Lets Talk "Sheathing"

I've been through about 4 studio build outs as well as two home remodels, some of these pretty extensive undertakings in construction. Because of this and because I live in earthquake prone So Cal, I'm very familiar with the term and use of sheathing in construction. The building inspector on my home remodel was wild and ecstatic about sheathing everything possible which I happily complied. After discussions with two contractors now regarding my new studio plans I'm baffled by their insistence that I sheath all the newly constructed "room within a room" walls. They tell me it's a necessity if I'm not going to tie my new constructed walls and ceiling into the existing structure. As this separation is sort of a main criteria in building isolated rooms, I'm not really impressed on many levels with what they're telling me. Still I just thought I'd inquire about the use of sheathing in studio construction. Perhaps the building codes have changed here in Los Angeles since my last studio build (2000). I can't find any mention of the need for sheathing on this site as well as others or in Rod's book. I also don't see anyone sheathing interior framing within any of the hundreds of studio construction threads I've seen here and elsewhere. My gut tells me that these contractors don't have any idea what they're talking about, but I thought I'd see what others have to say on this topic. For basic particulars we're talking about constructing a room with 4 walls and ceiling, 2x4 framing on 16" centers with one leaf of multi layers of drywall and Green Glue. All of this is being constructed within an existing framed shell with the requisite air space and insulation separating the two structures. Why would I need sheathing?

Greetings! By ‘sheathing’ we assume you mean sheet material such as 4’ x 8’ plywood or OSB perhaps ½”, 5/8” or even ¾” thick. We assume your contractors are advising you to nail/screw this sheathing to the studs inside your isolated studio rooms instead of drywall. If these assumptions are correct, then we speculate that you are being advised to use the sheathing for lateral support of the otherwise unsupported inner room framing. In the event of an earthquake, the framing of the inner room will rack without the lateral support of the sheathing. Use of the sheathing should not be problematic acoustically. It will not compromise the acoustic separation of the inner rooms and outer structure. You can also then add drywall on top of the sheathing to increase transmission loss further and provide a more standard interior finish. Just make sure your overall surface weight (psf) (sheathing plus drywall) is no less than what you planned with the drywall alone. An alternative is to provide resilient lateral supports (for example at the headers of the inner walls). These can be obtained from Kinetics Noise Control or Mason Industries. These resilient lateral supports would provide the necessary lateral support, maintain acoustic separation, and possibly negate the need for the sheathing. But, using the sheathing will avoid the added cost of the resilient lateral supports and forever allow you mount things to the walls (OSB or plywood substrate) in lieu of trying to find studs or using drywall anchors. We wish you the best of luck!

Yes, that's what I'm referring to as sheathing. I'm just curious why if this is a structural necessity for constructing a "room within a room" studio, I can't find any mention or diagram referring to this anywhere in John's manual or Rod's book. As mentioned, I understand the value of wood sheathing as my house remodel called for it everywhere. I have no problem using a layer of plywood or OSB if needed. It just seems like if this is a structural requirement for building a studio shouldn't it be called for in at least one of the 1000's of diagrams posted here. I'm especially curious as to how this applies to John's "Inside Out" designs. How many out there used a layer of wood "sheathing" even though it's not called for anywhere in the plans?

That question may need to be tightened up a little bit to those who have done it in an earthquake prone area. In southwestern Michigan, it may be a useless venture - the worst to hit here would be a truckload of snow or the occasional tornado - neither of which would be best served with sheathing on the inner leaf. However, with the earth racking underneath you, it begins to make sense to structurally support the studs with something other than gypsum. As to answering your question about the code - only an expert who works in an active earth zone can really answer that question with any qualifications.

"I can't find any mention of the need for sheathing on this site as well as others or in Rod's book. I also don't see anyone sheathing interior framing within any of the hundreds of studio construction threads I've seen here and elsewhere. My gut tells me that these contractors don't have any idea what they're talking about, but I thought I'd see what others have to say on this topic." Bob seems to be on target here. But a little thinking on the subject should help you to get more out of the process. The sheathing as was mentioned helps greatly in reducing the structures ability to rack which could lead to collapse. On the outside of a structure this helps in several environmentally impacted regions. Like here @ Xit 4 where hurricanes can crush a building with sustained high winds with the occasional projectile the size of a fence post. In an area that is prone to seismic activity it stands to reason. Actually I am a bit surprised that Bob mentions Michigan does not employ this building practice since the weight of snow or a tornado could both have the same kind of detrimental effect by weight of the one and force/pressure of the other. Still, sheathing for your purpose on the interior side of a room in a room makes perfect sense. One better is that you would most likely need to bolt the bottom plates of the walls to the slab since this is most likely common practice in your area. The thousands of studios you find here @ Mr. Sayers forum or of an International variety so it stands to reason that most will not use this technique so it isn't an omission as much as it is standard building practice for the many geographical areas. Like what does Australia have that would cause the need for sheathing outside of a lot of sunshine :)? Good luck and trust your contractors but question the bills, Brien

I guess I could have been a little more clear in my answer - I was only responding with regard to the inner leaf. I guess I was under the impression that sheathing ALWAYS occurred on exterior walls, for stiffness due to winds, snow (as Brien said), etc. I wouldn't live in a house that wasn't properly sheathed on the outside - just because I would have assumed it was built wrong! As they say, you learn something new every day!

Something for the OP to read while making decisions: This page verifies the requirement for bolting of wall panels: http://sanbruno.ca.gov/comdev_images/Ca ... g_Code.pdf This paper goes into the ideas that non-structural elements of buildings (like home theaters and sound rooms, in your case) often can be the cause of structural failure loss of life, etc. An excerpt: " As our existing stock of older buildings is seismically retrofitted, the nonstructural components and systems must also be seismically retrofitted to the same level as the structure." Certainly it applies to a broader area to include HVAC, pipes, ceiling grid, etc...basically anything that is not part of the actual structure support system but that can be an influence under seismic load.FEMA: Risk Management Series Designing for Earthquakes For me, I would also think that in a residential structure in an earthquake zone, it would require an engineer to make the decision on if the existing structure can support itself under seismic activity AND the non structural panels (the studio) in order to use any type of "resilient lateral support", basically creating a connection between structural and non structural that can effectively change the way a structure will behave under the influence.

I posted the same thread over at Gearslutz where Rod offered a lot of insight. Here it is for those interested. http://www.gearslutz.com/board/studio-b ... thing.html