Calculating Spans and Dead Ceiling Loads <<Calc Link&g

I am trying to get an idea of my ceiling loading and span requirements for figuring out what kind of joists to use. I have used a calculator here: http://www.awc.org/calculators/span/cal ... cstyle.asp If I am going to have 3 layers of 5/8 gyp, that gives me a base dead load of 3.9 PSF. I am amazed how little is needed to hold this up. The calculator is telling me I can use a structural grade Douglas Fir 2x4 placed 12" OC and get a max span of 11' 6". Does this sound right?? Am I missing something basic? If this is right, then that is great! I want to loose as little ceiling height as possible and 2x4's would be better than 2x6's. Anyhow, just trying to check out my facts here..... Thanks, ashley

Yes- you are missing something basic: 5/8" gypsum is 2.31 PSF: http://www.johnlsayers.com/phpBB2/viewtopic.php?p=51414 I would shy away from anything less than 2x6 for ceiling joists...also, doing 12" OC will tire you out real quick... How wide is the room?

studio_drums wrote:

Yes- you are missing something basic: 5/8" gypsum is 2.31 PSF: http://www.johnlsayers.com/phpBB2/viewtopic.php?p=51414 I would shy away from anything less than 2x6 for ceiling joists...also, doing 12" OC will tire you out real quick... How wide is the room?

Aside fromm the mistake you made in the drywall weight - you have to add in the weight of the joist themselves - carry numbers for the worst case scenerio - in other words - there will be weight for youtr duct runs - weight for lighting - probably weight for some ceiling clouds. sll of which adds up - make sure to look at the mech/elect carefully - those joist bays can easily pick up 5 or 6 psf of dead load. Rod

I knew I had to have missed something. I misread the gyp info from 5/16" instead of 5/8", DOH!!! :shock: :shock: :shock: Anyhoo, using a conservative 2.5 PSF for 5/8" Type X gyp, that gives me 7.5 PSF for three layers. Now to figure the rest of the stuff...... Ductwork: will be held by the upper floor joists. But the vents will be held up by the drywall where they go in. Vents will have fire dampers per code plus a bit of flex duct that isn't being held by the upper joists. 5lbs per damper, 2 lbs for extra metal stuff, times 4 ducts at most. Call it 30 lbs. Electrical Wiring and Lights: to minimize the penetrations, I want to use track lighting and only a few (3-4) boxes in the ceiling. I'd say 40 lbs outta cover it. Acoustic Treatment: OK, here's where there will definitely be some more weight up there.... At least one main cloud, call it 100 lbs. Toss in another 40 lbs for possible future treatments (diffusion perhaps). Round up to 150 lbs. Joists: I need to calculate the weight of the joists. I found this: http://www.csgnetwork.com/lumberweight.html Using 2x6 Pine, boardfeet=linear feet so roughly 160 boardfeet of white pine (??? they didn't have a douglas fir option) = 480 lbs green weight (round to 500) HVAC = 30 Electrical = 40 Acoustics = 150 Joists = 500 ________________ 720 Round up to 750 lbs extra weight over 203 SF. That's another 3.7 PSF dead load. That brings us up to 11.2 PSF. Still not bad a'tall. Using the Spruce/Pine/Fir structural grade 2x6 at 16"OC with a dead load of 15 PSF and a live load at the minimum 10 PSF since there is no live load on this ceiling, that gives me a span of 15' 2". That is very nice. Have I missed anything or vastly underestimated something? Thanks, ashley

Yes- you missed the part where I asked how wide your space is. I'm no expert- but I would just plan on using 2x6's for the joists and get on to worrying about something else...you want some flexibility for the reasons Rod mentions.

Well the span in question is around 11' so 2x6 will work just fine. I just had no idea of what was needed with 3 layers of 5/8", hence the thread. Here's the complicated part: this span of 11' needs to end in a beam, that is, the joists will be sitting on top of a wall on one side and then supported by a beam on the other side. I have to figure out how big that beam needs to be. Then this all affects how high the finished ceiling will be. this stuff is just so complicated and I really don't want three layers coming down on my head some time down the road..... :roll: :shock: :cry: The pic shows the area of detail.... -ashley

question: How long does the beam need to be? (it's 2 actually isn't it - one on each side of the existing steel? Comment: I have a concern for the lack of symmetry I see in what is obviously a critical listening room........... Rod

Hi Rod, 15'6" roughly for the beam on the side in question. Yes, there would also be a beam on the other side to carry the rest of the ceiling to the far walls. That one would be around 14' including bearing edges of 4" or so. That side should have much less of a dead load since the joists will be shorter. Haven't even got there yet... Regarding symmetry: it actually is symmetrical up past the listeners head. The idea was to maximize the volume of the room and use those back spaces to put bass hangers and plenty of treatment. With the splayed walls, the modes will be more chaotic anyhow so I didn't think symmetry in the rear would matter that much. The trade off for volume and trapping I hope is a good one. Here's a pic showing the geometry from the top including the yellow areas of bass trapping. -ashley