John Sayers' Recording Studio Design Forum Archive

Hi all,
I will be building an inside-out ceiling in my garage recording studio, and I’m wondering how people approach sealing the perimeter gaps between the ceiling module frame and the ceiling joists/blocking that they are attached to, or whether people prefer to install/caulk the layers individually (instead of lifting pre-built modules). I’m interested in your experience in terms of ease of installation and the resulting isolation.

Do people generally allow for a ¼” perimeter gap along the outside of the module frame (Ex. 2’ x 4’ module into a 2’ ½” x 4’ ½” space), and then fill the ¼” perimeter gap with backer rod and acoustic caulking? Or do people simply attempt a best-fit (Ex. 2’ x 4’ module into a 2’ x 4’ space), and then caulk any unavoidable tiny gaps along the perimeter? Or do people prefer to install and caulk each layer in, layer by layer, rather than raising pre-built modules?

1) pre-built ceiling modules, ¼” perimeter gap approach
My concern with the ¼” perimeter gap approach, is that it would be difficult to lift and install a heavy module with such precision. I’m envisioning lifting a 200 lb module up in the air while measuring and shimming the ¼” perimeter gap, while making micro-adjustments between the module and the ceiling joists/blocking. I know the gap widths don’t need to be exact, but even establishing an approximately balanced perimeter gap, seems very difficult to do while lifting a heavy module. I’m also concerned that I would have to squeeze so much acoustic caulking in the ¼” perimeter gap (to match the isolation of the OSB and 2 layers of sheetrock), that if there were some non-uniform sections of caulking that weren’t as thick, then these sections would be weak points in the isolation (potentially many weak points).

2) pre-built ceiling modules, best-fit approach
The best-fit approach seems easier for installation. You just make sure the module can fit in the space, lift it and install it without worrying about where the tiny gaps are. Since it’s hard to achieve a perfect fit, some tiny gaps would be unavoidable. However, I would think that most of the perimeter points of contact would be flush and tight (so no isolation break), and then any remaining tiny gaps would be minor weak points (since they are tiny breaks), so tiny gaps would require less caulking to establish the same level of isolation as the modules themselves? The counter-argument would be that, even though the gaps are tiny, it would still be difficult to squeeze/stuff enough caulking into these tiny gaps to bring their isolation level up to that of the module - but I’m wondering whether people have actually observed this in practice.

3) install and caulk layers between ceiling joists, layer by layer
I’ve also seen studio builds, where a variation on Rod Gervais’ approach is used, for beefing up sections between ceiling joists. Rod’s approach assumes that there already exists a ceiling surface. The variation I’ve seen in realdoyle’s build (http://www.johnlsayers.com/phpBB2/viewt ... 3&start=30), is to first install 1x3s along the ceiling joists using liquid nail and screws, as a base for installing the subsequent 3 layers. Then each 2’ x 4’ layer of OSB, sheetrock 1, sheetrock 2, can be screwed into the 1x3s, with caulking installed along the perimeter of each layer. This seems much more labor intensive, but I think it would also yield the best isolation, since each of the 3 layers is caulked individually. It avoids lifting a heavy ceiling module, however it involves the additional labor of installing and caulking the each of the 3 layers, one by one.

I’m looking forward to hearing about your inside-out ceiling build experiences and recommendations.

Thanks in advance for your help!

- Alex

I'm designing a 15' x 21' inside out control room. On one of my designs I plan to frame and drywall the ceiling on the ground and then lift it into place using many helpers and possibly a lift of some type. The ceiling structure will sit on the wall top plates perfectly without any space leftover on the sides and I'll install the ceiling over the wall frames before drywalling the walls. Since the walls will be drywalled on the outside, I'm leaving about 3.5 inches of extra drywall that extend over the wall top plates and will butt up against the ceiling frame, so from the outside going in there will be 2 layers of drywall > 1 1/2" of 2x4 stud on the ceiling perimeter.

Does that make sense.

I'm designing a 15' x 21' inside out control room.

That's a nice size. That should work out well. Very decent floor area.

On one of my designs I plan to frame and drywall the ceiling on the ground and then lift it into place using many helpers and possibly a lift of some type.

Right, that's the normal way to do "inside-out" ceilings. However, I normally do that as a series of several smaller modules that are lifted into place inside a "skeleton" or "grid" of large joists. The joists are design to support the weight of the modules, and the modules are built small enough that two or three people can lift them, perhaps with the help of a drywall lift or some similar device. You can't raise the entire ceiling at once, as it would be way too heavy: with 315 ft of area, and probably around 10 pounds per square foot at least, that's many thousands of pounds. Not even a dozen people cold lift that by hand....

The ceiling structure will sit on the wall top plates perfectly without any space leftover on the sides

Right. I normally put rim boards around the edges of the ceiling framing, standing up vertically on top of the wall top plates, and leaving enough room for the edge of the module to rest on.

and I'll install the ceiling over the wall frames before drywalling the walls.

I'd suggest a different approach: Don't use drywall for the first layer. Use OSB. You need sheer strength in the walls, and drywall does not provide that. OSB does. So put a layer of thick OSB on the studs first, then a layer of drywall over that, to build up your mass. If you need higher isolation, then use Green Glue between the OSB and the drywall, for damping.

You do need to have the OSB on before yo put the ceiling on top, as the OSB is part of the load-bearing structure. Without that, you could end up with warped or twisted framing, and no way to fix it.

install the ceiling over the wall frames before drywalling the walls. Since the walls will be drywalled on the outside,

I'm not getting the full picture here I think: That doesn't make sense if you are building your walls correctly, as a proper fully-decoupled two-leaf MSM system. You would not have any access to the outside face of those studs to put the sheathing on, since the outer-leaf wall would be in the way.

I'm leaving about 3.5 inches of extra drywall that extend over the wall top plates and will butt up against the ceiling frame,

As I mentioned above, it would be better to just put a rim board up there, to create the seal and provide the mass. You cold do it with drywall, but you run he risk that the drywall could be accidentally damaged as you raise the walls or the ceiling modules.

Here's a series of photos that shows how I normally do that with my customers:
In the above photo you can see the large joists that provide all the structural support, and the rim boards around the edge, on top of the wall top plates. You can also see the outer-leaf ceiling just above this one. It looks like they are touching in this photo, but that's just an optical illusion- There's actually a gap of about an inch between the tops of theses joists, and the bottom of the joists of the outer-leaf ceiling (which is really the floor of the room above).


That's with all the modules in place, between the "skeleton", except for the last module that is being installed, at the far end of the room. ( The guy on the ladder is working on it, and you can see some temporary framing that is being use to hold the module half way up the wall, while it is being raised).

In this case, each module is a simple 2x4 frame with one layer of plywood on top, then two layers of drywall over that. So even though the modules are not that big, they were still darn heavy! Each module was sealed into place with backer rod around the edges, and abundant caulk (the modules are built a fraction smaller than the size of the space in between the ceiling joists, to allow a bit of clearance and "wiggle room" while installing, an also to provide thermal expansion joints, and excellent sealing).


In this one, the bays between the ceiling module framing members has been filled with insulation (held in place with blue nylon packing strapping), and the black "light barrier" cloth, and final finish fabric are going up.


General view of the entire room, showing half-completed ceiling.


Decorative trim over the fabric. Also holds the fabric taught, and hides some seams in the fabric.


Almost completed ceiling.


Completed ceiling with trim and lights in place.


Final complete room, with musicians in place!!


Hope that helps!


- Stuart -

Hey Stuart,

I'm sorry to post on an old thread, but I have a quick question about the inside out-ceiling you posted pics of.
Do you know what those joists are on center? It looks like you are over 24" OC, and are sistering the joists?
I have been searching on the forums here, and have been reading mixed messages about whether sistering joists is a good idea.

It looks like you are over 24" OC, and are sistering the joists?

Right.

and have been reading mixed messages about whether sistering joists is a good idea.

What concerns do you have about that? Why would it not be a good idea to increase the load carrying capacity?

- Stuart -

I have been searching on the forums here, and have been reading mixed messages about whether sistering joists is a good idea.

You can get way more strength by just adding a few inches depth to your joist (9 1/4" instead of 7 1/4"), but when height is a luxury, I personally opt'd to sister 7 1/4" to get the engineers stamp instead! Sadly, LVL stud isn't cheap

Greg

What concerns do you have about that? Why would it not be a good idea to increase the load carrying capacity?

personally, I would PREFER to do that, as would the buddy who is helping me build this.
But then I read this thread:
http://johnlsayers.com/phpBB2//viewtopic.php?f=2&t=5986
where Rod G. said "Short - stocky square members do not necessarily gain you a lot"
And the joist span calculators I have been looking at don't really tell me a whole lot when it comes to sistering joists together.

I'm not trying to put your experience against Rod's or question your methods.. in fact I'm trying to implement your methods in my own project.
I'm just trying to get some clarification and to understand how sistering the joists will increase the load bearing capability of the ceiling.

I.e. with my 13' 9" span, I can use a span. calc to determine that if I go with 24" OC, I can get away with either 2x8's or 2x10's depending on the wood species and quality.
But I dont have any idea how to figure out how far I can push the joists on On Center for the same span, were I to sister those 2x8's or 2x10's.

There is a ton of info on the site, of course, but searching really only netted me with the thread above, and a vague comment by Rod, saying that sistering doesnt gain you much.

Thanks for any insight you can offer.

Jason

Gregwor wrote:

I have been searching on the forums here, and have been reading mixed messages about whether sistering joists is a good idea.

You can get way more strength by just adding a few inches depth to your joist (9 1/4" instead of 7 1/4"), but when height is a luxury, I personally opt'd to sister 7 1/4" to get the engineers stamp instead! Sadly, LVL stud isn't cheap

Greg

Yeah, my buddy suggested using LVL as well. He wants to try to push these joists out to like 36" OC or more. In theory, I would love that.
In practice, I dont want me ceiling to collapse and crush my head.
I'm too pretty to be flat!

Yeah, my buddy suggested using LVL as well. He wants to try to push these joists out to like 36" OC or more. In theory, I would love that.
In practice, I dont want me ceiling to collapse and crush my head.
I'm too pretty to be flat!

Contact an engineer. They can type all the values in their software and tell you if it will work or not. Here's some of one of mine: This is the only way your inspector will pass your construction. Actually, most places won't sell you engineered wood without paperwork.

Greg

But then I read this thread:

Right! Rod states it quite clearly: sistering joists is not the same as having larger joists, and having two 2x6 next to each other is also not the same as having a single 4x6: To start with, a real 4x6 measures 3 1/2" x 5 1/2", whereas a pair of 2x6s only measures 3" x 5 1/2", so it's already 15% narrower, and it does not add much extra support in the vertical direction... So each individual joist by itself can't carry more vertical load... True.

However, what Rod did not mention there, is that if you double up on joists, you can increase the spacing BETWEEN joists... The joist itself cannot carry more load, but you can share the SAME load among MORE joists. You can see this for yourself if you play with the joist spacing in the span tables. Adjust the load, and the joist spacing, for the same span, and see what you get...

Do also take into account that the modules themselves also have framing on them...

And the joist span calculators I have been looking at don't really tell me a whole lot when it comes to sistering joists together.

Right. But play around as above, with spacing and load, all other factors being held equal...

I'm just trying to get some clarification and to understand how sistering the joists will increase the load bearing capability of the ceiling.

Try it. If you have single 2x8 joists spaced 24", and 16" and 12", is there a difference in load carrying capacity? And is there a difference between having one joist ever 16", or two joists every 24", for the SAME load?

Yeah, my buddy suggested using LVL as well. He wants to try to push these joists out to like 36" OC or more.

With LVL (or any engineered joist/beam) you can go to pretty much whatever spacing you want, as long as the joist is big enough. But for ordinary 2x framing, I wouldn't go beyond 24". Nor do you need to. In fact, I would strongly suggest that you don't! Not just for structural reasons, but also for simple, practical reasons: the wider the spacing, the bigger the module, and therefore the heavier it is. Very heavy modules are very difficult to raise, and maneuver. You'll be hiring a small forklift and figuring how to get it into the room, to raise your modules if you manage to get them more than 36" OC. Not a good plan. Keep them small, and manageable.

In practice, I dont want me ceiling to collapse and crush my head.

Good move! Then, as Greg said, hire a structural engineer to check your design, and make SURE it won't collapse! It's never a good idea to guess, or estimate, or take chances, with potentially fatal things hanging over your head........ A structural engineer is the only person qualified to tell you what is safe, and what isn't safe. And a local one from your area, is the only guy who can tell you what is required by your local code and authorities, and what will pass inspection

- Stuart -

The joist itself cannot carry more load, but you can share the SAME load among MORE joists

And there was my head-slapping moment. I think I get it now.

But for ordinary 2x framing, I wouldn't go beyond 24". Nor do you need to. In fact, I would strongly suggest that you don't! Not just for structural reasons, but also for simple, practical reasons: the wider the spacing, the bigger the module, and therefore the heavier it is. Very heavy modules are very difficult to raise, and maneuver.

That is a very good point. I think I will stick with 24" OC for my room.

Thanks again for chiming in Stuart, and Greg.