Someone mentioned to me that there are some Jews who have a Jewish tradition to be careful to never close up/cover a window due to some sort of danger. Can someone give me some of the parameters for this "rule" - like how much of an opening has to remain, does it apply to glass windows or only open windows, can one cover a window temporarily?
Rav Yehudah HaChassid of Regensburg was the head of "Chassidei Ashkenaz" and the Rebbe of famous Rishonim. He lived from 1140 until 1217.
He wrote a "will" containing 78 mystical instructions for life. Among them is #20 which says that one should never close up a window or doorway. The idea is not what material the window is made of, but not to totally seal up the opening.
Some hold that he only intended it to be followed by his own descendants.
Rav Zev Smith of Kensington (my Rosh Yeshivah's(Karlin-Stolin) son-in-law) explained to me that the problem concerns trapping extra-dimensional beings who use the opening as a doorway from place to place. The mystic sources base this on the verse in Bamidbar (Numbers) concerning Balaam's reaching a narrow passage and not being able to pass through.
Stories abound where children sleeping in rooms with sealed window holes have become sick for no reason. When the parents seek a Rebbe's blessing, the Rebbe usually asks if any window or doorway holes have been sealed?
The answer always given is to drill a small hole through the sealed area so the creatures can use the passage once again. After that, the child recovers quickly. I personally know a family (and the boy in the story) that purchased a new home, who had a son fall ill sleeping in a room with a hidden closed off window. They asked the current Stoliner Rebbe and he told them to see if there was an old window that had been closed off during remodeling. The window hole was found and duly drilled. The boy recovered immediately.
(Disclaimer: the existence of such stories is provided in this answer to help show that there is common popularity among certain Orthodox Jewish communities for this custom. Whether you should believe in it or follow it is up to you and your Rav.)
On construction sites run by Chassidic Jews, I always see the workers drill holes even if the window or door is only temporarily closed off.
If we are so careful with the "spirits" right of way...we should always be careful of double parking and blocking a neighbor's driveway as well. :)
I hope this helps.