Most self-builders expect the early design discussions to revolve around architectural styling, internal layouts or even energy efficiency. Few expect detailed conversations about toilet flush volumes, bath capacities or the flow rate of a shower. But these are the sort of questions that need to be resolved to comply with Building Regulations and Approved Document G.
Without understanding its requirements you’ll risk choosing bathrooms and kitchen fittings that fail to satisfy the standards. And if the penny doesn’t drop until they’re fitted, changing specifications can become both costly and frustrating.
In reality, Approved Document G is quite easy to satisfy, provided it is considered at the outset of a project. Understanding what it covers, when it applies and how compliance is assessed will all help to avoid unnecessary surprises when it comes to final approval.
What exactly is Approved Document G?
At first glance, Approved Document G (often referred to as Part G), appears to be little more than a plumbing standard. In reality, it has a much wider influence on the design of a new home and how it will work. As an approved document it sets out pre-approved methods of compliance for sanitation, water efficiency, hot water safety and washing facilities, affecting everything from the specification of sanitaryware and hot water cylinders, to the calculations needed before Building Control will sign the project off.
Part G is typically one of the least discussed part of the Building Regs and as a result, probably the least understood. This isn’t because it's particularly complicated, but because most homeowners don't realise its importance and how it influences early stage design decisions.
Approved Document G is formally titled Sanitation, Hot Water Safety and Water Efficiency. Not exactly a snappy title, and more importantly doesn't convey its influence on a modern home.
The document is divided into six main areas covering the supply of water, water efficiency, sanitary conveniences such as WCs, washing facilities and bathrooms, as well as food preparation areas, kitchen sinks, and the safe production and storage of hot water. The overall intention is to ensure that a home is hygienic, safe to use and makes sensible use of one of our most valuable natural resources.
Although self-builders tend to think of Part G as something for plumbers, most of the important decisions are actually made much earlier by the architect, building designer and building services engineers. By the time the plumber starts, many of the key compliance decisions should already have been made.
The importance of water efficiency calculations
The part of Approved Document G that generates the greatest number of questions is the water efficiency requirement for new dwellings.
Every new home must normally be designed to limit predicted water consumption to no more than 125 litres per person per day. In parts of the country where water scarcity is a concern, local authorities have adopted tighter planning policies to typically reduce the requirement to 110 litres.
The calculation isn't based on measuring how much water you actually use, so you don’t need to worry that the tap will suddenly stop. Instead, it predicts likely consumption using a standard methodology based on every water-using appliance that’s installed in the property. This includes toilets, taps, showers, baths and even appliances such as washing machines and dishwashers. If rainwater harvesting or grey water recycling systems are incorporated, these can improve the overall result.
In practice, the water efficiency calculation is a similar design tool to SAP calculations, with the aim of having a positive influence on the efficiency of our homes.
Approved Document G and hot water safety
Approved Document G contains a host of important requirements for hot water safety. Stored hot water is commonly maintained at temperatures of around 60°C to minimise the risk of Legionella. However, water stored at this temperature can cause injury by scalding, so thermostatic or blending valves are required for baths in new homes.
These blend the hot and cold water before it reaches the tap, allowing the cylinder to remain hot whilst delivering water at a much safer temperature.
Part G also governs unvented hot water storage systems. Because these cylinders operate under mains pressure, they require safety devices to control pressure and safely discharge water if a fault occur. The standards are specific, so installation and commissioning is best undertaken by suitably qualified and competent installer.
How to comply with Approved Document G
Small choices can have surprisingly large consequences
A common misconception is that choosing bathroom fittings is largely an aesthetic decision. A rainfall shower with a very high flow rate might sound luxurious, but if it is installed in a new build property, it could consume a significant proportion of the water consumption target. Even decisions like opting for a WC with a larger flush volume rather than a dual-flush model will have implications that collectively could push the calculation beyond the permitted limit.
The last thing you want is to fit a beautifully designed bathroom that ultimately fails the final sign off when the building control officer checks the fittings against the original water efficiency calculation. The result will undoubtedly involve more work, and possibly fitting a different bathroom that’s not now quite so beautiful.
Fortunately these problems aren’t that difficult to solve, provided compliance is understood at the design stage, and upgrades aren’t made without fully checking their consumption levels.
Don’t think about Part G in isolation
As with most other Approved Documents, Part G overlaps with other parts of the regulations. Its relationship with Approved Document L is perhaps the most obvious, as reducing hot water consumption also reduces the energy needed to heat it, helping to improve the overall energy efficiency.
Bathroom ventilation falls under Approved Document F, whilst drainage design is covered by Approved Document H. Accessibility requirements in bathrooms are addressed by Approved Document M, and electrical installations around showers and bathrooms fall within Approved Document P. It can be all rather confusing.
Fortunately, competent designers will consider all of these documents together, rather than treating each independently. In practice, moving a bathroom may affect drainage gradients, ventilation routes, electrical zoning, accessibility and water efficiency calculations, so it's best to always check the design implications before making changes.
Does Part G apply to every project?
The simple answer is no. For a new build home, or a new dwelling created from a conversion, the requirements of Part G apply in full.
Extensions are slightly different. If you're simply adding extra accommodation to an existing home, you won't normally need to demonstrate compliance with the 125-litre water efficiency target. However, any new sanitary accommodation, kitchens, or hot water systems will still need to comply with the relevant sections of Part G.
Bathroom refurbishments are different again. If you're replacing an existing bathroom within an existing house, you won't have to complete a whole-house water efficiency assessment as Building Regulations acknowledges that bringing an older property up to current standards isn't always practical.
However, all new work should still comply with relevant parts of Part G, such as safety standards. For example, replacing an old vented cylinder with an unvented system requires modern safety requirements.
How compliance is checked
Unlike some aspects of the Building Regulations, Part G isn't assessed during a single inspection. Compliance starts in the design stage when product specifications are chosen. Water efficiency calculations are normally prepared, and once construction is underway, Building Control will inspect the plumbing installations.
At the end of the project they'll ask for supporting documentation confirming that the installed products achieve the water usage set out by the water efficiency calculation. If an unvented cylinder has been installed, they’ll also ask for commissioning certificates. As you’d probably expect, changing products without updating the supporting calculations can therefore become a compliance issue at completion.
Responsibility for Part G is shared
There isn’t a specialist Part G consultant as such and responsibility is generally shared across the design team, and ultimately the trades on site.
The principal designer will normally coordinate compliance and the water efficiency calculation is often produced by either the SAP assessor, energy consultant or building services designer, depending on who’s in the hot seat.
Ultimately, responsibility rests with whoever is carrying out the work on site. For self-build projects, and especially those being self-managed, it’s a good idea to ensure that everyone is working from the same specification and that product choices comply with the assumptions made in the water usage calculation.
Will Approved Document G change any time soon?
Whilst the core requirements of Approved Document G haven't changed much in recent years, water efficiency is becoming increasingly important.
Population growth, climate change and increasing pressure on water resources mean that we should expect tighter consumption targets in the future. Greater emphasis will therefore fall on the efficiency of sanitaryware, leak reduction and use of alternative water sources such as rainwater harvesting and greywater recycling.
Approved Document G isn’t the regulation that excites most self-builders as there aren’t any cutting-edge technologies to fantasise about. However, there are quite a few traps that could catch people out if they aren’t fully considered early in the design process.
From a self-builder's point of view, my advice is simple. Know that there are requirements but be confident that a competent design and construction team will take care of them.
And before splashing out on a lovely spa bath, the size of a small swimming pool, check the water efficiency calculation, otherwise you’ll find building control asking uncomfortable questions, just when you want to move in.
