Hanging Walls Because of Expansive Soils

midigod · Post by **midigod** » Wed Dec 17, 2003 12:31 am

Greetings:

I've been searching, but haven't been able to find information regarding hanging walls, and how they'll have to affect my plans.

According to code in the Denver area, and other areas with expansive soils, basement walls are hung from the joists of the floor above (basement ceiling). A double sole plate is also used. One plate is attached to the floor, the other is held laterally in place with spikes and floats about 2" above the bottom sole plate. Baseboard moulding is attached to the bottom sole plate and the drywall slides up & down behind it; the baseboard covers the gap.

This causes me concern on two levels:

1. This will prevent me from detaching the walls from the ceiling, thus increasing my STC. It seems to me that the sway brackets and other insulating techniques will be useless for this application, because they don't strike me as being a method for attaching the weight of the wall; only managing the wall's movement. Am I correct? If so, what options do I have in this case?

2. It also means that the ceiling will have to bear the entire weight of not only the studio ceiling panels, but also the walls. Am I correct in assuming I shouldn't even think of three sheets of gyp? How about two? Is that out too? My calculations show that for two layers in strategic places (i.e., ceiling and some walls, but not outer walls against the concrete), that adds up to about 25,000 pounds, not including the framing, screws, or mud. Just sheetrock.

Given the fact that the entire rest of the house also sits on those same joists, am I being paranoid in my concern, or justified?

Thank you for your help.

-Craig

midigod · Post by **midigod** » Wed Dec 17, 2003 12:35 am

One other thing I forgot to mention:

I'm also a *little* concerned about sealing the walls, because code dictates that I allow them to slide, even if they never actually do. I'm figuring I can caulk the sliding joint, and the caulk will tear if the wall ever moves. At that point I can re-caulk. Sound reasonable?

The floor is concrete, as well as the walls. Where soil reports dictate, structural subfloor is built, but the soil report for this lot did not indicate that soils would expand so much that concrete couldn't be used. But the code still demands that the sole plate be used.

-Craig

rod gervais · Post by **rod gervais** » Wed Dec 17, 2003 12:59 am

I have to admit ignorance with this type of construction.

You state the walls have to have the capacity to float - and the ceiling bears the weight of the walls.

Thus the space between the foundation (which may move) and the bottom of wall - which remains rigid.

What then (pray tell) holds the ceiling up?

Is it a series of piles driven into the ground with columns above them?

As to your question - if you seal the void between the 2 plates with real true acoustical caulk (floppy caulk) it should allow for slight movements (picture up to maybe a 1/2" or slightly more) with out a problem.

But still - explain the construction please.

Rod

midigod · Post by **midigod** » Wed Dec 17, 2003 1:44 am

<i>You state the walls have to have the capacity to float - and the ceiling bears the weight of the walls. </i>

The ceiling bears the weight, as the walls must be attached to the ceiling. My concern is that I will *not* be able to have the walls float (with respect to the ceiling), thus creating one big tuning fork, if you will.

The floating of the walls must happen between the wall and the floor, not the wall and the ceiling. Picture an upside-down U. That's going to be one solid structure, consisting of ceiling and walls, all attached to the joists. The legs at the bottom of the upside-down U must not be attached solidly to the floor. I'm afraid I'm not well enough versed to give a more technical explanation, but I'd be happy to clarify further if I can.

<i>if you seal the void between the 2 plates with real true acoustical caulk (floppy caulk) it should allow for slight movements (picture up to maybe a 1/2" or slightly more) with out a problem. </i>

I need to be educated on the void sealing thing. I was thinking that the seal could be between the baseboard and the sheetrock as an airseal only, but I think you're talking about sealing the entire 2" void with acoustical caulk. Can I really use caulk to fill that big a space?

dymaxian · Post by **dymaxian** » Wed Dec 17, 2003 2:01 am

Hey guys!

I just spoke to my dad, who happens to be the president and lead architect of the firm I work at

He's also done a few animal clinics out in Denver, so I figured he'd know the score.

I guess there just aren't many basements out that way, mainly because they're too much of a pain to build right. The expansive soil doesn't let them sit still easily. They'll usually build houses off piles or caseons, set a grade beam on that, and then build up the floor system from that. If there is a basement, they'll usually excavate down several feet past the lowest floor elevation, fill with 'good' material, and set the floor on that.

But the walls, as you said, are usually hung from the grade beam. So the first step, in my opinion, would be to find a structural engineer and ask him how much those grade beams can hold.

The next question is- how much space is down there? If those walls are hung from the grade beam, you're pretty much right on about structural isolation- it won't be happening. You can use resilient channels on the walls and ceiling, and that'll help. If you want to really isolate everything, and you have the space to do it, I'd float a floor off the basement, and build walls off that floating floor, and a second ceiling above that. But that'll take up a LOT of space and if you're not building new, you won't have much headroom left.

But yeah. Find out how much the upstairs floor will hold before you start hanging more stuff on it...

Good luck!

Kase
www.minemusic.net

midigod · Post by **midigod** » Wed Dec 17, 2003 2:21 am

Thanks Kase!

Actually, there are a lot of basements, but there aren't many that are finished.

Looks like I'm lookin' for a structural engineer!

Conceivably there's room for a subfloor, as the ceilings are at 9 feet 6 inches in their unfinished state. But I don't really want to go down to 7 1/2 feet finished, so I'd like to stay away from a subfloor. In this area, you never know until the soil report comes back what your floor will have to look like. There are neighbors less than a hundred feet away who have had to get a subfloor, and just as many who haven't.

goldstar · Post by **goldstar** » Wed Dec 17, 2003 10:55 am

Craig

It may be possible to do a caisson arrangement that could not be attached to the floor structure above and let you do a room within a room approach, esp. if you have 9-6 to work with, though it will be expensive. Which specific part of Denver are you in? Codes vary a bit around different parts of town depending on the prevalence of expansive soil. Contact me directly if you'd like, I'd be happy to have a look.

Frank Lambrick

knightfly · Post by **knightfly** » Sat Jan 10, 2004 1:50 am

Frank, Craig, please keep us posted on this - I too have never heard of this type construction, but it seems like there should be a way to isolate almost anything if you look far and hard enough - should be interesting... Steve

cadesignr · Post by **cadesignr** » Sun Jan 11, 2004 3:41 am

craig wrote

(i.e., ceiling and some walls, but not outer walls against the concrete)

I don't understand....concrete what? foundation walls(basement walls?) If so, are these supporting the whole house? If they are, isn't that standard construction? If not, what is holding the house up?, And if the basement walls are concrete, why would you need 3 layers of gyp bd? Maybe you could clarify this a bit. If the walls of the basement are NOT concrete, as you say they are hanging(thats the confusion), then WHAT is supporting the house above? Just curious. Some things need to be explicit for me to grasp. Sorry.
fitZ

cadesignr · Post by **cadesignr** » Sun Jan 11, 2004 3:48 am

PS....I tried to edit but it didn't work..

Could someone explain what a "caseon" is? Thanks.
fitZ

goldstar · Post by **goldstar** » Sun Jan 11, 2004 8:18 am

The soils report rules the roost in Denver construction. Some areas here have very expansive soil, which have moved conc. slabs and sometimes foundations, so it all depends on those soil test bores.

Usually in central Denver we use a regular spread footing and poured foundation wall, then the hanging wall arrangement describe in the first 2 paragraphs of Craig's initial post. Some areas in the suburbs use caissons drilled to bedrock, then a poured foundation wall set on a void-form with the rebar of the caissons (or pilings, if you like that term) tied to the foundation wall.

The basement partition walls here almost always "float" (hang from the above floor, really), and like Craig points out, would be difficult to isolate the ceiling from partition. The floor joist above are sized to hold these extra hanging partitions, and sometimes the beams can be pretty beefy, or have extra supports (w/ footing or caisson below) at mid span.

Looking up caisson in the dictionary doesn't work well for a description, I'm realizing. Piling is probably a better term, though no one here calls it that. Basically, it is a hole 10-24" in dia. with rebar hung vertically and poured full of concrete, used as structural support. Most times they are between 20-40 feet deep, the goal being to drill until you hit bedrock, which won't move (they say). You have to pour them as soon as you drill them, too, or they fill up with water. The trouble we'll go thru to live in pretty places!

Frank

cadesignr · Post by **cadesignr** » Sun Jan 11, 2004 12:39 pm

" caisson"

no wonder I didn't recognize it. DUH! Hey, thanks for the explanation Frank. Interesting construction info. I live on a hill in Coos Bay Oregon, which seems to have really soft soil which has allowed my house, which was built in 1925, to sort of sink, on one side. In fact, it looks as if half the house was built on the portion of grade cut out of the hill, and the other half on grade that was filled with what they removed from the cut. Ha! Talk about a flooring nightmare. Can't relevel it, as the previous owner built a level second floor, by extending the studs and posts, so the first floor is sunk by 4", and the second floor is level. Crap.
Anyway, thanks a lot.

fitZ

rod gervais · Post by **rod gervais** » Tue Jan 13, 2004 12:24 am

goldstar wrote:Looking up caisson in the dictionary doesn't work well for a description, I'm realizing. Piling is probably a better term, though no one here calls it that. Basically, it is a hole 10-24" in dia. with rebar hung vertically and poured full of concrete, used as structural support. Most times they are between 20-40 feet deep, the goal being to drill until you hit bedrock, which won't move (they say). You have to pour them as soon as you drill them, too, or they fill up with water. The trouble we'll go thru to live in pretty places!

Let's clear this up just a wee bit more.

A pile is a manufactured item which is shipped to a jobsite and is then driven into the ground by a pile driver - they may be wood - concrete - steel - or a combination - they may also be round or square.

The driving is done either to refusal or satisfy a particular design loading criterion determined by the force of the hammer and the friction of the soils involved.

A cassion is a cast in place concrete product - can often times be quite large - (we have 64" dia caissons on my current project) may often require the use of a steel sleeve in order to stabilize conditions for concreting procedures.

The terms are not interchangable. A pile cannot be poured onsite - a caisson cannot be driven.

I have however figured out what the construction is (finally) and how to solve the problem (now that i finally understand - duh - sometimes i am so friggen obtuse).

Going to a meeting right now - will post it in a bit.

Rod

Michael Jones · Post by **Michael Jones** » Tue Jan 13, 2004 3:19 am

I've worked on some pretty wild foundation designs. One in particular was for a 200,000 sq. ft. retail center in Galliano, LA. The design requirement for the foundation was to have a PVR (Potential Verticle Rise) of less than one inch.
The site was actually below sea level, and the soils were quite expansive; in fact, they had the consistancy of... jelly.

Piles were driven to a depth of 70 feet, and grade beams were constructed on those. The walls beared on those. There is NO bedrock! The lateral pressure on the pile and the strength of the soil assured that the piles wouldn't sink any further. There was a void between the finished floor and the soils below to allow for expansion.
The store is still there, and hasn't moved a bit, but... The parking lot has to be resurfaced every few years because its "sinking" and the store isn't.

rod gervais · Post by **rod gervais** » Tue Jan 13, 2004 3:35 am

Midi,

Any wall that you hang from structure above - if directly coupled with that structure - will transfer flanking noises into your room - and vis-versa.

It will definately hurt you from an isolation point of view.

The solution is to utilize isolation hangers capable of carrying the required load. It's important that they can not only carry the load - but that the design capacity of the hanger is such that they are constantly in a state of compression - somewhere between 1/2 and 3/4 compression.

Here is a link for a product that can work within your needs - capable of handling the loads:

http://www.acousticalsurfaces.com/vibra ... s.htm?d=24

(the company reps and their engineering department should do the actual engineering for your space to provide the details you need)

Good luck,

Rod

Rod