Part G and the Water Calculator

One of the big changes coming through in the next round of building regulations is the amendments to Part G, which is due to come into effect shortly (6/4/10). Part G deals with water and it's been one of the sleepier areas of the regs to date. But this is all set to change when people designing new homes have to get their heads around the dreaded Water Efficiency Calculator for the first time.

At the moment we, as a nation, consume something like 150lts/day of potable water each in our homes. I don’t know where this figure comes from, and it certainly doesn’t relate to any home I have ever lived in recently (my personal average seems to be around 250lts/day). Moves are afoot to lower this figure — the targets are all in the Code for Sustainable Homes — and the latest version of Part G brings a figure into the equation for the first time, that figure being 125lts/person/day.

This doesn’t mean that you will only be allowed to consume 125lts/person/day, but that you must install equipment which theoretically — as if is you just happened to be the average consumer — means that you could go on living your life normally and only consume 125lts/day rather than the 150lts/day that you are currently consuming.

And what that means, of course, is that whereas up till now you just plumbed in a shower or a bath because it looked good and promised eternal happiness, now you have to perform a calculation and show it to building control who will check that you are in fact allowed to have this bit of kit.

You can find the Water Efficiency Calculator online here.

In order to get it to work, you will have to know the flow rates of your showers and taps, the capacity of your bath and the flushing volumes of your loos. You have to fill them into the calculator to work out your notional usage. And the total has to come in at under 125lts/person/day or else.

The two things that are likely to have greatest effect on these calculations are showers and baths. A shower with a very average flow rate (say under 20lts/min) is likely to find it difficult to pass the new hurdle rate. So the hunt will be on for low flow showers which still do the business, whatever that might be.

This topic came up at a seminar I attended at Ecobuild chaired by Nick Grant (or not! see Nick's post below). A woman from an “upmarket housebuilder” asked what she should do as the current batch of low-flow showers were simply unacceptable to her clients. It was suggested that the Nordic Eco shower was a possibility, and that Hansgrohe had a 6lt shower that was OK. Wolseley Sustainable Building Center promotes Mira’s Eco handset which, it says, gives a good 6lt shower. But the woman seemed unconvinced. I suggested to her that they could have swimming pools instead, as theses weren't included in the water calculator, to which she replied “Oh, they already have, but no baths and feeble showers.”

What else is new in Part G?
• G3 is being extended to include thermostatic taps on baths (max temp 48°C) because 93% of home scalding accidents occur in baths. CLG claim that a cost benefit analysis had been carried out to do this — i.e. it costs more to treat scalds than it does to fix thermostatic taps. The decision to exclude other taps (i.e. basins) was made because of the fewer number of accidents though, it was noted that in Scotland, a wider range of taps now has to be thermostatic.

• The safety features in G3, which have up till now just covered unvented hot water systems, are being extended to other water storage systems such as ordinary cylinders and thermal stores. This was controversial as it was challenged by a number of European manufacturers who sell all manner of water storage gear without all the safety paraphernalia that is required in the British market. Essentially, the kit must be modified for the UK market and must include at least two additional safety features, being temperature and pressure valves.