DIY Doctor

5 inch hole in a 6 inch joist?

Postby zubin » Thu Aug 30, 2007 4:50 pm

I'm planning on installing a toilet/shower in a first floor room. I'd like to take the soil pipe out through an external wall at a level between the floor boards and ceiling below. This would allow other connections for the shower and sink to be made under the floor.

The orientation of the floor joists means that there is one against the wall I'd like to core through. If I support the joist either side by bolting into the external wall can I core drill a 5" hole through it to take the soil pipe?

Any advice gratefully received.

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Simply Build It

Postby thedoctor » Thu Aug 30, 2007 5:47 pm

You need to trim it Zubin. That is you need to fix a joist section at right angles to the 2nd joist in and build it into the wall on both sides of the pipehaving cut the 1st joist out where the pipe goes through the wall. Then you fix the 1st joist to the trimmers you have just built in on both sides. See our project on enlarging a loft hatch to see how to trim joists. In effect the wieght from this section of the floor and the 1st joist, is transferred via the trimmers, to the 2nd joist which should be then doubled up on to make it twice the thickness. This doubling can be done by bolting through as well as supporting in the normal way at both ends.
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