High performance homes, especially those striving to achieve zero energy performance, employ a number of materials and construction practices not found in conventional construction. Customarily designers and architects may not specify certain energy related details or may neglect to make certain decisions relating to energy performance strategies during the design phase. This lack of attention to energy related details and strategies could create obstacles and add costs for builders. Your zero energy home design project will be smoother, less expensive and more successful, and builders will thank you, if you use these twelve strategies in the design process and detail them on your plans.
1) Clearly define the thermal boundary. That means deciding what is inside and what is outside the conditioned space. (Example: vented attics and crawlspaces are outside.)
2) During conceptual design consider using fewer larger shapes, rather than many smaller shapes with lots of architectural complexity. Simpler building masses will be easier to build, air seal and insulate in the field.
3) Specify that wall insulation is 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, and fireplace enclosures. If you’re drawing 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.
5) Identify the type of air barrier system to be used. Will it be air-tight drywall approach, ZIP System, SIGA membrane and tape or something else? List air sealing materials and techniques on the plans.
6) Specify that blower door directed air sealing be conducted before insulation is installed in order to locate unexpected air leaks and to effectively seal them.
7) Locate all heating and cooling equipment, along with their pipes, ducts and refrigerant lines. Draw these on the plans and specify the need for sealing any penetrations.
8) Draw mechanical ventilation equipment and ductwork on the plans, locating equipment and ducts within the conditioned envelope of the building where feasible. Remember that heat recovery ventilators need a condensate drain.
9) 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 1,000 cubic feet of volume and a supply of waste heat. If gas-fired water heaters are used in an air-tight home, they must be sealed combustion models.
10) Consider using 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 “vault wall” can be very 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. (See 3 above.) If more than one ceiling height is present, develop clear details for air sealing, insulation and rigid backing.
11) Based on an accurate energy model, determine the optimal size of the photovoltaic system. Check that there is adequate roof area with the proper tilt and orientation to supply the energy needed to reach the zero-energy threshold. Make sure there will be nothing on the roof surface to interfere with solar panels, such as a chimney, plumbing vents, etc.
12) Early in the design process, engage the relevant building trades, including framers, insulators, plumbers, electricians and solar contractors, regarding the energy efficiency measures in the design and the most cost effective sequence for implementing these measures. Ask them to review the design and incorporate their feedback.
Following these 12 steps will make construction of zero energy homes considerably more efficient and more cost-effective for builders.
—Bruce Sullivan, Building Science Consultant, www.basezero.biz