Hi! In a bit of a rush as our LVT is coming on Monday. Our door installers have left the floor area under the door open and there’s a cavity there, and a tiny bit of dpm under the window.

My intention is to fill the cavity with PIR kingspan foam boards, with a cavity closer on the top and a dpm tucked under the window one.

Is this correct and can anyone draw me a detail? (Where does the dpm go?)

Do I need to put some mortar down?

The LVT installers will be doing a self levelling screed on top.

We took out all the rubble here.

Internal block with some membrane on top, cavity, new window with some membrane under.

It’s about 10cm deep.

Edited 4 hours ago4 hr by LDNRennovation
Details

This is what it looks like in section.

If you're bridging the damp course lower down then use a membrane down the inner skin, across and then up the outer skin. If you're worried about thermal bridging then 25mm PIR against the DPM and backfill with concrete?

In a few window openings I've used just PIR in there but it takes no load so at a door reveal I'd want something a bit more solid.

Thanks Paulie! Like this picture?

So do you think I need a cavity closer?

Can you just put concrete on top of the pir.

Or like this

The second one is what I had in mind, probably take the PIR up higher to minimise the thermal bridge leaving the top of it exposed, then just screed over it. Wouldn't bother with a cavity closer there, I'm not sure what it would bring to the table.

That seems sensible. I’m just wondering about if the top screed will crack. The inner blockwork is about 5-6mm less than the slab, so that’s the thickness of any mortar plus screed there. I was going to chisel some block off, but it has a dpm over the top of it and I feel like it’s best not to touch that.

I don’t know if we should do some mortar and make it level with the slab, and then the screed goes over all, or to just have thicker screed.