Question

I would like to insulate my attic before winter. What product do you recommend, and what thickness, for an attic floor?

Asked by mc
New Rochelle, NY

I replaced all windows a couple of years ago. The attic is used for storage, but has a fan to cool down in summer.

Answer

Anthony Addesso

Answered by Anthony Addesso

Hawthorne, NJ

Addesso Architecture

October 7, 2010

The best attic insulation options you have are fiberglass batt insulation, blown-in insulation, or spray foam insulation.

  • Spray foam insulation is on average 20% more expensive than fiberglass or blown-in insulation. Although spray foam is a great product, I would eliminate this product due to the cost.
  • Blown-in insulation and fiberglass batts will give you good coverage of the space, and a good R-value. The difference is in the material itself: fiberglass batts are in essence a solid piece of material, while blown-in is small pieces of material laid out over the entire attic area.

Therefore I would recommend using fiberglass batt insulation, to avoid having those loose pieces of insulation.  

  • In your area I would recommend an R-value of 30.
  • The depth of the insulation is 9½” and the floor joists in your attic are most likely 7½”, and using this product will keep the crushing of the insulation at the eaves to a minimum, while balancing the most R-value in the attic space.

When you are having the insulation installed, keep in mind the eaves have to be ventilated and baffles installed to allow air flow over the insulation to eliminate trapped condensation.

If the fan you mentioned is a whole-house fan, the batts will stay in place better than the loose blown-in product. If you have an attic ventilator fan, it will help in keeping the air moving in the attic, but do not rely on it, and make sure the gable vents are open.

 

For more information:

Read Ian MacLeod's Q&A "What is the safest and most effective insulation for our attic crawl space?"

Tagged In: attic insulation

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