John Sayers' Recording Studio Design Forum Archive

I've read in a few places (and searched) about decoupled slabs, this is something we see a lot in colorado anyway because we have lots and lots of sand and clay and the ground heaves over time. So expansion joints in large slabs are fairly common. I was curious how much it makes sense to use these in concert with isolation in a studio? Like put a control room and it's booth/airlock on one part of the slab and then a live room on the other side of an expansion joint? In this context can/do they make a smaller footing to support walls that are on the edge of an expansion joint?

Also I understand that a slab poured on blueboard EPS for thermal purposes isn't acoustically "floating", but I was curious what acoustic side effects it does have? Mostly will it still have the same damping effect as when poured on the ground?

I was reading this blog (http://ana-white.com/2011/09/momplex/he ... stallation) and saw how they pour the floor inside the ICF walls (so footing first, then walls then EPS on tamped earth then floor slab). And it made me curious, I live on an uninsulated slab now and it isn't very comfy in the winter.


To answer the questions for the rules, I'm years away from breaking ground. My wife and I bought a house with commercial zoning on a big lot (13000sf) and the back yard borders a park, so it could eventually be a good place to build (or could just end up as an investment property). But first we have a lot of building codes (and zone district overlays) to meet so for now this is a bit of an investigation. The exterior building size for the studio would be 24'x92' with around 16' ceilings (depending on excavation). I've been looking at ICF construction. This would be a commercial project that would qualify as 'redevelopment' of the site and require proper everything (engineering, design etc) with the city so I'm not trying to DIY this. What I am trying to do is learn and start up a dialog with the zoning and planning office so i don't have to pay a designer or engineer a fortune to re-work plans that get rejected by the city. Also we need to look at budget and we are investigating the feasibility of building a residence above the studio (which would be on the outer shell isolation wise). Thanks for the feedback!

So I managed to have a little more success googling with different terms etc. I'll try to consolidate some info here if it is helpful to others looking into this. I found this thread

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=4538

and specifically this image that is very helpful.



I'm still curious if anyone has any insight on concrete floor insulation like this-

EDIT this picture is huge, resized and attached.

It seems between the ICF wall and the floor everything is decoupled, but does that EPS type insulation transmit vibration? Also does anyone know of an an insulated floor system or technique that allows footers? And the other question I think relates is what risks are there with drain pipes and conduit transmitting vibration from one decoupled slab to another?

Thanks-

In my experience a slab on EPS is a really bad choice for a studio because EPS can't act as a damper since it's basically made of air. To properly float floors you need damping materials like springs who need to be calculated having in mind the weight of the slab in order to work properly.

I tried EPS a couple of months ago when I didn't know shit about acoustics (not that I know much now too) and it worked out horribly, the slabs vibrated like crazy at around 40Hz. There was nothing to damp the slabs since EPS is basically air. Knauf (compressed wool) doesn't work too.

I've been to studios who are underground that used 2cm XPS under a 6cm slab and it worked out fine since XPS isn't elastic and it's much more dense.

Here is a thread Stuart showed me and I understood I had no need to float floors since I have mother earth as a damper in a zone where there is no heavy car traffic: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

Here is another cool thread explaining floors by Thomas from Northward Acoustics: http://prorecordingworkshop.lefora.com/ ... e2RKrSzJHg

One more thing, don't do anything without checking with construction engineers and or acoustic designers. (Forum's advice).

And another thing: don't believe a thing people who sell thermal insulation say, they don't have the acoustical knowledge on a level a studio needs.

If you can develop the area and have formed and placed concrete that will give you isolated slabs per room, then this would be a great thing. Since vibration travels faster thru dense material than not so dense you eliminate the path from room to room.

Obviously something like this has to be thought out and well planned. Electrical/audio wiring if needed from one room to the next has to be taken into how you do it and not re-couple the slabs with your conduit.

The select choice to damp a concrete slab is often sand on top of the packed and prepped Earth. This allows you to still have the damping required but with sand as a base you can remove any potential hard connections from the ground to the concrete slab.

You want to have a plan drawn up and have it run passed your local code persons as this can be a specific procedure in your neck of the woods. The room in a room that you are shooting for is a system, if you need that then do that. Otherwise there are options that do not require as much of a budget. A typical room might be sheathed with OSB that would not need sway braces since the framed walls would stand on their on, all things considered like length and height and added mass.

Your budget is going to be based on isolation requirements. You can start at 3X the cost of a custom built home in your area no matter what they are(isolation requirements).

Scavneck wrote:In my experience a slab on EPS is a really bad choice for a studio because EPS can't act as a damper since it's basically made of air.

Thanks Marko but I think we are talking about two different things...you are talking about floating a new slab on top of an existing one no? I'm looking into pouring a new slab foundation from scratch, and having the slabs of adjoining rooms (CR A and CR B for example) being decoupled. So no floating, just pouring different adjacent pads that are not connected.

xSpace wrote:If you can develop the area and have formed and placed concrete that will give you isolated slabs per room, then this would be a great thing. Since vibration travels faster thru dense material than not so dense you eliminate the path from room to room.

Obviously something like this has to be thought out and well planned. Electrical/audio wiring if needed from one room to the next has to be taken into how you do it and not re-couple the slabs with your conduit.

The select choice to damp a concrete slab is often sand on top of the packed and prepped Earth. This allows you to still have the damping required but with sand as a base you can remove any potential hard connections from the ground to the concrete slab.

You want to have a plan drawn up and have it run passed your local code persons as this can be a specific procedure in your neck of the woods. The room in a room that you are shooting for is a system, if you need that then do that. Otherwise there are options that do not require as much of a budget. A typical room might be sheathed with OSB that would not need sway braces since the framed walls would stand on their on, all things considered like length and height and added mass.

Your budget is going to be based on isolation requirements. You can start at 3X the cost of a custom built home in your area no matter what they are(isolation requirements).

Thanks Brien-

So you think using XPS or in some way trying to thermally insulate from the ground would compromise slab to slab transmission? Could there be sand (and obviously tamped earth etc) below the insulation? I'm not hoping the insulation adds to the TL, just to have it for it's actual thermal benefits. Which would clearly not be worthwhile if it compromised the isolation. I think the sway braces would be a good idea here in CO no matter what, the ground here heaves a lot. I have already started the dialog with the city.

Can fernco's be used to decouple conduit?

I know a guy in your part of the world that used insulated construction on his place. I will get back with you before the weekend. As to decoupling with fern cos I would have to see it. But if it modifies a rigid pipe to a damped and water proof pipe it should work.

The rule is run electrical wire high and audio wire low and do.not run them parallel within 2 feet of each other and to only cross at a 90 degree angle if it cannot be avoided.

Bear that in mind if you are thinking to run both electrical and audio wire low.

xSpace wrote:I know a guy in your part of the world that used insulated construction on his place. I will get back with you before the weekend. As to decoupling with fern cos I would have to see it. But if it modifies a rigid pipe to a damped and water proof pipe it should work.

The rule is run electrical wire high and audio wire low and do.not run them parallel within 2 feet of each other and to only cross at a 90 degree angle if it cannot be avoided.

Bear that in mind if you are thinking to run both electrical and audio wire low.

Great thanks, is it ICF by chance? and yeah the fernco are these things (I'm guessing there are other names for these)-

http://www.amazon.com/Fernco-P1056-44-4 ... B000BQQU52

So you can cut a section of the pipe and then put these over the gap and tighten the hose clamps.

Are there ballpark STC, and/or TL numbers that one can expect from one slab to an adjacent decoupled one?

Yes it is ICF...but I do not recall how the slap was prepped...may be interior radiating tube heat.

I think there is a better sleeve than the fernco, that may be too short and too ridgid.

"Are there ballpark STC, and/or TL numbers that one can expect from one slab to an adjacent decoupled one?"

Yes. Zero. That is the goal. The deciding factors that increase the TL will be the Earth and how the slab interacts with it, I.E. is it dense rock substrate or firm dirt, and also that decoupling area can maintain the levels from one slab to the next if it is not a decoupled type connector.

Well, come to find out he lives in PA...no where near you. Circumstances are most likely different as well since he has a high water table but a clay base.

Anyway, he did not use sand as was the thinking earlier. Reason being the ground has such a high water table the engineer was concerned with erosion of the sand, even if above the vapor barrier. But he did use tube type radiant heat.

He did, however, install a 1" thermal break below slab level.

I think the biggest thing at this point is to have determined what type of substrate you have. As best as
I can tell, Denver can have an issue with water but seemingly that is more accumulation than underground but there seems to be a thriving basement business.

So expansion joints in large slabs are fairly common.

Expansion joints in large slabs are common and typical for concrete. You can only place so much concrete so you have to either have a construction joint to control cracking or isolation joints to terminate the pour.

The geography suggests your ground is made up of sand already. So this could work to your benefit. At the end of the day, you should be able to develop multiple isolated slabs with thermal insulation. But the drainage requirements and how this structure is actually built may be the impediment.

Also one of the things that I saw in the build for the guy I mentioned earlier I didn't like as it pertains to isolation. Due to the water table in PA there was a requirement for the footers to be 42 inches wide. Then the slab was placed directly on top of the footer at the end most areas of the slab.

Short circuit and flanking path. But, that was a requirement to maintain the integrity of the structure, so I get it and would have done it as well.

I know I said a lot but not sure if this helps much at this point.

Thanks Brien-

Very helpful. So in a nutshell more packed soil or sand is better for damping a pad and crushed stone etc is worse, if that is the case that makes sense. The crushed stone is providing more of a flanking path...

There is a ton of construction in the area and I've been watching what they are doing for footings, i don't see any crushed stone, usually it looks like just damping/packing the soil that's already there. but I will pay more attention. There is a big 5 story unit going in down the street so it will be interesting to pay attention to what they are doing there.

I'm not sure if it would have any effect but we do have a well on the property, it's on a bit of a hill and the existing house on there built in 1942 hasn't had any really major settling issues (a few cracks in stucco...but nothing majorly out of square/plumb).

I'm not sure how crushed stone got into this conversation but I would think of crushed stone is a limp mass, kind of like sand only way bigger. If crushed stone is used usually it's because of a drainage issue or something to that effect. Sand is not the be all end all it is just a matter of decoupling hard substrate, like a granite that might be found in Tennessee, you know from the concrete.