Shower waste through floor joists

16 Sep 2004
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United Kingdom
We are researching replacing our ensuite, shower, enclosure, tray, basin, WC and replacing a radiator with a towel rad. Currently, the shower waste runs inside a small bulkhead (made of a skirting board) on the floor along 2 walls (approx 6 foot, then a 90 degree turn a further 4 foot). The 6 foot run is against the direction of the floor joists so this would need running through the joists. I have yet to lift the chipboard floor so don't know what size the joists are. What is the maximum permissible hole I can make in a joist to accept the waste pipe. House is approx 7 years old, if that helps identifiying an approx joist size.

Thank you
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House is approx 7 years old, if that helps identifiying an approx joist size.
Yes - MINIMAL! Don't go there.
Lift the shower cubicle a few inches and run the waste in boxing against the skirting - or bring the skirting forwards.
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don't you start again.

I know its a bit late in the day for this response but I have just installed a new shower and had the same problem. I didn't fancy drilling through joists even if 25% is an allowable figure which it is. However I solved the problem very neatly indeed. To explain, the shower room is above our kitchen. The kitchen is decorated with "classic" coving available from Artex and most DIY stores. I carefully measured where a hole from outside the kitchen would penetrate behind the coving and then inserted a 40 mm pipe though the hole and behind the coving. I then trimmed the kitchen ceiling plasterboard from below the shower room joists and plastic welded a right angle fitting - hey presto the makings of the shower waste without disturbing the coving and drilling joists! Works a treat with absolutely no visible evidence anywhere of a pipe.
Only word of warning is to make sure your hole from outside aligns with the free space behind the coving. The classic coving gives plenty of clearance and a reasonable amount of wiggle space. For further security the pipe was foamed in and this also reduces completely any drainage noise one might hear in the kitchen.
Hope this helps someone.
... and you thought you were late in the day !

Just out of curiosity - what slope do you have on your waste pipe ? ;)

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