Do plastic waste pipes expand under heat and cause cracking noise?

15 Jul 2018
Reaction score
United Kingdom
Now we have moved into our newly renovated house, we are noticing odd things occurring.

I noticed when the Mrs gets in the shower above the kitchen, along the run of the waste pipe in a certain area, there is an odd tap/crack noise every 5-10 seconds while she is showering.

I'm certain it isn't a drip as the fall is barely a few inches and there is insulation under the pipes which would dampen the noise.

I am thinking it could be the pipe expanding under the heat of the shower water and causing it to move somewhere in its run.

Is this possible? What else could it be? It only happens when the shower or bath are draining.
Sponsored Links
I have experienced this in a previous house. Believed it to be the waste pipe expanding and contracting with the flow of warm water.
Yes ,plastic pipes expand when hot water runs through ,and contract quickly if cooler water runs through shortly after. The noise you hear is usually when the pipe is hard up against something ,like plasterboard ,wooden joists etc.
We had that before with a soil stack, it only did it when the shower was running, it turned out to be galvy banding that they had used to tie the stack to the wall and when the warm water ran into the stack, the stack would expand slightly when heating up and would click against the banding.

One pair of cutters later!
Sponsored Links
Parents have been in their house since 1983, and the stack makes a tapping noise every time someone flushes the upstairs WC. Has done it since the place was built in 1979 they were told.
Enormous expansion rate for plastic soil and waste pipes which must be allowed the manufacturers installation guides and all will be explained.
Polypipe, Osma, Hunter etc
Yes, I get a very loud cracking from my waste pipes instantly when, for example, I empty hot water into the sink when I strain off pasta, rice, boiled potatoes, peas etc etc

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local