If your building isn't net zero, you can still be an energy hero. Drawing near can be just as good.
Targeting "near zero" instead – which the New Buildings Institute defines as an energy use index (EUI) of 16-20 kBTU per square foot per year or less – still brings staggering savings and green gains, even if true zero status isn't in the cards right now.
To hit anywhere near the bullseye of zero energy use, however, you need an extra-efficient building. Focus on optimizing your building's tightness, equipment, and operation inside and out before looking at renewables.
The Double-Edged Sword of Existing Buildings
Predictably, retrofitting an existing building to achieve such low energy consumption carries considerable challenges – but it may also offer previously unnoticed opportunity.
"You can look at any existing building and assess its existing green components, and if the building is currently in its end use, you can assess its actual performance. There's some benefit to having an existing building to work with," explains Ralph DiNola, executive director of the New Buildings Institute. "In a lot of historic buildings, you'll see features like high window head height, good daylighting, a design that favors natural ventilation, and a big thermal mass – you're potentially given a host of features that work well when aspiring to net zero."
You don't need the features of a historic building to put zero in your sights, however. Mark Frankel, technical director of the New Buildings Institute, says the key is integrated design and a strong, thorough team working with you, though some buildings can pose extra problems.
"Some of my favorite examples in our database are existing buildings that are not historic – they were total dogs, but now they're net-zero or super-efficient buildings because the design team was committed to making them work," says Frankel. "However, there are features that can be liabilities to net zero, primarily excessive glazing. That's a very difficult feature to work with because you have to fight solar gain and extreme heat loss, which are challenging features for managing energy."
Where to Start: Site, Facade, and Envelope
Start by assessing the building's orientation and the condition of the facade and envelope. Your location, climate, and building type will have a major impact on what strategies are feasible, says Jim Gabriel, partner of architectural firm Hanna Gabriel Wells, which renovated a former auto repair garage with cinderblock construction into its net-zero Bacon Street office in San Diego, CA, in 2009. The original structure was built in 1955.
"Office buildings have relatively low energy use compared to other building types, so they're a good target just because you're already part of the way to zero," says Gabriel. "The physical form of the building also plays a role. Ours is long and narrow in proportion, so it easily lends itself to natural ventilation and daylighting. The more things you can do passively, the more you start to drive down the energy consumption."
The Bacon Street office didn't require much insulation due to its breezy, temperate location, but more severe seasonal variations in other parts of the country make that step a must.
"If you can insulate the exterior and add a rainscreen on the outside of a relatively simple building, that will be less expensive than a total gut rehab of the interior spaces," notes Laura Blau, principal of sustainable architectural firm BluPath Design. "It's easier to attend to air sealing from the outside where more surfaces are open to you rather than trying to do things with existing interior conditions where floors meet walls and walls meet the foundation and roof. Maybe you have a building where you can change out the windows and put on a new facade. If you're adding a new wing, you can orient it to invite winter sun in or keep summer sun out, depending on the thermal dynamics."
The Historic Green Village on Anna Maria Island, FL, is a unique mixed-use combination of four 100-year-old buildings containing a cafe, outdoor equipment outfitter, and jeweler, as well as a new building with a small art gallery and bakery. The team opted for spray foam instead of exterior insulation because its historic buildings were unoccupied at the time of renovation.
"The biggest single factor in reducing energy is insulation, along with double windows and low-E glass," says Tom Stockebrand, the village's technical consultant and energy expert.
As Frankel noted, if your building is overglazed, sometimes a second skin can both mitigate the negative effects of too much glazing and contribute to a tight envelope, another requirement in creating an ultra-efficient building. Addressing envelope issues first will help clarify what to do inside and protect against envelope failure from condensation and freeze-thaw cycles, which invite rust, rot, mold, and mildew.
"With any deep energy retrofit, the first consideration is whether you're near the end of the useful life of your mechanical systems," says Blau. "That's a great time to think about putting money into the envelope so you reduce the load and can use smaller mechanical equipment. If you replace your mechanical systems and then look at your envelope afterward, you will have oversized systems that won't run as efficiently."