UFH membrane - advice please

[Walshie]

Hi,

I’m installing wet UFH over a new block & beam concrete floor.

 

I need some advice on:

 

The best material to act as a membrane over the block & beam before I lay the insulation layer?

 

The best membrane to lay over the UFH once clipped to the insulation before we pour the liquid screed.

 

Best product to go over the screed (once laitance has been taken care of, before laying engineered wood floor.

 

I’d really appreciate some advice and recommendations please?

 

Thanks v m,

W

[mistake_not]

I'm not sure you need membranes / materials for a lot of that, depends what exactly you are doing. 

 

Probably just a normal polythene DPC between block and beam and insulation 

 

Insulation that's well taped and foamed might not need anything above it before liquid screed. Normally the membrane (if used) would be above insulation, below pipes. You want your pipes to be in the screed to transfer head.

 

Re between screed and floor - depends what wood. Some supplies will want a super level finish before wood and will apply a smoothing compound, some planks can go straight on top.

 

Hope it helps.

[nod]

You need a 1200G black membrane on the top of your BB Then insulation All joints taped Before you lay the pipes it’s normal to lay a slip membrane Which is a finer gauge clear polathene 

[JohnMo]

2 minutes ago, nod said:

Then insulation All joints taped Before you lay the pipes it’s normal to lay a slip membrane

The purpose of this membrane is to stop micro bubbles forming when the cement in the screed reacts with aluminium foil on the insulation. The reaction gives of hydrogen.

 

You do this membrane before the pipes and just clip through it.

[marmic]

we used 1200g/300mu polythene dpm over B&B lapped/sealed to preformed dpc and corners which wrap up onto masonry upstands (with marmox) which timber frame sole plates are fixed to and lapped/sealed with dpc coming up from under beams - bit belt and braces. 2 layers insulation staggered/taped with upstands to perimeters/structural walls. 1200g/300mu again over that lapped up walls (more than usual) for screed and air tightness. UFH pipes onto that then 75mm liquid screed.  polythene upstand then carefully cut and air taped to smartply airtight walls. worth the effort getting wall to floor interface right with preliminary air test before plasterboarding at ACH50 0.56    But depends on rest of your construction.

agree with previous comments you could use 500g polythene under screed but couldnt see the point as little cost difference in grand scheme of things and wouldnt have right for me for the air tightness - would have split everythere!  also agree no foil / foil tape in contact with screed

[Walshie]

Thanks all - very helpful!

[Nickfromwales]

On 01/10/2025 at 13:51, Walshie said:

Best product to go over the screed (once laitance has been taken care of, before laying engineered wood floor.

Don't use a gypsum screed, use Cemfloor instead and then no need to feck about taking off what you just paid to put down