How were the IECC Climate Zones maps developed?
Were high resolution zone maps developed and then adjusted to match the county boundaries—perhaps with a generous safety margin—or something different entirely?
My brothers’ houses, 150 feet apart, are in different counties. One house is in Zone 3 (Johnston County, NC), the other in Zone 4 (Harnett County, NC). Should my Zone 3 brother be concerned that he’s really experiencing Zone 4 conditions (and vice versa)?
A generous safety margin might imply that some true zone 3 climate locations are well into Zone 4 map areas which can have a large impact on those with a tighter budget.