Spray foam guide: open vs closed cell, R-values and costs by climate zone
Every city page on this site links here for the general guidance, so the city pages can stick to local facts. Find your zone on your city page, then read that section.
Questions to ask every installer
- Foam type, brand, thickness and resulting R-value for each area, in writing.
- Which climate zone and code edition they're designing to.
- Whether removal of old insulation, air sealing, and any required ignition/thermal barrier coating are included.
- Which utility or state rebate programs they participate in, and who files the paperwork.
- Whether they'll do (or coordinate) combustion safety testing if you have gas appliances.
Climate zone 2A
Attic roofline: in climate zones 1–3 an unvented ("sealed") attic with open-cell foam sprayed under the roof deck is a common way to bring attic ductwork and air handlers inside the insulated envelope. The International Residential Code (Section R806.5) allows unvented attics with air-impermeable insulation such as spray foam; for a hybrid "flash-and-fill" assembly the foam layer at the deck must be at least R-5 in zone 2A.
Humidity: in a hot-humid climate, a sealed attic becomes part of the conditioned house. Ask how the installer and your HVAC contractor will handle attic humidity (for example a small supply-air connection or dehumidification).
Closed cell earns its higher price where you need a vapor retarder or water resistance: crawlspace walls, rim joists, below-grade walls.
| Where | ENERGY STAR, zone 2A |
|---|---|
| Attic, uninsulated | R-49 |
| Attic with 3–4" existing | add R-38 |
| Floor over unconditioned space | R-13 |
Foam alone to R-49: about 13.2–14.0" of open cell or 7.0–9.8" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 2B
Attic roofline: in climate zones 1–3 an unvented ("sealed") attic with open-cell foam sprayed under the roof deck is a common way to bring attic ductwork and air handlers inside the insulated envelope. The International Residential Code (Section R806.5) allows unvented attics with air-impermeable insulation such as spray foam; for a hybrid "flash-and-fill" assembly the foam layer at the deck must be at least R-5 in zone 2B.
Dry climate note: zone 2B is a dry ("B") zone, so winter condensation in roof sheathing is less of a concern than in humid regions; the bigger issue is extreme attic heat, which is why roofline foam and duct location matter.
Closed cell earns its higher price where you need a vapor retarder or water resistance: crawlspace walls, rim joists, below-grade walls.
| Where | ENERGY STAR, zone 2B |
|---|---|
| Attic, uninsulated | R-49 |
| Attic with 3–4" existing | add R-38 |
| Floor over unconditioned space | R-13 |
Foam alone to R-49: about 13.2–14.0" of open cell or 7.0–9.8" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 3A
Attic roofline: in climate zones 1–3 an unvented ("sealed") attic with open-cell foam sprayed under the roof deck is a common way to bring attic ductwork and air handlers inside the insulated envelope. The International Residential Code (Section R806.5) allows unvented attics with air-impermeable insulation such as spray foam; for a hybrid "flash-and-fill" assembly the foam layer at the deck must be at least R-5 in zone 3A.
Humidity: in a hot-humid climate, a sealed attic becomes part of the conditioned house. Ask how the installer and your HVAC contractor will handle attic humidity (for example a small supply-air connection or dehumidification).
Closed cell earns its higher price where you need a vapor retarder or water resistance: crawlspace walls, rim joists, below-grade walls.
| Where | ENERGY STAR, zone 3A |
|---|---|
| Attic, uninsulated | R-49 |
| Attic with 3–4" existing | add R-38 |
| Floor over unconditioned space | R-19 |
| Basement or crawlspace walls | R-5 continuous or R-13 cavity |
| Exterior walls (when re-siding) | add R-5 insulative wall sheathing beneath new siding |
Foam alone to R-49: about 13.2–14.0" of open cell or 7.0–9.8" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 4A
Attic roofline: both foams are used. The IRC (R806.5) does not require a vapor-retarder coating on open-cell foam under the roof deck in zone 4A (that requirement starts in zone 5), but for hybrid assemblies the foam layer at the deck must be at least R-15 to control condensation. Ask the installer how they manage winter moisture at the roof sheathing.
Closed cell is the usual choice for rim joists, basement and crawlspace walls, where its vapor resistance (about 1.5–2" makes it a Class II vapor retarder) matters most.
| Where | ENERGY STAR, zone 4A |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-19 |
| Basement or crawlspace walls | R-10 continuous or R-13 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 4B
Attic roofline: both foams are used. The IRC (R806.5) does not require a vapor-retarder coating on open-cell foam under the roof deck in zone 4B (that requirement starts in zone 5), but for hybrid assemblies the foam layer at the deck must be at least R-15 to control condensation. Ask the installer how they manage winter moisture at the roof sheathing.
Closed cell is the usual choice for rim joists, basement and crawlspace walls, where its vapor resistance (about 1.5–2" makes it a Class II vapor retarder) matters most.
| Where | ENERGY STAR, zone 4B |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-19 |
| Basement or crawlspace walls | R-10 continuous or R-13 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 5A
Attic roofline: in zone 5A, IRC Section R806.5 requires that air-impermeable insulation under an unvented roof deck either be a Class II vapor retarder itself or be covered with a vapor-retarder coating. Closed-cell foam meets that on its own at typical thicknesses; open-cell foam needs vapor-retarder paint. In a hybrid assembly the foam layer at the deck must be at least R-20.
Rim joists and basement walls are where spray foam pays off fastest in cold climates: closed cell air-seals the leaky band joist and blocks moisture in one pass, which is hard to do with batts.
| Where | ENERGY STAR, zone 5A |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-30 |
| Basement or crawlspace walls | R-15 continuous or R-19 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 5B
Attic roofline: in zone 5B, IRC Section R806.5 requires that air-impermeable insulation under an unvented roof deck either be a Class II vapor retarder itself or be covered with a vapor-retarder coating. Closed-cell foam meets that on its own at typical thicknesses; open-cell foam needs vapor-retarder paint. In a hybrid assembly the foam layer at the deck must be at least R-20.
Rim joists and basement walls are where spray foam pays off fastest in cold climates: closed cell air-seals the leaky band joist and blocks moisture in one pass, which is hard to do with batts.
| Where | ENERGY STAR, zone 5B |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-30 |
| Basement or crawlspace walls | R-15 continuous or R-19 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 6A
Attic roofline: in zone 6A, IRC Section R806.5 requires that air-impermeable insulation under an unvented roof deck either be a Class II vapor retarder itself or be covered with a vapor-retarder coating. Closed-cell foam meets that on its own at typical thicknesses; open-cell foam needs vapor-retarder paint. In a hybrid assembly the foam layer at the deck must be at least R-25.
Rim joists and basement walls are where spray foam pays off fastest in cold climates: closed cell air-seals the leaky band joist and blocks moisture in one pass, which is hard to do with batts.
| Where | ENERGY STAR, zone 6A |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-30 |
| Basement or crawlspace walls | R-15 continuous or R-19 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Climate zone 7
Attic roofline: in zone 7, IRC Section R806.5 requires that air-impermeable insulation under an unvented roof deck either be a Class II vapor retarder itself or be covered with a vapor-retarder coating. Closed-cell foam meets that on its own at typical thicknesses; open-cell foam needs vapor-retarder paint. In a hybrid assembly the foam layer at the deck must be at least R-30.
Rim joists and basement walls are where spray foam pays off fastest in cold climates: closed cell air-seals the leaky band joist and blocks moisture in one pass, which is hard to do with batts.
| Where | ENERGY STAR, zone 7 |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" existing | add R-49 |
| Floor over unconditioned space | R-38 |
| Basement or crawlspace walls | R-15 continuous or R-19 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
Foam alone to R-60: about 16.2–17.1" of open cell or 8.6–12.0" of closed cell. Roofline jobs are often thinner and justified through the code's performance path or unvented-attic rules.
Sources: ENERGY STAR, Recommended Home Insulation R-Values (based on 2021 IECC); IRC Section R806.5; PNNL-33270, Guide to Determining Climate Zone by County (IECC 2021).
Coastal and flood-prone homes
FEMA Technical Bulletin 2 lists closed-cell foam among flood-damage-resistant materials; open-cell foam is not.
Metal buildings, pole barns and shops
For uninsulated metal roofs and walls, closed-cell foam sprayed directly on the panels is used both as insulation and as a vapor retarder to stop condensation from forming and dripping on the underside of the metal. When you request quotes, choose "Metal building / pole barn" and give the building's footprint and wall height; ask each installer for foam type, thickness, and whether a thermal or ignition barrier coating is required for how the building will be used.
What spray foam costs (national published ranges)
We don't publish local prices until we have real local quotes.
| Example job (typical thickness) | Estimated installed range |
|---|---|
| 1,000 sq ft attic roofline, open cell (6") | $3,600–$9,600 |
| 1,000 sq ft attic roofline, closed cell (3") | $3,900–$9,300 |
| 1,500 sq ft walls, open cell (3.5") | $3,150–$8,400 |
| 1,500 sq ft walls, closed cell (2") | $3,900–$9,300 |
| 200 sq ft rim joists, closed cell (2") | $520–$1,240 |
Board feet × Angi's 2026 installed price per board foot. Check a quote you already have →
Where the cost numbers come from
- Per-board-foot installed prices: open cell $0.60–$1.60, closed cell $1.30–$3.10. Source: Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026).
- Per-square-foot installed prices: open cell $1.50–$3.50, closed cell $3.00–$5.00; many companies have job minimums of $1,000–$2,000+. Source: HomeGuide, "How Much Does Spray Foam Insulation Cost? (2026)" (Dec 1, 2025).
- Typical thickness defaults: Profoam spray foam price sheet (prices valid Aug 1, 2026): "2" avg in walls / 3" avg in roof lines" (closed cell), "3.5" avg in walls / 6" avg in roof lines" (open cell).
These are national published ranges, not local prices. We don't publish local prices until we have real local quotes.
FAQ
Open cell or closed cell: which is better?
Neither in general. Open cell is cheaper per inch and common under roof decks in warm zones; closed cell costs more but adds vapor and water resistance, which matters for rim joists, crawlspace and basement walls, metal buildings and flood-prone areas, and for unvented roofs in zone 5 and colder.
How thick should spray foam be?
Ask every installer to write foam type, thickness and resulting R-value for each surface on the quote, and explain how it meets your local code. ENERGY STAR targets are recommendations for existing homes; your code sets the minimum for new work.
Is there a federal tax credit for spray foam in 2026?
No. The 25C credit does not apply to insulation placed in service after December 31, 2025. Utility programs and state Home Energy Rebates are what remain; see the rebate tracker.