Short answer: Most of Interior Exterior’s Southeast service area falls in IECC Climate Zones 2 and 3 (coastal Gulf and Florida in Zone 2; most of Georgia, Alabama, Mississippi, Louisiana, Tennessee, and the Carolinas’ Piedmont in Zone 3). Typical code-driven targets are roughly R-13 to R-20 walls, R-38 to R-49 attics/ceilings, and R-13 to R-19 floors. Exact minimums depend on your local adopted code, the assembly, and whether you add continuous exterior insulation — always confirm the current local code.
The Southeast spans two main zones. Zone 2 (hot-humid) covers south Florida, the Gulf Coast, and coastal Louisiana/Mississippi. Zone 3 (warm) covers most of Georgia, Alabama, Tennessee, the Carolinas, and inland Louisiana/Mississippi. A few higher-elevation or northern spots edge into Zone 4. Because cooling load dominates here, the biggest wins usually come from attic insulation, air sealing, and radiant/roof strategies rather than thick wall assemblies.
| Assembly | Zone 2 (hot-humid) | Zone 3 (warm) | Notes |
|---|---|---|---|
| Attic / ceiling | R-38 to R-49 | R-38 to R-49 | Biggest bang for the buck in cooling climates. |
| Wood-frame walls | R-13 to R-15 | R-13 to R-20 (or R-13 + continuous) | Continuous exterior board reduces thermal bridging. |
| Mass / CMU walls | R-4 to R-6 c.i. | R-5 to R-8 c.i. | Continuous insulation values, common in commercial. |
| Floors (over unconditioned) | R-13 | R-19 | Over crawlspaces/garages. |
| Crawlspace wall | R-0 to R-5 | R-5 to R-13 | For sealed/conditioned crawlspaces. |
Ranges reflect common IECC targets; adopted codes vary by state and jurisdiction and change over time. Verify the current local requirement for your project.
R-value measures resistance to heat flow — higher R resists more heat transfer. But two details matter as much as the number. First, installation quality: a batt compressed, gapped, or stuffed around wiring loses much of its rated R. Second, thermal bridging: heat bypasses cavity insulation through the studs, so a wall of R-13 batts performs below R-13 overall. Adding continuous insulation (rigid board over the framing) closes that bridge and is why many codes list assemblies as “R-13 + R-5 c.i.”
For cavity fill in walls and floors, fiberglass or mineral wool batts are the common, economical choice. For continuous exterior insulation and for reducing thermal bridging, rigid board (polyiso, XPS, EPS) is used over sheathing. Mineral wool adds fire and acoustic benefits and holds its shape well, which is why it’s popular in commercial and multifamily assemblies and in rated walls. In hot-humid Zone 2, vapor and moisture control is critical — the assembly should be designed so it can dry, and product/facer choice should follow the building science for the wall, not just the R-number.
Prioritize the attic first — it’s the cheapest R to add and the biggest cooling-season payoff in the Southeast. Air-seal before or with insulating, since leakage undermines any R-value. For walls, hit the code cavity R and consider continuous board on higher-performance or commercial projects. And always confirm the R-value against your local adopted energy code, because the same city can update requirements between projects.
Attics in the Southeast (Climate Zones 2–3) commonly target R-38 to R-49. Attic insulation is the highest-value upgrade in a cooling climate, so hitting the upper end and air-sealing the ceiling plane pays off. Confirm your local code minimum for the exact requirement.
Most of Georgia and Alabama are in Climate Zone 3, where wood-frame walls commonly target around R-13 to R-20, or R-13 cavity plus continuous exterior insulation. The exact figure depends on the adopted local code and the wall assembly, so verify before ordering.
Up to a point. Beyond code minimums the returns diminish, and in the Southeast air sealing, attic insulation, and moisture control often matter more than adding wall R. A properly installed R-13 outperforms a poorly installed R-19, so installation quality is as important as the number.
Continuous insulation is rigid board installed over the framing so it isn’t interrupted by studs, which stops heat from bridging through the wood or steel. Many current energy codes require it (for example “R-13 + R-5 c.i.”) on certain assemblies, especially in commercial and steel-framed construction. Check whether your assembly and code call for it.
Yes. Interior Exterior Building Supply stocks batt, rigid board, and mineral wool insulation across its Southeast branches, with jobsite delivery. Tell your local branch the assembly and target R-value and our team will help match the right product and confirm availability.
