Interior Wall Insulation


Senior Member
All this talk of new construction got me wondering... is it common to use insulation inside interior walls these days? Seems like you would want it to soundproof a Home Theater room at least. Bedrooms would also benefit from some sound deadening. Is this commonly done?
Depends on the quality of your builder (and the price of the house). Your higher end houses now insulate the bedrooms and bathrooms (bedrooms for noise coming in, and bathrooms for noise coming out :lol: )
Ah yes. Forgot that one. Also forgot about around and above the furnace room in houses with finished basements
The "high end" custom homes here have all of their walls insulated. The latest is to place a mesh over the studs and use this "filler" material over the traditional asbestos sheet insulation. (My friend just had this done to his house he is currently building).
We plan on insulating serveral rooms for both sound and climate control. Doing the entire interior of the house seems like overkill but we'll see. The lab / server room / wiring closet will be its own HVAC zone so will be insulated for both noise and climate control. Home theater, master bedroom, laundry, etc. are all good candidates as ell.

Also, it seems like I read somewhere that the icynene foam insulation is the best for soundproofing so we'll likely use that in these applications. Blown in cellulose everywhere else.
upstatemike said:
BraveSirRobbin said:
... and use this "filler" material over the traditional asbestos sheet insulation...
I didn't see the final product, but its sort of like "peanuts" and I'm not sure if it is some sort of stryofoam or other insulating material.

I will try to find some additional details and see if he has a pic. (If he hasn't taken one already we are to late as drywall just got installed last week).
In my home I built the Theater room into the core plans. I used 9 inch thick foam form walls for the below grade exterior walls. I also extended these walls around the perimeter of the theater room. After the forms are in place (like lego blocks), they are trimmed at the top for level (easy) and then filled with concrete that creates a "mesh" of concrete and foam.

Above the foam wall (the blocking) is SilentTruss system that replaces conventional 2X10 floor joists. But the name Silent is only in regards to walking on the floor above from squeeks. As a material it is very thin and passes noise quite readily from room to room. So, the answer was to use spray foam on all blocking on exterior walls (great cold insulator) and to use it on interior walls for noise blockage.

Now, for the ceiling. In my theater room, I put 8 inches of fiberglass roll insulation between the ceiling joists (floor joists for the room above). Below that I have a track ceiling system where I have handmade coffered ceiling tiles inserted. The ceiling is probably the weak sound insulation component in my system. If I were to do it again, I probably would have put some heavy (really heavy) vinyl material stapled to the bottom of the ceiling joists that is made for this purpose as another sound insulation layer. This still would allow access to plumbing / electrical above if needed to be peeled down (unlike drywall).

In the rest of the lower floors, the ceiling is drywall. The drywall is mounted to "Z" strips where the screws holding up the drywall goes into one side of the metal Z strip, and the other side is then screwed to the ceiling joists. This allows the drywall to be sound insulated from the joists minimizing sound transition. You can also use these Z strips of walls. They take up about 1/4 inch of space. For partition walls, you can also stagger space 2x4 studs every other so that the inside drywall and the other side drywall are mounted on different studs for sound insulation. Effective wall thickness is then typically same as 2x6 wall. I did this for walls that had to hide large steel posts that support the roof structure and had to be 2x6 anyway.

All interiour walls (which because my house is post and beam construction and therefore has few interiour walls) are filled with fiberglass insulation for sound. All floors / ceilings have fiberglass as well.

Doors: In my theater room, I used an exteriour grade door that included a full frame and gasket system. The door (steel) was also filled with pourable foam to further insulate it. Makes for a very solid door with minimal sound leakage.

Exteriour walls are 2x6 and cellulose filled. Excellent for both it's insulation and sound deading properties. I have several walls that are 2x4 that are inbetween window banks. These are insulated with spray foam for its higher R value and the structural stiffening that it provides.

Obviosly insulation for exteriour walls makes economic sense as well as sound insulating reasons. On the interiour, it makes for a more pleasant living space.
Our house has insulated interior walls and it makes it a pain in the bottom to run new wiring.
For serious soundproofing or control treatments, you can pick up a book on building recording studios or other sound-deadening systems. You can also buy various acoustic foam panels and blocks at online music stores, such as . Note that soundproofing is different than tuning a room for best listening.

Regular fiberglass insulation does little to control sound when compared to acoustic treatment systems. In a standard 2x4 studded 5/8" drywall both sides wall with the top and bottom plates insulated with a 1/2" sponge rubber shield, adding 3.5" of fiberglass insulation may net you about 5 STL points compared to a non-insulated wall. But every bit helps!

I think some of the newer spray-in foams work to better treat acoustic issues, as well as better seal the wall/floor/ceiling, than standard fiberglass insulation. IMO, by far the best investment in tuning any listening room would be to reduce or eliminate direct sound reflections by applying absorbers on the reflective surfaces, as opposed to sound proofing.

The book entitled "Sound Studio Construction on a Budget" by F. Alton Everest has a couple chapters devoted to home theater and listening rooms.

Another good book with actual drawings of the various ways to make walls and ceilings to reduce sound transmission (the STL rating), is "Building A Recording Studio" by Jeff Cooper.

Each book carries a list price of $30.
Rupp brings up a good point. If you think cellulose / fiberglass is tough to route wires after the fact, it's impossible with spray foam (unless you cut drywall and foam to make slots).

Huggy also brings up a point that in my theater room (the one with all foam walls), I streched acoustic cloth over a wood frame as the interiour surface. This had the advantage of a very nice custom look, as well as using the foam surface to deaden sound reflection for a slightly audio dead room (no reflections). Not to mention is was a lot nicer to work with than drywall (which I hate to do).
I was just thinking in terms of insulation but I suppose if you were really serious about soundproofing there are a lot of other techniques you can consider. My favorite would be to construct the media room so it is essentially suspended in it's own space without any real contact with the rest of the house. You could have a double set of "airlock" doors at the entrance and pump all the air out of the space between the suspended room and the rest of the house so no sound could be transmitted. The method of suspension must also be soundproof so I suggest a set of magnets that work similiar to the ones on a maglev train. This has the added advantage that you can tie your subwoofer into the suspension magnet circuit for some really awesome "room shaking" effects.
Weren't you the one who recently questioned using a control system for your media room(s)? So how the heck are you going to monitor the polarity of the maglev train suspension system?
DavidL said:
Weren't you the one who recently questioned using a control system for your media room(s)? So how the heck are you going to monitor the polarity of the maglev train suspension system?
I questioned the value of automating the media equipment, not the room that contains it.