Attics are measured to R-value, and the bag chart is what counts. This gets you close before you check the bag.
How it works
Settled depth = target R ÷ R-per-inch. Bags use a typical rate at R-38, scaled by R-value, or your own number from the bag chart.
Before you order
- Mark depth rulers on the joists so coverage stays even.
- Keep insulation back from can lights unless they are rated for contact, and baffle the soffits.
- Seal attic air leaks first, since that often pays back faster than more insulation.
Common questions
Why do bag charts matter?
Coverage must be stated at settled thickness by law, and it varies by product. Use the chart on your bag for the order.
Cellulose or fiberglass?
Cellulose gives more R per inch and settles more. Fiberglass is lighter per bag and needs more depth.