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Old 09-10-2012, 08:30 AM   #1
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Attic Insulation


I recently purchased a 1965-built home and found that there is only about 4" of insulation in the ceiling.

It's seems easy enough to add insulation where no attic floor currently exists, but I'm wondering what to do underneath the floor boards.

The height of the floor itself is only about 4", so if I replace the insulation under the boards, it would be very compressed. Since this would reduce its effectiveness, would it be worth going through the trouble, or should I just work on the areas that wouldn't be compressed?

I guess I'm really asking, is 15" of compressed insulation better than 4" of non-compressed insulation?

For what it's worth, the home is heated with oil, so it can get very expensive. I'd like to be as energy efficient as possible.

Thanks!


Last edited by panorama; 09-10-2012 at 08:33 AM.
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Old 09-10-2012, 08:42 AM   #2
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Attic Insulation


Compressed insulation is useless.
Are these trusses or stick built joist and rafters?
The best way would be to remove the boards, sister wider 2 X's, add insulation then but the boards back in place.
Why are the boards even there?
2 X 4 bottom cords or joist are no where close to being able to support a load, such as using the area for storage.

Do you already have soffit vents, a ridge vent, baffles to keep added insulation from blocking the soffit vents.
You also need to air seal the attic before insulation. Just means sealing up any place inside air can get into the attic. Around ceiling fixtures, any place wires or plumbing go through the top plates.

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Old 09-10-2012, 09:21 AM   #3
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Compressed fiberglass is worthless as an insulation.

Compressed cellulose is just fine.

Best thing for and attic is not to be used as a storage location. That being the case, remove the floor boards, air seal, and blow in loose fill to 14-15" and you are good.
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Old 09-10-2012, 10:11 AM   #4
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Attic Insulation


I guess I have to learn a lot more about my attic. I'm a first time homeowner, so I'm kind of learning everything as I go along.

To be honest, I'm not sure how it's built, but I believe it's with trusses. I'll have to double check.

So, are you saying that I should "stack" another layer of joists so that it is twice as high?

The boards are there for storage, I suppose. I don't have much up there right now, but did plan on using it for storage...I guess that's not a good idea based on your comment.

I know that there are ridge and soffit vents, and I'm pretty sure there are baffles...I'll have to double check that as well.
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Old 09-10-2012, 10:15 AM   #5
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Quote:
Originally Posted by Windows on Wash View Post
Compressed fiberglass is worthless as an insulation.

Compressed cellulose is just fine.

Best thing for and attic is not to be used as a storage location. That being the case, remove the floor boards, air seal, and blow in loose fill to 14-15" and you are good.

If I remove the floor boards, is there any benefit to blowing in loose fill vs. laying down rolls?
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Old 09-10-2012, 11:35 AM   #6
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No point in dense packing once the boards are off.

You need something to dense pack against.
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Old 09-10-2012, 06:16 PM   #7
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"Compressed insulation is useless." and "Compressed fiberglass is worthless as an insulation."---- Not really.

Fiberglass batts (with the same amount of material) at 9-1/2"; R-30 (0.57#c/ft. density) are compressed to 7-1/4"; R-26 (0.7#c/ft. density) further compressed to 3-1/2"; R-15 (1.4#c/ft. density).

Fiberglass batts (with the same amount of material) at 6-1/4"; R-19 (0.55#c/ft. density) is compressed to 3-1/2"; R-13 (1.0#c/ft. density).

As f.g. is compressed the density/R-value per inch increase as does the air-movement resistance. The over-all R-value decreases with the total existing amount, but not it's value as an insulation. It actually improves by slowing drafts from going right through it (wind-washing from soffit venting).

R-30 = R-3.1 per inch; R-26 = R-3.7 per in.; R-15 = R-4.3 per in..
R-19 = R-3 per inch; R-13 = R-3.7 per in. The R-value numbers get bigger as the same amount of material is compressed. Just now you have less R-value per total thickness (but more per inch).

Blown-in cellulose gives the "most bang for the buck", it slows wind-washing if applied at enough density. http://michaelbluejay.com/electricity/insulation.html

Air-seal the attic first, as WoW said already, this is imperative; http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

Your 1965 batts are probably R-9, cover them with new insulation after air-sealing, they may flatten out to a new 1" thick form at 1.75#c/ft (a good thing). Compress them to 7#c/ft. and you will have a good sound barrier, LOL; http://www.owenscorning.com/comminsu...s700Series.pdf

Lift them carefully and inspect to help you find the air leaks from below; http://www.finehomebuilding.com/PDF/Free/021105092.pdf

More info I previously gathered, if interested: The "biggest loser" in fiberglass insulation....

Gary
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Old 09-10-2012, 09:36 PM   #8
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Gary,

I was was referring to blown in fiberglass in this case but I am intrigued by your data. I have followed you posting on high density batts and agree wholeheartedly.

Do you have some data on blown in fiberglass. While in theory, the numbers should translate the same, why do so few dense pack with fiberglass?

There must be a reason.

Reading up...

Last edited by Windows on Wash; 09-10-2012 at 09:40 PM.
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Old 09-11-2012, 08:04 AM   #9
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Attic Insulation


Thanks for all the great info everyone. I did a quick check of the attic last night and already see a few opportunites to seal up air leaks.

My plan is to get started on sealing leaks up this weekend. I'm still not sure what type of insulation to add and how to address the issue with the floor boards, but I'll start reading up on some of the info provided by Gary. It turns out that the AC unit is sitting on one of the boards, so the area underneath won't be easily accessible.

It looks like this will be a bigger project than I anticipated, but I'm looking forward to being a little more energy efficient.
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Old 09-11-2012, 08:49 AM   #10
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You must, must, must air seal.

Not air sealing is only gets you less than 50% of the performance improvements (rough averages).

Gotta stop the air leaks. Your home will thank you and so will your wallet.
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Old 09-11-2012, 09:07 AM   #11
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Attic Insulation


Quote:
Originally Posted by Windows on Wash View Post
You must, must, must air seal.

Not air sealing is only gets you less than 50% of the performance improvements (rough averages).

Gotta stop the air leaks. Your home will thank you and so will your wallet.
Yes, maybe my last post wasn't very clear. I did a lot of reading on air sealing last night after reading your comments and will be making this the number one priority. I won't rush to add any insulation until I've thoroughly gone through the attic and taken care of the air leaks.

That being said, I plan on identifying leaks through a combination of visual inspection and by using this Thermal Leak Detector from Amazon.

I will be sealing cracks with Dow Great Stuff Pro.
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Old 09-11-2012, 03:41 PM   #12
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Attic Insulation


Happy Hunting.

The IR thermometer is a fun gadget but largely unnecessary here. You will see where the leaks were and the research you have already done will tell you where the historical leaks are.

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