Insulation R-Value + Type Reference
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