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View Full Version : A question for you pro drywallers.



Richard McComas
05-28-2011, 3:26 AM
I have a room in my home I want to install 1/2" drywall on. It now has one layer of 5/8'' rock, one layer of 1/2'' plywood and some some 3/8'' cedar. The rock and the plywood was screwed on.

My question, can I count on the 1/2 plywood to hold the drywall without hitting the ceiling joist?

Larry Edgerton
05-28-2011, 7:25 AM
I routinely do a thermal break ceiling where there is a layer of 1/2" Sturdy R, 3/4"pine strips, and then 5/8" drywall screwed to the strips. I have never had a failure.

My question is how well are the layers fastened? If they are secure I think I would not be afraid of it, as long as you used a few more screws and a bit of glue. Again, it can only be as strong as what you are fastening it to.

Another thing is you are adding a lot of weight overall. How strong is your ceiling structure? I would consider that as well.

Larry

Disclaimer: not a drywaller, just a contractor.......

Phil Thien
05-28-2011, 8:46 AM
(1) Not a pro.

(2) Typical penetration of drywall screws into framing is only 5/8". 1/2" plywood will hold screws even better than two-by material. Just make sure the plywood is secured well to whatever is above them.

(3) If you are concerned, you can probably run longer screws through the plywood into whatever the plywood is attached to. Just look at the nailing/screw pattern on the plywood, and mark the walls so you know where to run your screws when you're holding the drywall over your head.

(3a) But I think that would be overkill. Screwing into the plywood alone would be fine.

David Thompson 27577
05-28-2011, 10:23 AM
I have a room in my home I want to install 1/2" drywall on. It now has one layer of 5/8'' rock, one layer of 1/2'' plywood and some some 3/8'' cedar. The rock and the plywood was screwed on.

My question, can I count on the 1/2 plywood to hold the drywall without hitting the ceiling joist?

IMO, good advice from the others here so far.........

And you might want to consider using 3/8" drywall for your new surface -- achieves much the same result, and is way lighter. Easier to install, less concern about the long-term weight on the joists, less concern about the screws holding..........

scott vroom
05-28-2011, 11:05 AM
As others have said, as long as the 1/2" plywood is securely fastened to the joists you are fine with screwing 1/2 DW to the plywood. If it were me I'd use 12" screw spacing in the field to ensure zero sag. If you have any doubts about how well the 1/2" ply is attached to the joists then use 2-1/2" DW screws directly into the joists.

I'd also want to know the joist dimensions and unsupported span distance. You've already got lots of weight hanging from the ceiling.

Carl Beckett
05-29-2011, 9:28 AM
I did a couple walls and a ceiling in my house where for various reasons I just skinned with 1/4" drywall.

So I would consider the same in your case, since you dont need the strength. Its easier and lighter to work with (and cheaper), and if you were at all concerned you could always put some glue down first.

scott vroom
05-29-2011, 11:27 AM
1/4" drywall is very flexible and will conform to any uneveness in that cedar ceiling. Unless your existing ceiling is very smooth and flat I'd go with 1/2" or 5/8". The thicker drywall is heavier but it will give you a greater chance of a smooth & flat final finish.

Chris Fournier
05-29-2011, 11:42 AM
I think that this becomes a static load question! There's a lot of stuff hanging off those ceiling joists and they may well be supporting a floor above. Hey remove the existing materials and you gain headroom and have a crack at running new electrical too.

scott vroom
05-29-2011, 12:25 PM
I think that this becomes a static load question! There's a lot of stuff hanging off those ceiling joists and they may well be supporting a floor above. Hey remove the existing materials and you gain headroom and have a crack at running new electrical too.

Chris is right. The OP should check the ceiling joist dimensions & wood species, and unsupported joist span distance and determine whether additional load can be safely added. There are tables available that calculate the maximum sum of top live load, top dead load, & bottom dead load. It may or may not be necessary to remove the existing finished ceiling, but I'd make sure before proceeding. The local building department is often a good resource.

David Helm
05-29-2011, 12:53 PM
The 1/4 inch will work just fine. Did the same in my old house and did a smooth finish (no texture). Looks great and doesn't add dramatically to the load on the joists.