Is plastic plumbing the way of the future? Or a nightmare best left well alone? Since it’s introduction, in the late 70s, it has had a chequered history, and that is being polite. There have been some spectacular failures where joints have blown apart, usually because they were incorrectly assembled, and in the USA, one form of plastic pipe, polybutylene, is subject to thousands of class action law suits and is no longer commercially available, although, curiously, it continues to be sold almost everywhere else, without causing any undue concern or long term problems.
Plastic plumbing received a big boost in the late 90s when a number of new manufacturers entered the field and it started to become widely available from builder’s merchants and DIY stores. It’s also benefited from the uptake in underfloor heating systems which all have to be plumbed in plastic: underfloor heating (UFH) is seen as an upmarket product and so the cachet has rubbed off onto plastic pipe generally. But perhaps the single most important factor in explaining the gaining popularity of plastic pipe is the huge take-up of manufactured joists or I-beams as intermediate floors. Now when it comes to fitting pipework through an I-beam floor, it’s actually about fifteen times easier using flexible plastic pipe than it is using rigid copper — remember, I-beams cannot be notched at the top, the traditional route through floors for copper pipe.
The NHBC technical literature doesn’t have a huge amount to say about plastic plumbing but they do raise occasional concerns. The first one is also a perennial question on the selfbuild forum.
Does plastic plumbing require earthing? The answer is basically no, but it’s not quite as straightforward as that. What is clear is that, from the point of view of electric shocks, plastic plumbing makes a house a little bit safer as you reduce the risk of suffering a life-threatening shock. If some electrical appliance develops a fault and becomes ‘live’, the danger to someone touching it increases when they are making a good electrical connection with something else. Being naked in a wet bathroom makes you an A1 electrical contact.
Now you won’t find any mention of ‘earthing’, let alone ‘supplementary bonding’ in the NHBC regulations, though there is some guidance in Part P of the E&W building regs. It’s a subject about which most housebuilders are blissfully ignorant: it’s just some safety routine that the electrician has to do for reasons that are pretty obscure. But the facts are that if you plumb in copper, you have to link the pipe systems together so that you can’t have hugely different voltages between them. If you plumb in plastic, even if you use copper tails on the exposed pipework, you don’t need to earth bond the pipes.
Another FAQ on plastic plumbing is/was “Do plastic pipes require thermal insulation?" It is usual to wrap insulation abound hot water pipes in certain locations, notably between the boiler and the hot water tanks, to prevent excessive heat loss. Plastic pipe will lose less heat than copper but not that much less, so the answer is, “Yes, plastic pipes do require thermal insulation sleeving in the very same places as copper pipe.”
Finally, what are the recommended fixing centres for plastic pipe supplying hot and cold water and central heating? Hot plastic pipes tend to sag. Does it matter? Not a great deal. The critical question involves running plastic pipes through joisted or I-beam floors: the word seems to be that floor beams 600mm apart — the standard distance — really don’t need additional support. But if the pipework is exposed, the supports should be more frequent.