Once you’ve decided on spray foam over fiberglass or blown-in, the next decision is which type of spray foam. Open-cell and closed-cell foam are both polyurethane, both expand on application, and both will air-seal your home — but they perform very differently, cost very differently, and belong in very different parts of a Tennessee home. Here’s how to choose.
Which spray foam should I use in a Chattanooga home?
Use closed-cell in crawl spaces, rim joists, basement walls, metal buildings, and below-grade applications — anywhere moisture or structural rigidity matters. Use open-cell in attic roof decks and interior walls of conditioned living space, where its lower cost and better sound dampening shine.
Side-by-side specs
| Spec | Open-cell | Closed-cell |
|---|---|---|
| R-value per inch | R-3.6 to R-3.8 | R-6.5 to R-7.0 |
| Density | 0.5 lb/cu ft | 2.0 lb/cu ft |
| Vapor permeability | Permeable (10+ perms) | Impermeable (<1 perm) |
| Air barrier | Yes (3.5" minimum) | Yes (1.5" minimum) |
| Adds structural strength | Minimal | Yes (up to 250% rack strength) |
| Flood resilience | Holds water | Sheds water |
| Sound dampening | Excellent | Good |
| Installed cost (TN) | $1.10–$1.55/bd ft | $1.85–$2.85/bd ft |
Where open-cell belongs
Open-cell foam expands ~100x its liquid volume, completely filling a wall or roof-deck cavity. In Chattanooga’s Climate Zone 4 (mixed-humid), the right home for open-cell is:
• Attic roof decks in conditioned attics (R-19 to R-30 at typical 5–8″ depth)
• Interior walls where soundproofing between rooms matters (open-cell beats batts for STC rating)
• Vaulted ceilings with limited rafter depth and no need for vapor control
The catch: open-cell is vapor-permeable, so it should never be used on the cold side of an assembly that sees big temperature swings (crawl spaces, basements, metal building skins).
Where closed-cell belongs
Closed-cell is denser, more rigid, vapor-impermeable, and roughly 2x more expensive. It’s the right call when any of these matter:
• Crawl space walls and rim joists — the vapor barrier alone justifies the cost
• Basement walls — closed-cell is the only foam approved against below-grade concrete
• Metal buildings and pole barns — bonds to steel, controls condensation on metal panels
• Flood-prone areas — closed-cell is the only insulation rated FEMA Class 5 (sheds water)
• Tight cavities — 2″ of closed-cell hits R-13, matching a 2×4 fiberglass batt
Common Tennessee home configurations
| Home type | Recommended approach |
|---|---|
| 1980s ranch on crawl space | Closed-cell on crawl walls + rim joists; open-cell attic roof deck |
| New construction stick-built | Open-cell on roof deck + interior walls; closed-cell on rim joists only |
| Lookout Mountain cabin | Closed-cell throughout (moisture + rodent resistance) |
| Barndominium / metal building | Closed-cell on all metal-contact surfaces; open-cell OK on interior framing |
| 1920s craftsman (St. Elmo, Highland Park) | Closed-cell in basement; dense-packed cellulose in walls (preserves vapor profile) |
Cost reality check
On a 2,000 sq ft Chattanooga home, the typical hybrid spec — open-cell attic plus closed-cell crawl space and rim joists — runs $9,500 to $14,500 installed. Going all-closed-cell pushes the same project to $17,000–$24,000. The hybrid approach is where 80% of our Chattanooga customers land because it captures the durability where it matters without paying premium prices on every interior wall.