drewdin

I have recently put strapping on the ceiling in my sun-room in preperation for 1/2" drywall. I have 1" foamboard installed onto the joist and then on top of the 1" foam board I have 1x3" strapping.

My question is, I used 3" drywall screws to attach the strapping to the joists, is that going to be sufficient to hold the weight of the drywall, was it too little, overkill or what? I am at the point where if it needs to be changed, i can change it.

nealtw

Two screws at each joist, I think it will be fine.

drewdin

The foam is 1" thick and the strapping is 3/4" thick so I used 3" screws. My thoughts were that at least an inch would go into the joist. So right now I have one screw per joist. I will have to go buy some more screws!

nealtw

1" into the wood should be fine. I was just looking at having as many screws as you wood have holding drywall itself.

drewdin

Thanks, I appreciate the help!

Wuzzat?

There are tables on the Net for
pull out/pull over/pull through
force for screws in softwoods.
Divide the weight to be supported by the number of screws; this should be 4x less than the ultimate strength of each screw/wood connection.

Plus, it's a static load; no impacts, no vibration. No problem.

What are they, #8?

drewdin

yes, there # 8

Ill look for one of those calculators. What does a sheet of 1/2" blueboard with plaster on it weight?

Wuzzat?

"standard 1/2" drywall that is used in interior residential construction generally weighs about 1.6 pounds per square foot, totaling 51.2 pounds for one sheet. "

so with four screws/sheet each screw should pull out at >51/4 x 4 = >51 lbs. There's "working load" computed with some built-in safety factor, and "ultimate strength" where you decide the safety factor.

You are more diligent than almost all DIY'ers. Good.

drewdin

Thanks, I try my best to research and do a good job. I hate when things are hacked!

nealtw

If you normally have 30 screws to hold up a peice of drywall [4x8 ], then having 30 screws holding up the straping in a 4x8 area that will give you the same safety factor