Polystyrene used to fill gap - New floor

[jackpot]

Have just taken old engineered wood floor up ready for screeding and new floor to be fitted. The room is an extension.

However on the outside wall, we have french doors and whoever built extension seems to have left a gap from what looks like block work to the doors and filled the gap with polystyrene to enable the existing floor to be laid.
Could I just infill with concrete and put a dpm on the door side (to cover red bricks) as there doesn't seem to be any sort of damp protection from under the French doors although there is a dpm showing throughout the outside wall?

Any advice appreciated.

 

[jackpot]

Or is this the cavity in the cavity wall? Either way, I'm assuming this will need filling somehow to enable a screed and support for the floor.

 

[JohnD]

it appears to be against the outside leaf of the cavity wall.

I'd clean it out well, then lay DPM so it forms a trough or tray completely filling the gap and reaching upwards, then fill it. I'd use concrete, though if you used plastic foam it would prevent heat loss. You can trim excess DPM, that shows above the finished floor, away afterwards with a stanleyknife. This will prevent the wood touching the frame that may sometimes be damp with condensation.

It's possible the builders were going to fit a hardwood sill, then didn't.

 

[jackpot]

Thanks. Just doing a bit of research myself

How about a cavity closure? Obviously I can't install the lip under the door frame now and but I can with the block work but the block work seems to protrude to high to the rest of the floor so a screed will be uneven or have to be over 100mm thick.

Could I fit as best I can the cavity closure and possibly take 100mm off the block work to allow an all even screed.. Or am I complicating things?

 

[foxhole]

It’s insulation to prevent cold bridging , though should be dense material like celotex or kingspan .

 

[jackpot]

Thanks. I've read that the infill has to be 225mm below the dpc. This looks like it has been infilled so I need roughly 225mm in height x 1750mm x 750mm twice... (2 French doors)

What type? Is there a ready mix I can use. Don't have a mixer or the correct gear but can purchase a few things if needed.

So to confirm, a trough of dpm including sides which will need a good overlap, infill with concrete flush with block work.. Floor is slightly below block work so will this cause an issue...

The floor is going to be an lvt so levelling compound will be used.

Would a strip of 25mm kingspan or similar be better to use along the outer leaf to avoid and cold bridging and the rest unfilled with the concrete.

Also would I cut the dpm at the out leaf or wrap it around the concrete infill encasing like an enveloped or wrapping a Christmas present..

Sorry for the stupid questions.