RC in a home studio - construction question

A

adam

New member
Summary: How to you take into account the airspace between the interior wall and exterior wall of an old house?

Long Story:
I have been a member of this board for years now and have read up on lots and lots of the sound treatment and attenuation techniques and the related construction ideas. I have recently purchased an old house. It is about 50% updated (a/c, kitchen, 1 bath, etc.). The plan has been to do some renovations, starting off small and waiting on some of the bigger stuff (incl. studio). One of the projects I am working on is renovating the downstairs bathroom.

After stipping it down to the studs halfway up the wall (where tile had been) I noticed that the exterior wall construction (inside out) was 2'inches plaster, lathe, ~4" air space, wood sheathing, stucco). I had suspected that the walls were not insulated as the house is moderately drafty and the heating bills were HIGH.

Now I have been thinking about insulating this air space (expanding foam perhaps as I don't want to rip down every plaster wall - need to research more) to improve heating/cooling efficiency (windows are original single pane - big source of heat loss too, and the inefficient boiler -- those are whole nother story!). I also began to think about it as way to attenuate the sound (and block out street noise-mostly car 'wooshing') in the upstairs bedroom studio I am planning. I am currently using 1 room 'as is' - meaning plaster has lots of reflections, and more than I would like sound escaping outside.

Given the interior/exterior air pocket, would I treat this as the RC? I have read that you don't want 2 air spaces. But also obviously the Interior/Exterior walls are coupled. How do I reconcile this? Insulate+ adding mass to interior wall?

I am a few months away from any serious designing and work on this, but FYI the plan was to treat 1 room:
*Moderately treated (insulate, caulking, new windows? for attentuation, then panels etc. for treatment, but without hampering too much the 'sale-ability')
*Currently I don't record drums at home, and if I did it would be during the day. The goal would be to dampen the sound for the neighbors and rest of the house (usually tube amps). I have other methods to help (DIs, reamps, etc.) so it doesn't have to be the illusive totally soundproof envirnoment.
*I like recording in the house as there are a number of interesting spaces - bathrooms, closets, halls, foyers etc. but if I ever need/want/can-afford more I have room to build an outbuilding.
*I am officially babbling now
 
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"*I am officially babbling now" -

This is how you know you've finally started to understand about acoustics :=)

I'm working on a reference for soundproofing existing construction, but it's nowhere finished as yet - when I get there, (or at least close) I'll post it on John Sayers' site under Construction.

Basically, if you want SERIOUS sound isolation you need to remove the inner wallboard and beef up the outer paneling some, then either put up Resilient Channel on the studs and at least two layers of wallboard, or build a separate frame inside the existing one and panel that.

Check out John's site for more on this, I don't remember which topics I covered this type of construction on at the moment - Here is the Construction forum, maybe search for "existing" , or "existing wall"??

http://www.johnlsayers.com/phpBB2/viewforum.php?f=2

I'll try to get back on this in a day or two... Steve
 
thanks for the reply steve! i went and read some of the posts on jon's site.

I guess I was trying to ask what could be done without removing the plaster (it it original plaster as opposed to wallboard/drywall). There is a chance I would have to tear it out anyway given that there are layers of wallpaper and paint - so it depends on the state of the underlying plaster.

My hope was to add some sort of blown in insulation, and/or add another layer to the existing interior wall, while also insulating and plywooding the attic, coming up with a window/door solution etc. Would this be all for naught? The main objective is to block out traffic noise and attenutating loud amps inside/outside the house.

This room may end up being temporary as a studio (if we have kids), and then I would go full out on a new construction outbuilding to optimize sound characteristics. I would hate to invest all that time and $ into a room that ends up being a kids room ;)
 
Blown in cellulose insulation can improve sound isolation by several dB, around 6-8 dB if I remember correctly - adding another layer on top will also help, usually about 4 dB for one extra layer of 5/8 sheet rock added to ONE side of the wall, and if it's an interior wall and you add a layer of 5/8 rock to EACH side you gain about 6 dB total. This is assuming 2.4 studs, and only calculating for either one or two layers of 5/8 sheet rock on either side. I don't have software at the moment that will do real plaster, even if we DID know the exact thickness.

Removing the plaster on one side and replacing it with not only two layers of sheet rock but also adding Resilient channel on the studs before putting up the panels, would raise the STC of the wall by about 8-9 dB.

Besides, why would you NOT want your kids' room to be sound proof?? :=) Steve
 
Adam,

I would venture a guess that when you get inside your walls that they are bone dry and nice clean framing.

The reason for this is that they breathe feely - and due to this the moisture in the home never reaches dew point when passing from the home to the putside - even in winter.

If you add blown insulation to your walls without dealing with a proper vapor barrier on the inside face - you will (please note that i said will - and not "may") completely destroy the structure within the walls.

I worked on a home - it was a fire restoration project - that had blown celulose added for insulation - the insulation was done about 5 years before the fire - and the only thing holding the house from collapsing was the corner posts - the stairwell walls and the newer addition on the rear of the home - all the studs in the body of the walls we rotted about 2' above the plate - if this house wasn't ballon framed - with a wrap around deck on the outside - you could have taken the walls and swung them freely (which is what i did once i pulled the deck off - much to my surprise.

It is critical that any insulated wall have a proper vapor barrier to stop the warm moist air within from condensing on the inner face of the exterior sheathing.

The best way to do that is with a poly-vapor barrier applied to the inside face of the studs after insulation and prior to drywall.

However - if you do choose to go with the blown insulation - there are vapor barrier paints that can be used effectively to acheive the same thing.

HOWEVER - they need to be repainted periodically - and i wuld not reccomend then if there is going to be a room within a room situation.

Good luck,

Rod
 
Rod, thanks for your comments. I have been grappling with the vapor barrier issue. As I mentioned I first confirmed the exterior wall contruction while working on a bathroom downstairs. I haven't done any insulation there yet as I was trying to get an answer to the vapor barrier issue.

I have read about slow expanding foam that supposedly lets the house breathe and doesn't hold moisture. A good solution? And I wonder about its STC and R characteristics.

Thanks again.
 
adam said:
I have read about slow expanding foam that supposedly lets the house breathe and doesn't hold moisture. A good solution? And I wonder about its STC and R characteristics.
Click to expand...


Adam,

R Values are excellent - STC values are garbage.

The fact that it lets the house breathe suggests to me that the claim they make that it shouldn't require a vapor barrier is bulls**t. Most states that require a vaport barrier do with this product as well.

When it's used inside of an STC rated wall assembly it does quite well - but only if it's trimmed back so as to not touch the faces of both sheets of drywall - when it touches both surfaces - it's properties create a rigid bridge that then acts as a sound transmitter rather than an isolator.

It weould not be possible for you to trims this back without removing the plaster - and if you remove the plaster you don't need it - so it's a catch 22 for you with this material.

Rod
 
Rod, thanks for watchin' my back (as usual) - As you know, I sometimes get so caught up in the acoustic side of things, I don't give quite enough attention to the more practical (but I AM getting better about that, usually :=) Steve
 
yes, thanks to both of you! I have been doing more research and have found that they do often recommend a vapor barrier/retardant at times for foam. Perhaps a spray? The last thing I want to do is undermine the construction of my house, which has been standing for 85 years. I would however like to improve the energy and sound efficiency.

Perhaps I will start with treating the windows and attic first for saving energy and see how that does, and get some estimates on the foam (incl. seeing if there is a spray barrier that could be used). I did read in one article how the foam effectively joins the opposite wall surfaces. I read this as a nightmare for STC. Though perhaps it would fix the potential problem of 2 RC's if I build a room in room.

For sound purposes, I guess I am somewhat back at the start. Steve, interestingly in looking over at your forum I found a post or two on those www.soundproofingwindows.com products. I am sure that my windows are a main culprit od sound (and energy) loss. these may be the ticket and will sure be better than storms (looks nicer, perhaps more efficient, certainly quieter) or replacement windows (expensive, removed some of the home's character, perhaps not as effective).
 
Know what you mean, Adam - in some cases, the cost of (isolation quality) glass sure makes video gear seem like a good idea... Steve
 
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