Looking for input on insulation

[Tushar]

I am having insulation (Optima) blown into my exterior walls and wondering whether to insulate an interior wall as well.

Supposedly the material is not sound dampening but acts as a reasonably good sound barrier. Definately cuts down the air motion. I have a big room (38'x 19') with a hallway entrance along one of the long walls. The hallway has a bedroom and a bathroom along it's side and 3 more at it's end.

The question I have is whether it is useful to insulate the wall between the hallway with bedrooms and the big room. The bed rooms at the end of the hallway are more important (kids and our room) than the rooms adjacent to the great room (guest room and baths). I am trying to figure out whether better insulation that won't absorb sound will help SPLs for the sub but shoot high and low frequency sounds down the hallway or will it restrict the overall sound transmission.

[davef]

The question I have is whether it is useful to insulate the wall between the hallway with bedrooms and the big room. The bed rooms at the end of the hallway are more important (kids and our room) than the rooms adjacent to the great room (guest room and baths). I am trying to figure out whether better insulation that won't absorb sound will help SPLs for the sub but shoot high and low frequency sounds down the hallway or will it restrict the overall sound transmission.

I am not sure I follow you, insulation within the walls will have no effect on high-frequencies within the room.

[Tushar]

I was not very clear. I am having my exterior walls insulated with blown-in fiber-glass insulation. It was suggested to me that putting the same insulation into interior walls will help reduce sound transmission so people in bedrooms adjacent or near our home theatre will have an easier time sleeping during late night movie watching.

I was wondering whether people have experience with this type of insulation and if so their thoughts.

[sapo916]

I am building a wall soon to seal a room so I would also be curious.

[davef]

I was not very clear. I am having my exterior walls insulated with blown-in fiber-glass insulation. It was suggested to me that putting the same insulation into interior walls will help reduce sound transmission so people in bedrooms adjacent or near our home theatre will have an easier time sleeping during late night movie watching..

Yes --- insulation placed within your interior walls can be very beneficial in subduing the transfer of sound from room to room. However, I do not have any experience with the blown-in type of insulation so I can not comment on how effective it would be. Certainly it would be better than nothing at all -- but I strongly doubt it can compare with something like OC 705, which is very dense.

[Tushar]

Had the insulation installed.

From what I've read, it's not as good as OC 705 but it does significantly affect transmission through the walls. The noise I hear both from outside or between rooms is mainly from double-pane windows and doorways. The house is now very quiet during rush hour. I think once I add a solid core door, I can have a kids HT room right next to our main HT without too much noise transfer.

Unfortunately, sound doesn't have to bounce off too many surfaces to move down the hallway so the bedrooms at the end of the hall minimally benefit from the insulation.

For those looking at options, another thing my contractor suggested is something called Air Krete which is a pumped cementitious material that doesn't expand much and has very good thermal isolation and acoustical properties (like OC705 I think). However it was 3x as expensive as the blown-in fiberglass so I opted against it.

[davef]

Hi Tushar,

I am curious -- did you go with a local company or a nationwide firm? I have heard that prices vary considerably for this service and a customer of ours was asking me for a recommendation. Did you consider using cellulose?

[Tushar]

I went with a regional company here in Nor Cal ("West Coast Insulation") that a friend had previous experience with but I collected a few bids anyways since many places give free estimates. All bids were in a $200 range with similarly scope, similar calculated sq ft. One exception was a guy who was 2x higher than the rest. I didn't go with the lowest bid.

The company I went with also does a cellulose (which was approximately same cost as fiberglass for all exterior walls, might have been more expensive for small scope of work due to the equipment they use for that) and a non-expansive cementitous material called Air-Krete which was 3x more expensive but supposedly (1) safe enough to eat and (2) excellent for sound isolation.

I went with blown-in fiberglass because a colleague had used it and was very happy with the results. I didn't look into cellulose, though the limited I have read about it was very positive.