Shower Tray Installation

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I want to put a quadrant shaped stone resin shower tray in a first floor bathroom which has a one-inch boarded floor over nine-inch joists. I would like the tray to sit as low as possible on the floor, so I don't want to mount in on a platform. I know the tray has to be supported on a ply base with a sand & cement bed and I'm thinking that as most of the boards are missing from where the shower is to go, can I cut out the rest of the floor boards in the shape of the tray, then screw a half inch ply base on the joists with a half inch mortar bed on top, so the tray should end up at about the same height as if it was simply resting on the original floor?

The other problem is that as a joist runs directly beneath the trap opening in the tray can I get away with cutting about two inches out of the joist to take a very shallow trap? The floor span is only about eight feet.
 
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HandyAl said:
can I cut out the rest of the floor boards in the shape of the tray, then screw a half inch ply base on the joists with a half inch mortar bed on top, so the tray should end up at about the same height as if it was simply resting on the original floor?

Yes but I would use 1" ply in that case. + It will help with your other problem

The other problem is that as a joist runs directly beneath the trap opening in the tray can I get away with cutting about two inches out of the joist to take a very shallow trap?
15% >> {thats 1 1/3" on a 9" joist} is the max you are supposed to cut out of any joist for any pipe and that is only permitted within 1/4 of its span from the wall ie. 2' in your case. Cut any more than this at your own risk!
A HepV0 valve instead of a trap may work out better for you to avoid having to cut the joist so deeply
 
Sorry not time to look it up but I don't think you can cut the joist near the end. You can cut between 7% and 25% of the length, from the end, iirc. But the cut you need is too deep anyway.n A hole in the middle of the joist can be big enough - but look it up.

Do the sensible thing and raise the tray. Then you can access the trap when it leaks and you get a better fall.

NB the shallow shower trap most widely used has a seal depth inadeqate for building regulations.
 
Many thanks for the advice.

What about cutting a six to nine inch section out of the obstructing joist to allow space for the trap, then bolt-through a nine by three timber to one side of the two parts with something similar on the other side, so the original joist is sandwiched. The new timbers could be about four feet long so plenty of overlap past the cut-out section and could even be supported at the outer wall on hangers. Wouldn't it all end up as strong or more so than the existing? Access is no problem from below as the bathroom is above a garage and there will be a removable panel in the ceiling under the shower tray area.

Your thoughts would be appreciated.
 
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i am no builder but.....

its done all the time...staircases..loft access..
joists are cut and re-supported with cross sections (if thats the right word)..

cut it and support both floating ends with a cross section to the next joist..
 
JPC said:
i am no builder but.....

its done all the time...staircases..loft access..
joists are cut and re-supported with cross sections (if thats the right word)..

cut it and support both floating ends with a cross section to the next joist..

Its called trimming the joist. You need joist hangers to do it properly and doubling up of the other joists carrying the extra weight is sometimes required in a lot of circumstances but for an 8' span you 'should be' ok.
Might be worth consulting council planning dept as this may be classed as structural and the garage ceiling is or should be flameproof material.

Is it really worth the chew ? Just depends on how important it is for you to have the shower the exact way you want it and how much time and money you want to throw at it
 
Many thanks for the advice each of you. I've trimmed the joists as suggested and the problem is solved.
 

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