Dee Posted July 2, 2017 Author Share Posted July 2, 2017 @nickfromwales.....how much can I notch out the top of 2x4 joists? These joists only support a plasterboard ceiling and the notches are needed to provide fall for a poo pipe Link to comment Share on other sites More sharing options...
PeterW Posted July 2, 2017 Share Posted July 2, 2017 Not much ... although you could hang the lower joists from the upper ones to stop any movement. Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 2, 2017 Share Posted July 2, 2017 49 minutes ago, Dee said: @nickfromwales.....how much can I notch out the top of 2x4 joists? These joists only support a plasterboard ceiling and the notches are needed to provide fall for a poo pipe You can take more out if you sister each joist with plywood, one each side of each joist. You'd need to fit these the same height as the joists and about 1200mm long. Glued with proper resin based waterproof wood glue, clamped and screwed every 100mm an inch down and inch up ( so two screws at each 100mm interval ) which will replace almost all of the strength in the section you have cut away. Pre cut the plywood according to the notches you've made in the joists . Hanging them off 'binders' as @PeterW suggests will also help with the worst affected ones but not needed all the way if only taking half inch or so out of start / end of the run. Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 2, 2017 Share Posted July 2, 2017 Inch ( 25mm ) plywood would be best. Local yard may have a saw and be able to rip it down for you. Link to comment Share on other sites More sharing options...
Dee Posted July 2, 2017 Author Share Posted July 2, 2017 Oh poo! could I double up 12mm ply? It is only taking the weight of existing pb and the new poo pipe! So, is the strength of a joist compromised that much by notching? I've seen some massive chunks taken out and holes drilled! Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 2, 2017 Share Posted July 2, 2017 @Dee If it genuinely is only performing the duty of ceiling rafter, not floor joist, then whack away ma'am. A couple of binders ( timbers to connect upper joists to lower rafters ) will be a belt for the braces, and if the above is correct then the ply is unnecessary. Link to comment Share on other sites More sharing options...
Dee Posted July 3, 2017 Author Share Posted July 3, 2017 Definitely only supporting the ceiling below so I feel confident it won't collapse! Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 3, 2017 Share Posted July 3, 2017 I think a few binders for the worst affected rafters would be a good idea, and no more.. Try and lay the soil pipe on some 50mm fluffy rockwool to offer some sound deadening to the room underneath. It'll compress down to 5-10mm. Link to comment Share on other sites More sharing options...
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