sections:

  • G1 - Cold water supply - ‘There must be a suitable installation for the provision of wholesome water’

  • G2 - Water efficiency - ‘Reasonable provision must be made by the installation of fittings and fixed appliances that use water efficiently for the prevention of undue consumption of water’

  • G3 - Hot water supply and systems - ‘There must be a suitable installation for the provision of heated wholesome water or heated softened wholesome water’, including safety measures

  • G4 - Sanitary conveniences and washing facilities - ‘Adequate and suitable sanitary conveniences must be provided in rooms provided to accommodate them or in bathrooms’

  • G5 - Bathrooms - ‘A bathroom must be provided containing a wash basin and either a fixed bath or a shower

  • G6 - Food preparation areas - ‘A suitable sink must be provided in any area where food is prepared’

  • Water Efficiency Calculator tables


Water efficiency calculators estimate water consumption for new homes, as well as some conversions and renovations, in order to help make homes more sustainable. Part G building regs applies to most building work carried out in England - including extensions, refurbishments, new builds and a material change-of-use - as well as excepted energy buildings in Wales.


What is Part G water consumption building regulations? What are the changes?

Part G Building Regulations state that the average water use must not exceed 125 litres per person per day (PPPD) in a residential building, and in some cases the limit is 110 litres PPPD. This will be stated on the planning permission. In order to work out the water use, the Water Efficiency Calculator should be used. Building Regs Part G sets out the average use per second for standard toilets, appliances and taps to help with the calculation.


Approved Document G was first published in 2010, and the latest version - which took effect on 1 March 2016 - merges the 2015 version with the 2016 updates. The latest amendment in 2016 was a change to section G2, which states that:

  • The water efficiency calculator must be completed for new dwellings where there is no shower


The 2015 version’s main updates included:

  • The introduction of the Water Efficiency Calculator methodology as part of the Code for Sustainable Homes

  • An optional requirement for tighter water efficiency in G2


When putting in new or replacement sanitation units, or hot water services, building work must meet Schedule 1 of Part G. Note that the Part G Building Regulations do overlap with Building Regulations Part A, Part B, Part C, Part J, Part L and Part P.


Building Regulations: water pipes in walls and floors

The Part G Building Regulations for water pipes in floors and walls set out the safety criteria for installing new or replacement pipes in a property. The Building Regulations water supply pipe rules state that service pipes should be a minimum of 750mm below the ground surface, and Approved Document G includes the materials and workmanship needed, as well as which British Standards need to be met for different pipes. 

The Part G Building Regulations for water pipes in walls state that pipes must be of a certain size and hydraulic resistance for their needs, which is set out in detail in G1 and G3.


Are there any exemptions to the Part G Building Regulations?

For many new build projects, renovations and extensions, the local building control body (BCB) must be notified and the work signed off before completion. However, there are some exceptions (known as ‘non-notifiable work’). Schedule 4 of the Part G Building Regulations states the type of work where you don’t need to notify a BCB. These include:

  • Minor work, with little risk to health and safety

  • Repairs and maintenance of existing items (eg. sinks and taps)

  • For an existing hot water system, the replacement of any part which is not a combustion appliance

  • Replacement of sanitary items if they use the same amount of water as the old ones

  • Pipes which don’t affect underground drainage

  • Replacing part of a cold water supply

  • Providing a hot water storage system that has a storage vessel under 15 litres

  • A competent person self-certification scheme under Schedule 3


Please note that any electrical work will require electrical certification. The Part G Building Regs should still be followed, even if you don’t need a compliance report or certificate for Building Regs sign off.


What is a Part G compliance report?

To meet Part G2 of the Building Regulations (water pipes in floors, walls, sanitation, water heating systems and maximum water usage from appliances) the appropriate water efficiency calculations should be done before work is completed. A registered competent person or approved third party can produce a Part G compliance report for you, to demonstrate to the BCB (and/or planning officer) that your project conforms to water efficiency laws.


There are lots of ways to reduce a home’s water usage (such as low flow toilets, taps and showers, or harvesting rain water), and many companies encourage an assessment to be done at the design stage too. 


Who does Part G water calculations?

Water efficiency calculations (also known as water calculations) give results based on occupancy, fittings and flow rates for a new or repurposed residential property. They’re based on the water consumption figures given by each product’s manufacturer for every fitting. These must meet the Part G regulations for average water use to be under 125 litres PPPD (and in some cases 110 litres PPPD or less). Anyone who is involved in the design and build of a new home can use the government approved water efficiency calculator, to ensure the building is compliant.


Alternatively there are many private companies and registered plumbers nationally who can do the water calculations for you, to make sure your project is within the limits, and these are relatively inexpensive. 

You can find more information on all updated Building Regulations on our dedicated Travis Perkins Building Regs hub.


Disclaimer: Information displayed in this article is correct at the time of publication, but note that legislation changes periodically. Please refer to the latest publication of each approved article. The information contained on this page is intended as an overall introduction and is not intended as advice from a professional building control officer. The definition of ‘building work’ and when Building Regs approval is required is set out here. Travis Perkins aims to avoid, but accepts no liability, in the case that any information stated is out of date. Always consult the approved local authority building control team when considering any exemptions, and before undertaking any work.