Like many new developments, the shift toward zero energy building occurs in steps. The basic principles go back to the 1970s when the first passive solar and super-insulated homes were built. Energy efficiency has improved continuously and public response has been positive, although progress has moved more slowly than some would like. Today, we have arrived at a point where most consumers can live in a zero energy home at the same cost (or lower) than living in a home built to a conventional building code.
To achieve zero energy, designers and builders everywhere are employing an array of design concepts, product choices, and financing approaches. These ideas are covered in detail on the Zero Energy Project website and elsewhere on the web. Because there are so many ideas, it seems appropriate to offer a quick rundown of the most cost-effective measures for getting to zero energy. Good design is specific to the building site and climate. Not all of these ideas will work in all situations, and some ideas may be mutually exclusive. If you have thoughts of your own, please share them in the comments, or continue the discussion in the Zero Energy Project Forum.
Best Practices for Affordable Zero Energy Home Design
- Start with clear goals. Identify and agree to the zero energy goal(s) on day one. Involve only subcontractors and materials suppliers that share this vision.
- Adopt an integrated approach. Involve all the players. Get feedback and adjust the design accordingly. Make several rounds of changes to be sure that all the details are included and are compatible.
- Engage a third-party certification program. Standards and services of programs such as ENERGY STAR Home or Built Green address many of the basic building science and durability issues. Advanced programs, such as Zero Energy Ready Home, Earth Advantage Zero Energy, or International Living Future Zero Energy, build on these fundamentals.
- Keep it small. Start planning at about 300 square feet per person.
- Reduce complexity. Simple shapes without architectural intricacy are cheaper to build, insulate, and air seal.
- Shorten pipes. This reduces wasted water and heat. Locate the water heater near the center of the buildings footprint.
- Stretch living spaces. Include outdoor areas such as porches, balconies, and gardens. Include extra storage space in the unconditioned garage and under stairwells.
- Optimize design. Use a computer energy model to get the most cost-effective balance of architecture, building shell, equipment efficiency, and solar technology.
- Limit window area. 15 to 20% of the floor area is optimal. This reduces heat transfer and significantly reduces cost.
- Site for solar gain. Orient the building so that roughly half of the window area faces within 30° of south.
- Teamwork pays. Demand close collaboration between the designer and builder to avoid costly mistakes.
- Think multifamily. Attached buildings can be affordable and have some advantages for energy savings, too.
- Document it. Write everything down and keep copies. Building plans often omit the very details that make a home efficient. Plans and other construction documents must explicitly state or illustrate all construction details, material specifications, and installation requirements. Don’t omit the mechanical equipment and the associated pipes, wires, and ducts.
Smart Zero Energy Construction
- Focus on process. Inevitably zero energy requires extra steps, attention to detail, and specific products. Successful zero energy home builders use clear processes and checklists to make sure all tasks are completed efficiently.
- Affordable doesn’t mean “cheap.” Use only durable materials, especially for structural elements.
- Start on a familiar foundation. Dig a foundation that is common in your market. If most homes in your area are built on basements or slabs, there is probably a reason. But don’t forget to factor in the cost of the high levels of insulation needed for ground-coupled floors. Consult the energy model for guidance.
- Wrap it right. Insulate to a level determined by the energy model, not by code minimums or arbitrary rules of thumb. As the efficiency of mechanical equipment improves and the cost of renewable energy generation declines, shell measures may not need to go as far. Optimize for the climate and economic conditions.
- Choose tried and true. Subcontractors can’t be affordable and efficient if they are always on a steep learning curve. Whenever possible, use common materials and construction techniques that have proven the test of time.
- Stick with wood-frame construction. Both double-stud walls and insulating sheathing can be very cost effective.
- Keep it tight. Air seal to no more than 2.0 air changes per hour at 50 Pascals. Leakage as low as 0.05 ACH50 are possible. A few simple practices and pre-planning can keep costs low.
- Choose mid-priced windows. While super-efficient windows are available, they are expensive. A good-quality double-glazed unit with a heat loss rate of around U-0.22 is a good balance between cost and efficiency.
- Go for good bones. Spend money on the building’s structure, not the skin. Interior finishes will eventually be replaced as they wear out and styles change. Don’t cut costs on the structure, especially insulation, air sealing, and windows in lieu of expensive cabinets, carpets, or fixtures.
- Make it mod. Consider modular or panelized products when available locally, especially when the construction timeline is tight.
- Do double-duty. Find materials that can be both structure and finish. A good example is a slab-on-grade floor that is tinted or polished to be the finished floor, too.
- Scale up. Production builders can reduce costs by increasing the economy of scale. This works for all the zero energy features. Just be sure to keep an eye on quality.
Energy Efficient Equipment
- Don’t force it. Forced air heat is not needed for small, super-efficient spaces. For larger homes where forced air may be necessary, make sure the air handler and all ducts are inside the conditioned envelope.
- Right-size it. Size space heating and cooling equipment to match the lower demands of the highly-efficient building shell. Smaller capacity comfort systems will cost much less.
- Pump it up! Embrace heat pump technology for space heating and cooling as well as for water heating and clothes drying.
- Join forces. Consider integrated systems for space and water heating when they improve efficiency, such as a CO2 heat pump for small homes and ground-source heat pumps for larger buildings.
- Shoot for the stars. Select only high-efficiency appliances. Use the ENERGY STAR products list to choose appliances in the top 10% for low energy use. Focus on actual kiloWatt-hour consumption instead of efficiency ratings. Pick the smallest size appliance that will meet needs.
- Air it out. Heat recovery ventilation may not always be required. Explore less expensive means to remove stale air and deliver fresh air to the home, such as the Panasonic Whispercomfort ERV.
- Be positive. Size solar panels to exceed the needs of the home, so the additional energy can fuel an electric vehicle for savings on top of savings.
- Make the most of the sun. Squeeze in more solar for sites with marginal sun exposure by using micro-inverters and power optimizers that better accommodate partial shading.
Zero Energy Home Financing and Ownership
- Get credit. Research and take advantage of government tax credits, manufacturer equipment rebates, and utility incentives. Good places to start research are the Zero Energy Project and DSIRE.
- Think long term. Finance all energy improvements in a mortgage or other long-term loan. Spreading the upfront cost over many years reduces the monthly payment enough that energy savings can cover the entire additional loan amount. In many cases, the financial benefits can meet or exceed the monthly cost, so that a zero energy home costs less to own.
- Get it right. Demand an accurate appraisal of the building’s true value. This might mean some legwork on your part, but the added effort will pay off in real dollars.
- Target transportation. There’s more to living than a roof over your head. Select a location that is close to work and shopping and close to public transportation.
- Share it! Tell your family, friends and neighbors about the benefits of zero energy building and living. The more people that adopt zero energy lifestyle, the cheaper it will be for everyone!
Using these ideas as a guide will yield a home that is affordable to build and affordable to live in. Learn more about affordable zero energy building and design here.