Elements of an energy-efficient home
by Norman Aceron Garcia
Energy-efficient homes are healthier, more environmentally friendly, and economically smarter than the average home. They have design features, technologies and products that provide healthier indoor air, increase the occupants’ comfort, reduce water usage, and preserve natural resources. Latest technological advancements in building materials and construction methods permit most energy-saving ideas to be integrated into any type of house design. Among the important features of an energy-efficient home include: a high RSI-value; a tightly air-sealed thermal envelope; balanced ventilation; and lower heating and cooling costs.
A thermal envelope is the building’s component that separates that indoor environment from the outdoor environment. It consists of the wall and roof assemblies, insulation, windows, doors, finishes, weather-stripping, and air and vapour barriers.
Wall and roof assemblies
Aside from the common conventional “stick” (wood-stud) framed wall and roof construction, there are numerous wall and roof assembly systems that are now widely used in Manitoba. Some of these systems include optimum value engineering (OVE), structural insulated panels (SIP), and insulating concrete forms (ICF).
Energy-efficient homes have much higher insulation RSI-values than required by the building code. A well-designed and constructed energy-efficient home located in Winnipeg would have insulation levels in the range of RSI 3.52 to 5.28 (R-20 to R-30) in the foundation walls and RSI 8.81 to 12.33 (R-50 to R-70) in the ceilings. Carefully installed insulation such as fiberglass batt or roll, wet-spray cellulose, or foam insulation will fill wall voids completely.
Air and vapour barriers
Water vapour condensation is a main hazard to the structural integrity of a home. Our building code contains prescriptive requirements on the air and vapour barriers to mitigate these risks. In cold climates like Manitoba, big pressure differences between the indoor and outdoor environments can draw warm, moist indoor air into exterior walls and attics. Once the assembly cools, the warm moist air condenses into the surfaces. Any water vapour that gets into the walls or attics must be permitted to get out again to prevent mould growth and deterioration of the wall and ceiling assemblies. A well-constructed thermal envelope entails that insulating and sealing be accurate and detailed. Sealing air leaks can significantly reduce energy losses by as much as 50 per cent when compared to other similar homes.
Foundation walls and basement floors
Under-insulated foundation walls and basement floors can have negative impact on home energy consumption and can affect occupants’ comfort, especially if they use the basement as a living space. Equipment and appliances that generate heat, like furnaces, domestic hot water tanks, washers, dryers and freezers, are often located in basements. Hence, properly insulating the foundation walls and basement floors would allow this equipment and appliances to operate efficiently.
A typical home loses around 25 per cent of heat through the windows. Generally, the most efficient windows are the awning and casement types as they close tighter than sliding types. Metal window frames are not recommended for use in cold climates like Manitoba. Ensure that the air and vapour barriers are tightly sealed around the window frame edges to prevent air and water vapour from entering the wall assemblies.
Heating, ventilation and air-conditioning
Because energy-efficient homes are more airtight than typical homes, it is important that the ventilation system is balanced to reduce air moisture infiltration and minimize health risks from indoor air pollutants. Heat-recovery ventilators (HRV) or energy-recovery ventilators (ERV) are effective in controlling ventilation in tight homes. During the heating season, this equipment recovers around 80 per cent of the energy from the stale exhaust air, and then transfers that energy to the incoming fresh air. Because energy is recovered and not wasted, energy-efficient homes incorporating the above components would require relatively small heating and cooling systems.
In summary, energy-efficient homes feel more comfortable to occupants because higher insulation levels keep the interior wall temperatures steady. A tightly air-sealed building envelope reduces the likelihood of moisture intrusion. With a properly designed HVAC system, back drafting is minimized and indoor humidity is better controlled. Construction costs of energy-efficient homes can vary significantly, depending on the specified materials and construction method, builder’s profit margin, experience, and the type of HVAC selected. Nevertheless, the primary benefits from designing and building energy-efficient homes are its greater comfort level, lower operating costs, and lower greenhouse gas emissions.
Norman Aceron Garcia, P.Eng. is an accredited professional in Leadership in Energy and Environmental Design specializing in Building Design + Construction. In 2015, Norman founded Mr. Peg Property Inspections, a social enterprise that advocates green building design and climate change adaptation strategies.