Worked example: topping up a 1,200 sq ft attic to R-49
Blown-in at $1.75/sq ft is $2,100, plus $420 of air sealing first — total $2,520. Estimated savings of ~$265/year on heating and cooling give a 9.5-year payback, and the 30% federal credit (up to $1,200) cuts effective cost to ~$1,764, a 6.7-year payback. In cold climates the savings run higher; this is one of the few home projects with an honest, measurable return.
- • Removing old insulation (+$1.25/sq ft) is only needed if it's contaminated (pests, mold) — topping over clean old insulation is fine.
- • Baffles at eaves keep soffit vents open; blocking them trades an insulation gain for a moisture problem.
- • Recessed lights must be IC-rated or boxed before burying them in insulation — fire code, not preference.
Attic first, always
Heat rises and attics are the leakiest boundary — attic insulation returns 2–3× the savings of wall insulation per dollar. The correct order of operations: air seal the attic plane, insulate the attic, then consider walls (drill-and-fill) and rim joists. Spray-foaming the roofline instead converts the attic to conditioned space — the right move when HVAC ducts live up there.
FAQ
How much does attic insulation cost in 2026?
Blown-in to recommended depth runs $1.25–$2.25 per sq ft installed — $1,500–$2,700 for a typical 1,200 sq ft attic. Spray foam rooflines run $3,500–$7,500 for the same footprint.
Is spray foam worth the extra money?
When you need air sealing + insulation in one step (leaky older homes, conditioned attics, rim joists), yes. For a simple open attic top-up, blown-in delivers the same R-value for a third of the price.
What R-value do I need in my attic?
DOE climate-zone guidance: R-38 minimum in warm zones, R-49–R-60 in cold zones. Most pre-2000 homes have R-19 or less — half of what current code wants.
Is there a tax credit for insulation?
Yes — the federal Energy Efficient Home Improvement Credit covers 30% of insulation material and install costs, capped at $1,200 per year, through current law. Keep the itemized invoice.
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