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Insulation R-Value + Type Reference

Reference Equipment Updated Jun 19, 2026 · HVAC · Roofing · Painting

Why this matters

Insulation type + R-value drives energy bills, comfort, code compliance, + cost. The wrong insulation in the wrong place wastes the customer's money OR causes moisture problems. Knowing each type's strengths + R-values + applications turns a generic "we'll insulate" job into a specific recommendation customers trust. This is the field card.

R-value per inch (typical)

Material R/inch
Fiberglass batt R-3.0 - R-3.8
Fiberglass loose-fill R-2.2 - R-2.9
Cellulose blown-in R-3.2 - R-3.8
Mineral wool batt (rock wool) R-3.0 - R-3.3
Mineral wool loose R-2.8 - R-3.0
Open-cell spray foam R-3.5 - R-3.8
Closed-cell spray foam R-6.0 - R-7.0
Polyisocyanurate rigid (polyiso) R-5.8 - R-7.0
XPS rigid foam R-4.5 - R-5.0
EPS rigid foam (white) R-3.6 - R-4.4
Reflective foil (radiant barrier) R-2 effective (gap-dependent)
Vermiculite R-2.1 - R-2.4
Cotton (denim) R-3.4 - R-3.7

Recommended R-values by climate (US 2021 IECC)

Zone 1 - 2 (hot - Florida, Hawaii, south Texas):

  • Attic: R-30
  • Wall: R-13
  • Floor (over crawl): R-13

Zone 3 (warm - Georgia, Arizona, south California):

  • Attic: R-38
  • Wall: R-13 to R-15
  • Floor: R-19

Zone 4 - 5 (mixed - Pennsylvania, Ohio, Missouri):

  • Attic: R-49
  • Wall: R-20 (cavity) + R-5 (continuous)
  • Floor: R-30

Zone 6 (cold - Michigan, Minnesota):

  • Attic: R-49 to R-60
  • Wall: R-20 cavity + R-7 continuous
  • Floor: R-30 to R-38

Zone 7 - 8 (very cold - Alaska, northern Maine):

  • Attic: R-60
  • Wall: R-23 + R-15 continuous
  • Floor: R-38+

Insulation types

  • Mineral/rock wool: slag + rock fibers, fire-resistant + doesn't melt, sound dampening, water-resistant.
  • Spray foam closed-cell: R-6 - 7/in, air-seals + vapor barrier, rigid + structural, best for tight spaces + cold climates.

Application matrix

Attic floor (blown-in over ceiling):

  • Blown fiberglass OR cellulose most common
  • Bury joists; goal R-49 typical zone 4 - 5
  • 16 - 20" depth for R-49

Attic roof deck (rafters, conditioned attic):

  • Closed-cell spray foam (R-6/in × 8" = R-48)
  • Open-cell + sealing (less common; needs ignition barrier)

Wall cavities (existing):

  • Cellulose blown-in (dense-pack)
  • Spray foam (best but $$)

Wall cavities (new construction):

  • Fiberglass batts (standard)
  • Mineral wool (fire-rated walls)
  • Spray foam (best performance)
  • Blown cellulose (alternative)

Continuous insulation (outside sheathing):

  • Rigid foam board (Polyiso typical)

Below-slab:

  • XPS rigid foam
  • 2" R-10 minimum cold climates

Basement walls (interior):

  • Closed-cell spray foam
  • Rigid foam + framing + drywall

Basement walls (exterior):

  • Rigid foam below grade (XPS typical)

Crawl space ceiling (vented crawl):

  • Fiberglass batts (face down to crawl)
  • Encapsulated crawl preferred (see Crawl Space Encapsulation)

Ducts in unconditioned space:

  • Fiberglass duct wrap R-6 to R-8
  • Spray foam coating for sealing

Pipes (anti-freeze):

  • Foam pipe insulation
  • Heat tape with insulation

Vapor barriers + insulation

Cold climate:

  • Vapor barrier on warm side (interior face)
  • Kraft-faced batt OR poly sheet
  • Prevents condensation in wall

Hot/humid climate:

  • Vapor barrier on warm side (exterior face)
  • OR no vapor barrier (let wall dry both directions)
  • AVOID interior poly in humid south

Mixed climate:

  • Variable-perm vapor retarder (MemBrain)
  • OR no vapor barrier; allow drying both directions

Common insulation mistakes

Compressed batts: stuffed into too-small cavity → loses R-value (compressed = lower R).

Gaps + voids: airflow through gaps defeats insulation.

Missing air seal: insulation doesn't air-seal; need separate air barrier.

Wrong vapor barrier: trapped moisture → mold.

Insufficient for climate: under-insulated for zone.

Insulating crawl ceiling but leaving ducts unwrapped: ducts heat-lose more than walls.

Buried recessed lights: fire hazard unless IC-rated; wrap clearance per spec.

Wet insulation: doesn't recover R-value; replace.

Tools + safety

Installation tools:

  • Insulation knife (long blade)
  • Staple gun (for faced)
  • Blower / cellulose machine
  • Spray foam rig
  • Tape (vapor barrier)
  • Personal protection (mask, gloves, eye protection)

Safety:

  • Respirator (N95 minimum for fiberglass)
  • Long sleeves + pants
  • Eye protection
  • Avoid contact (fiberglass irritates skin)
  • Ventilation when spray foam

Reading insulation labels

Federal Trade Commission required label:

  • R-value at specific thickness
  • Coverage area per package
  • Settled vs initial value
  • Type identification

Look for:

  • R-value match to design
  • Square footage coverage
  • Settled value (cellulose, blown-in)

Specialty insulation

Acoustic insulation:

  • Mineral wool excellent sound damping
  • Cellulose good
  • Fiberglass mediocre

Fire-rated:

  • Mineral wool best
  • Closed-cell spray foam (with thermal barrier)
  • Fiberglass less

Pest resistance:

  • Cellulose (borate-treated)
  • Mineral wool
  • Fiberglass attracts no pests but doesn't deter

Moisture resistance:

  • Closed-cell spray foam (highest)
  • XPS rigid
  • Closed-cell foam pipe wrap

The single highest-leverage insulation habit is the AIR-SEAL-BEFORE-INSULATING approach. Insulation slows heat transfer; air sealing stops air leakage that bypasses insulation. Without air sealing, even R-60 attic insulation loses 30 - 50% of its effective value to air infiltration. Caulk + foam seal + weatherstrip BEFORE adding insulation. Customer pays you for one job that includes both → 2x the energy savings vs insulation alone. Most contractors don't air-seal; the ones who do deliver real savings.

References

  • ASTM C518 (heat flow measurement)
  • DOE Building America publications
  • ICC IECC (current edition)
  • NAIMA + ICAA industry resources
  • Manuall internal: Building Envelope Fundamentals, Moisture Control Construction

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