Cost & material estimator
Attic Insulation & Payback Calculator
Insulation calculators give you a depth. This gives you the depth, the honest payback, and the two things that must happen before any insulation goes down.
- Your current R-value from depth and type
- DOE target for your climate zone
- R-value and depth to add, and bags needed
- Material and labour cost
- A deliberately conservative saving and payback
- The air-sealing and downlight checks that come first
Attic Insulation & Payback Calculator — interactive tool
The attic
Measure in several places — it is rarely even.
Climate and cost
What's up there
Non-IC-rated fittings must never be covered. This is the most common serious mistake.
Region
1200 sq ft · Zone 5
Add 13.4" to reach R-60
to add on top of your existing R-13
- Total cost
- $1,072
- Annual saving
- $206
- Payback
- 5.2 yr
Air seal before you insulate. In most attics, air moving through gaps carries more heat than conduction does — and insulating over unsealed penetrations drives warm moist air into the insulation where it condenses.
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Air sealing comes first, and it is not optional
Insulation slows heat conduction. It does nothing about air moving through gaps, and in most attics air leakage carries more heat than conduction does. Sealing top plates, plumbing and wiring penetrations, the attic hatch and any chase before insulating typically costs a few hundred dollars in foam and caulk, and it is the difference between the saving modelled here and a much smaller one. Insulating over unsealed penetrations also drives warm moist air into the insulation, where it condenses.
Recessed lights must be identified before anything is blown
Older non-IC-rated downlights must not be covered with insulation — they overheat and are a recognised fire cause. Check for an IC rating stamped inside the housing. If they are not IC-rated, either fit airtight covers rated for the purpose or replace the fittings with IC-rated LED units before insulating. This is the most common serious mistake in attic insulation work.
Do not block the soffit vents
Blown insulation pushed into the eaves blocks the airflow that keeps the roof deck dry and prevents ice dams. Fit baffles at every rafter bay before blowing, so there is a clear path from soffit to ridge. A blocked soffit turns an insulation upgrade into a moisture problem.
Payback in 5.2 years
That is a strong return for a home improvement, and this model is deliberately conservative — it discounts the theoretical saving by a quarter because real-world performance rarely matches the calculation.
The numbers
- Current R-value
- R-13
- DOE target for your zone
- R-60
- R-value to add
- R-47
- Depth to add
- 13.4 in
- Final depth
- 18.4 in
- Bags needed
- about 42
- 10-year net saving
- $988
Insulation types
| Type | R per inch | DIY | Note |
|---|---|---|---|
| Blown fibreglass | R-2.5 | Yes | Lightest, does not settle much, and blowers are free to hire with a bulk purchase at most stores. |
| Blown cellulose | R-3.5 | Yes | Higher R per inch and better at filling awkward gaps. Settles about 10-20% over time, so overfill accordingly. |
| Fibreglass batts | R-3.2 | Yes | Only sensible where joists are regular and clear. Gaps and compression destroy performance, and attics rarely cooperate. |
| Closed-cell spray foam | R-6.5 | Professional | Highest R per inch and it air-seals as it goes. Expensive, professional only, and it changes how the roof assembly breathes. |
- Attic area
- 1200 sq ft
- Climate zone
- Zone 5
- Materials
- $1,072
- Payback
- 5.2 yr
Take these numbers further
What this estimate assumes
- · R-value targets are the DOE recommendations for your climate zone. Local code minimums are usually lower and are a floor, not a target.
- · R per inch is 2.5 for blown fibreglass, 3.5 for blown cellulose, 3.2 for batts and 6.5 for closed-cell foam.
- · Existing R is estimated from the depth and type you entered. Compressed, damp or contaminated insulation performs worse than its depth suggests.
- · The saving model assumes the attic accounts for about a quarter of envelope heat loss, and then discounts the theoretical saving by 25% because real performance rarely matches calculation. It is deliberately conservative.
- · Payback excludes any federal, state or utility incentive. Insulation rebates are widespread and can shorten payback substantially — check separately.
- · Cellulose settles 10-20% over time. Blow to the higher target depth to allow for it.
The saving model is deliberately conservative — it discounts the theoretical figure by a quarter, because real performance rarely matches calculation.
Attic insulation is the most reliably worthwhile energy improvement available to most houses, and it is also the one most often done in the wrong order.
Insulation slows heat conduction. It does nothing about air moving through gaps, and in a typical attic air leakage carries more heat than conduction does — up through top plates, around plumbing and wiring penetrations, past the hatch, and out through every chase and light fitting. Blowing insulation over unsealed penetrations buries the problem rather than solving it, and it drives warm moist air up into the insulation where it condenses.
So the sequence is air seal, then insulate. Sealing typically costs a few hundred dollars in foam and caulk and half a day, and it is the difference between the saving this calculator models and a considerably smaller one.
The second thing that comes first is checking for non-IC-rated downlights, because covering those is a recognised fire cause and it is the most common serious mistake in attic insulation work.
What R-value you actually need
The Department of Energy publishes recommended attic R-values by climate zone, and they are considerably higher than the code minimums that most houses were built to. R-30 in the far south, R-49 across most of the southern half of the country, R-60 through the middle and north.
Working out what you have is straightforward: measure the depth in several places — it is rarely even — and multiply by the R per inch of the material. Blown fibreglass is about 2.5 per inch, blown cellulose 3.5, fibreglass batts 3.2, closed-cell spray foam 6.5.
A house with six inches of blown fibreglass has roughly R-15, which was normal in the 1980s and is less than a third of what zone five now calls for. That is why attic insulation so often pays back quickly: the gap between what is there and what is recommended is usually large.
One caution on measurement. Insulation that has been compressed, walked on, or wetted performs considerably worse than its depth suggests, and old insulation that has settled has lost some of its original value. If it looks flat and grey rather than fluffy, treat the calculated figure as optimistic.
| Zone | Where | Target R | Cellulose depth | Fibreglass depth |
|---|---|---|---|---|
| 1 | South Florida, Hawaii | R-30 | 9" | 12" |
| 2 | Gulf Coast, south Texas | R-49 | 14" | 20" |
| 3 | Southern US | R-49 | 14" | 20" |
| 4 | Mid-Atlantic, Pacific NW | R-60 | 17" | 24" |
| 5 | Midwest, New England | R-60 | 17" | 24" |
| 6 | Northern Midwest, upstate NY | R-60 | 17" | 24" |
| 7 | Northern Minnesota, Maine | R-60 | 17" | 24" |
DOE recommended attic R-values by climate zone, and what that means in depth.
The two checks that come before anything is blown
Air sealing first, and it is not optional. The largest leaks are usually where you cannot see them: the tops of interior walls where the drywall meets the top plate, holes drilled for wiring and plumbing, the chase around a chimney or flue, and the attic hatch itself. Canned foam for gaps up to about three inches, caulk for smaller ones, and rigid material with fire-rated sealant around anything hot.
The attic hatch deserves particular attention because it is often the single largest leak in the house and it is trivially fixable — weatherstripping and a rigid insulated cover, an hour's work.
Second, downlights. Recessed fittings that are not IC-rated must never be covered with insulation, because they rely on air circulation to shed heat and they overheat when buried. Check inside the housing for an IC rating stamp. If they are not IC-rated, either fit airtight covers made for the purpose or replace them with IC-rated LED units before insulating.
This is the most common serious mistake in attic work, and it is the reason insulation appears in fire investigation reports.
- Fit baffles at every rafter bay before blowing, so soffit vents stay clear. Blocked soffits cause moisture and ice dams.
- Keep insulation clear of the flue on any fuel-burning appliance, at the clearance the appliance specifies.
- Do not compress batts to fit. Compressed insulation loses R-value in proportion.
- Cellulose settles 10-20% over time — blow to the higher target depth to allow for it.
- Work from the far corner back toward the hatch, and lay boards to walk on. Stepping between joists puts a foot through the ceiling.
Why the payback figure here is lower than most
Insulation marketing is consistently optimistic about savings, and the mechanism is easy to see: assume the attic is responsible for a large share of heat loss, assume the theoretical R improvement is fully realised, and the numbers look excellent.
Real houses do not behave that way. Insulation performance is degraded by gaps, compression, thermal bridging through joists, and the air leakage that the insulation does not address. Ducts running through an unconditioned attic leak into a space that is still outside the thermal envelope. And the attic is one part of an envelope that also includes walls, windows, floors and doors.
So this model assumes the attic accounts for about a quarter of envelope loss, and then discounts the theoretical saving by a further twenty-five per cent. The result is a payback figure that is usually a few years longer than the one a contractor will quote, and it is still frequently under seven years — which is a strong return for a home improvement.
Where payback comes out beyond fifteen years, that usually means the existing insulation is already reasonable. Insulation obeys diminishing returns sharply: going from R-11 to R-38 captures most of the available benefit, and going from R-49 to R-60 captures very little of what remains.
The comfort argument, which the payback does not capture
There is a reason to insulate an attic that has nothing to do with the payback calculation, and for a lot of households it is the more compelling one.
A poorly insulated attic makes the top floor of a house uncomfortable in a way that heating and cooling cannot fully fix. Upstairs bedrooms that are hot in summer and cold in winter, a system that runs constantly without ever getting the temperature even, and a marked difference between floors — all of these are usually the attic rather than the equipment.
That improvement arrives immediately and is felt every day, whereas the energy saving is invisible and arrives as a slightly smaller bill. If the payback figure looks marginal but the top floor is unpleasant, insulating is still very likely the right decision.
It is also worth checking for utility and federal incentives before starting. Insulation rebates are widespread, frequently substantial, and not modelled here — they can shorten a payback considerably.
What this tool assumes
Every number this tool produces rests on these. Change your inputs and they change with you.
- R-value targets are the DOE recommendations for your climate zone, which are higher than most code minimums.
- R per inch is 2.5 for blown fibreglass, 3.5 for blown cellulose, 3.2 for batts and 6.5 for closed-cell foam.
- Existing R is estimated from depth and type. Compressed, damp or settled insulation performs worse than its depth suggests.
- The saving model assumes the attic is about a quarter of envelope heat loss, then discounts the theoretical saving by a further 25%. It is deliberately conservative.
- Payback excludes federal, state and utility incentives, which are widespread and can shorten it substantially.
- Cellulose settles 10-20%. Blow to the higher target depth to allow for it.
Mistakes that cause rework
Each of these costs money or a whole weekend to undo.
Insulating before air sealing
Air leakage carries more heat than conduction in most attics. Insulating over unsealed penetrations buries the problem and pushes moist air into the insulation, where it condenses.
Covering non-IC-rated downlights
They rely on air circulation to shed heat and overheat when buried. This is a recognised fire cause and the most common serious mistake in attic work. Check for the IC stamp before anything is blown.
Blocking the soffit vents
Insulation pushed into the eaves stops the airflow that keeps the roof deck dry. Fit baffles at every rafter bay first, or an insulation upgrade becomes a moisture problem.
Compressing batts to fit
R-value falls in proportion to compression. A batt squashed into a space performs like the thinner batt it has become.
Adding to insulation that is already at target
Diminishing returns are sharp. R-49 to R-60 saves a fraction of what R-15 to R-38 does. Spend the money on air sealing or ducts instead.
Walking between the joists
There is only drywall between the joists. Lay boards to work from, and work back toward the hatch.
Safety & honest limits
- Non-IC-rated recessed lights must never be covered with insulation. They overheat and it is a recognised fire cause.
- Keep insulation clear of flues, chimneys and any heat-producing equipment at the clearance the appliance specifies.
- Wear a fitted respirator, eye protection, gloves and long sleeves. Fibreglass and cellulose dust irritate skin, eyes and airways.
- Never step between joists — there is only drywall there. Lay boards, use a light, and work back toward the hatch.
- Attics reach dangerous temperatures in summer. Work early in the morning, take breaks, and do not work alone.
- In houses built before 1990, insulation of unknown type should be identified before disturbance. Vermiculite in particular may contain asbestos and must not be disturbed without testing.
Frequently asked questions
How much insulation do I need in my attic?
The DOE recommends R-30 in the far south, R-49 across the southern half of the US and R-60 through the middle and north. In blown cellulose that is roughly 9, 14 and 17 inches respectively; in blown fibreglass about a third more depth for the same R. Measure what you have in several places and subtract.
How many inches is R-38?
About 11 inches of blown cellulose, 15 of blown fibreglass, or 12 of fibreglass batts. Closed-cell spray foam reaches R-38 in around 6 inches, which is why it is used where depth is limited despite costing several times more.
Should I air seal before insulating?
Yes, always. Air moving through gaps carries more heat than conduction in most attics, and insulating over unsealed penetrations both wastes much of the benefit and drives warm moist air into the insulation where it condenses. Sealing costs a few hundred dollars in foam and caulk and takes half a day.
Can I put insulation over recessed lights?
Only if they are IC-rated — look for the stamp inside the housing. Non-IC fittings rely on air circulation to shed heat and overheat when covered, which is a recognised fire cause. Either fit airtight covers made for the purpose or replace them with IC-rated LED units first.
How much does attic insulation cost?
Roughly $0.60 to $1.20 per square foot for DIY blown insulation to add R-30, so about $900 to $1,700 for a typical 1,200 square foot attic. Professional installation adds around $0.85 per square foot. Spray foam is several times more and is professional only.
Is attic insulation worth it?
In most under-insulated houses, yes — payback is frequently under seven years even on a conservative model, and the comfort improvement on the top floor arrives immediately. Where existing insulation is already near the target, returns fall off sharply and the money is better spent on air sealing or duct sealing.
Should I remove old insulation before adding new?
Usually not. Adding on top of existing loose-fill is standard practice and preserves the R-value already there. Remove it only if it is wet, mould-damaged, rodent-contaminated, or of unknown type in a pre-1990 house where vermiculite is a possibility — that needs testing before disturbance.
Last reviewed July 25, 2026 · Home & Garden Living
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