Tiling a loft..

[Pete G]

Hi there. Firstly thanks to those who answered a previous post on this subject. I have some more details now..

Basically i'm getting a loft extension done & plan to tile most (if not all) of the loft floor. I undertand this is not common, but not unheard of.
The floor structure will be 2 metal beams at each end, across the width of the house. Wooden joists (not sure if 4"x3" or 6"x4") will be laid across these, from front to back. (Floor area is @22'x18').
It will be 1 large living space, except for a 10'*6' walled area containing a bathroom.

The builders generally lay tongue-&-groove mdf floorboards, 18mm thick. Following advice here i've said i'll need 12mm ply sheets screwed on top of that. However, the intention is to lay down electric matting underfloor heating. I understand that, with a wood substrate (ie. not concrete), i won't need insulation board, but i read a post earleir where travertine tiles had cracked on ply with underfloor heating, which a member suggested was due to expansion/contraction of the ply, & somthing that a layer of Durabase CI (between the ply & tiles) would have prevented.

SO question is, will i need to use Durabase (or similar) matting to be on the safe side, & if so is it expensive? And does the combined
18mm mdf + 12mm ply (screwed every 300mm) + (underfloor heating mat) + flexible adhesive + 1cm thick (prob. ceramic) tiles sound solid enough not to move? (Sorry for the long explanation, i tried to cover all the details!)

I've negotiated the ply into the quoted cost but anything else i'll have to pay for & the budget is pretty stretched..

[Sir Ramic]

I am not sure where you have got the idea that you dont need insulation boards. They are there to push the heat up into the tile and stop heat going down. A timber floor will let the heat go down through the floor , hence waste.

[grumpygrouter]

Originally Posted by Pete G

Hi there. Firstly thanks to those who answered a previous post on this subject. I have some more details now..

Basically i'm getting a loft extension done & plan to tile most (if not all) of the loft floor. I undertand this is not common, but not unheard of.
The floor structure will be 2 metal beams at each end, across the width of the house. Wooden joists (not sure if 4"x3" or 6"x4") will be laid across these, from front to back. (Floor area is @22'x18').
It will be 1 large living space, except for a 10'*6' walled area containing a bathroom.

The builders generally lay tongue-&-groove mdf floorboards, 18mm thick. Following advice here i've said i'll need 12mm ply sheets screwed on top of that. However, the intention is to lay down electric matting underfloor heating. I understand that, with a wood substrate (ie. not concrete), i won't need insulation board, but i read a post earleir where travertine tiles had cracked on ply with underfloor heating, which a member suggested was due to expansion/contraction of the ply, & somthing that a layer of Durabase CI (between the ply & tiles) would have prevented.

SO question is, will i need to use Durabase (or similar) matting to be on the safe side, & if so is it expensive? And does the combined
18mm mdf + 12mm ply (screwed every 300mm) + (underfloor heating mat) + flexible adhesive + 1cm thick (prob. ceramic) tiles sound solid enough not to move? (Sorry for the long explanation, i tried to cover all the details!)

I've negotiated the ply into the quoted cost but anything else i'll have to pay for & the budget is pretty stretched..

Firstly, if it was my home, I would ask for the joists to be as big as possible so go for the 6"x3" if possible and have them at 300mm centres. Flooring is normally 18 or 22mm chipboard not mdf but in any case why don't you specify 22mm ply straight away screwed every 300mm. This should give you a really solid foundation for your tiling. You could then lay your Ditra/Durbase instead of the insulation board and then put the matting on that. Skim over the cables with SLC and tile straight on the top.

Bear in mind I am NOT a builder so my comments are only ideas and I do not know the practicallities of what I have suggested, but if it was me I would investigate the possibility of what i have said.

[Dave]

I agree with grumps....the 6x4 will be better ( joist deflection) and use 22m ply onto the joists and not mdf and ply.......Ditra/durabase would be ideal to stop any stress cracks as well..from the lateral expansion from timber and ufh combined......the ply subfloor will help with the heat transfer.....

[Pete G]

Thanks for the replies.

I got the idea that a wooden substrate would not require insulation from an old thread on here, where it was suggested that a concrete substrate would leach heat, whereas a wooden substrate wouldn't.

I will try & ring the builders tomorrow with the 22mm ply suggestion, but i think they said at the initial meeting on thurs. that they already had the chipboard.

So it sounds like that ditra matting would make a suitable insulator over the ply? I've never used it, but was planning on some under the shower tray.. Thanks again!

[wetdec]

Hi Pete

Come back when you know m8 and we can try again with the best solution


tiler

..

[bal]

I would ontop of sub floor use ply then insulation boards cross bonded to be safe , wood can shrink with the heat and crack the tiles.

[Pete G]

ok, had a word with the builders, & unfortunatly they have already ordered the chipboard. They have not yet ordered the ply, so i may have the option of ordering thicker ply to go over the chipboard.

The joists are apparently 2"x8" (laid on end).
So at the moment, it looks like 18mm tongue & groove chipboard, & 12mm ply on top of that.

So if the heat from the underfloor heating is the main course of concern for expansion/shrinkage of the wood floor, then it looks like i'll have to consider adding insulation board (cross-ways) on top of this, & then ditra matting?

[Dave]

Originally Posted by Pete G

ok, had a word with the builders, & unfortunatly they have already ordered the chipboard. They have not yet ordered the ply, so i may have the option of ordering thicker ply to go over the chipboard.

The joists are apparently 2"x8" (laid on end).
So at the moment, it looks like 18mm tongue & groove chipboard, & 12mm ply on top of that.

So if the heat from the underfloor heating is the main course of concern for expansion/shrinkage of the wood floor, then it looks like i'll have to consider adding insulation board (cross-ways) on top of this, & then ditra matting?

hi pete..

ok..so it's the chip board and ply option......

That will be sufficient insulation for the UFH...imo....lay your uFh onto the ply and latex level over this then use the Ditra on top.......this will stop the lateral expansion from the ufh and timber....

keep us posted......

[Holohana]

what about using 6mm Hardie backerboard?

Better job than 6mm ply, should really be 15mm, and keeps the height down and it also has insulation properties, but isnt insulation board.

[Pete G]

Holohana - i started looking at NoMorePly, but as it turns out the ply arrived this morning so it's academic now.

It will be a few weeks untill i can start on the UHF. Once liad, Should i do any kind of sealing to the ply before using latex leveller, or at least tape the joints?

Is there such a thing as a cheap latex leveller? And any recommendations for UHF mat systems?

[wetdec]

Hi Pete

If you want to email me I will try and help you out with the systems and methods you could use.


tiler