Un-level bathroom floor

[Mr-Mechnic]

Hi,  I have a bathroom in a converted barn we bought which has limited headroom as its in the roof, I am in the process of converting it into a wetroom and in general have no issues troubling me apart from the floor from the middle of the floor to the edge falls away about 20mm in 1000mm. where the former for the shower is going is perfectly flat but the floor falls away from its edge, I know I need to raise the level to get a slight fall the other way, whats the best way to build up the floor as I`m on floorboards, Do I spend ages planing down a sheet of 18mm ply or can I build it up another way, Cheers All

[Mr-Mechnic]

Just to add there will be very little foot fall on this area as its the end under the eaves and headroom there is 1.2 metres

[Russell griffiths]

Can you sister another joist onto the sides of the original joists but at the correct level. 

[Mr-Mechnic]

That is an option that I didnt think of Russell,  there are eaves cupboards and a stud wall covering the floorboards, if I can find the joist and its near enough to the edge I could cut the floorboards and re lay them 

[Nickfromwales]

What size are the joists ?

[Mr-Mechnic]

12 by 4 inch Nick across a 3.5 metre span

[Onoff]

Add some firings to the tops of the existing joists? That would rely on all the existing joists being out by the same amount.

 

 

[Nickfromwales]

If I'm reading this correctly then the middle of the room is the issue. What I've done previously, so as not to raise the floor level at the door, is to lift all the floorboards and get the room back to the exposed joists. I then fitted full lengths of 3x2" on the inside face of each joist, as parallel ( sister joist ) rails, set to the height of the lowest joist -18mm. 

A laser is your friend here for sure, but you can use a level and get good results ( like the good old days  ). 

So say the lowest point is your doorway. You measure down 18mm from the top of the joist, and clamp a full length of 3x2" accordingly, level it as required making sure your start point stays exactly where it should be. Double check as this will dictate the rest of the floor level ! Screw that to the joist using 10x3's and put plenty in. Gluing will help too if you can work quickly enough. 

Cut 2 pieces of 3x2" narrow enough to fit between the joists. Clamp another full length of 3x2" opposite the first one and repeat with levelling. Sit the off cut of 3x2" from the first rail onto the next and then sit your 600mm level onto that. That'll allow you to make sure that each rail on each joist is level with the previous one. The purpose of the 3x2" off-cuts is to allow you to bridge over the joists when you get to the middle of the room, where you should find the joists higher than the rails plus 18mm ply. 

Repeat until you've railed the whole room, then get a piece of 18mm ply on its side sat on the rails, to use as a guide for trimming the

joist tops down to suit with an electric plane. 

Once you've got level rails throughout, and they're 18mm lower than the lowest point in the room, you can then rip 18mm plywood down to i film inbetween the joists. Once that's done, ( plumbing and tray etc omitted at this point as it's a separate subject ),  you can glue and screw 6mm plywood in full sheets over the top of the lot. Loads of PVA spread around with a floor layers comb ( 3mm notch ) and 1"x8's BZP screws at 120mm centres to fix the ply down nice and tight. 

By the time you tile, and posibly UTH ( under tile heating ) wire too, you'll not have pushed very far past the existing door level. You can plane the joist tops down after the plywood goes down, up to you. 

My 2 cents. 

PS if the joists are at all loose or excessive movement is detected, alter the 18mm dinension to 38mm and I fill with 3x2" on flat instead of the ply. You can park a car on that   

 

[Mr-Mechnic]

Thanks Nick, I will get the level out again, I was hoping for a miracle fix but I guess there is only the correct way to do things

[Nickfromwales]

Just now, Mr-Mechnic said:

Thanks Nick, I will get the level out again, I was hoping for a miracle fix but I guess there is only the correct way to do things

If it wasn't a wet room you could use lollipop sticks tbh, but a wet room is a different beast altogether.

[Nickfromwales]

How it looks infilled with 3x2". 

 

 

Cuts around the waste to allow a bit of movement when connecting to the tray. 

 

 

Troughing out for pipework / cables etc. 

 

 

Happy days. 

 

 

Plenty of acoustic roll so folk downstairs can't hear the shower or tall people peeing . 

 

 

End result. Not a wetroom as this was a very small room. But all tanked and membraned so as good as. 

 

 

Nice level entry shower, compared to the 160mm step to get into the old one