3.      Climate

The International Code Council has divided the country into climate zones that help determine what qualities are important for homes in a given location, per their IECC Map. Each zone represents locations with progressively higher heating degree days, used to calculate how much heat a house will need to stay warm in winter. Sometimes confused with the USDA plant hardiness map, which shows the lowest average annual temperature and is not relevant for home design. At the borders of the climate zones and in micro-climates within climate zones there may be different conditions than at the center of the climate zone. The country is further divided into “dry,” “moist” and “marine” zones. A similar, useful map is from the US Department of Energy’s Building America program, which classifies regions into Hot-Humid, Mixed-Humid, Hot-Dry, Mixed-Dry, Cold, Very Cold, and Marine zones. The IECC map is what designers and code officials generally use.  

Zone 1 is hot and includes the southern tip of Florida, as well as Hawaii, Guam, Puerto Rico and the Virgin islands. (From what I’ve heard, Hawaii isn’t particularly hot, but it’s also never cold, so it fits this zone.)

Zone 2 is hot and includes most of Florida, the gulf coast and southern Arizona.

Zone 3 is mixed, with both heating and cooling needed to maintain comfort. It covers much of the south, from Georgia and the Carolinas west to northern Texas, Oklahoma and southern New Mexico, and much of California. 

Zone 4 is mixed, covering most of Virginia and Maryland west to southern Kansas and southern New Mexico, and also the Pacific coast of Washington, Oregon and far northern California.

Zone 5 is considered a cold climate, including southern New England and New York west to the Rocky Mountains, and the bulk of Washington, Oregon, Nevada, Utah, northern Arizona and northern New Mexico.

Zone 6 is solidly cold climate and is where the Pretty Good House team is based; most of us work in Zone 6 and a bit in Zone 5. We have a climate dominated by heating, but technically we also need some cooling in summer to keep temperatures within comfort ranges. Zone 6 includes most of northern New England, northern Michigan, most of Wisconsin and Minnesota, South Dakota, most of Wyoming and all of Montana. 

Zone 7 is very cold, including the northern tip of Maine, part of Michigan’s upper peninsula, the northernmost parts of Wisconsin, Minnesota and North Dakota, and parts of the Rocky Mountains. Zone 7 also includes most of Alaska.

Zone 8 is sub-arctic, i.e., wicked cold.

The climate zones are sub-divided into Moist, Dry and Marine categories. The dividing line between Moist (A) and Dry (B) runs roughly north-south, just east of the continental divide at the Rocky Mountains, with the east being Moist and the west being Dry. The Pacific Coast has its own designation as a Marine climate.

For our Canadian neighbors (or neighbours): according to building scientist Allison Bailes in his Energy Vanguard blog, your climate corresponds to the following US zones:

Vancouver: 4C

Toronto: 5A

Ottowa, Montreal and Quebec: 6A

Calgary: 7B

Changing climate. Like it or not, the world’s climate zones are shifting due to climate change, primarily due to human activity. The results are hard to predict accurately but most scientific models show that by 2050 climate zones will have shifted about 500 miles toward the poles. In Maine, we can expect to have a climate comparable to today’s Virginia climate. We all need to do what we can to mitigate climate change, but we should also plan ahead for future requirements—before long, we will need less heating and more cooling and dehumidification than we do now.