Williamson County is in IECC Climate Zone 2A (Hot - Humid). Get accurate Manual J load calculations with official ASHRAE design temperatures for Williamson County.
Williamson County, Texas is classified under IECC Climate Zone 2A (Hot - Humid), a cooling-dominated region with humid moisture conditions. With 29 ZIP codes and 1 communities, every HVAC installation in Williamson County must use the ASHRAE design temperatures of 28°F (99% winter heating) and 100°F (1% summer cooling) for accurate Manual J load calculations.
As a cooling-dominated zone, controlling solar heat gain is essential in Williamson County. Windows must have an SHGC of 0.25 or lower, along with R-13 wall and R-30 ceiling insulation. Proper sizing prevents oversized AC systems that short-cycle and waste energy.
Minimum insulation R-values and window performance for Climate Zone 2A in Williamson County, TX.
| Building Component | Minimum Requirement | Unit |
|---|---|---|
| Ceiling / Attic Insulation | R-30 | R-value |
| Wall Insulation | R-13 | R-value |
| Floor Insulation | R-13 | R-value |
| Window U-Factor | 0.4 | BTU/hr-ft²-°F |
| Window SHGC | 0.25 | Coefficient |
| Air Infiltration | 0.25 | ACH50 |
Climate Zone 2A requires precise load calculations. Upload your Williamson County blueprint and get a professional Manual J report in 60 seconds— first report is FREE. Pre-loaded with Williamson County's exact design temperatures (28°F winter / 100°F summer).
Enter your ZIP code to confirm it's in Williamson County and get climate zone details.
Official ASHRAE design temperatures for Williamson County, TX, used for accurate Manual J load calculations.
Minimum insulation and window requirements for Williamson County per IECC 2021 energy code.
Climate Zone 2A: Hot - Humid - Cooling-dominated with hot, humid summers and mild winters. Significant cooling loads with moderate heating needs.
1 cities and communities in Williamson County share Climate Zone 2A requirements.
Compare climate zones with other counties in Texas. Different zones require different HVAC equipment sizing.
Upload your Williamson County blueprint and get a professional Manual J load calculation using official Zone 2A design temperatures. First report is FREE.
Join 10,000+ Texas contractors who trust AutoHVAC