I'm currently diagnosing a cold bedroom above a garage extension, I know many people post about this. But rather than the common questions I have a new one (I think anyway). FYI I am a DIYer.
The garage below the room has an exterior door. The concrete lintel is alongside a steel plate. This steel plate has holes in it and is covering a void of 15x88cm, not sure how deep it goes but atleast 10cm straight up. Within this, half of it seems to have a block of polystyrene in it but the other half is empty. The gap is roughly where the skirting is in the room above, and there is a draught coming from under the skirting.
So my question is, 1) why is there this gap? 2)can i fill it? Maybe just squirting expanding foam inside it or cover the outside with some concrete/fabric? 3) if I did any of those would I cause more problems further down the line?
I'll try add some photos
Any help really appreciated. Cheers guys.