ND Association of Builders

Building for Energy Efficiency

Building Your Energy Efficient Home

There are many basic house design characteristics that can lower heating and cooling costs. By doing some planning up front, your new home can be heated and cooled with minimal energy usage.

Even though low utility bills will pay back the higher initial building costs in the long run, you may not be able to afford all the energy-saving features right away. Get cost estimates on the features, and make your choices.

When planning a home with budget constraints, there are three major design factors affecting the energy usage of a house:
    *Basic design and shape
    *Type and amount of insulation and air-tightness
    *Quality of the mechanical systems

Many specific factors within each of these three general categories affect your utility bills to varying degrees. Under the basic design category, you should consider the:
    *Type and shape of the house
    *Potential for solar utilization
    *Amount and type of window glass area

For a given interior floor space, a square-shaped house minimizes the total outside wall area. Less outside wall area means less energy loss. A two-story house is better than a single-story one because it reduces the amount of roof area for a given floor space area.

Insulation
For thermal protection, the higher the level of insulation, the better. Rigid foam insulation sheets on the exterior provide the highest insulating R-value per inch thickness. These also form a natural air barrier for reduced air leakage. Pre-manufactured complete foam core building panels are an excellent choice for energy efficiency.

Recommended Insulation Levels for North Dakota
For North Dakota, the Department of Energy recommends these insulation levels:
    Attic: R-49
    Cathedral Ceiling: R-38 (R-60 if electric furnace)
    Wall*: R-18 (R-28 if electric furnace)
    Floor: R-25
    Crawl Space**: R-19
    Slab Edge: R-8
    Basement Interior Walls: R-11 (R-19 if electric furnace)
    Basement Exterior Walls: R-10 (R-15 if electric furnace)

*R-18, R-22, and R-28 exterior wall systems can be achieved by either cavity insulation or cavity insulation with insulating sheathing. For 2 in x 4 in walls, use either 3-1 /2 -in thick R-15 or 3-1 /2-in thick R-13 fiber glass insulation with insulating sheathing. For 2 in x 6 in walls, use either 5-1 /2-in thick R-21 or 6-1 /4-in thick R-19 fiber glass insulation.

**Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, and all ventilation to the crawl space is blocked. A vapor retarder (e.g., 4- or 6-mil polyethylene film) should be installed on the ground to reduce moisture migration into the crawl space.

To meet these recommendations, most homes and additions constructed with 2 in x 4 in walls require a combination of wall cavity insulation, such as batts and insulating sheathing or rigid foam boards. If you live in an area with an insulation recommendation that is greater than R-20, you may want to consider building with 2 in x 6 in framing instead of 2 in x 4 in framing to allow room for thicker wall cavity insulation—R-19 to R-21.

When shopping for insulation watch for the ENERGY STAR® label and the National Association of Home Builders (NAHB) certification.

Windows
Unless you are designing a passive solar house, minimize the window area, especially on north and west walls. It is generally worth the additional cost to get windows that are highly efficient (glass R-values up to R-9). Plan to build a large roof overhang on south-facing windows to shade them from the intense summer sun.

When you’re shopping for new windows, look for the National Fenestration Rating Council (NFRC) label; it means the window’s performance is certified. Remember, the lower the U-value, the better the insulation. In colder climates, a U-value of 0.35 or below is recommended. These windows have at least double-glazing and low-e coating. Select windows with air leakage ratings of 0.3 cubic feet per minute or less.

Heating and Cooling
Select energy efficient mechanical systems – furnace, air conditioner, and water heater. Locate them near the center of the house to minimize duct and hot water pipe length.

When buying heating and cooling equipment, look for high Annual Fuel Utilization Efficiency (AFUE) ratings and the Seasonal Energy Efficiency Ratio (SEER). The national minimums are 78% AFUE and 10 SEER.

Be sure air conditioning units are not in direct sunlight. Plant trees or shrubs to shade the unit, but be sure they don’t block airflow. A unit operating in the shade uses approximately 10% less electricity than the same one operating in the sun.

Water Heaters
Buy a new energy-efficient water heater. While it may cost more initially than a standard water heater, the energy savings will continue during the lifetime of the appliance.

 

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