The Gemara (in several places, here's one) lists a group of three halachos related to walls that were taught to Moshe at Sinai:

  • gud [asik/achis] - extending a partial wall up or down under certain circumstances
  • lavud - a 3 tefach gap is considered closed for many purposes
  • dofen akumah - you can regard a ceiling as part of the wall next to it

The first two are applied all over the place, such as eiruvin and kilayim. On the other hand, I've never heard an application of dofen akumah outside of sukkah. Are there any?

I'm wondering because from the way they're grouped, it sounds like the three halachos are all generally applicable to walls, not localized to one specific area of halacha like sukkah.

  • Where else do you have a concept of Dofen? – Double AA Jul 13 '18 at 18:13
  • @DoubleAA well it's a deoraisa concept and dofen is not AFAICT a biblical word, so it's hard to conclude anything from where that word does or doesn't show up. – Heshy Jul 13 '18 at 18:23
  • Ok where else do you have a concept of distinguishing betwee ceiling and wall? Where else in fact do you have a specific concept of ceiling? – Double AA Jul 13 '18 at 18:31
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    @DoubleAA the examples I can think of for a ceiling are tumas ohel, ביתא כמאן דמליא, and (this one is I think more promising) the mishkan. I was actually thinking of dofen akumah as a potential answer to Rashi's question on Meleches Hamishkan. The Malbim does a complicated leshitasam with various Gemaras, but as a simpler answer I wonder if you can apply dofen akumah to extend the paroches over to the kerasim. In this question I wanted to see if someone else applies it outside of sukkah. – Heshy Jul 13 '18 at 18:52
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    @DoubleAA maybe tzaraas on the ceiling within 4 amos of the wall (assuming והנה הנגע בקירות הבית) is davka which I'm not sure of). – Heshy Jul 15 '18 at 10:58

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