I live in a 1930s house with a small, open porch (as in no external door) in front of my main UPVC front door. Not long ago, the original lath and plaster ceiling in the hallway fell down quite spectacularly. We've had the ceiling replaced with a modern 9mm plasterboard (screwed to the joists this time!), skimmed with a thin layer of multifinish plaster
Unfortunately, the original hallway ceiling extended out over the timber structure that comprises the front door frame and surrounding glazing in to the open porch (the top piece you can see in the photo looks like upside-down skirting), and the thickness of the new ceiling is less than that of the old ceiling - as such we have a varying gap of between 6-9mm that spans the width of the hallway above the front door. As you can imagine, this has a resulted in a not insignificant draft.
My first thought was something as simple as caulk or silicone sealant to fill the gap, however the gap is quite awkward in the corners, so will likely look pretty shoddy if it works at all.
My second thought was expanding foam, but I don't see how I could get close to good finish, and the nozzle won't go in the gap at its narrowest.
My third (and probably best so far) thought was to cut and corner some timber beading of some kind (perhaps with expanding foam in the gap first) and caulk around that.
Is beading the right way to go or is there something else I should consider?
This may only need to be a temporary solution as we are considering replacing the front door and surrounding glazing when funds allow.