Gap between door frame and concrete flooring

[Vykistwo]

Hi all,

Hope someone can help.

I have ripped up laminate flooring in the hall as was going to get the carpet fitted. Under the flooring I have discovered this gap between the door frame and the conrete flooring underneath. I was hoping to run the carpet all the way to the door frame so would prob be best to fit a bit of wood into the gap but was hoping for advice.

 

[Wayners]

Looks like a cavity. My house is the same and it was bridged with felt and concrete over but cracked up.
I dug out a run of bricks under the floor and put plastic in and concrete.
If you look in the gap floor side can you see bricks?

I think it was just the way 1950 60s 70s houses were built Vs not having a cavity along doorways.

All the houses on my estate are the same. 1000s of them

 

[Vykistwo]

Yeah I do see bricks, house was build 1987 so clearly the practice was used then as well. Any advice of how I should finish it off for the carpet fitter guys?

 

[Wayners]

Cut a plastic rubble sack up
Clean out gap.
Masking tape along uPVC door bottom.
Put plastic in gap.
Buy ready mix concrete from DIY.
Fill gap
When dry cut plastic off level.

Get as tidy as you can. Don't have to be perfect