ASK THE EXPERTS: Net-Zero-Energy Apartments

Thoughtful site planning and building orientation, plus energy-efficiency measures and renewable energy technologies, can combine to create a net-zero-energy housing development.

I’m part of a cohousing group in the very preliminary planning stages. We’re contemplating designing a small apartment complex, with two- or three-story buildings that will include some common spaces and dwellings of various sizes for 12 to 16 families.

Some of us are environmentally oriented, and wonder what renewable energy and energy-efficiency technologies could be incorporated into our design. Is it out of the question to consider a “net-zero-energy” strategy for this community? We are looking at suburban properties in western Washington state.

James Thomas • via

Making a net-zero-energy (NZE) apartment building in western Washington state, which gets 3 to 4 average daily peak sun-hours (that’s the measure of total solar energy available) should be possible. Many people in your region already have NZE homes.

With a multistory building, it’s crucial to maximize the solar roof area since that’s your energy collector (unless your property includes an open field, in which case you could consider a ground- or pole-mount community solar installation). Design your buildings with a large south-facing roof and seek local advice about the best roof angle. Be sure to get good shading analysis to assess the solar window. And make sure that your south roofs are clear of all obstructions—locate all penetrations and structures, such as stacks, vents, and dormers, on other roof faces.

Heating will be your building’s largest energy load, so achieving high thermal efficiency is paramount. Systems such as SIPs (structural insulated panels) for external walls can make a super-insulated, tight building easy to attain. And it’s certainly possible with other methods, though in all cases you’ll need a builder and contractors who understand and apply energy-efficient construction principles.

Heating with ductless minisplit heat pumps may be the most cost-effective option. These are tried-and-true, fairly straightforward to install, and use a small amount of electricity to grab heat out of the ambient air. Other heating options are more complicated and expensive, and also can compromise your building envelope and your indoor air quality.

A solar hot water system may be a good option for providing domestic hot water, though often it turns out that a standard electric water heater powered by solar electricity can be more cost-effective. I advise avoiding the glitzy appeal of heat-pump water heaters, since they are expensive and complicated, and there can be issues with their placement.

Choose carefully for all of your other loads. Don’t buy anything that uses energy without taking a hard look at the options. Even if it’s a higher up-front cost, choose the highest-efficiency product you can afford. Look at “life-cycle” cost—the cost of the appliance, how long it lasts, plus the cost of powering it for its lifetime.

If you design and build a conventional building, you will get conventional—that is, mediocre—energy performance. Most architects, builders, and subcontractors are not focused on energy efficiency. They design and build things “the way it has always been done” or cheaply. If you want a high-performance building, you’ll need specialty professionals on your design/build team, and you or your consultants and contractors need to keep a significant focus on energy throughout the process. It can be done, but it requires attention to detail and a continuing focus on your goals.

Ian Woofenden • Home Power senior editor

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