Cold and Very Cold Climate Zone

This map shows the Cold & Very Cold Zones of the United States. The far tips of North Dakota, Maine, and southern Alaska are shown as Very Cold. The northern half of the United States is labeled Cold.

Cold and very cold climates present several challenges for home building. In the cold and very cold climates, houses must be nimble in response to changing temperature and moisture conditions.

The combination of cold winters and hot summers is common in these climates. Finding methods to enhance building performance under cold conditions is a priority, but the house also must accommodate summers, which often bring blistering heat and, in some places, humidity.
During the winter heating season, vapor may be driven from the building interior into the walls, roof, and floors. Ice dams are an example of a cold climate problem that involves temperature, air leakage, and moisture. In summer, air conditioning can force vapor flow in the opposite direction, with cold, dry air on the inside, and hot, moist air from the outside being forced in. Houses in the cold and very cold climates cannot be built as if they are one-way streets for moisture transfer.
The use of full basements and crawlspaces is common in these climates and presents another set of challenges. These design features may bring extra living and storage space, but they also bring their own moisture and temperature management challenges.

Cold and Very Cold Climate Best Practices

Housing types vary greatly throughout the cold and very cold climates.

In the face of this diversity, no single set of measures will achieve the 30 percent energy savings in space conditioning and water heating that qualifies a home as ENERGY STAR^®-qualified. The principles included in these best practices need to be adjusted for different circumstances. A building scientist, such as a home energy rating professional, can help homeowners determine which combination of best practices is most appropriate.

These best practices are derived from Building America's research on tens of thousands of homes. Building scientists have tried and tested these measures on actual homes in the field. While not every measure will be right for a specific home, achieving high-efficiency performance and a healthy indoor environment depends on making informed decisions about interactions among all aspects of the building system.

Special Considerations for the Cold and Very Cold Climate

Site Design

In the cold and very cold climates, planners should do all they can to use the sun for daylighting and solar gain. Site planners have two important tools to help manage solar gain: lot orientation and shade trees.

Xeriscaping

In the low-water environments of the western plains, lots should be landscaped to take advantage of plants that use less water than traditional turf-dominated approaches. Many communities have been faced with increased demands on existing water supplies. Consequently, there is a greater focus on water conservation, not just in times of drought, but in anticipation of future population growth. Water can no longer be considered a limitless resource. Conserving water through creative landscaping has engendered the new term, xeriscape. The term is taken from the Greek xeros, meaning dry, in combination with landscape.

The goal of a xeriscape is to create a visually attractive landscape that uses plants selected for their water efficiency. Properly maintained, a xeriscape can easily use less than one-half the water of a traditional landscape. Once established, a xeriscape should require less maintenance than turf landscape.

By grouping plants with similar water needs together in specific zones, a xeriscape landscape can use water more efficiently. Low-water-use plants should be grouped together, away from high-water-use plants and turf. Take advantage of warm or cool microclimates (climatic conditions influenced by the placement of walls and shade trees) to create areas of interest and diversity.

A well-planned and well-maintained irrigation system can significantly reduce a traditional landscape's water use. For the most efficient use of water, irrigate turf areas separately from other plantings. Other irrigation zones should be designed so low-water use plants receive only the water they require. Proper irrigation choices can also save water. Turf lawns are best watered by sprinklers. Trees, shrubs, flowers, and groundcovers can be watered efficiently with low-volume drip emitters, sprayers, and bubblers.

The information presented here was adapted from the City of Albuquerque's Web site.

Foundations

Slabs, crawlspaces, and basements are all found in the cold and very cold climates. Building foundations should be designed and constructed to prevent the entry of moisture and other soil gases such as radon.

Slabs in this climate should be insulated at the perimeter with one to two inches of borate-treated foam board insulation or rigid glass fiber insulation.

Walls

Wood Frame Walls

Best practice for frame wall construction involves advanced framing techniques. However, these techniques are not required to achieve 30 percent space conditioning energy savings in the cold and very cold climate zones. More information on gaining greater efficiency using advanced framing can be found at the Building Science Consulting Web site. If advanced framing is to be used, a detailed plan should be developed showing framing placement.

External walls with 2 x 6 framing are often used in the cold and very cold climates. These walls should include the following features:

Exterior sheathing, preferably insulating sheathing with joints taped to provide a water and air barrier. (Use insulating sheathing that does not have a film facing.)
R-19 friction-fit insulation, kraft-faced fiberglass insulation or blown-in cellulose insulation.
Unfaced or kraft-faced insulation on frame walls between the garage and the conditioned space, including bonus rooms. (Kraft facing is needed in severe cold climates.)
Rim joists that have kraft-faced R-19 friction-fit batt insulation cut to fit.
Foam-sealed or caulked top-plate and exterior wall penetrations.
Sealed gypsum board to control air leakage through the walls, especially in penetrations to garages and porches and where the walls meet the ceiling.

Structural Moisture Control

Annual precipitation in the cold and very cold climates varies substantially, but often the precipitation comes in heavy doses as part of intense storms. Moisture can come from other sources, such as landscape irrigation and indoor activities. In some regions, periodic humidity is also present.

Carefully install insulation and air barriers to avoid ice dams. Ice dams are a particular problem in cold and very cold climates. When roof snow melt refreezes, it can build up ice that blocks water flow. Newly melted snow adds to the ice dam and may cause water to back up under shingles and flashing, creating safety hazards with suddenly released snow and ice. Snow could be melted by warm air that leaked from the house into the attic. The control of outwardly leaking air is the most effective means of stopping ice dams. This can be accomplished by the installation of air barriers (see the section on Structural Air Sealing). Well insulated roof areas also help to keep the surface of the roof cool to avoid the melt-freeze cycle (see the section on insulation). Install a water protection membrane at eaves and in roof valleys to protect against snow-melt and rain that backs up behind ice dams.
In cold climates, air barriers and vapor retarders are installed on the interior of the building assemblies. And building assemblies are designed to dry to the exterior by installing permeable sheathings and building paper or housewraps toward the exterior (Lstiburek 2004). Unless specifically required by local building code, a polyethylene vapor retarder (between the framing and the drywall) is not recommended because it limits a wall's ability to dry to the inside. In a wood frame wall with carefully installed batt insulation, the kraft facing on the batt would provide the necessary protection against vapor diffusion from interior sources for this climate. In the case of other exterior wall assemblies, drywall painted with latex paint suffices (Broniek, 2003).

Insulation

Slab Foundation Insulation

Exterior insulation should be applied from the top of the foundation wall to the bottom of the frost line. Cover the exterior face of the insulation exposed to outside air using material such as flashing, fiber cement board, parging (stucco type material), treated plywood, or membrane material.
Building America teams suggest extending the under-slab insulation for the entire surface area of the slab. With this approach the rigid insulation can replace the otherwise needed polyethylene vapor retarder under the slab. This is not needed to achieve 30 percent energy savings in space conditioning, but the resulting warmer floors help prevent the formation of condensation on the floor and improve comfort.

Basement Insulation

Basements are a common foundation system in the cold and very cold climate. Wall insulation in basements is similar to the approaches described for crawlspaces, and basement floors are insulated in ways similar to slabs.