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Attic Insulation
Attic Insulation
From Lori:
"Is there a certain depth of insulation that I need in my Arizona home, in other words can I measure the depth with a yard stick to know if it is the proper amount of blown insulation in the attic.
The builder used, I believe, blown cellulose and I was wondering if I could add the pink rolls of fiberglass on top of it? PS If so how do I know how much I would need -- I think I am supposed to have at least R-38 value in my roof.
Thanking you in advance, Lori"
Hi Lori,
Yes, there is a certain depth of attic insulation that you need in your home.
As you correctly stated, you need at least an R-38 value in your attic. (Insulation Calculator)
Cellulose provides a thermal resistance of R-3.2 to R-3.8 per inch.
So, using the more conservative R-3.6 per inch, you would need 11.9 inches to have an R-38value.
Cellulose settles with time, more so than rock wool or fiberglass, so you might be a little shy on R value by now.
If you need to add depth, I would consult with a professional insulation contractor as to the best way to do it and how much it would cost.
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Obtain written cost estimates from several contractors for the R-value you need. Don't be surprised to find quoted prices for a given R-value installation to vary by more than a factor of two.
I’m not sure I would try putting Fiberglass (rolls) over the cellulose. The weight of the fiberglass would most likely cause compression of the cellulose.
Good Luck,
Carl

