Climate Zones
By Kenton Shepard
Climate Zones
Climate varies considerably Across North America. A crawlspace or attic configuration which works well in one climate may perform very poorly in another. For energy code compliance, North America is separated into climate zones, each with special recommendations for insulation levels and ventilation including configurations of crawlspaces and attics and recommendations for foundation types.
You can learn more about existing and proposed climate zones at the U.S. Dept. of Energy climate zone web page.
Here are examples of climate zones is use in various parts of the country.
The Building Envelope
The building envelope is that part of the building which separates indoor conditioned-air space from the unconditioned exterior. It includes the roof (or attic floor, whichever is insulated), exterior walls, windows, doors and lowest level living space floors.
Crawlspaces and attics are both part of what might be called “transition zones”. Typically, they’re not part of the home exterior, exposed to weather and free air movement, but they’re not part of the conditioned-air home interior either. They act as something of a transition zone between outside and inside, each subject to unique conditions and problems.
Crawlspaces
Crawlspace problems are mostly moisture and often temperature problems.
Moisture problems may be caused by rising groundwater, springs, surface runoff seepage under and through foundations and from moisture generated in the home such as leaking pipes and improperly vented clothes dryers. In addition to activating wood decay fungus, high moisture levels can cause the growth of mold fungus to a point at which mold spore concentrations in indoor air rise to unhealthy levels.
Installing a layer of plastic on the floor of the crawlspace (commonly called a soil cover or ground cover) is considered a good idea almost everywhere. This helps reduce crawlspace humidity by preventing moisture from the soil from evaporating into the air, although under certain conditions it may encourage the growth of mold fungus or soil-borne bacteria.
Other decisions in crawlspace construction involve whether to install a vapor barrier between the living space and the crawlspace, whether to insulate the floor or crawlspace walls, whether to insulate the interior or exterior of the crawlspace walls, whether to ventilate the crawlspace, to what extent and where to install vents.
Attics
Attic problems are mostly temperature and sometimes moisture problems.
Attics have typically been configured with insulation installed in the attic floor and a ventilation method of some sort used to remove hot air. This means that the attic space serves as a thermal buffer between the roof assembly and living space.
Attics are ventilated in an effort to achieve different results depending on the season…
Summer (cooling season)
Roof covering materials absorb sunlight as heat and radiate it both back toward the sky and down toward the living space. Some heat is also transferred to the living space through convection, meaning that heat is transferred from roof framing to ceiling framing by heated air. Ventilation is designed to replace heated air with cool air before it can transfer its heat to the ceiling framing and then to the living space, raising cooling costs.
Winter (heating season)
Roofs perform better if kept cool. Heat leaking from the living space can melt snow on the roof. When this melted snow freezes, the ice can damage roof material and create dams which prevent snow and icemelt from draining off the roof. This added moisture can damage roof material and cause leaks. |
