# Is sound isolation necessary under a garage?



## mrshanes (Mar 3, 2010)

We built a new home about a year ago and used superior walls for our foundation. During construction, my builder introduced us to a product called insul-deck (learn about it here: http://www.insul-deck.org/product.htm) to use for our garage floor (on the main level). This would allow us to have an insulated space under our garage with no weight bearing supports required. I jumped on it right away knowing it would allow me to construct a home theater under our garage.

Now onto my questions. The sides of the theater will be insulated 8" thick concrete superior walls and the ceiling is the insulated insul-deck floor. The ceiling has 3 inches of foam with 9 inches of concrete on top of that. Aside from building a insulated stagger stud or double wall to form the fourth wall, do I really need to do any other type of sound proofing of this room?

I'll try to attach some pictures to help clarify what I'm talking about.


----------



## bpape (Sep 14, 2006)

Just from the standpoint of having insulated drywall cavities, that would be an improvement in terms of the walls giving a little and providing a small amount of bass absorption as opposed to a concrete wall that's not going to give at all. Also, the rigid foam insulation ,while great for thermal isolation, will yield basically zero in terms of acoustic benefit.

Bryan


----------



## mrshanes (Mar 3, 2010)

Trying again with pictures...


----------



## mrshanes (Mar 3, 2010)

bpape said:


> Just from the standpoint of having insulated drywall cavities, that would be an improvement in terms of the walls giving a little and providing a small amount of bass absorption as opposed to a concrete wall that's not going to give at all. Also, the rigid foam insulation ,while great for thermal isolation, will yield basically zero in terms of acoustic benefit.
> 
> Bryan


I realize I will still need plenty of acoustic treatments within the room, but I'm really asking about how these walls and ceiling will help with keeping unwanted noise out and the theater noise in from the rest of the house.


----------



## SAC (Dec 3, 2009)

Is additional isolation necessary?

Regardless of what material may hare been utilized in fabricating a surface, there is much more to proper isolation simply as there are a myriad more ways for sound to travel from space to space - namely by vectors known collectively as flanking paths.

The simplest and most conclusive determinant is to measure. Play a full range sound source (pink noise) at a measured gain in the space and then measure the same source in the adjoining space. The difference is the amount if isolation provided by the structure. 

That will provide you with the quantified amount of isolation. Now determine the maximum sound level that will be experienced in the HT space and determine the maximum gain level that is 'permitted' in the adjoining area. If your measured delta is equal or greater than the calculated difference in maximum levels, you're good. If not, you have more work to do in determining the specific paths of ingress - most likely in the flanking paths, and addressing them. 


Owens Cornng Acoustical Wall Insulation Design Guide 
(http://www.owenscorning.com/worldwide/admin/tempupload/canada/30011340.pdf)

NRC (National Research Council) docs (Choose the docs that are appropriate to the construction type):

Gypsum Board Walls: Transmission Loss Data
By Halliwell, R.E.; Nightingale, T.R.T.; Warnock, A.C.C.; Birta, J.A.
www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir761/ir761.pdf

Sound Transmission Loss Through Concrete and Concrete Masonry Walls
by Albert Litvin and Harold W. Belliston
www.cement.org/bookstore/profile.asp?itemid=RD066

Sound Transmission Loss of Masonry Walls
by Warnock and Monk
www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/brn/brn217/brn217.pdf

Sound Transmission Loss Through Drywall and Block Walls
by Warnock
www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir586/ir586.pdf



Flanking information:

Controlling Interoffice Sound Transmission Through a Suspended Ceiling
by R.E. Halliwell and J.D. Quirt
www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc33097/nrcc33097.pdf

System Details That Work (Leaks and Flanking)
by David Quirt
www.nrc-cnrc.gc.ca/obj/irc/doc/leaks-flanking.pdf

Guide for flanking sound transmission in wood framed construction - airborne sources
by Nightingale, T.; Quirt, J. D.; King, F. 
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc49468/nrcc49468.pdf

Airborne Sound Insulation in Multi-Family Buildings
by J.D. Quirt and T.R.T. Nightingale
http://www.nrc-cnrc.gc.ca/obj/irc/doc/ctu-n66_eng.pdf


----------



## bpape (Sep 14, 2006)

What I'm saying is that you'll need to fill the cavities with insulation and not count on just the foam board which will do little to nothing. This goes for the walls and the ceiling prior to putting up drywall. 

Also understand that the way this is built, you're tying the drywall directly to supporting members of the upper (and balance) of the structure as a vibration path albeit not a terribly efficient one and being under the garage, farther from places where you 'd be more concerned in terms of sound getting out.

Bryan


----------

