In the current Tools & Shops issue there’s a fine little article by Mark Corke about how to soundproof a basement shop. I need to do just this, and am therefore very glad for his article.
However, I find I’m confused about something. Perhaps someone here can clarify, or the Forum Monitor can provide some additional information.
For the exterior concrete basement walls, the author constructed an isolation wall comprised of 2×6 bottom and top plates with 2×4 studs vertically alternating front and back. They’re spaced 12″ OC, or 24″ OC on each side. At first glance, this made great sense to me: the front studs support the (double-layered) drywall, while the back studs — sonically isolated from the front studs and the drywall — structurally anchor the whole thing to the concrete basement walls.
Only, that’s not what he’s done. Upon a closer look, you’ll see that the 2×6 plates are set 1″ away from the concrete walls, and the back studs don’t extend beyond this to tie to the concrete. So what, exactly, are those back studs doing? Do they have ANY function? The front studs (those facing into the shop) support the drywall. The isolation wall itself bears no load — it is simply a barrier to prevent soundwaves from reaching the exterior concrete (and dramatically improves the appearance of the basement, too, I imagine). So, again I ask: what function do the back studs fulfill?
Yes, the insulation is woven among them. But for much less cost, you could just as easily nail on 1x1s, or even metal strips, at the back side of the top and bottom plates to serve as retainers for the insulation.
Of course, this double stud arrangement would make great sense for dividing walls (e.g., a wall separating his shop area from a basement bedroom), where you’re going to want to hang drywall on both sides. But how does it make any sense on an exterior wall, as shown in the magazine?
Replies
I noticed that too, and I don't know for sure why it would be done that way on an outside wall. The gap between the framing and the concrete should be sufficient isolation for sound.
I do understand the gap between the concrete and the new framing. Its to prevent problems from condensation, or from weeping walls. It allows water to drip to the floor, where I'm guessing there is a perimeter drain.
Actually, I think the 1" gap is intended here as a accoustical isolation measure. It prevents vibration from transmitting through the drywall, hence through the studs and plates, into the concrete and on up into the house above.
The illustrations show no drain, and I don't think one's needed -- unless you have an awfully wet basement. (Then again, I don't live in a notably humid environment, just a rainy one. So what do I know?)
In Fine Homebuilding, The Journal of Light Construction, and elsewhere they've had articles about finishing out basements (without the concern over sound). I don't remember if any of those had a 1" "condensation gap" or not, but it doesn't really strike a bell.
Marsman,
I read the article last night and I think that outside wall soundproofing treatment is a big overkill. I can see the ceiling soundproofing including the ducts in the ceiling (except 6" around the ducts is taking up a lot a space and height). I can see the advantage of the rubber feet on the big tools. But that outside wall is a lot of materials and space lost.
I'm interested in more basement shop opinions. I use a detached garage.
Enjoy, Roy
I agree, the design really sucks up space. My basement already has low overhead -- about 6'9" -- and beneath the ductwork, running along one wall, it's just around 6'. Fortunately, in my case that might be a good area (once I'm done) for just lining up a long bench and storage ... no need for much headroom. And vents, after all, really DO transmit sound.
But I'm not sure I agree with you that sound-proofing the concrete walls is overkill. I mean, putting framed walls up makes the whole space more pleasant, and allows for better insulation, nevermind sound transmission. It really is true that concrete transmits low-frequency sounds pretty well, and if you could use 2x4 plates and a single row of studs at 24" centers, it wouldn't be that expensive, nor quite so wasteful of space.
I'm not sure about 2 layers of drywall, though. Makes sense for the wall that'll be dividing my shop from a bedroom and bath (on BOTH sides, even), but it looks like overkill on the exterior concrete walls.
From my days as a framer you always leave a one inch gap between a concrete foundation wall and a stick framed basement wall. The main reason is that concrete walls are not always plumb or flat. By stepping your framed wall out one inch you can build it plumb and flat without having to shave or cope it to match the concrete wall. Mark was just following standard framing practices in his article.
Secure the framed wall to the concrete floor with ramsets and then secure the top of it to the floor joists above, then add draft stops.
As for the alternating 2x4s on 2x6 top and bottom plates that is also standard framing practice for exterior walls when building for higher R values of exterior walls. A stud that touches both the wall board and outside sheeting in an exterior wall is essentailly a direct heat transfer conduit. By using 2x6 top and bottom plates you eliminate direct heat transfer because no sutd is in contact with both the outside sheeting and the intrior wallboard, thus a higher R value in that wall.
It might be overkill for soundproofing your basement but I think Mark was just using standard framing conventions.
Hey, MPHarper, thanks for the good insights!
I hadn't thought about the relative ease of building a basement wall when you no longer have to worry about trying to make it plumb against a very rough concrete wall. Makes the whole task a lot less intimidating, that's for sure.
But now I'll have to reveal my ignorance about something: what's a ramset? (Maybe I know the technique, just not the word). Mr. Corke said he didn't attach the baseplates at all, which struck me as odd. I figured I'd attach them with a combination of construction adhesive and concrete screws (I've got a great Bosch rotary hammer that goes through my basement's concrete like butter!). But if there's an easier way, I'm all ears.
Ramsets are just hardened steel nails that are shot into the concrete with a cap, like shooting a bullet. You can buy one from your hardware store for about $20.00, there are several manufaturers, the least expensive ones are set off by pounding them with your hammer and work as well as the more expensive triggered versions.
If you have a hammer drill and want to set concrete anchors that's a great option too. It's a stronger fastener than just nails.
Marsman--I worked with Mark Corke on that article. Glad to hear from Harper here that Mark was following standard framing convention, but he told me he did it that way to make it easy to install the fiberglass insulation by weaving it between the alternating layers.
Regarding the double layer of drywall, a second layer and staggered seams does make a considerable difference.
Also, he did use construction adhesive on the bottom plate, but no screws or nails into the concrete.
Bill, thanks for the clarifications. And thanks to everyone else who's answered. Between all of the kind comments posted here, I think my questions have been answered.
Resilient channel was mentioned in the article. Where can one obtain it ? HD ? Lowes ? Special order from a supplier ?
Mark--I don't know for sure whether Home Depot and Lowes sell resilient channel, though I suspect that they probably do. One reliable (and probably cheaper) source is a drywall supplier. Look in your local yellow pages under "Dry Wall Equipment and Supplies."
Hi Guys:
I'd like to wade in here. I'm an architect, so have some technical knowledge concerning sound transmission.
1. I haven't read the subject article, but I gather from the discussion that the intent of finishing the basement wall was to i) provide a finish surface, ii) provide additional insulation, and iii) limit sound transmission to other parts of the house (not necessarily to the outdoors). These comments are relevant where the climate is COLD in the winter, warm in the summer, such as you might find in Ontario Canada.
2. In this case, it's important to know that i) although high mass walls/materials, like concrete/concrete block will transmit sounds, the sounds they transmit are not airborne sounds, but impact sounds. Therefore, the high mass foundation wall is about as good as it gets.
3. The double studs are not necessary in a furred wall situation, which this is. The idea of leaving a 1" gap is the way to go, but first attach a layer of building paper to the inside of the foundation wall, so that any moisture that makes it through the wall will not pass through to the wood stud furring/insulation. Then just install the insulation. Don't forget about a vapour barrier on the warm side of the insulation to prevent interior humidity from condensing within the insulation layer.
4. The idea is to isolate the wall board/drywall from anything that can transmit sounds to the rest of the house. To this end, use resilient channels. They do just that - create an isolation space between the wall board and the studs. If you plan on attaching tools, racks, etc. to the wall surface, use plywood instead of wallboard. You don't want to fasten anything directly into the studs, except for the resilient channels. Another suggestion is to use one layer of plywood, say 5/8", with a layer of drywall on top. Then you can fasten anything with abandon. In the case of heavy loading situations, like lumber racks, more detailed design of the entire system has to be undertaken.
5. Don't rigidly fasten the top and bottom plates to the concrete floor slab or joists above. One suggestion might be to use a foam sill gasket, use acoustic caulking under the plate. Ramset or tapcon the plate.
6. The double layer of drywall contributes to the reduction of sound transmission a great deal. Remember, high mass means low air-borne sound transmission. Unless you plan on banging on the walls alot, it's the way to go.
7. Stagger all joints in the wall membrane.
8. Gasket your wall outlets and foam/caulk all pipes passing through the wall membrane. Studies show that even the smallest air hole in the wallboard membrane allows airborne sound to magnify on the other side of the membrane.
9. Use isolation hangers for anything that hums, vibrates, etc. in the shop. Reduce transmitting these sounds to the house structure.
Naturally, consult with a professional whenever making any significant alterations to any building structure.
Joel
You've said it better than I could, but my question on the wall framing was. . . .why? Or rather, what does it have to do with sound insulation? I can't imagine that the wall he's framed is anywhere near as "dead" to sound vibration as the concrete wall he just covered up. I've framed walls in my basement shop as well for the other reasons given - they're plumb, the framing allows me to hang counters and cabinets, it's prettier - but I don't think it has anything to do with sound insulation. I just don't think those concrete walls are transmitting much sound.
Here is the #1 sound insulation secret: just before you go down to the shop, tell your wife to watch TV in the bedroom rather than the family room.
I agree with you. Don't think the insulation is there for sound - most likely as thermal insulation. The only place sound insulation might be beneficial at the basement exterior wall would be up at the top, in the joist space. It will dampen sound transmission upwards at the perimeter of the floor above, near the rim joists.
Joel
Edited 11/25/2003 1:36:22 PM ET by FwdThinker
Edited 11/25/2003 1:36:42 PM ET by FwdThinker
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