Flooring above underfloor heating

[Emtoucan]

Hi all,

On Monday we are due to have UFH installed in our new extension. The UFH system is on a suspended floor, with insulation between the joists on batons, and aluminium spreader plates on top of the insultion.

We had chosen engineered wood flooring and the plan was to glue this directly to the spreader plates and joists.

BUT at the last minute we've been told that this isn't possible because we want the flooring to run in the same direction as the joists rather than across the joists, therefore not allowing enough support between joists for the flooring.

The solution we're vering towards to to now use ply board underlay, glue this to the spreader plated and then glue the flooring to the ply board. Does this sound the best soloution? How thick should the ply board be a: to give enough support, but b: to not stop the heat through? We've been told 12mm but I would like to use less if possible.

Any other options? We can't raise the flooring too much as it will then not run flush with the new doors at the rear of the extention.

All advise welcome.

Thanks
Emtoucan

 

[JohnD]

we want the flooring to run in the same direction as the joists rather than across the joists,

why?

 

[Emtoucan]

Because the flooring will be running through the hallway and into the extension. If we had the flooring running across the joists it would mean the flooring in the hallway would run across it rather tahn along the hall (hope that makes sense). It would just look wrong.

 

[mointainwalker]

For a reply on ply thickness you need to give spacing of joist centres : having said that, for the range of normal spacings, 12 mm sounds too thin to me.

You don't give the thickness of your engineered wood, however would expect it to be at least 10 mm. This plus the 15 mm / 18 mm ply i would expect you to need means that you are probably beyond the maximum thickness recommended for UFH, especially since you are using spreader plates.

It will be rather inefficient.

Edit: Comment on your original plan. Engineered wood has to be 18/20 mm thick ( according to joist spacing) before it can act as a floor-board (i.e. no support other than joist.

 

[Emtoucan]

Hi, the thickness of the engineered wood is 15mm and the joist spacing is about 330mm - 340mm

I'm now thinking our best option is to remove the insulation and fix 18mm ply to batons at the bottom of the joist to give a 'solid' base to the joist spacing, therefore allowing us to not have any on top of the joists.

 

[mointainwalker]

So that's insulation,spreader plate, ply flush with top of joist , engineered wood ?

Well it should work, but it'll be a lot of work fitting the battens and in restricted space and you still have the issue of 33 mm of wood insulation making it quite inefficient.