How Much Insulation for an Attic?
Most US attics should reach R-38 to R-60 โ roughly 12โ20 inches of blown fiberglass or equivalent batts. A 1,000 sq ft attic at R-38 needs about 30 bags of blown insulation or 1,000 sq ft of batts plus air sealing. This guide sets the target and the quantity, and explains why air sealing comes first.
Step-by-Step Takeoff
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1
Find your zone target: R-38 minimum (R-49+ in cold zones) per IECC โ check your zone.
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2
Air-seal first (cans, chases, top plates), then insulate โ model it in the Insulation Calculator.
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3
Blown: 1,000 sq ft รท coverage per bag at R-38 (~30โ35 sq ft) โ 30 bags.
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4
Batts: 1,000 sq ft of R-38 batts in full-width runs, no compression.
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5
Keep soffit vents open with baffles in every bay โ buried vents grow mold.
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6
Do not cover junction boxes or bury exhaust fans; box them out first.
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7
Lay walk boards to the air handler so future service does not crush the insulation.
Guide FAQ
What R-value for my attic?
R-38 to R-60 in most of the US; R-30 minimum in hot climates. Zone maps are in the calculator.
Blown or batts?
Blown fills gaps and wins on coverage; batts win for DIY control and walkable storage decks.
Can I add insulation over old insulation?
Yes if it is dry and flat โ add unfaced batts or blown perpendicular to the old layer.
Do I need to remove old insulation first?
Only if wet, moldy, or vermiculite (possible asbestos โ test before touching).
How much does attic insulation save?
Typically 10โ15% of heating/cooling bills; air sealing often pays back in year one.
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