High-performance homes, especially those striving to achieve net zero-energy
performance, employ several energy efficient materials and construction practices that need to be integrated into the earliest phases of design including:
Site Selection
The ideal site for a zero-energy home would have unobstructed sun, flat topography, and
little exposure to the weather. It would also be located near access to services, shopping, and mass transit. While few sites will be perfect, being selective about the site will certainly pay off in lowered costs and better living. Solar access is especially important. A solar energy contractor can perform a site analysis to be sure that sufficient sunlight is available on the wall or roof surfaces and suggest the optimal orientation and size of the solar surfaces. As is often the case, a site may have less than perfect solar access. Even with less than optimal solar access, or no solar access, you can still employ all the strategies discussed here to make the home as close to net zero as possible.
Building Orientation
Orient the building to take greatest advantage of seasonal sun angles for both passive heating and cooling and for maximum solar energy production. Depending on climate, this could involve maximizing passive solar heat gain in cold climates or natural shading in warm climates. For solar panels, a direct northern roof orientation is preferable. However, when northern orientation is not possible, consult with your solar installer to determine the optimal orientation for optimizing solar gain for your local climate conditions.
Climate
Consider how the local climate affects design. One size does NOT fit all climates. Insulation
levels, air tightness, moisture control strategies, daylighting opportunities, and many other
design elements must reflect climate zones and local conditions.
Shape
During the conceptual design phase, consider using fewer, simpler shapes, rather than
many smaller shapes with lots of architectural complexity. Simpler building masses will be
easier and less expensive to build, air seal, and insulate in the field.
Size
Think small and design spaces for uses of the homebuyer rather than for resale value. Many
families can live comfortably in a well-designed 100-150m 2 home with well thought out
functionality, storage, and traffic flow. The building itself may cost hundreds of dollars per
square metre, so shaving a few square metres from the total can save thousands of dollars
in construction costs. With careful planning, reducing the home size will save energy and
pay for all the energy improvements needed for the home to achieve zero net energy.
Thermal Boundary
Clearly define the thermal boundary on design plans. That means deciding what is inside
and what is outside the conditioned space. For example: vented attics and crawl spaces are
outside the conditioned space. If a ducted heating and cooling system is selected, it is especially important to allow space within the conditioned envelope to hold all the elements of the system.
Ceilings
Use only one type of ceiling throughout the house: either flat or cathedral. Whenever ceiling
heights change, there will be a wall separating the room with the high ceiling from an
unheated space, usually an attic. This “high wall” can be tricky to air seal and insulate. The
insulation level of that wall should equal other exterior walls, and it will need to be covered
with a rigid material to enclose the insulation. If more than one ceiling height is present,
develop clear details for air sealing, insulation, and rigid backing.
Roof Eaves
Design a solar shading strategy that allows the sun to heat the building when needed and avoid overheating when not needed. One strategy is to design and build fixed roof overhangs, especially on the north and west sides when they are exposed to direct afternoon sun. Calculate and specify the northern roof overhang to maximize winter sun exposure and minimize heat from the summer sun. These fixed overhangs must be a compromise between similar sun angles in spring and fall when the heating or cooling requirements are much different. An alternative would be to consider a shorter fixed overhang of 300-600mm along with exterior shading, such as awnings, sunscreens, or vegetation. This will allow greater heat gain during spring and less heat gain during autumn.
R-Values
Specify R-values on the plans for wall, ceiling, and floors and U-values for windows and
doors. In cold climates, typical minimum R-values are R2.8 for walls, R4.1 for ceilings and
R2.25 for floors. In warm climates typical R-values are R2.8 for walls, R4.1 for ceilings, and
R1.5 for floors. Optimal R-values and U-values for your specific climate zone should be
determined using energy modelling.
Thermal Bridging
Clearly specify measures for avoiding thermal bridging on the plans. These may include using advanced framing techniques for the wall, floor, and ceiling systems as well as exterior foam sheathing, staggered-stud, and double-stud framing.
Enclosing Insulation
Specify that wall insulation be fully enclosed with rigid sheets of OSB, Thermoply, or similar
materials and never design walls where it is difficult to properly cover insulation. Pay
particular attention to soffits, attics, bathtub surrounds, HVAC chases, and fireplace
enclosures. If you are including double-stud walls, be sure to include details for enclosing the
framing cavity, including a plywood cap, across the parallel top plates and plywood bucks
inside window and door openings.
Air Sealing Goal
Specify the air tightness standard to be achieved on plans. This is generally expressed in air changes per hour at 50 Pascals (ACH50 – Air changes per hour). The threshold needed to
reach net zero energy should be 2.0 ACH50 or less.
Blower Door Directed Air Sealing
Specify that blower door directed air sealing be conducted, after ceiling has been installed
and before insulation is installed, to locate unexpected air leaks and to effectively seal them.
This process is especially useful if you are pushing your air leakage goal lower.
Heating and Cooling Equipment
Locate all heating and cooling equipment, along with their pipes, ducts, and refrigerant lines.
Locate the hot water system and specify its efficiency rating. Locate these on the plans and
specify the need for sealing any penetrations. For ducted systems, strive to bring the air
handler and all ducts inside the thermal boundary. Consider ductless mini-split heat pumps as they are highly energy efficient.
Ventilation
Include mechanical ventilation equipment and ductwork on the design plans and locate
equipment and ducts within the conditioned envelope of the building where feasible.
Remember that heat recovery ventilators need a condensate drain. Specify all equipment
efficiency ratings on the plans.
Water Heater
Decide on the type of water heater to be used and the best location. Electric resistance
water heaters should be centrally located inside the conditioned space in heating-dominated
climates and outside the conditioned space in cooling-dominated climates. In heating-
dominated climates, heat pump water heaters should be located outside the conditioned
space in areas with about 25-30 cubic metres of volume. A garage or basement is often
good, because these locations are not heated directly, but stay relatively warm all year long.
Heat pump water heaters also offer ducting options that can allow them to be located inside
the home.
Solar Energy System
Based on an accurate energy model, determine the optimal size of the photovoltaic system
to meet the energy needs of the home. Check that there is adequate roof area with the
proper tilt and orientation to supply sufficient energy to reach the zero-energy threshold.
Make sure that chimneys, plumbing vents, and other roof protrusions are located outside of
the roof area planned for solar panels.
Appliances
Specify energy-efficient appliances and their ratings that were selected during energy
modelling. The E3 (Equipment Energy Efficiency) program is a good resource for choosing
efficient appliances. And be sure to consider electric heat pump clothes dryers and induction
stove tops because of their high level of energy efficiency.
Engage the Team
Early in the design process, create a project team including all the relevant building trades,
including framers, insulators, plumbers, electricians, and solar contractors. The team can assist identify the most cost-effective energy efficiency measures in the design and the most cost-effective sequence for implementing these measures. Ask the team to review the design and incorporate their feedback.