Tiling extension. Suspended timber floor. Use 22mm chipboard? - TilersForums.com

[Jason Smith]

I have a extension that is approx 20m2. The floor will be suspended timber, with wet UFH fitted below. Joists are at 400mm centres, and span about 2.6m

I was going to fit 18/22mm chipboard over. I am reluctant to over ply, as it will reduce heat transmission from the boards, and I have very limited height avaliable. Can I tile directly onto 22mm chipboard?, do I need to use a decoupling mat? Boarding with ply directly would mean that it is not T&G, What is the best solution/

 

[Chalker]

Best to use is 22mm fermacell flooring, straight onto the joists. You can tile straight onto it too, as its gypsum based.

 

[matthew_uk_666]

I'm certainly not a professional, but I've had to do similar while renovating my house...

I used 22mm t&g chipboard glued on all edges and screwed down to the joists and additional noggins on all sides, I then over-boarded with 12mm plywood screwed every 150mm with 30mm screws. Agreed this is not to British standards (I.e. 15mm ply) however it makes for a very sturdy floor with virtually no deflection.

It's tanked with tilesafe and the tiles stuck down with keraquick and latex plus...

I solved the problem of the door opening with a saw...:regular_smile::regular_smile:

 

[Ajax123]

Screed it??

 

[Chalker]

I'm certainly not a professional, but I've had to do similar while renovating my house...

I used 22mm t&g chipboard glued on all edges and screwed down to the joists and additional noggins on all sides, I then over-boarded with 12mm plywood screwed every 150mm with 30mm screws. Agreed this is not to British standards (I.e. 15mm ply) however it makes for a very sturdy floor with virtually no deflection.

It's tanked with tilesafe and the tiles stuck down with keraquick and latex plus...

I solved the problem of the door opening with a saw...:regular_smile::regular_smile:

the trouble with all that is it will insulate too much. Defeating the object of underfloor heating.

 

[Ajax123]

the trouble with all that is it will insulate too much. Defeating the object of underfloor heating.

Not if you get rid of the sheet timber over lay and use a screed instead....

 

[matthew_uk_666]

the trouble with all that is it will insulate too much. Defeating the object of underfloor heating.

I have wet underfloor heating too... it takes longer to warm up than other rooms but still happily gets to temperature.

 

[Ajax123]

I have wet underfloor heating in my lounge, kitchen and bathroom in anhydrite (Gypsol) screed. It warms up really quickly compared to the rooms that still have rads.

If I could work out how to upload pics I could show you how I did it....

 

[Ajax123]

 

[Chalker]

How thick is the screed?

Nice way of doing it over timber floor.

how do you work out the weight?

 

[Ajax123]

How thick is the screed?

Nice way of doing it over timber floor.

how do you work out the weight?

in my case I went 25mm over the tops of the joists which gave me 35 to 40mm between the joists. i could do that as it was my own house but from a technically correct point of view it should have been another 10mm thicker. The joists themselves are original so are around 150 years old and are 4x2 inch at roughly 400mm centres (varies joist to joist) with a span into the bay window of just 2.2m.

They were here quite bouncy when I took the floorboards up so to add rigidity I used the sterling board as a "flat noggin"

The sterling board is screwed to 19x35mm tile batten which is in turn screwed to the sides of the joists. This actually adds very very significantly to the rigidity of the subfloor to remove as much bounce as possible. The undersides of the joist remain open so that the wood can "breathe".

The 500g polythene is there to act as a slip membrane and to "tank" the floor and the screed is Gypsol TimBRE screed which weighs in at 2tinnes per cubic meter so 20kg per square meter per 10mm depth.

It works really really well and because I used anhydrite it warms up very quickly..... Typically takes less than an hour to warm the floor. Keeps me toes nice and toasty....

 

[Jason Smith]

Weight issue is a problem for using a screed. Looks like 22mm chipboard is not recommended.

What is the correct fermacel to use? Is there a link? How does it compare to chipboard?. Alternatively, would it be better to use ply straight onto the joists?

 

[Chalker]

Weight issue is a problem for using a screed. Looks like 22mm chipboard is not recommended.

What is the correct fermacel to use? Is there a link? How does it compare to chipboard?. Alternatively, would it be better to use ply straight onto the joists?

i get it through MKM builders merchants.

i think Wundafloor stock I too.