Country’s Climates Not Created Equal: Climate Zones

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When it comes to building homes, renovating homes, or simply improving homes, the building must be suited to its climate. This is a fundamental principle of building science. In order for a home to function at its best, the home must be suited for the outdoor climate. For this reason, our country is split up into different climate zones based on both temperature and moisture.


The Building Science Corporation developed the map above, which is split into hygrothermal regions (humidity and temperature). The International Code Council developed a more detailed map of each region, in which each zone has a number (shown below).


The zones begin at the southernmost tip of the country: Florida. As the zone number increases, the climate’s temperature drops. The temperature divisions are determined by the accumulated temperature calculations called “degree days;” they are not simply based on how hot or cold the regions are. These “degree days” use a formula of both time and the temperature difference between outside and a given base temperature. For example, the typical base temperature for heating your home is 65 degrees F. If the outside temperature is 55 degrees F for 24 hours, then that region receives 10 “heating degree days” (HDD). The same goes for cooling a home. With a base temperature of 50 degrees F, let’s say that the outdoor temperature is 90 degrees F for 24 hours. This then accumulates to 40 “cooling degree days” (CDD). After collecting each HDD and CDD for the year, each category is added up to report how hot, cold, or mild the respective climate is.

The climate zones consider both temperature and moisture level. For example, a home that is in a zone with tropical humidity has different needs than a home in a desert. Generally, the East is moist, the West is dry, and the humidity levels are “marine” along the West Coast. A “dry” climate is determined by the amount of precipitation and the annual mean temperature. A “marine” climate is one that is not too hot in the summer and not too cold in the winter (and vise versa). A “marine” climate has a mean temperature about 50 degrees F for at least four months annually, and also has its dry season in the summer. The “moist” regions are essentially the regions that do not fit into the “dry” or “marine” category, and that have a fair amount of annual rainfall.

At Dolphin, we build for our climate zone. Some contractors disregard either temperature or moisture, and end up insulating a home in Massachusetts for how a home in Georgia should be insulated. With Dolphin, you can be certain that your New England home will be ready for New England weather. We know the facts and we are here to let you know too. To someone in building science, knowing the climate zones should be like knowing your home address. We insulate and seal homes for our climate in order to help your home achieve its maximum potential.