Planning for Net Zero Energy

Planning for Net Zero Energy

  • Lexington deep energy retrofit front elevation

This is the second in a series of posts on a deep energy retrofit project in Lexington (click here to read the first post and here to read the third). We’re aiming for net-zero energy: a house with such a low energy load that roof-top solar panels can provide as much energy as the homeowners need to heat, cool and power their home on an annual basis. For this post, Rachel sat down with Cador and the project’s architect, David Foley, to find out what it took to plan a project with such an ambitious goal (and get approval from the town’s historic commission).

Rachel: In his introductory post on this project, Paul described the original house as “an environmental liability”. Would you agree with that?

David: I’d call it a mixed bag. The clients are pretty frugal energy users, and when they bought the house in the 80s they did so in part because of its close proximity to services and public transportation. They also did what they could over the years to reduce their energy footprint: they insulated when they bought it, upgraded the boiler, changed out lights, and so forth. In the bigger picture, I would say there are many homes in the area that are bigger environmental liabilities than this one.

Cador: Probably deferred maintenance was the biggest liability. Many exterior components needed work.

Rachel: Was this the primary motivation for the project?

David: Their kids were grown and they felt it was time to see to the maintenance of their house, yes. But they also wanted to walk their talk and show a commitment to their values. I’ve known both of them since college, where we studied with Donella and Dennis Meadows, pioneers in systems thinking and sustainability. J— was especially influenced by the Meadows and ended up making sustainability his life’s work. I think he saw this project as an opportunity to put some skin in the game.

Cador: I think they were also worried that if they didn’t fix up the house a subsequent owner might tear it down and replace it with a McMansion.

David: Cador’s right, at the beginning they were concerned about this. But that was before they knew that their house is in a historic district. Because of this it can’t be torn down.

Rachel: So was the historic district location a surprise?

David: We didn’t find out until about a week before we were scheduled to start. So we were really thrown for a loop. But in many respects, the historic commission’s review was helpful.

Rachel: How so?

David: Some of their aesthetic suggestions, which were based on the historic character of the house, improved the look over what I had originally designed.

Rachel: Were there also some downsides?

Cador: Definitely. They insisted that we use wood windows, which from a durability standpoint seems crazy. The sash of the aluminum clad windows we had originally specified are warrantied for 20 years compared to 10 years for wood. But in order to maintain the historic character of the home, the commission required that we switch to wood windows—

David: —and wood doors. The other problem with wood is that it will make it much harder for us to meet our air tightness target.  But it’s important to keep in mind that we succeeded in convincing the commission to accept a crucial and controversial component of our energy specifications.

Rachel: Which was?

David: The solar electric panels. Because of the home’s orientation these have to be installed street-side, which was a big red flag for the commission. Of course we could never get this house to net-zero without solar, so we worked really hard to make our case. We found precedents for solar installations in other historic districts, as well as guidelines from the National Park Service. Ultimately we were successful in allaying the commission’s concerns—and I think we helped educate them that buildings are what they do, not just what they look like.

Rachel: Of course we couldn’t get to net-zero without a super-insulated building shell either. So let’s talk about that aspect of the project. While we strive to improve the energy performance of every home we work on, we rarely do a full-enchilada, deep energy retrofit. What makes this house a good candidate for that?

Cador: It’s really not possible to achieve steep energy reductions by adding insulation just to the interior; you really have to add it to the outside. But it only makes sense to do this when exterior components need replacing. What was somewhat unique in this case compared to many other homes we work on is that most exterior components needed to be replaced at the same time.

David: I agree. If there was ever going to be a reasonable time to do a deep energy retrofit it was now because the house needed a major exterior upgrade anyway. It’s also important to note that we’re fixing multiple problems, not just cutting energy use. We’re addressing serious indoor air quality issues, including radon, lead paint, mold and mildew. We’re solving ice dams problems. And we’re fixing structural deficiencies. Finally the clients are conscientious, and will really pay attention to their energy use. A DER isn’t just hardware.

Rachel: And the goal of net-zero energy, how important is that?

David: When we started this project, I thought we’d be able to cut the operational energy use roughly in half and the solar would offset half of what was left. But in the course of exploring and modeling we realized that we could reduce the heating load a lot more. I remember when I told the clients, you know what, we’re in striking distance of net-zero energy. Ever since that became a possibility, they deepened their commitment. They really want this to happen, and because they’re so mindful I am very confident that it will.  As engineer Marc Rosenbaum, who did some energy modeling for this project, likes to say, there are no net-zero homes, only net-zero families. Well, this is the quintessential net-zero family.