PROJECT SUMMARY
Insulation project summary
Area300 sq ft · attic
- Target
- R-38
- Type
- Fiberglass batts / rolls
- Layout
- 20 × 15 ft
- Vapor barrier
- None
- Air-seal
- Foam included
- Difficulty
- Beginner
- Build time
- ½–1.5 days
- Estimated materials
- $477–$645
Insulation Calculator
Batts, blown-in or foam board by area and R-value, with cost.
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Insulation calculator
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Type
Advanced optionsfine-tune the details…
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ Recommended R-value depends on your climate zone — for attic, a common target is R-38 to R-60. Check the DOE/ENERGY STAR zone map for your area and don't under-insulate.
⚠ Air-seal first: caulk and foam the gaps around wiring, plumbing, top plates and fixtures before adding insulation — insulation slows heat, it doesn't stop air leaks.
⚠ Don't compress batts (it lowers the R-value), never bury non-IC-rated recessed lights, and keep a 3" clearance around flues. Wear a respirator, goggles, gloves and long sleeves.
Cost breakdown
Material only · national-average rates
| Insulation | $451–$611 |
| Finishing & Sealant | $20–$28 |
| Fasteners & Hardware | $5–$7 |
| Total | $477–$645 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
Shopping list
Every item · grouped by store sectionThese are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
Insulation
- 8× bagsFiberglass batts — R-38 — 300 sq ft · ~44 sq ft/bag
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- 14× eaRafter / soffit vent baffles — keep insulation from blocking soffit airflow
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Fasteners & Hardware
- 1× packStaples (for kraft-faced batts)
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Finishing & Sealant
- 3× cansGaps & cracks spray foam — air-seal penetrations before insulating
Find ↗
Tools
✓ required · ○ helpful
- Utility knife + straightedge — cutting batts/board
- Tape measure
- Insulation blower (rental) — often free with bag quantity
- Staple gun / hammer tacker
- Caulk gun — air-sealing
- Respirator, goggles, gloves, long sleeves — irritant fibers
- Kneeling boards / planks — spanning joists safely
- Work light / headlamp
Project notes
- Estimates are a planning aid. Coverage per bag varies by brand and — for blown-in — by the installed R-value, so check the bag chart; batt bags list square-foot coverage right on the label.
- Insulate to your climate zone, not a single number. Under-insulating wastes the whole effort, and going far above the recommended R has diminishing returns.
- Blown-in is fastest for open attic floors and irregular cavities; batts suit standard stud/joist bays; rigid foam board is for basement walls, rim joists and continuous exterior layers.
- The biggest efficiency win is usually air-sealing, not R-value — foam and caulk the leaks first, add attic baffles to protect soffit ventilation, then insulate.
About this calculator
How to estimate an insulation
Enter the area you're insulating and your target R-value, and the Insulation Calculator works out how much to buy — bags of fiberglass batts, bags of blown-in loose fill, or sheets of rigid foam board — plus the air-sealing foam, vapor barrier and attic baffles to do the job right, with a cost estimate.
Pick the location (attic, walls or crawlspace) for an R-value recommendation, choose your insulation type, and the takeoff updates instantly. R-value should match your climate zone, so treat the recommendations as a starting point and confirm against your local energy code.
Step by step
How to install insulation
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
- 1
Check your target R-value
Look up the recommended R-value for your climate zone and the area you're insulating, and measure the square footage. The calculator turns that into a bag or sheet count.
- 2
Air-seal first
Before any insulation goes in, foam and caulk the gaps around wiring, plumbing, light boxes, top plates and the attic hatch. Sealing air leaks matters as much as the insulation itself.
- 3
Protect ventilation and fixtures
In attics, install baffles at the eaves so insulation can't block the soffit vents, and keep it clear of non-IC recessed lights and flues.
- 4
Suit up
Put on a respirator, goggles, gloves and long sleeves — fiberglass and cellulose irritate skin, eyes and lungs. Set up good lighting and safe footing on planks in attics.
- 5
Install the insulation
Fit batts snugly into each bay without compressing them, cutting around obstructions; or blow loose fill to an even depth to the marked R-value; or cut and fasten foam board tight with taped seams.
- 6
Add a vapor barrier if needed
Where your climate and assembly call for it, install the warm-side vapor retarder and seal its seams before closing the wall.
- 7
Verify even coverage
Check for gaps, thin spots and compressed areas — insulation only works as well as its weakest, thinnest section. Fill any voids before you close up.
Equip the job
Recommended gear for this build
Hand-picked categories that match the shopping list above. Links open a current selection so you can compare brands and prices.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
InsulationFiberglass insulation battsThe standard, budget-friendly choice for stud and joist bays — buy the R-value your zone needs.
$45–80/bag
InsulationBlown-in cellulose / fiberglassFastest way to top up an attic to a high R-value; the blower is usually free with the bag count.
$12–15/bag
Finishing & SealantGaps & cracks spray foamAir-seal the leaks first — it's often the biggest efficiency win before you add insulation.
$7–10/can
InsulationRafter / soffit vent bafflesKeep attic insulation from blocking the soffit vents so the roof deck can still breathe.
$2–3 ea
ToolsRespirator + PPE kitInsulation fibers irritate skin, eyes and lungs — a respirator and cover-up are non-negotiable.
$20–40
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Answers
Frequently asked questions
How much insulation do I need?
Measure the square footage of the area (length × width for an attic floor, or wall run × height), then divide by the coverage on the package. Batt bags list their square-foot coverage on the label; blown-in coverage depends on the installed R-value, so a bag covers less area the higher the R you're targeting. This calculator does the math for your area, type and R-value.
What R-value do I need?
It depends on your climate zone and where you're insulating. As a rough guide, attics commonly target R-38 to R-60, 2×6 walls R-19 to R-21, 2×4 walls R-13 to R-15, and floors/crawlspaces R-19 to R-30. Colder zones need more. Check the ENERGY STAR or Department of Energy climate-zone recommendations for your area before buying.
Batts, blown-in, or foam board?
Batts and rolls are cheapest and easiest to fit into standard stud and joist bays. Blown-in loose fill is the fastest way to hit a high R-value across an open attic floor and fills irregular gaps that batts miss. Rigid foam board is best for basement walls, rim joists, and adding a continuous insulating layer. The calculator switches the materials to match your choice.
Do I need a vapor barrier?
It depends on your climate and assembly. In cold climates a warm-side vapor retarder (like kraft-faced batts or poly on walls and crawlspaces) helps control moisture; in hot-humid climates it can trap moisture and cause problems. Attics generally rely on ventilation rather than a poly vapor barrier. When in doubt, follow local code and the insulation manufacturer's guidance for your zone.