22mm ply onto joists, ufh, which board to use and why?

[Scott HAZARD]

Hi all, been browsing through the forum trying to find a definitive answer. I'm in the process of qouting for a 33m2 floor. The floor is not ready yet, but it will be 22mm wbp plywood primed on all surface and then down directly on to the joists, noggins will be added and bricks built up under the joists to give added support also.

UFH will be installed, now I'm split on using 6mm no more ply or 6mm jackonboard beforehand. As far as i understand it, no more ply installed correctly will give added strength comparable to 18mm ply, which is great. But I feel jackonboard, will not give us much structural strength but much better heat and sound insulation, both will then have self leveller over the top before being tiled.

The tiles are porcelain wood effect look, therefore I believe an uncoupling membrane is not necessary as the both boards are dimensionally stable?

What would you do and why?

Thanks

 

[J Sid]

have you concerned using 22 mm Hardie floor Structural Fibre Cement Interior Flooring - HardieFloor - http://www.jameshardie.co.uk/hardiefloor
rather than 22mm ply?

 

[Scott HAZARD]

No, what an awesome product, glad I asked the question and got your answer already! have you used the product yourself?

 

[J Sid]

not the 22mm , no, but I would if I was ever asked 'how should I prepare the floor for you ' by a builder

 

[Kevbos]

I always think you need 18mm over joists then another 18mm .this makes floor rigid and no bounce .lay the ufh. Self level then use ditra or equivalent .I always coat over the decoupling membrane with adhesive too to fill holes properly

 

[Rizzle from the Portizzle]

the first part is right but first layer of ply should be 12.5 mm screwed down then coated with wood glue then cross plied with anther layer of 12.5mm ply then screwed down when the glue drys between them it will have the strongest bond with no ruining
joints and take out any flex .next its better to go over with 6 mm insulation board for electric ufh then self level with firba reinforced floor leveler then tile

 

[Kevbos]

That's not what I was taught by a tta founder

My builder.com says 18mm then 12mm

Weber say over board with 9mm ply if no bounce

 

[Dan]

That's not what I was taught by a tta founder

My builder.com says 18mm then 12mm

Weber say over board with 9mm ply if no bounce

Dude, try not to double and triple post! I keep needing to merge all your posts. Edit your original post and add to it, or wait until somebody else replies before replying again.

Thanks

 

[Scott HAZARD]

Thanks for the replies guys, although slightly conflicting lol, I've suggested the hardifloor and tbh am quite keen to give the product a go.

On another note Ufh, biggest matt sold I can find at the moment is 12m2 roll. I havent installed anything bigger than this, I'm guessing its possible to combine matts? meaning you can run them all to one thermostat or something?

 

[J Sid]

you can go bigger, @Uheat - Jake can advise

 

[Uheat - Jake]

Thanks for the replies guys, although slightly conflicting lol, I've suggested the hardifloor and tbh am quite keen to give the product a go.

On another note Ufh, biggest matt sold I can find at the moment is 12m2 roll. I havent installed anything bigger than this, I'm guessing its possible to combine matts? meaning you can run them all to one thermostat or something?

You can have numerous mats off one thermostat, however you need to think about a difference in temperature from one side of the room to the other if it's a big area and espcially if it's a kitchen / diner, as you have to take appliances into account as they generate heat and could cause contradiction on the thermostat leaving the other half of the room unheated.
A normal electric ufh stat can take up to 16amps which is 22m2 of 160w/m2 mating.

 

[Rookery]

You can have numerous mats off one thermostat, however you need to think about a difference in temperature from one side of the room to the other if it's a big area and espcially if it's a kitchen / diner, as you have to take appliances into account as they generate heat and could cause contradiction on the thermostat leaving the other half of the room unheated.
A normal electric ufh stat can take up to 16amps which is 22m2 of 160w/m2 mating.

Please will you clarify. Surely it's the latter not the former?

 

[Uheat - Jake]

Please will you clarify. Surely it's the latter not the former?

Should have made that a bit clearer, the biggest single mat we do is 10m2 in any wattage, therefore to get to 22m2 you need to make it out of three mats which are then wired in parallel to the thermostat. However if you require more then 22m2 of mating then they can all be wired to a contactor, a contactor will switch the load down to under 16amps which the thermostat can then handle, enabling you to have 30, 40 or even 50m2 off one thermostat.

 

[Flintstone]

Only a week or two ago I fitted 2 x 15m kits down. I'm sure I've used a 19m kit before as well. Remember you need to calculate the area right, not just the size of the room.

 

[Flintstone]

Personally i would over board with 10mm insulation board over the 22mm ply, this will decouple and insulate. I don't think there's any need to over complicate with multiple layers of ply wood etc.