1/2” plywood ceiling

[Jakemedic]

Hello! Doing my rough in for electric on my ceiling. Originally was planning on using metal on my ceiling. The more I think about it, I think I may want to use 1/2” bcx plywood. My reasoning? Sound control, ease of placing lighting and outlets. On a previous shop, I used 7/16” OSB but painted, it still looked like ****. That shop had 24” on center trusses. The new project has 48” on center trusses. My question? Will 1/2” plywood screwed directly to trusses sag over time with a foot of fiberglass insulation? Thanks in advance for any advice that can be given.

 

[SALIV8]

Speak with your builder and truss manufacturer. Most are not intended for ceiling loads.

 

[MushCreek]

Most trusses I've seen are rated for ceiling loads. Otherwise, houses wouldn't have drywall and insulation. It's not a lot- usually 10 pounds/sq/ft, but that's all you need. I think 48" is too big a span, even for plywood. I would cross-strap it with 2X4's laid flat.

 

[JamesW84]

Ideally, this sorta thing would be planned before you order your trusses. When I ordered mine, he said 5 lb/sq ft load was standard, but I could bump it up to 10 lb, so I did.

I'd bet that 2x4 bottom chord is only rated for 5 lb, but that would probably depend on the span. And I'd bet it would sag also without strapping.

https://www.sbcindustry.com/content/1/bottom-chord-dead-load

 

[purediesel]

Most trusses I've seen are rated for ceiling loads. Otherwise, houses wouldn't have drywall and insulation. It's not a lot- usually 10 pounds/sq/ft, but that's all you need. I think 48" is too big a span, even for plywood. I would cross-strap it with 2X4's laid flat.

Probably true for a house truss, since it makes complete sense that its going to be finished on the interior. An out building like what is commonly built around here can use weaker trusses to save money since most of the time they are not finished. This is exactly what I ran into on my barn. Luckily the truss manufacture always builds in a 2psf to all their trusses, which will barely hold a ceiling.

 

[mike93lx]

4' is too far to span if you are concerned with sagging. You will need strapping, probably 2x4

 

[matt_i]

With plywood I think you could get away with something like a 1x2, screwed on-edge and ideally also glued to the back side as a stiffening rib.

I'm thinking 5 ribs across the 48" dimension, making them slightly shorter, lets say 42" long with 3" of clearance each side. The placement of 5 goes across the 96" dimension so there would be a rib roughly every 24". If you play your cards right, you might be able to integrate a 2x2 or 2x4 that would also lap over to the next sheet and be attached from below to commonize.

Definitely need a drywall lift if working alone.

Imo this is why 24" oc is best for trusses. It would already be ready to just pick your cover material and go.

Also imo it would be worthwhile to pull some strings and check truss planarity and also squareness. Plywood is unforgiving as it relates to nesting the edges of the sheets, vs. drywall where one can easily patch and fill. Since the first row of sheets set the dimension for the rest of them, the errors at the start get translated and compounded as you go across.

 

[NUTTSGT]

I wouldn't use plywood on 48" centers. I have no doubt it will sag. I'd save the plywood for the walls and put metal on the ceiling. However, thats not what you want.

Once you start hanging stuff on the walls and turn on some music, that will take care of any metal echo sounds.

Lighting, mount your lights between the ribs and surface mount them, albeit with a small standoff. Stub a short section of pvc conduit out the knock out, through the ceiling and tall enough to be seen above the insulation. Just feed your romex through it and make the connection..

 

[Jakemedic]

Thank you! I called the truss manufacturer this morning and it is rated for 5#, although the top of the truss is rated for 40# snow load. I could add 2x4 runners and add wood or use as is with metal. Guess I have some thinking to do about that. Thank you for all your thoughts, I genuinely appreciate it!