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I was planning on installing drywall on my basement ceiling and realized that I have nothing to screw the drywall on after the last joist. On one corner of the room there is 12 inches from the last joist to the wall and on another side I have about 6 inches that the drywall would be floating on.

If I just screw it to the joists and let it float in those spaces will it be an issue? What can I do?

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2 Answers

The overkill direction (which is actually appropriate for some circumstances, such as a ceiling that needs to hold up a lot of insulation, as for an attic above) is to run 1x3 strapping opposite to the joists. An advantage in the application I mention is that this strapping can be on 12 inch spacing, so the drywall can be attached with a screw every foot, even if the roof trusses are on 2 foot centers.

In general, it is actually advantageous to leave the edges of the ceiling to float for the last foot or so, so long as you drywall the ceiling first and the walls after, butting them up to the ceiling before screwing them in place - the wall drywall then ends up supporting the edges of the ceiling drywall, but the whole is slightly less prone to crack in the case of small building movements as there's a little give from the floating edge. Here's a reference (they also suggest using corner clips.) Scoot down to photograph 4, and you won't be surprised to find that they mention the other point of view as being commonly held. As for it being "a developing point of view" only in building would something code approved for 30 or more years (per the above reference) be "developing..." An additional reference. And another. Search on drywall floating corner cracks for more references. And one in my comment on @bib's answer from the Gypsum Association; they might just know a thing or two about hanging drywall.

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I have not heard of leaving the edges floating, but have I heard the recomendation to hang the ceiling first all the way to the edge so the wall drywall adds additional support along the edge. –  auujay Nov 22 '13 at 18:58
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It is okay to leave it floating if you use clips. However, you would generally only do that on the top floor; you leave it floating so that truss lift doesn't crack the drywall joint. This is a basement so truss lift is not an issue. –  Eric Gunnerson Nov 23 '13 at 3:05
    
Truss lift is one of many reasons for buildings to move. As is pointed out over and over, the floating corner helps to reduce cracks from all causes of building movement. –  Ecnerwal Nov 23 '13 at 4:14
    
Go with the corner clips only, they are cheap and easy to install. The drywall otherwise would rest wonderfully on the wall mounted boards, but the addition of the clips would prevent the walls pushing the ceiling sheetrock to high and bowing the ceiling up in the corners if not watched carefully. In my 42 years in the trade I have seen drywall hung in many ways and drywall will crack athe places were framing moves, (done that myself) and were the drywall was not supported properly, the wall will do that, the clips are for control. –  Jack Nov 23 '13 at 5:07
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No, it would not be okay. Drywall needs to be attached at its edges.

The standard approach is to build a pont to attach the edge of the drywall. Generally, you screw a dummy joist at the edge of the wall. It is hard to see what is above the top plate of the right wall, but that is where an attachment beam needs to be installed. If there is no joist to tie to, you could screw several braces on top of the plate to serve as attachment points. You then screw the dummy joist to those. This beam is not structural, just a fairly solid point to anchor the edge of the drywall.

Without this attachment, the natural shifting of the building/walls will likely result in cracks in the corners.

Supplemental Note: I looked at the references for the contrary opinion offered by @Ecnerwal and find them interesting. But everything I have ever heard from builders is to the contrary. Also I believe that most building department inspectors expect to see support (in addition to the edge of the horizontal drywall sheet). However the floating edge may be a developing point of view.

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It's sometimes amazing we ever moved out of caves ;-) Note the dates on those - the JSC article is 12 years old. Here's one you might find more persuasive, considering the source: gypsum.org/using-gypsum-board-for-walls-and-ceilings/… Sorry I can't quote code at you, the code folks like to charge money for codes to keep themselves employed. Not all inspectors keep up with what's actually current code, unfortunately. –  Ecnerwal Nov 22 '13 at 19:52
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I also recommend following gypsum.org installation instructions. This assumes there will be wallboard on the walls as well, which helps support the floating edges. If not, the 12" is too far, the 6" is still OK. The gypsum.org instructions have been in place for at least 20 years, from when I first saw them, probably longer, it is hardly a "developing point of view". "New" ideas in construction are extremely slow to spread out to the folks "in the trenches" so in that respect perhaps the idea is still developing :) –  bcworkz Nov 22 '13 at 21:26
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