Screed before or after timber kit erected (and DPM question)

[MarkW1979]

We are erecting a timber kit this summer and am just trying to arrange the trades and understand the build a little better.

 

We are having underfloor heating within a 75mm concrete screed (see detail below). I had assumed the ufh pipework and screed got installed before the timber kit went up but my groundworker says that he has only ever done it after the kit is up (because the screed could get damaged). I thought it might be easier to do it before (and might save me time on the long run as I have time before the kit is up to get it done).

 

If the ufh/screed was installed after the kit was up wouldn't the dpm have to be laid first in order for it to go underneath the sole plate of the timber kit before it arrived meaning it would be exposed and susceptible to damage when the kit is getting erected?

 

As always thanks in advance! 

 

[JohnMo]

Many, if not nearly all, will do after the house is watertight.

 

I am one of the exceptions, and found it was extremely easy doing that way. You need to know where your internal walls are going and not change. You need to use concrete, not a screed generally.

 

Looking at your drawing I have the following comments

 

For UFH, your insulation in floor is poor.  You need to increase to 150mm minimum, ideally to 200mm. This is your only opportunity to change this really, you will need to increase the whole floor build-up depth. I would leave the screed thickness where it is, or add subtract a little to make the floor perimeter blockwork work out.  I ended up increasing mine to 100mm.

 

 

[MarkW1979]

Thanks for the advice John. 

 

There seems to be differing opinions on whether the dpm should be below or above the 100mm slab?

[Redoctober]

@MarkW1979 take a look at my blog  - ours went down after the TF went up -

 

 

[MarkW1979]

Thanks RedOctober, I'll certainly be referring to your blog in the coming weeks. Did your dpm go below your slab then? 
 

Cheers, 

 

Mark

[JohnMo]

DPM - goes above your hardcore, you also need a layer of sand above the hardcore, to stop stones making holes in the DPM - then your DPM. You need a thin polythene later also between the insulation and the screed. It goes on before the UFH pipes and they get stapled to the insulation through the membrane.

[ETC]

Either will work as long as you make sure the DPM is overlapped with the DPC in the walls.