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Bruce Koch
08-24-2009, 8:48 PM
My son is building a new house six miles from the Canadian border in Minnesota. It has been down to a balmy -40 a few times. He has been pricing insulation for the attic and cellulose costs about half of fiberglass. Is it worth the extra cost? They say R 60 or about 20 some inches deep

Thanks,Bruce

Scott T Smith
08-24-2009, 10:53 PM
If he really wants great insulation, have him check into having spray foam installed. It is much more effective than either cellulose or fiberglass (albeit more expensive).

Karl Brogger
08-24-2009, 11:37 PM
Another vote for spray foam, all the way around its the best way to go.

-40*F is nothing for northern MN, I live in southern Minnesota and it can reach that pretty easily here.

Alan Trout
08-25-2009, 12:25 AM
Out of those two fiberglass without question. If it is an option formaldehyde free fiberglass is the best.

Good Luck

Alan

Chris Damm
08-25-2009, 7:22 AM
Just remember that moisture in the air cuts the R value of fiberglass in half. It is worth going with foam. You only pay for it once!

David G Baker
08-25-2009, 9:49 AM
Another vote for foam especially with the temps in your area.

Cliff Rohrabacher
08-25-2009, 12:03 PM
Foam is best plus it offends the bugs so they don't get at the lumber so easy - at least not from inside.

I'd not go with Cellulose because I don't trust it's ability to shrug off moisture. The instructions for Cellulose requires a vapor barrier. Great what does the vapor barrier do about ambient humidity? Not a thing. Moist air will get in everywhere and cellulose will retain and trap it way far better than glass will. Glass is inert.

Ben Hatcher
08-25-2009, 3:07 PM
With temperatures that low humidity is not an issue. I prefer fiberglass as it seems to compact less and doesn't turn into a powdery mess like cellulose can.

Doug Swanson
08-26-2009, 3:28 PM
Just remember that moisture in the air cuts the R value of fiberglass in half. It is worth going with foam. You only pay for it once!

Why not both?...Here is a theory I've been kicking around awhile...Fiberglass doesn't settle like cellulose. However because of what you said above it does lose some of it's Rvalue...So my theory is first put down blown fiberglass to X rvalue...then top it off (2-3 inches) of cellulose...as the cellulose settles it acts as sort of a cap on the fiberglass...

It's just a theory I was thinking of...others may have some good reasons why you shouldn't do that.

thanks
Doug

Dick Strauss
08-28-2009, 12:20 AM
I'd go with cellulose over fibergalss because cellulose increases in r-value with a larger temperature difference between inside and outside. In areas like Minnesota with very cold winters, this can mean that fiberglass' r-value decreases to only 50% of its rated value while the r-value for cellulose increases by 20%.
http://www.foam-tech.com/theory/rvaluedrift.htm

Cellulose also blocks air infiltration much better than fiberglass (35-40% better).
http://rvalue.net/page5.html

Closed-cell foam is the gold standard but is more expensive. It gives the best r-value with least drift for temperature and wind. During construction will be the most cost effective time to install foam if it is in your son's price range.

FYI-I was quoted $2.15/sq ft for the less expensive open-cell foam by Seal-Tech as a retrofit. This translated to $8000 for an 1800 sq ft home. The return on investment would have been at least 20 years so it was not a viable option.