With todays rising energy costs, designing and building energy-efficient homes is becoming more popular than ever. Improved designs, materials and construction methods can contribute to heating and cooling bills that are much lower than we are used to. With the demand for energy-efficient homes constantly rising, more and more people are leaning towards this type of home due to recent reduction in building costs and incentive programs sponsored by the government.
Below is an overview of the elements of energy-efficient home design.
The Thermal Envelope
The "thermal envelope" are features of the house that serve to protect the living space from the elements. It includes the wall and roof systems, windows and doors, insulation and weather-stripping, and air/vapour barriers.
Wall and Roof Systems
There are many alternatives to the conventional framed wall and roof construction now available. They include:
Insulation
Homes that are designed to be energy-efficient will have higher insulation R-values than a standard home. Typically a home built in Simcoe County should have a minimum attic insulation value of R-31. A home designed to be energy efficient will have the same insulation at a much higher value, R-50 or higher for example. Insulation is available in many different forms, fiberglass batt or rolls, wet-spray cellulose, blown fiberglass or even spray foam.
Air / Vapour Retarders
These are two things that sometimes can do the same job. Water vapour condensation is a major threat to the structure of a house. In cold climates, pressure differences can drive warm, moist indoor air into exterior walls and attics which condenses as it cools. It is important to minimize water vapour movement by using a carefully designed thermal envelope when constructing a home. Any water vapour that does manage to get into the walls or attics must be allowed to get out again.
Foundations and Slabs
Foundations should be as well insulated as the living space walls. Uninsulated foundations have a negative impact on home energy use and comfort, especially if the family uses the lower parts of the house as a living space. Also, appliances that supply heat as a by-product, such as domestic hot water heaters, washers, dryers, and freezers, are often located in basements. By carefully insulating the foundation walls and floor of the house, these appliances can assist in the heating of the house.
Windows
The average home loses over 25% of its heat through windows. Since even modern windows insulate less than a wall, in general an energy-efficient home in heating dominated climates should have few windows on the north, east, and west exposures. A rule-of-thumb is that window area should not exceed 8-9% of the floor area, unless your builder is experienced in passive solar techniques. If this is the case, then increasing window area on the southern side of the house to about 12% of the floor area is recommended. At the very least, Energy Star rated windows or their equivalents, should be specified according to the Energy Star regional climatic guidelines.
The best sealing windows are awning and casement styles. Metal window frames should be avoided, especially in cold climates. Always seal the wall air/vapour diffusion retarder tightly around the edges of the window frame to prevent air and water vapour from entering the wall cavities.
Air-Sealing
A well-constructed thermal envelope requires that insulating and sealing be exact and complete. Sealing air leaks everywhere in the thermal envelope reduces energy loss significantly. Air-sealing alone may reduce utility costs by as much as 50% when compared to other houses of the same type and age. Homes built in this way are so energy-efficient that specifying the correct sizing heating/ cooling system can be tricky.
Controlled Ventilation
Since an energy-efficient home is tightly sealed, it's also important and fairly simple to deliberately ventilate the building in a controlled way. Controlled ventilation of the building reduces moisture infiltration and thus the health risks from indoor air pollutants, promotes a more comfortable atmosphere, and reduces the likelihood of structural damage from excessive moisture accumulation.
A carefully engineered ventilation system is important for other reasons too. Since devices such as furnaces, water heaters, clothes dryers, and bathroom and kitchen exhaust fans exhaust air from the house, it's easier to depressurize a tight house if all else is ignored. Natural draft appliances, such as water heaters, wood stoves, and furnaces may be "back drafted" by exhaust fans and lead to a lethal build-up of toxic gases in the house. For this reason it's a good idea to only use "sealed combustion" heating appliances wherever possible and provide make-up air for all other appliances that can pull air out of the building.
Heat recovery ventilators (HRV) or energy recovery ventilators (ERV) are growing in use for controlled ventilation in tight homes. These devices salvage about 80% of the energy from the stale exhaust air and then deliver that energy to the fresh entering air by way of a heat exchanger inside the device. They are generally attached to the central forced air system, but they may have their own duct system.
Heating and Cooling Requirements
Houses incorporating the above elements should require relatively small heating systems (typically less than 50,000 Btu/hour even for very cold climates). Some have nothing more than sunshine as the primary source of heat energy. Common choices for auxiliary heating include radiant in-floor heating from a standard gas-fired water heater, a small boiler, furnace, or electric heat pump. If an air conditioner is required, a small (6,000 Btu/ hour) unit can be sufficient.
Beginning a Project
Houses incorporating the above features have many advantages. They feel more comfortable since the interior temperatures are more stable. The humidity is better controlled, and drafts are reduced. A tightly sealed air/vapour retarder reduces the likelihood of moisture and air seeping through the walls. These homes are also very quiet because of the extra insulation and tight construction.
There are some potential drawbacks. They may cost more than a conventional home. Because some systems have thicker walls than a "typical" home, they may require a larger foundation to provide the same floor space.
Before beginning a home-building project, carefully evaluate the site to determine the optimum design and orientation. Prepare a design that accommodates appropriate insulation levels, moisture dynamics, and aesthetics. Decisions regarding appropriate windows, doors, and heating, cooling and ventilating appliances are central to an efficient design. Some schemes are simple to construct, while others can be complex and expensive.
An increasing number of builders are participating in the federal government's Energy Star Homes programs, which promote energy-efficient houses. Many builders participate so that they can differentiate themselves from their competition. Construction costs can vary significantly depending on the materials, construction techniques and the type of heating, cooling and ventilation system chosen. However, the biggest benefits from designing and building an energy-efficient home are its superior comfort level and lower operating costs. This relates directly to an increase in its real-estate market value.