I'm formally known as arathercoolguy (aka Rushfan33) but "arathercoolguy" takes too much time to type all the time.
Anyways, my question.... I have an existing "A" framed room that's exposed 2x4's on the inside. I want to add mass to the roof but I'm concerned about the weight. Would it benefit me to add shhetrock between the rafters? I was thinking either 1/4" or 3/8" sheetrock. Is this advisable? After that, would I negate my efforts if I insulated the rafters and then hung sheetrock over that? There will be another ceiling about 1 1/2' below that with 5/8" sheetrock. My understanding is that it would basically be a 2 leaf system with no inner plys, which is why I question rocking the rafters.
Thanks,
John
If you only have 2x4's for rafters I wouldn't add ANYTHING to the weight they support - even with a steep pitched roof, 2x4's won't take much weight.
When figuring whether another "leaf" is OK, take into consideration whether the outermost leaf ( the roof) is sealed or not. If so, then it counts as a leaf and you should only have one more leaf, separated by as much air/insulation as you can get.
Most roofs are ventilated to prevent moisture buildup from causing rot/mold. If that's the case, I'd leave it that way and build a double-leaf barrier inside that. I just posted a drawing showing that basic layout in the "sticky" "Complete Section" thread - however, if your walls are already OK, you'd need different approach in order to maintain a complete "double envelope" around your space (see the "toybox" pic in that same thread, before any of the wall diagrams)
If you could post a drawing of what's already there, it would be a big help... Steve
John, if your existing roof is vented at the eaves you could put two more centers of mass (with air or insulation between them) between you and the world. If the existing roof seen in the pic is SEALED to the outside, then you get ONE more center of mass (leaf) before you start messing up your isolation compared to materials used.
If those are only 2x4's, what is the span from the ridge board to the eave (1/2 the width of the total)? You may already be at the maximum weight allowance for your framing. If that's the case, maybe there's a way to VENT the roof (without making it leak, of course) and then build a double leaf ceiling over your room with its own support system.
Gotta go sleep 5 hours so I can work another 12 tomorrow, but let me know and we should be able to come up with something... Steve
What you have there, John, are genuine rafters, as opposed to roof trusses.
Roof trusses can handel a lot more weight than rafters.
What type of connection is at the rafter - ridge beam?
Looks like they're just toe-nailed in.
Is there a splice right there at the ridge beam? In the pic?
You could apply some joist hangers, and increase the bearing capability of the rafters. But not a whole lot....
John, one more question to add to Rod's list - are those boards in the pic the end of your roof other than tar paper/shingles or whatever, or is there insulation and another layer above? and, what is the venting/circulation situation?
OK, that was two - but we need to know ALL these things to be able to give relevant advice, and if you get it wrong the LEAST that will happen is you'll be unhappy with the isolation. The WORST is you'll be "SMUUSHED", or, as you might say, "A rather flat guy"... Steve
as far as the collar beams and joists, I've removed nothing! I was actually going to fortify the existing structure before I did anything. Here's a pic of how it is now. It's a top view. The red lines going across are the existing joists. The black lines going across are the rafters. Here it is.
Here's what I want to do to help the structure. The the reason there are so many joistes on the right (control room) side is because I'm going to hang the sheetrock from those. As of now you can see there is only one joist on that side. This is odd to me because the large garage door was on that side.
Instead of having collar beams, this is what they did. It's only on the one joist closest to the middle. My plan was to move this joist to the actual middle using a 2x6 on either side of the rafter and replicating the system used in this pic.
On the left side (live room), this is what I propose for the ceiling.... which is why I cant put joists on every rafter like the control room.
By the way..... the dimensions for the entire structure are 12'3" x 20'. The rafters are 8'3" at the low end to about 10'6" in the middle.
Install a beam below the existing ridge and tie it to the rafters - let it bear at the exterior walls...... if you do this you won't need any cross ties (joist) to stop the walls from deflecting outwards.
The only load that will exist on them will be gravity. Anf that exists no matter what.
For a 20' span a 2 2x12 beam with a 3/8" steel flitch plate will be more than enough to carry dead and live loads for this. use 3/8" carriage bolts - 2 at each end and then staggered @ 18" centers throughout the body of the beam.
