Insulation Calculator
How much insulation your attic, walls or crawlspace floor needs to hit target R-value, what it costs, what it saves every year — and how fast it pays for itself.
Estimates for planning. Savings depend on your climate, air sealing, and how your house actually performs — insulation only works if air leaks are sealed first. Attics also need ventilation and safe clearances around recessed lights, chimneys and flues. A blower-door energy audit beats any calculator.
Usually close to the footprint of the floor below.
Perimeter × wall height, minus windows and doors.
The heated footprint sitting above unheated space — not the whole house if part of it is on a slab.
Prices are DIY material only; installed prices are compared in the cost section below.
Used to estimate savings — the attic is typically 25–35% of a home's heat loss.
The 25C credit expired. The One Big Beautiful Bill Act ended it for work placed in service after December 31, 2025. Insulation done in 2026 gets no federal credit — though state and utility weatherization programs often still pay, and some cover low-income households entirely.
You need
Enter your area
| Detail | Amount |
|---|---|
| R-value added | — |
| Material cost | — |
| After tax credit | — |
| Estimated annual saving | — |
| Simple payback | — |
DIY or Hire It Out?
The calculator above prices the material you'd buy yourself. Here's what the same job costs installed, and how that changes the payback period.
| Option | Cost |
|---|---|
| Do it yourself | — |
| Professionally installed | — |
| Payback if installed | — |
Installed figures use the material selected above. The federal 25C credit that used to offset 30% of this cost ended December 31, 2025 — check your state energy office and utility instead, since weatherization rebates are still widely available and some programs cover income-qualified households in full.
What insulation costs installed in 2026
| Type | Installed per sq ft | R per inch | Best for |
|---|---|---|---|
| Blown cellulose | $0.70–1.50 | R-3.5 | Attics; recycled content, settles slightly |
| Blown fiberglass | $0.85–1.70 | R-2.5 | Attics; doesn't settle, needs more depth |
| Fiberglass batts | $0.80–2.60 | R-3.2 | Open wall cavities and new construction |
| Closed-cell spray foam | $1.50–5.00 | R-6.5 | Rim joists, crawlspaces, air sealing |
A 1,500 sq ft attic blown to R-38 with cellulose typically runs $1,400–2,200 installed. The DOE recommends R-30 to R-49 in attic floors for southern climates and R-49 to R-60 for northern ones.
Where DIY makes sense — and where it doesn't
- Batts in an open wall or accessible attic: genuinely DIY. Material is most of the cost, the tools are a utility knife and a staple gun, and mistakes are fixable.
- Blown-in is DIY-adjacent. Many home centers lend the blower free with a minimum bag purchase. It's a two-person job — one feeding the hopper, one on the hose — and a dusty one; wear a proper respirator.
- Spray foam is not a DIY job at scale. Closed-cell foam is a chemical reaction with a mixing ratio and a temperature window; get it wrong and it never cures, smells permanently, and has to be cut out. Kits are fine for rim joists, not for an attic.
- Air sealing beats adding R-value if you haven't done it. Caulk and foam around penetrations, top plates, and can lights first — it's cheap and often saves more than another six inches of fluff.
- Don't bury attic can lights or block soffit vents. Older non-IC-rated fixtures are a fire risk under insulation, and blocked soffits cause ice dams and moisture problems.
How Insulation Savings Are Calculated
Heat loss through a surface is proportional to 1 ÷ R-value. Doubling R doesn't double your savings — it halves the remaining loss, which is why the first inches matter enormously and the last inches barely register.
- Depth needed = (target R − current R) ÷ R-per-inch of your material.
- Loss reduction = 1 − (Rold ÷ Rnew), counting the assembly itself. Even a bare wall has about R-4 from drywall, sheathing, siding and air films, and a bare ceiling about R-3 — so an empty cavity is never truly R-0. Going R-19 → R-49 cuts attic loss about 58%.
- Dollar saving = that reduction × the share of your bill lost through that surface (attics ≈ 30%, walls ≈ 25%).
- Payback = net cost after any rebate ÷ annual saving.
Worked example — 1,200 sq ft attic, R-19 → R-49, blown fiberglass, $1,500/yr bill: 12 inches added, about $1,080 in material, ~$260/yr saved → roughly 4.2 years payback at full material cost. It was closer to 3 years while the federal credit existed; a utility rebate brings it back down.
Why the First Inches Pay and the Last Ones Don't
| Upgrade | Heat loss removed | Verdict |
|---|---|---|
| R-0 → R-19 | ~86% of what was escaping | Enormous — do this immediately |
| R-19 → R-38 | 46% of remaining | Excellent return |
| R-38 → R-49 | 21% of remaining | Still worth it in cold climates |
| R-49 → R-60 | 17% of remaining | Marginal outside cold zones |
R-Value Per Inch by Material
| Material | R per inch | Inches for R-49 | Notes |
|---|---|---|---|
| Blown fiberglass | 2.5 | ~20" | Cheapest per R; settles slightly |
| Fiberglass batts | 3.2 | ~15" | Easy DIY between joists |
| Blown cellulose | 3.5 | ~14" | Better air blocking, recycled content |
| Closed-cell spray foam | 6.5 | ~8" | Air seals too; several times the price |
Floors and Crawlspaces — and When Not to Insulate the Floor
Floors over an unheated crawlspace account for roughly 12% of a home's heat loss — less than the attic (30%) or walls (25%), so it's third in line on pure economics. A bare 1,200 sq ft floor taken to R-19 saves around $143 a year and pays back in about three and a half years.
But the reason people do it usually isn't the bill. It's the cold floor. An uninsulated floor over a vented crawlspace is the single most common source of "this room is never warm" complaints, and no amount of attic insulation fixes it.
The trap: if your ducts or water pipes run through the crawlspace, don't insulate the floor. Insulating between the joists puts the crawlspace *outside* your thermal envelope — colder than before, because you've just cut off the heat that was leaking down and keeping it above freezing. That's how people insulate a floor in October and burst a pipe in January.
In that case the right move is the opposite one: seal and insulate the crawlspace walls instead, bringing the whole space inside the envelope. Ducts and pipes stay warm, and you get the same comfort improvement. It costs more and usually wants a contractor, but it's the correct answer for a house with services down there.
Moisture matters more here than anywhere else in the house. Put a proper ground vapour barrier over the soil first — insulating over damp ground traps moisture against the joists and you'll be replacing subfloor instead of saving money. Use unfaced batts held up with wire supports, not stapled facing that sags and leaves gaps.
Before You Buy
- Air seal first. Insulation slows conduction; it does nothing about air leaking around wires, pipes and top plates. Sealing before insulating is what separates a good result from a disappointing one, and caulk and canned foam are the cheapest materials in this whole calculation.
- Don't block soffit vents. Use baffles at the eaves; a smothered attic traps moisture and rots the roof deck.
- Keep clearance around heat sources — recessed lights that aren't IC-rated, chimneys, and flues need dedicated spacing.
- Never lay faced batts over existing insulation. The vapor barrier ends up mid-assembly and traps moisture. Unfaced or blown only.
- Insulate before sizing a heat pump. A tighter house needs a smaller unit — sometimes a full ton less — which cuts the equipment bill and improves cold-weather performance.
Frequently Asked Questions
What R-value should my attic be?
R-49 to R-60 across most of the US; R-30 to R-49 in the warmest zones. Many older homes sit at R-19 or below.
How much does attic insulation save?
R-19 → R-49 cuts attic loss ~60%. On a $1,500/yr bill that's often $150–$300 a year, paying back in 3–6 years.
Is there a tax credit for insulation in 2026?
No — the 30% federal 25C credit (capped at $1,200/yr) expired December 31, 2025 under the One Big Beautiful Bill Act. Work finished by then can still be claimed on a 2025 return. State and utility weatherization rebates still exist and are worth checking.
How many inches for R-49?
~20" blown fiberglass, ~14" cellulose, ~8" closed-cell foam.
Insulate before a heat pump?
Usually yes — a tighter house needs a smaller unit, which is a direct saving on the bigger purchase.
Can I add over old insulation?
In an attic, yes, if it's dry and uncompacted; R-values add. Never faced batts on top.
What R-value for a floor over a crawlspace?
R-19 in mild climates, R-30 in cold ones. Floors are ~12% of heat loss, so savings are smaller than the attic — but it's the fix for permanently cold floors.
Should I insulate the floor if pipes run below?
No. Insulating the floor makes the crawlspace colder and can freeze pipes and ducts. Seal and insulate the crawlspace walls instead so the space stays inside the envelope.
My rebate program just says "properly insulated" — what R-value does that mean?
Programs like this usually don't publish their own number; they're pointing at the same R-49–R-60 attic target ENERGY STAR recommends for most US climate zones. If your program doesn't state a figure, use that as your baseline before applying for the rebate.
Insulate first, or install the heat pump first?
Insulate first when a rebate program makes it mandatory (increasingly common) or the house is old enough that envelope losses would throw off the heat pump's sizing. Otherwise either order works — but insulating first means the installer sizes the heat pump off real numbers instead of a guess.
References
- ENERGY STAR — Seal and Insulate (recommended R-values by climate zone, air sealing): energystar.gov
- ENERGY STAR — sealing and insulating, and federal tax credits: energystar.gov
- Oak Ridge National Laboratory — insulation performance research: ornl.gov