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Home > Forums > Materials Engineers > Materials > Wood design and engineering Forum

Blown Insulation Specific Weight

Read More Threads Like This One

RFreund (Structural)

13 Aug 12 21:38

Most attics around here (Midwest USA) are insulated with blown cellulose (I believe) insulation. Has anyone come across an average density or average thickness/weight used in homes?
Or how about the insulation that has a 'paper' side and the other-side has the fiberglass insulation.

Thanks!

EIT
www.HowToEngineer.com

JAE (Structural)

13 Aug 12 22:08

Pretty light - I'd only use 2 psf or so. That might be heavy.

Ron (Structural)

13 Aug 12 23:04

JAE is right. It is about 0.1 to 0.2 psf per inch of thickness, as long as it hasn't compressed with time.

Fiberglass batt insulation is about 1/2 those values.

RFreund (Structural)

14 Aug 12 8:21

Thanks guys.

EIT
www.HowToEngineer.com

MiketheEngineer (Structural)

14 Aug 12 10:51

I usually just ignore it IF I spec 10 psf for ceiling load which would include drywall, insulation, lights, etc. That is typical around here.....

msquared48 (Structural)

18 Aug 12 0:40

.3 psf per inch of thickness is what I use.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

MiketheEngineer (Structural)

29 Aug 12 13:10

Call the mfg

MikeHalloran (Mechanical)

7 Sep 12 12:20

Blown cellulose, layered at least as deep as the rafters as is usual in SoFla, gets pretty heavy when it gets wet, like after a hurricane has peeled away your shingles. Fiberglass doesn't absorb and hold water to the same extent.

Maybe that's not a legitimate design condition, but it does happen.

Mike Halloran
Pembroke Pines, FL, USA

msquared48 (Structural)

7 Sep 12 15:04

I think you guys in Florida need to design airtight houses so that just before a Hurricane hits, you can suck all the air out and keep the shingles tight to the roof membrane. Just a thought...

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

MikeHalloran (Mechanical)

7 Sep 12 22:19

As part of an ad-hoc repair team after Andrew, I inspected a condo's roof where the membrane had been lifted, mostly intact, a couple of feet above its plywood support, and settled down, mostly intact but with a few leaky wrinkles.

After Wilma, I intend to ride out future hurricanes in some other state, say Idaho.

Mike Halloran
Pembroke Pines, FL, USA

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