1. I would like to close up a skylight. It can be opened but hasn’t been opened- it’s just decorative as it’s hard to get to to actually open. It does make the house very cold however. May I close it up?
2. My attic is not easily accessible and just used for storage. it has a vent. I want to close the vent and have the attic filled with foam. May I close up the vent?
The reason why we don’t close up a window or doorway is for kabala reasons, which is mentioned in the Tzava’ah of R’ Yehuda Hachasid. The poskim say that this only applies if the window or doorway is being permanently closed, for example taking down the doorpost, shows that it is being permanently closed. The same would apply for the shy light which essentially is considered a window. The poskim also say that what can be done to avoid this issue is to close the window, or door and even if it going to be sealed up, but a hole should be left, it can even be with a straw that goes from one side to the other. Then the straw can be be stuffed with a piece of paper. This way there is still a hole left there.
Regarding the vent, R’ Vosner writes that this issue only applies to windows and doors, but not to other holes such as vents. Therefore closing a vent or the whole from an air conditioner won’t have an issue.
Tzava’ah of R’ Yehuda Hachasid -20, Sefer Chasidim 946, Kovetz Bais Halevi – Inyonei Yoreh Deah pg. 115-116.