drywall span

I have lots of low hanging ductwork that make it difficult to frame out because the ducts are arranged so close to each other.

Can someone give me input on the maximum span without support for both 1/2 in and 5/8 inch drywall?

I am worried about my drywall sagging.

Any help would be appreciated

 

Don't know what the experts will say, but I wouldn't span more than about 2 feet with either.

 

You are going to have to run 2x4's across your duct work 16" o.c. for best results.

 

lee330,

This should help you,

1/2" for 16" O.C. rafters

5/8" - 24" O.C. rafters - 1/2" would eventually create a rolling effect unless you get hardened drywall which is more expensive.

Hope this helps!

 

Thanks for your help. I was hoping to not have to sacrifice the headroom by using additional supports, but I probably don't have a choice. Thanks again.

 

The general rule of thumb is that drywall can span up to 24 inches horizontally without support. This allows you to make a small soffit up to that wide without any framing. All you need is a board at the joists to hang the vertical piece from, and a board at the intersection of the vertical drywall and the horizontal drywall, so that you have something to screw both of them to in the corner.

You can go up to 48" horizontally supported by a 2x4 on its side, and up to 72" with a 2x4 on its edge.

In spite of all I said in the first paragraph, personally I'd still prefer a 2x4 on its side for a small soffit if headroom permits. It will just provide a firmer soffit.

 

John Nelson,

The general rule doesn't always work and as such Inspectors are not allowing 1/2" drywall on 24" O.C. for horizontal surfaces (ceilings) as to the problems I mentioned above especially around here.

Just a thought.

 

If you can't bear to lose headroom due to 2x4s, you could consider using plywood/OSB over the joists, then covering with sheetrock and applying fasteners every foot or so. The 8 foot edge will need to be at 90 degree angle to the joists.

It won't be cheap, but it would do an excellent job of resisting sag. I doubt you would need to exceed 3/8" thickness since there is only the weight of sheetrock.

 

Yes, I am aware that 1/2" drywall on 24" o.c. joists is a bad idea. But we're not talking about that. We're talking about a soffit. Besides, I never said 1/2" -- you did.

 

John,

No problem. I just wanted to make sure your "General Rule" was not misunderstood by others. It is important that 1/2" may be applied by many including contractors but is not recommended on 24" spans.

 

General rule of thumb don't mean squat when it comes to hanging a lid. All lids regardless are to be framed at 16" on centers. So spaning rock 24" will never pass inspection. Not really sure what you're dealing with Lee, but send me a picture and I'll find away to get it hung.

 

Thank for all of the input. I will try to post a picture later today if i can. I'm having trouble with my camera software.
I think I figured out a way to solve my problem.

I have a bi-level heating/cooling system, so I have the main supply and cold air returns for each system that span a total of about 9 feet wide. I have ducts that are 20" wide themselves

Between the ducts I only have a few inches to work with, so I was going to cut some 2X2's and attach them length-wise to the joists using metal wood braces and screws.

There isn't enough room to get my nailer in there, so I figure I can buy or come up with a extension for my drill to use a hex nut driver with the wood screws.

Then, I'll attach 2X2's as a bottom track and use that for my drywall support.

Any comments...

 

lee,

You dead set on drywall? See, with a suspended grid ceiling, all you'd have to do is install two t-bars along both sides of the ducts, push in some cross-bars and jam 4 foot panels in there. Nothing to frame. Just a suggestion

 

Yeah, I am. I already did the rest of the ceiling framing already.

Plus...the wife wants it to feel like a regular room.


Lee

 

how about 3/8 ply covered in 1/4 rock? you can screw it all over