What Is R-Value?
R-value (resistance value) is the standard measure of an insulation material's thermal resistance — how well it slows the transfer of heat. The higher the R-value, the better the insulation performance. R-values are additive: two layers of R-19 equal R-38.
R-value is affected by material type, thickness, and density. Spray foam achieves the highest R-value per inch of any commonly used insulation product.
Important: R-value measures resistance to conducted heat. It does not measure air infiltration resistance. This is why air-sealing with spray foam often saves more energy than simply adding insulation — you address both heat conduction and air leakage.
Connecticut Climate Zones
The U.S. is divided into 8 climate zones for building code purposes. Connecticut spans climate zones 5 and 6 — both require significantly higher R-values than southern or coastal states. Fairfield County is primarily Zone 5; northern CT is Zone 6.
| CT Region | Climate Zone | Heating Degree Days | Insulation Requirement Level |
|---|---|---|---|
| Fairfield, New Haven counties | Zone 5 | ~5,500 HDD | High |
| Hartford, Litchfield counties | Zone 6 | ~6,500 HDD | Very High |
R-Value Requirements by Location
| Location | Zone 5 (Min) | Zone 6 (Min) | Recommended (optimal) |
|---|---|---|---|
| Attic / ceiling | R-49 | R-49 to R-60 | R-60 |
| Exterior walls (new) | R-20 | R-20 to R-25 | R-25 |
| Exterior walls (retrofit) | R-13 | R-15 | R-15 to R-21 |
| Basement walls (interior) | R-10 | R-15 | R-15 |
| Crawl space walls | R-10 | R-15 | R-15 |
| Rim joist | R-10 | R-15 | R-20 |
| Floor over unconditioned space | R-30 | R-30 to R-38 | R-38 |
Spray Foam R-Values at Different Thicknesses
| Thickness | Closed Cell R-Value | Open Cell R-Value |
|---|---|---|
| 1 inch | R-6 to R-7 | R-3.5 |
| 2 inches | R-12 to R-14 | R-7 |
| 3 inches | R-18 to R-21 | R-10.5 |
| 4 inches | R-24 to R-28 | R-14 |
| 6 inches | R-36 to R-42 | R-21 |
| 10 inches | R-60 to R-70 | R-35 |
How to Check Your Existing Insulation
- Attic: Measure the depth of blown-in or batt insulation with a ruler. Multiply by the material's R-value per inch (fiberglass blown: ~R-2.5/inch; cellulose: ~R-3.7/inch; fiberglass batt: ~R-3.2/inch).
- Walls: Remove an outlet cover plate on an exterior wall and probe the depth with a wire. Newer batts will be labeled on the facing paper.
- Basement/crawl space: Look for insulation between joists or on foundation walls. Old fiberglass batts often have an R-value printed on the kraft paper facing.
EcoFoam offers free assessments — we'll inspect your home, measure existing insulation, identify problem areas, and give you a written report with recommendations. No obligation.
Frequently Asked Questions
Does more R-value always mean better performance?
Up to a point. There are diminishing returns above certain thresholds. Going from R-11 to R-38 in an attic has a large impact; going from R-38 to R-60 has a smaller marginal gain. Air sealing often delivers more savings per dollar than adding insulation in a well-insulated home.
What R-value does Connecticut code require for new construction?
Connecticut follows the IECC 2021 energy code. Requirements vary by zone: attics R-49 minimum, walls R-20 cavity or R-13+5 continuous, basements R-10 continuous or R-13 cavity. EcoFoam can review your project specifications to confirm compliance.
Can I add more insulation on top of existing insulation?
Often yes. In attics, you can typically add blown-in or batt insulation over existing material. In basements and crawl spaces, spray foam can be applied over existing insulation in some cases. EcoFoam will advise based on your specific situation.