Shower Tray and Joists

[Nedman87]

Hello all,

Decided to give replacing my bathroom a go and probably over thinking it. Just trying to see if I need extra support or if I should be ok.

My joists under the shower are running parallel with the tray. (1700Lx700Wx40H)

The 18mm 22mm T&G chipboard flooring is running perpendicular with the joists.

I was going to use 12mm Hardieback cement board as a base on top of the chipboard. (I'd prefer to use 6mm Hardieback if that's safe? The 2-3mm of tile cement holding it down along with the 8mm of sand/cement for the shower bed is adding up to make up the height with the rest of the floor. I have 18mm max to door threshold)

Will this be enough without ripping up all the chipboard the length of the shower and installing extra noggins and 18mm 22mm ply instead?

If I did have to add additional support, would I get away with just adding the noggins/braces between joists labeled 1 and 2 in the picture attached?

Been enjoying this project so far with successfully rerouting the pipes (in copper! Didn't want to go the plastic route unless a last resort haha) and replacing the plasterboard with cement board.

Thanks For any advice, much appreciated

 

[denso13]

Just trying to see if I need extra support or if I should be ok.

It should be 22mm flooring with joists at 600mm centres. Are you sure it's 18mm?

 

[Nedman87]

It should be 22mm flooring with joists at 600mm centres. Are you sure it's 18mm?

You are correct, I just assumed 18mm. I have corrected my original post.

So basicly is the 22mm ply chipboard OK with the joist locations and ideally using 6mm hardiebacker board on top without needing to add any supports?

 

[denso13]

So basicly is the 22mm ply OK with the joist locations and ideally using 6mm hardiebacker board on top without needing to add any supports?

Yes, no problem (I take it you mean the existing chipboard).

 

[Nedman87]

Yes, no problem (I take it you mean the existing chipboard).

Yes 22mm chipboard!

I'm losing the plot today. Please bare with me!

 

[Madrab]

Personally I always replace P5 chipboard where a tray has to sit with OSB3/ply. Too many times I've been called in to re-do a shower and found the chipboard floor below has got wet and turned into mush.

I also take the approach that the tray must be supported properly around it's outside edges, if they fall on a void in the floor, between joists, then I would always add extra support to minimise any deflection in the floor

 

[Nedman87]

Personally I always replace P5 chipboard where a tray has to sit with OSB3/ply. Too many times I've been called in to re-do a shower and found the chipboard floor below has got wet and turned into mush.

I also take the approach that the tray must be supported properly around it's outside edges, if they fall on a void in the floor, between joists, then I would always add extra support to minimise any deflection in the floor

If I laid 6mm hardieback board down on top of the chipboard (Tile cemented+screwed) and it spanned both the joists, would that be sufficient.

It will be siliconed and tanked from walls to the hardieback floor aswell.

I'm just trying to avoid taking up any more of the floor than needed as the chipboard runs under the stud walls and a couple pieces wouldn't be supported by the current joists. It's about 350mm from joist 2 in the picture which is into a bedroom I can't take the floor up on .

 

[denso13]

If I laid 6mm hardieback board down on top of the chipboard (Tile cemented+screwed) and it spanned both the joists, would that be sufficient.

Yes, I think it's more than sufficient.

 

[Madrab]

If it is to be tanked and sealed at the corners/edges then that's certainly a great idea to stop any moisture getting to the P5. A 6mm cementitious board over the top will also help guard it from any water, if the seal was ever compromised.

Will it be a full depth stone resin tray? If so that should be able to sit on that void easier than say a lightweight or acrylic tray, with minimum deflection. As it's 22mm P5 with the 6mm on top then that would normally provide enough support, if you can't get underneath.

 

[Nedman87]

If it is to be tanked and sealed at the corners/edges then that's certainly a great idea to stop any moisture getting to the P5. A 6mm cementitious board over the top will also help guard it from any water, if the seal was ever compromised.

Will it be a full depth stone resin tray? If so that should be able to sit on that void easier than say a lightweight or acrylic tray, with minimum deflection. As it's 22mm P5 with the 6mm on top then that would normally provide enough support, if you can't get underneath.

40mm height stone resin and acrylic capped.

Wickes 40mm Pearlstone Rectangular Shower Tray - 1700 x 700mm | Wickes.co.uk

Wickes 40mm Pearlstone Rectangular Shower Tray - 1700 x 700mm

www.wickes.co.uk