Hi, I was wanting some advise about how to seal a gap above an upstairs window frame. We missed it when we bought the house, but there is a significant gap in one corner about one of our upstairs windows. No evidence the house has shifted, no cracks in the plaster, I think it is simply from when the house was built. We noticed it a few months ago and it has not changed.
The gap is ~30cm long, but at it's widest 3mm tall. I am not comfortable on ladders so can't inspect the outside without getting a professional in to look at it. But I am worried about just sealing it from the inside in case water gathers in there and sealing the inside stops airflow and we end up with mold.
Would it be safe to seal it just from the inside and if so what would you use? It is too small to get expanding foam nozzle in and I feel like silicone sealant wouldn't have much of an insulating effect, although it would stop the draft.
Thanks
