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Community and Q&A

Attic insulation

Kellybeth | Posted in Energy Efficiency and Durability on

We are planning on converting our attic into living space and are very interested in using mineral wool.    The house was built in the 40’s, it has 2″ x 6″construction. 
It appears that the highest R value available is R 30?  Is that sufficient for what we are wanting to do.  Will that fit properly into the space?  We live in Albany, NY. 
Thanks in advance for any help with this.

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  1. user-2310254 | | #1

    Hi Kellybeth,

    I assume you are talking about creating a cathedral ceiling in the attic. Here is an article to give you some background on how to approach this type of project:

  2. Expert Member
    BILL WICHERS | | #2

    There is a lot more info needed to get you a good answer. Are the rafters 2x6? If they are, that doesn’t leave you enough room for a vent channel and much insulation regardless of what type you choose. You’ll probably need to either add some furring to get more room for insulation, or consider making it an unvented roof which is best done with spray foam.

    Regarding mineral wool, box stores don’t usually stock many sizes (my own local stores only stock R15 for 2x4 walls and the thinner sound dampening stuff), but it’s available in many sizes. If you need more than R30, you can always layer the batts to get more thickness, and this is easier with mineral wool than it is with fiberglass. You can also get blown-in mineral wool.

    For a typical attic conversion, you can use mineral wool in the knee walls, and in the floor. Whether or not you can use mineral wool in the roof depends on if this needs to be a vented or unvented assembly, and how much physical space you have to work with.


  3. Kellybeth | | #3

    The rafters are 2" x 6" x 14' with 15-16 inches in between them. The roof has new asphalt shingles and it's vented.

  4. user-2310254 | | #4


    Is it a simple roof, or are there lots of angles and dormers? How much headroom is there in the space?


  5. Kellybeth | | #5

    Yes, it's a simple roof. I think the attic is 25 W x 32 L. Plenty of head room.

  6. Kellybeth | | #6

    We'd keep it to cathedral, with 4' knee walls.

    1. user-2310254 | | #7

      Be sure to check out the article in my first reply. While you have several options for insulating a cathedral, it is important to follow the guidelines to avoid ending up with a damp ceiling. And be wary of contractors who deviate from Martin's advice.

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