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Question Help with soffit insulation ( AVS Forum Dedicated Theater Design Construction )
Updated: 2010-07-24 08:35:19 (12)
Help with soffit insulation

Need some advice on how to insulate my soffit. It is VERY wide (40+ inches at some points, then it narrows down). The inside edge (closest to the wall) of main trunk is still at least 15-16" from the wall. I've framed it with 2x4 (and some ripped down to 2X2). THere is space between the outside edge of the trunk (closest to the room) and between the trunk and the bottom of the soffit.

I've managed to get SOME R19 insualation across the top of the trunk up in the joists, but not ALL joists are insulated this way. in some csaes, takesoffs for upstairs runs are in the way. So, how to insualte?

Here is the Bottom inside of the soffit:


Here is the botom outside of soffit:


Here is the outside sideview of the soffit:



Use the same soft stuff? I have a roll of R13 plus a lot of scraps and I'll have a pretty good aomount of the R13 24" wide stuff left. Solid foam panels? How much to put in the area bewtween the inside of the trunck and the wall...that's where all my wirirng is.

Any ideas on insulating would be greatly appreciated.

Answers: Help with soffit insulation ( AVS Forum Dedicated Theater Design Construction )
Help with soffit insulation


Ted White

Help with soffit insulation

AAAHHHHHhhhhhh (that's the sound of my mind at ease!)

tlogan6797

Help with soffit insulation

Quote:
Originally Posted by Ted White
Nope. Less isn't more. The point is that more isn't more, either.

Generally R19 is the way to go in larger framing members
I totally disagree.

Putting more in the joist just costs MORE money.

Johnsteph10

Help with soffit insulation

Nope. Less isn't more. The point is that more isn't more, either.

Generally R19 is the way to go in larger framing members

Ted White

Help with soffit insulation

NOW I know what to do and when to call it quits! Thanks for that.

So, as a mental exercise (because it's already done I REALLY don't want to go back and do it again), what's yout take on this case?

The joists in the theater area are 2X8 at 10"oc. I used the same R19 as I did in the higher part of the room which is 2X10 at 16"oc. So the 2X10 would be at that 40-60% cavity fill level, the 2X8 would be more like 75-80%. Would R13 in the 2x8s perform any better?

tlogan6797

Help with soffit insulation

Thanks! Will be this weekend's project!

tlogan6797

Help with soffit insulation

Keep us posted!

As a rough guide, if you had perhaps 40% to 60% of the cavity with fluffy stuff, you'd be as good as it could get.

I'm making a rough correlation to joist cavity test data. A 50% filled joist cavity (R19) gets you to about peak performance (from a practical perspective), so I'm venturing that a very similar situation would exist with the soffit.

Ted White

Help with soffit insulation

The good news is that you have a large air cavity. You want insulation within the cavity so don't worry too much about gettingsulation all around the tight spaces

You could work a layer of R19 in that space to the right. Or take scrap insulation and add in there also.

Ted White

Help with soffit insulation

Insulation doesn't seem as itchy as it used to. Am I getting used to it or has manufacturing changed?

Anyway, more specific questions....How much insulation do I need to add to the right side of the trunk in the first picture? Is one layer of R19 sufficient? Do I need to add R19 to the josits above that same area if I just insulate the bottom? Does it matter if the cables sit above or below the insulation?

TIA,
Tom

tlogan6797

Help with soffit insulation

Yeppers, just use all of your scraps. Time to invest in a mask if you start tearing up a bunch of insulation. Your lungs will thank you.

Cathan

Help with soffit insulation

You can use the fiberglass. Just make sure that it is not packed in, especially next to that duct. Otherwise the insulation will conduct vibration. Tear pieces thin if necessary

Ted White

Help with soffit insulation

Thanks for all the advice!

Update and pics here:

http://www.avsforum.com/avs-vb/showt...7#post16610717

tlogan6797

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