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drilling through floor joists

Postby sheffield » Fri Oct 30, 2009 4:17 pm

Drilling through joists?
I would like to drill through a 19.5cmx7.3cm joist in my bathroom floor to take a 40mm waste pipe. I know to drill on the centre line (and its just less than 25% of depth) but this joist has 19.5cmx4.6cm joists hung from it at 38cm centres supporting the bathroom floor. I don't want to compromise the whole of the floor strength which will be taking the usual weight of a full bathroom suite. Can I safely do it or do I rethink my waste route?
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Postby stoneyboy » Sun Nov 01, 2009 7:39 pm

Not possible to say from the information given - suggest you rethink the waste pipe route to avoid weakening the 19.5x7.3 joist.
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Postby rosebery » Sun Nov 01, 2009 8:27 pm

No thats far too big a hole. In any case you notch joists for pipes and drill for cables but 40mm is really far too big. Its not only the depth of the notch as a percentage of joist you need to consider its the distance from the end of the span too.

You need to rethink your waste run. Run waste parallel to 2" joists as far as possible. Allowing for correct fall you should be able to come out of the wall underneath the 3" one rather than cut through it.

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