Screed Queries (Doors/Thresholds)

Hi All,

Back on it, which means lots of questions of course! Building my small extension, insulation over slab - just had BCO sign off everything so far, so need to crack on with the floor.

First is a quick one - I assume normal practice is to screed before the UPVC door goes in? I've seen a few mentions of "making watertight" beforehand, but it feels a bit backwards. Happy to be corrected, of course.

Second, I'm still a bit unclear on the cavity/threshold detail. I get I need to flow the insulation and screed up to the outer leaf (with upstands, presumably) but what do I put UNDER the insulation, as obviously there's currently a...cavity.

Cheers all!

I'd be screeding after installing the doors, then the screed will cover the back of the door sill etc. It depends what you've done with your levels and where/how you've positioned your slab and insulation though. Do you have cross section drawing of your floor buildup?

garyo said:

I'd be screeding after installing the doors, then the screed will cover the back of the door sill etc. It depends what you've done with your levels and where/how you've positioned your slab and insulation though. Do you have cross section drawing of your floor buildup?

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I don't have a drawing, but essentially slab is currently ~200mm lower than DPC. DPC should be finished floor level to match existing house if I was accurate - I won't quite know for sure until we open up the doorway between the two.

Haven't done anything else yet, so in terms of engineer bricks up to DPC, it's just a continuous wall around the slab both inside and ouit.

Yeah you’d screed after door normally and screed up to the door cill.
Ideally you wouldn’t have done a cavity under the doors, you’d return the inner skin at that point so it’s effectively single skin onto which the door sits, with the slab and screed carried through to that outer skin.
So in your case trough it with some DPM, insulate, concrete/screed

23vc said:

Yeah you’d screed after door normally and screed up to the door cill.
Ideally you wouldn’t have done a cavity under the doors, you’d return the inner skin at that point so it’s effectively single skin onto which the door sits, with the slab and screed carried through to that outer skin.
So in your case trough it with some DPM, insulate, concrete/screed

Click to expand...

Wouldn't that return have created a cold bridge or something?* Just wondering if it's worth lapping the DPM and dropping some concrete in to match the existing slab

*Edit: I guess not, because it's under the DPC and under the insulation

No because of the upstand 25mm insulation