


Windows like that were more then likely recessed originally. The actual windows would sit on the inside edge with a roof overhang the recessed window. You probably can’t open the window when it rains right because water flows in. Waters probably getting in the frame and rotting the wood.
I rarely open the window, not the most convenient location. Last time I tried, it was fine. The building is brick if that makes a difference.
Any damage you don't notify your landlord of can be taken out of your security deposit. Water will get into that opening, and mold and rot will form. That can be very expensive to repair, so it's best to fix it before that type of damage develops.
You should text the picture to your landlord. Any home owner will want to caulk that gap before water gets in there. My parents had tiles in their bathroom and one day the tiles fell off the wall because water got behind them.
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Looks like a shitty caulking job. But equally, could be expanding wood due to rot or water ingress.
Is the area wet? Do you feel air blowing in?
Either way, post that pic to your landlord before trying to fill it with caulk.
Brick building, no air blowing.
Put some caulking on it to prevent spiders getting in or water
Your landlord will just shoot some silicon caulk in that crack.
Looks like a leak behind there.
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