Basement - Insulation size/thickness

[JimmyD]

Hello All, I'm in the process of finishing my basement. The ceiling is (will be) a drop ceiling. The rafters above the drop ceiling don't have any insulation in them. The basement is where my home theater will be, so sound insulation is of high importance. My local hardware store carries Johns Mansville insulation, and I decided to get kraft faced insulation for ease of installation. I was wondering what thickness of insulation to buy. The rafters are 9 inches deep (and 15 inches wide). The two thickness of insulation I was looking at are 8 1/4 and 10 1/4. I didn't know if it was better to go with the 8 1/4 and have a small gap or go with the 10 1/4 and compress it a bit when I install it. Here's the brochure for the insulation if that helps:

Also, I live in South Dakota, if that makes any difference.

Thanks.

Jim

[Joseph Meehan]

. Also, I live in South Dakota, if that makes any difference.

If you want sound insulation, I suggest you don't bother trying to make do with heat insulation.

Check out:

In general you want to block air exchange. Air caries sound very well. (Try opening your car's window as a train is going by.)

Next you want weight. Heavy things (drywall lead sheets etc.) block sound well.

You also want to prevent any direct solid connections. Stagger wall studs or use special isolation devices to keep the sound from traveling through the wall (remember the two cans on a string (well wire actuarially worked) you want to break the wire).

Filling in wall cavities with sound absorbing materials (accustical fiberglass bats) will do a little.

Point source control (special absorption material) at the source of the sound will also help.

[JimmyD]

[Edwin Pawlowski]

Why? I know it is needed in the wall, but why in the ceiling since the basement is a livable space?

[JimmyD]

Crud, I dunno...I'm a self-admitted dummy when it comes to this stuff, that's why I ask. I guess I was thinking: Hot air rises, cold air settles, so I'll install insulation in the ceiling to keep all the warm air from rising to the upstairs and all the cool air from settling in the basement, thus keeping the temp of the two areas similar. Am I flawed somewhere in my thinking.

Thanks.

Edw> > Thanks for the info. I checked out the site and will try and implement

[Joseph Meehan]

Don't worry. Any heat you loose as it rises goes into your living area, so it needs less heat. The normal floor is quite sufficient to maintain any normal difference between the two floors.

[tgdenning]

You should think about temperature and moisture differences between the two areas. The kraft paper acts as a vapor barrier, so if the basement is colder than the upstairs, moisture can condense in the insulation. Maybe someone with more experience in your area can give you some idea of common practices.

-tg

. Also, I live in South Dakota, if that makes any difference.

[Goedjn]

There are really only four tricks to limiting sound transfer:

Closing off air gaps, decoupling surfaces, weight, and getting rid of large flat reflective surfaces.

So you start by spraying a thin layer of urethane foam on the underside of the floor. This seals any open air passages, adds a tiny but of mass, and creates a bumpitty surface to break up sound. Then you stuff some asphalt roll roofing into each rafter bay, holding it up with wire. After that, if you have the headroom, you stick resilient-channel crosswise to the joists (cheap, but takes a lot of space) or add 2x6 joists between the existing floor-joists, only with the bottom edges 3/8" lower, and attach 1 layer of homasote 440, and one layer of

1/2" sheetrock to that.

If, for some reason, you must use a suspended ceiling, invest in a great many extension springs, (tearing apart certain kinds of bed is a good way to find those) And cut up a bunch more squares of that asphalt roll-roofing to put on top of the tiles. to add weight. Use the heaviest metal gridwork you can find.

If you have ceiling-mounted light fixtures, move them to the walls, since they form a pathway right past your sound-deadening structure.

Remember that you are no longer going to be able to hear things like telephones, fire-alarms, and doorbells through the floor, so you'll want some sort of repeater.

--Goedjn

[tksirius]

I put in encapsulated r14 insulation in there. (walls and ceiling)

The sound deadening worked out ok. Its not like someone can scream down there and not be heard, but you dont hear much upstairs when the tv or stereo is on.

Tom

JimmyD wrote:

. Also, I live in South Dakota, if that makes any difference.