I've been told recently that there is a halacha to drill a hole where you seal up a gap in an outside wall to let the shin-daleds out or something. I'm pretty skeptical about that, as is my rav, but he asked about it and was told it is a real thing. However, he says he isn't sure of the exact scope of this "halacha" (quotes are his!) and isn't sure if I need to worry about somewhere where a window was, or somewhere which now has a brick missing from what was an external wall but the gap was only there once a new room has been built on the other side.
Does anyone have a reliable source for the details of this "halacha"?