The 30-Second Verdict
Closed-cell spray foam delivers the best Florida performance — air sealing and insulation in one application, with excellent moisture resistance. Blown-in cellulose is the cost-effective standard for attic floors.
Head-to-Head Breakdown
Spray Foam Insulation
Pros
- Air barrier AND insulation in one product — eliminates infiltration
- Closed-cell: R-6.5/inch — highest R-value per inch
- Excellent moisture vapor resistance in Florida's humid climate
- Rigid — adds structural strength to walls and roof deck
Cons
- Highest cost: $1.50–$4.00/sq ft per inch of depth
- Requires professional installation
- Off-gassing during installation requires vacating home 24–48 hours
- Cannot be re-used or recycled
Blown-In Fiberglass/Cellulose
Pros
- Most cost-effective for attic floor insulation — $1.00–$2.00/sq ft installed
- Cellulose is fire-resistant and has excellent sound attenuation
- Easy to add depth for increased R-value
- Good for retrofitting existing Florida attics
Cons
- Air permeable — doesn't seal air leaks like spray foam
- Cellulose can settle 15–20% over time, reducing effective R-value
- Can absorb moisture if there's a roof leak — monitor in Florida
Side-by-Side Comparison
| Spray Foam Insulation | Blown-In Fiberglass/Cellulose | |
|---|---|---|
| Cost Per Sq Ft (attic) | $1.50–$4.00/sq ft (closed-cell) | $0.80–$2.00/sq ft installed |
| R-Value Per Inch | Closed-cell: R-6.5 | Open-cell: R-3.5 | Fiberglass: R-2.5 | Cellulose: R-3.2 |
| Air Sealing | Excellent — forms continuous barrier | None — must seal separately |
| Moisture Resistance | Excellent (closed-cell) / Moderate (open) | Good when dry — vulnerable to leaks |
| Florida Code Requirement (attic) | R-38 minimum | R-38 minimum (blown-in achieves easily) |
| Best Application | Attic rafters, crawl spaces, walls | Attic floors, wall retrofits |
| Federal Tax Credit | 30% (up to $1,200 cap) | 30% (up to $1,200 cap) |
| Best For | Maximum performance, new construction, coastal FL | Attic floor top-up, cost-conscious upgrade |
Frequently Asked Questions
What R-value does Florida code require for insulation?
Florida Energy Code requires R-38 for attic insulation in most climate zones (R-30 in some South FL zones). Walls: R-13 cavity + R-5 continuous or R-20 cavity. Floors over unconditioned space: R-19. Most Florida homes built before 2005 are significantly under-insulated by current standards.
Is spray foam worth it in Florida vs. blown-in?
Closed-cell spray foam on the underside of roof rafters (converting to unvented attic) is the premium Florida solution — it dramatically reduces attic temperatures and keeps HVAC ductwork in conditioned space. It costs 3–4x more than blown-in but delivers proportionally greater energy savings. For attic floor applications, blown-in cellulose or fiberglass is the cost-effective standard.