per wiki,

A joist is a horizontal structural member used in framing to span an open space,

often between beams that subsequently transfer loads to vertical members.

This tutorial mentions ceiling joist.

Is the wood part pointed out by red arrow (img_1) the ceiling joist?

enter image description here

consider the following image (img_2), is the part pointed out by blue arrow a ceiling joist, the red one another ceiling joist? enter image description here

Consider the following image (img_3), which comes from wiki.

enter image description here

there are 2 lay of joists, one is for ceiling, the other is for floor, is my understanding right?

  • So where does the rest of it go? You should be able to tell by how it is supported and what it connects to...
    – Solar Mike
    Jan 29, 2020 at 10:09
  • Neither of the sketches show a clear idea of a joist doubling or in other words, acting as, a ceiling joist and floor joist. Regarding img_3, if the lower joists in the sketch had a living space under it and not a crawlspace, those joists would work or act as or double as ceiling and floor joists. If the upper joists in the sketch clearly shown walls and another set of joists, then that set of joists purpose would act as floor joist for the second floor and the same joist would act as ceiling joists for the first floor.
    – Jack
    Jan 30, 2020 at 4:21
  • @Jack Would you please give a link that show a clear idea of a joist doubling?
    – zghqh
    Jan 30, 2020 at 5:58
  • Please understand this is not referring to 2 different joists, but one joist, because of where it is placed in the house is serving 2 different purposes. As in double purpose. Doubling is a past tense American English term to describe one object that serves 2 purposes
    – Jack
    Jan 30, 2020 at 6:45
  • Here is a link which you may find helpful. awc.org/pdf/codes-standards/publications/wcd/… Figure 1 pg 17, figure 2 page 18 and figure 6B on page 21 are examples of joist acting as floor joists and ceiling joists simultaneously, "doubling" or perhaps "doubles" as it was called. Figure 6B is the best example since it clearly shows drywall on the ceiling of the basement, also shows that there is a floor surface on the upper side of the same joist.
    – Jack
    Jan 30, 2020 at 6:57

1 Answer 1


Yes that is a ceiling joist if that is in a room over your head. If there is another space above that as another floor then that it probably also serves as a floor joist as well.

It is somewhat conventional to refer to the joists seen overhead in a basement as just the floor joists for the first floor that caps the basement.

  • Thanks for you answer. Does "probably also doubling" means 2 lays of that structural member, one is for the ceiling of 1st floor and another is for the floor of the 2nd floor?
    – zghqh
    Jan 29, 2020 at 14:53
  • The "doubling" means the same joist serves 2 purposes. The bottom side serves as the ceiling, and the top serves as the floor. I think in proper terms, if this is the basement with another floor above, these would be called floor joists even though they create the ceiling of the basement. If this was the second floor of a house and there was no other living space above, then these would be called ceiling joist. Position and purpose further define the term "joist"
    – Jack
    Jan 29, 2020 at 15:26
  • Removed the word doubling from the answer,
    – Michael Karas
    Jan 29, 2020 at 16:15
  • Thanks for you answer. Consider img_2, is the part pointed out by blue arrow a ceiling joist, the red one another ceiling joist?
    – zghqh
    Jan 29, 2020 at 23:35
  • @Jack Thanks for your comments. Is img_3 showing the "doubling" situation?
    – zghqh
    Jan 29, 2020 at 23:47

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