Insulation R-Value Calculator

What is R-Value?

R-value measures thermal resistance—the ability of insulation to resist heat flow. Higher R-values provide better insulation performance. The "R" stands for resistance, and the value indicates how well a material prevents heat transfer per inch of thickness.

Understanding R-value is critical for energy efficiency, comfort, and building code compliance. Proper insulation reduces heating and cooling costs by 15-50%, prevents moisture problems, and maintains consistent indoor temperatures year-round.

R-Value Requirements by Climate Zone

Zone	Attic	Walls	Floor	Basement
Zone 1-2	R30-R49	R13-R15	R13	R5-R10
Zone 3-4	R30-R60	R13-R21	R19-R25	R10-R15
Zone 5-6	R49-R60	R20-R21	R25-R30	R15-R20
Zone 7-8	R49-R60	R21	R25-R30	R15-R25

Common Insulation Types and R-Values

Fiberglass Batts

R-Value per inch: R-2.9 to R-3.8

• Most common and economical
• DIY-friendly installation
• Available in pre-cut sizes for standard stud spacing
• Loses effectiveness if compressed or gaps exist
• Best for: standard framed walls, attics, floors

Blown Fiberglass

R-Value per inch: R-2.2 to R-4.3

• Fills irregular spaces and around obstacles
• Less prone to gaps than batts
• Requires blower equipment
• Can settle over time, reducing R-value
• Best for: attics, retrofitting existing walls

Cellulose (Blown)

R-Value per inch: R-3.2 to R-3.8

• Made from recycled paper products
• Excellent air sealing properties
• Treated for fire and pest resistance
• Settles 10-20% over time
• Best for: attics, dense-pack wall retrofits

Open-Cell Spray Foam

R-Value per inch: R-3.5 to R-3.7

• Expands to fill all gaps and cracks
• Excellent air sealing
• Lighter and less expensive than closed-cell
• Vapor permeable (requires vapor barrier in some climates)
• Best for: interior walls, attics, sound dampening

Closed-Cell Spray Foam

R-Value per inch: R-6.0 to R-7.0

• Highest R-value per inch
• Acts as air barrier and vapor barrier
• Adds structural rigidity
• Most expensive option
• Best for: exterior walls, crawl spaces, rim joists

Mineral Wool (Rock Wool)

R-Value per inch: R-3.3 to R-4.2

• Non-combustible, excellent fire resistance
• Water-repellent
• Superior sound dampening
• Retains R-value when wet
• Best for: fire-rated assemblies, soundproofing

Rigid Foam Board

R-Value per inch: R-3.6 to R-6.5 (varies by type)

• XPS (extruded polystyrene): R-5 per inch
• EPS (expanded polystyrene): R-3.6 to R-4.2 per inch
• Polyisocyanurate: R-5.6 to R-6.5 per inch
• Used for continuous insulation
• Best for: exterior sheathing, basement walls, under slab

Where to Insulate First

Prioritize insulation projects by their return on investment and impact on comfort:

1. Attic: Up to 30% of heat loss occurs through the roof. Highest ROI.
2. Air Sealing: Seal gaps and cracks before adding insulation. Air leaks waste more energy than insufficient insulation.
3. Basement/Crawl Space: Prevents cold floors and reduces heating costs.
4. Walls: More expensive retrofit but significant impact in extreme climates.
5. Windows: Consider only after insulation and air sealing are complete.

Understanding U-Factor vs. R-Value

While R-value measures resistance to heat flow, U-factor measures heat transmission. They're mathematical inverses:

Common Insulation Mistakes

Compressing Insulation

Fiberglass insulation's R-value depends on trapped air pockets. Compressing it reduces effectiveness. Never compress R-19 insulation into a space designed for R-13.

Ignoring Air Sealing

Air leaks can reduce insulation effectiveness by 50%. Seal gaps around pipes, wires, ducts, and at the rim joist before insulating.

Blocking Soffit Vents

Attic insulation should never block soffit vents. Use baffles to maintain airflow while insulating up to the roof edge.

Wrong Vapor Barrier Placement

Vapor barriers belong on the warm side of insulation (interior in cold climates, exterior in hot-humid climates). Incorrect placement traps moisture and causes mold.

Covering Recessed Lights

Never cover non-IC-rated recessed lights with insulation. They generate heat and can cause fires. Replace with IC-rated or LED fixtures before insulating.

Energy Savings from Insulation

Proper insulation provides measurable energy savings that vary by climate, current insulation levels, and heating/cooling costs:

Upgrade	Annual Savings	Payback Period
Attic R-11 to R-38	$300-$500	2-4 years
Walls R-0 to R-15	$400-$600	5-10 years
Basement R-0 to R-10	$150-$300	3-6 years
Crawl Space R-0 to R-19	$100-$200	3-5 years

Frequently Asked Questions

Can you have too much insulation?

Generally no, but diminishing returns exist. Going from R-30 to R-40 provides much less benefit than R-0 to R-15. Beyond code requirements, focus budget on air sealing rather than additional insulation depth.

Does insulation need to be replaced?

Most insulation lasts 80-100 years if undisturbed. Replace if water-damaged, contaminated by pests, compressed, or if you're doing renovation work anyway. Fiberglass and mineral wool don't degrade; cellulose may settle and need topping up.

What's the best insulation for soundproofing?

Mineral wool provides superior sound dampening (STC rating of 45+ vs. 39 for fiberglass). Dense-pack cellulose also performs well. The key is filling all cavities completely—gaps dramatically reduce sound blocking.

Should I insulate interior walls?

Only for sound control or if separating conditioned from unconditioned spaces. Interior walls don't need thermal insulation, but insulating bedroom and bathroom walls improves privacy and reduces sound transmission.

Can I install insulation myself?

Attic batts and blown insulation are DIY-friendly. Wall retrofits and spray foam require professional equipment and expertise. Always wear proper safety equipment: mask, goggles, gloves, and long sleeves when handling fiberglass.

Does insulation qualify for tax credits?

Yes, the Energy Efficient Home Improvement Credit (2023-2032) provides a 30% tax credit up to $1,200 annually for insulation that meets IECC code. Check current IRS guidelines and keep receipts.