Sub floor for marble tiles, help needed!

[GG1]

Hello,

I live in a 1930's house with a suspended wooden floor. The joist centers are around 360 mm. I say around as they vary slightly from joist to joist. The joists are 4" x 2" and currently have 22 mm floorboards.

My plan is to remove the existing floorboards and put celotex insulation between joists, then install a water underfloor heating system, which would then have a small biscuit mix screed to the top of the joists and then install plywood over this. I was thinking about 18mm WBP, but I am not sure of the best option to take, hence why I am have joined this forum.

The marble tiles are 305 mm x 305 mm x 10 mm.

Any help or alternative options would be appreciated. Looking for the best price to achieve the finished result I require.

Thank you!

 

[ree]

Dont remove any floor boards until, and if, its necessary.

Which room or rooms are you planning on working on?

How come you've decided on the above arrangement?

Who will install any wet UFH?

4" x 2" joists in a 1930's house sounds unusual - is this all the suspended floor joists?. Are you certain its 4 x 2? Whats the longest span?

Have you crawled under the floor - if not then perhaps have a practice?

 

[GG1]

Hello, thank you for your reply.

I am planning to work on the dining room, living room, hallway and office.

I decided on the above arrangement from previous jobs seen and described online.

I will be having a plumber to install the wet UFH, but am looking to do the work myself to get to this level.

Yes it is all suspended floor joists and I am certain of the measurements of the joists, as some are exposed currently and they are all 4 inches high and 2 inches wide. They are supported on brick walls with a timber wall plate. These walls are about a meter apart and spread the load.

I have not crawled under the floor, as currently there is no access unless I remove some more floorboards.

 

[GG1]

Out of curiosity what is so unusual about 4" x 2" joists in a 1930's house, what is the usual or normal size joists associated with a building of this age?

 

[ree]

In essence, dont do anything until you have had a heads up from the plumber who is going to do the UFH. Note the plumber's observations and then come back here.

Knee walls 1m apart are new to me.

What depth do you have below the joists to the oversite?

Most all suspended floors have access hatches - sometimes under stairs. If you dont have access to a crawl space then you will have to lift tiles to locate any future underfloor difficulties.

 

[GG1]

I have already spoken to my plumber about this and he seems to think it would work, but after some research it gave me doubts.

Joists to oversite is 10 inches.

No hatch, maybe due to such a low joist height?

 

[GG1]

Forgot to mention that even if there was a hatch, those kneewalls are literally every meter, so I could only travel that distance, before I hit a dead end.

 

[ree]

So, as i understand it, you are installing insulation up level with the joist top edges (is this right?) and then laying UFH on top. Next you will screed in the UFH. Then you want to install 18mm WBP ply.
You will then lay 300 x 300 marble tile on the ply?

 

[GG1]

The insulation will be fitted 20-25 mm below joist level, then install UFH to insulation via staples and removing notch from end of joists. Then biscuit screed on top of this to the top of the joist then 18 mm fitted on top of this, so no loss of height.

 

[GG1]

Forgot to add then marble 305 x 305 x 10 on top of the ply and will probably use ditra mat to avoid any cracking. Or any other options if anyone has a better solution?