Adding Drywall Layer to Existing Ceiling - Calculating Static Load - AVS Forum
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post #1 of 4 Old 03-24-2011, 12:32 PM - Thread Starter
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Hello All,

I have a space that I am considering using for a secondary listening area and I would like to reduce the acoustic transmissions both into and out-of the room.

The room is an unused bedroom approximately 10' x 12' with a single door for access. I'm swapping out the existing hollow-core door with a solid-core version and will be adding an extra layer of 5/8" drywall to the walls. The ceiling in this room is existing 1/2" drywall covered with spray "popcorn". I've already had this tested as being asbestos free but I still loathe the idea of removing it. Instead, I've read that I can install firring strips and then layer on a second layer of drywall, sandwiching the popcorn in and avoiding the godawful mess. This would be of double benefit as I would likely see reduced sound transmission.

My question is, how can I determine whether adding the second layer of drywall to the ceiling will result in a safe static load? There are no living spaces above and the beams are 24" OC, solid no-knot pine. I want to make sure that anything I add doesn't bring the whole thing down on my head!

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post #2 of 4 Old 03-24-2011, 01:54 PM
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Is this modern construction? You're only adding 2.5 pounds per square foot more dead load to the structure. But it all depends on how that roof is framed.
What size are the joists?
Do they carry roof load too, or just the ceiling?
Is the roof pitched?
Is it a truss structure or "stick framed"?

Might be a good idea to have a qualified builder look at it.

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post #3 of 4 Old 03-24-2011, 02:13 PM - Thread Starter
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Home was built in 1979.

Definitely a truss structure, the roof is pitched. From the design of the home, the center of the roof trusses come directly down onto supporting interior walls so the beams do not appear to carry the roof load.

I can take pictures later if that helps.

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post #4 of 4 Old 03-24-2011, 05:04 PM
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A truss is generally supported at the ends only, unless it's a complicated design. I'd say go for it. It won't fall down. Trusses are over engineered.

Keep in mind, the bottom chord of the truss is carrying load. It is under tension load (stretched horizontally) from the overall roof loads, and is subjected to bending (deflected down) from the weight of the ceiling and any crap in the attic that is bearing on the bottom chord. So never take a sawzall or hole saw to any part of an engineered truss.

You don't have your location in your profile - do you have snow/wind/hurricanes/earthquakes?

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