Zack Semke: Can we jump right in with an overview of the project, some of the basic data points and what’s special about Finch Cambridge?
Michelle Apigian: Sure. It is 98 units of affordable rental housing in a single building in Cambridge, Massachusetts. The owner is Homeowners Rehab, and they have been doing affordable housing in Cambridge and a lot of other community development work for a very long time. They have a very, very strong track record. We have worked with them on several projects.
They are an inspiring leader on sustainability. At every level of their staff, they understand that sustainability makes sense. So one of the things that’s special is that the many benefits of Passive House that go beyond energy are completely aligned mission-wise with what they’re hoping to provide their residents. They want healthy environments with a reduced burden to bear on resident pocketbooks. They want durability. They want comfort. Those are the things they’re trying to provide so that residents can concentrate on the rest of their lives. It’s a really nice synergy to be working on Passive House projects with affordable housing clients in general.
On top of having a very enlightened owner here, we also have an enlightened city. Cambridge is definitely pushing ahead of many communities and is a leader in terms of thinking about energy and thinking about carbon. There’s also very much a focus on resiliency. This parcel is within the 2070 flood plain, so we were also thinking a lot more broadly about where we’re sitting, where we’re hitting the ground, et cetera.
James: I’ve been waiting for a city like Cambridge or Boston, or a policy or a code, to really make things happen—that, coupled with an expectation on the user end of what’s possible in a high-performance building—because I thought those would be the kinds of things that would trigger an acceleration in high-performance buildings rather than the mechanical engineer saying it was a good idea for other people in the design and build side or people just voluntarily doing it out of the goodness of their hearts. I didn’t think that those would ever be modes for ramping things up. We’re seeing just more and more activity that’s pushing things forward. There is a lot of activity in cities and municipalities within Massachusetts. What I’m hoping for, which will really be great, is for the consumer to know what they can have. They’ll come to expect it.
Zack: Right. We have the Brussels model and example to suggest that when there’s significant uptake, and a policy catalyst, that you can see the market transform in terms of expectations.
Michelle: Related to that, we have had some real policy catalysts in Massachusetts in the last year, so that’s also helping. Initially, there was a $4,000/unit incentive for affordable housing projects offered by Mass the Clean Energy Center last fall, and that funded eight affordable Passive House projects. And then, through a lot of advocacy with Passive House Massachusetts and many other organizations, we were able to get our three-year plan for the Energy Efficiency Advisory Council to include Passive House incentives for multifamily—both affordable and market. And so now we’re seeing a lot of market rate clients at least consider asking the question, which definitely was not happening a year ago.
Zack: Yeah. I got a chance to speak with Beverly Craig, Julie Klump and Nate Thomas last week, and I was super excited to hear about what you just described. It’s great to hear how the market is responding to those policy catalysts. What is the nature of the catalysts that are coming from the city of Cambridge?
Tom: It hasn’t been finalized, but the new zoning article will allow compliance through either LEED, Enterprise Green Communities, or Passive House certifiability verified through a certified rater. While the language hasn’t been finalized yet, they are allowing projects currently going through zoning approval to start to use the new language, so it’s kind of expressly codified in the zoning.
Zack: So that, coupled with the fact that there are financial incentives available for Passive House, you start to see some multiplication effects happening I would think, right?
Tom: Definitely.
Michelle: Cambridge also invested very, very heavily in the development of this project. Not every community is able to do that. In fact, most are not—certainly not at the level that Cambridge did. They used their Community Preservation Act funds to jumpstart the first phase of this project’s construction.
Tom: And the city has a net-zero action plan, as well. So, certainly the buildings they own but also the projects they’re involved in—they’re pushing for net-zero by 2050.
Zack: So, in terms of doing a Passive House multifamily building, what were some of the key challenges that you all encountered, and how did you deal with those? How did you overcome them?
Michelle: I think one huge challenge is to design it well and to be able to communicate the intent clearly and effectively so that it can be executed well. They’re totally separate. The vast majority of the builders who are operating at scale and are in our communities do not know about Passive House and have not worked on a project like that before. We tried to really work in collaboration with the builder, even during the design phase. We were lucky in this project that the owner brought on a GC early on so that we could kind of test things, evaluate different alternatives, and really do real-time value engineering. That was helpful to some degree. It tested the costs in particular; it also, affected how we communicated and when we communicated.
That was really a key challenge, and I think we’ve done quite well given how new to all of this most everybody on the project was. It really was a process of looking at that three-week lookahead and noting which details are coming together, which trades are going to be involved, which of those involve a transition or tricky spot from our perspective, and then talking through that: who’s going in first, who’s going second, and often rethinking the whole approach because we realized, in those conversations, that the sequencing wasn’t going to work or it just didn’t make sense how we’d initially envisioned it.
James: I would add that the systems we design for heating and cooling, ventilation, domestic hot water—we’ve been designing those same systems for dozens of previous projects. Air source heat pumps for heating and cooling, energy recovery for ventilation, and trying to be super efficient in domestic hot water design to eliminate standby losses. The engineering wasn’t any different for us on this project.
I think what’s different, and it’s not unique to this project, is acceptance of those systems by the installing contractor. It would be nice if there was more experience, for example, with air source heat pumps in the marketplace than there is—particularly VRF systems. Another area that’s important, like the air barrier on the building, is the airtightness of ductwork. There’s an industry reset that has to occur within sheet metal contractors, balancing contractors, mechanical contractors on what is “tight.” The old definition wasn’t so tight. There’s a real retraining that needs to go on in order to implement a good Passive House project.
Zack: What were some of the stories or examples of how that played out specifically with your team? It sounds like you got to a place of success. If you were advising another team about how to make it easier to get to that place of success, what would you say?
James: In terms of ductwork air leakage, our standard recommendation now is to mastic the joints like you usually would, but then use an airborne sealing approach to air seal the ductwork. That’s the level of effort that’s required. For us, that is something we want to see on every job in order to ensure that you’re going to be able to sufficiently pressurize the ductwork and get it where you want it to go effectively.
On this specific project, I think there was a starting-from-scratch component for folks to understand what’s entailed in pressure testing and air sealing ductwork.
Tom: From our perspective, it’s really the large, central ventilation ductwork that is the most challenging. We have really economical ductwork design in the units and the same contractor for both. They were able on the first pass to hit duct tightness requirements in the unit, which was great to see. But the complexity of a large system in a phased multifamily project where you have parts of the building that haven’t started framing yet and parts of the building that are starting to receive ductwork installation is really…it comes down to coordinating at the GC level and the subcontractor level to make sure the ducts are installed and exposed at the right time and the right places to do the sealing. Confirming that throughout is difficult as the system comes together in pieces.
I think we are still a little way away from confirming our final duct tightness test. We’ve had better results as we’ve gone along and tested portions of the system together. Testing very often in a phase project has been necessary since we won’t get to do the whole system until the very end of the project.
Zack: That’s a good pivot point here in the conversation because I think that the role of testing and performance data can be really important to projects. Were there other stories around the role of testing throughout the process and the data you were getting back from that shaped project delivery?
Tom: We always do unit compartmentalization blower door tests as soon as we have a unit that’s accelerated [in construction] enough and ready to go. We paired that initial testing with a review of all the air barrier details in the unit, so that the very first unit that was ready we could test and find the weak points, and then go forward with any changes we needed to so we could make sure any future units pass. We passed on our first test, but we’re passing by a lot more on subsequent tests, which is a good sign that that approach is working well.
I’d say we have a similar experience with window infiltration testing—both air and water. It’s a really good practice that’s not necessarily required for a Passive House certification, but both help us eliminate windows as a major source of air leakage and makes sure that the installs will be durable over time. We didn’t do the testing for that; a third-party envelope consultant did the testing for those two functions of the windows, and they were able to catch some pitfalls and address them before we got too far along.
Michelle: Related to that, I think, the air barrier continuity on the building is clearly critical, and so we—as a matter of course—have window mockups that are typically not on the actual building, but are freestanding so that we can physically watch the process of putting in a single window.
I don’t think I’ve ever done a mockup that didn’t change some choice or part of the sequence along the way after the fact. In this case, we made a rather wholesale change and went with a completely different air barrier after the fact.
Zack: Interesting.
Michelle: We were seeing the effort and the complexity of the installation required for the particular product that we’d arrived at, and it seemed inconceivable that we could install windows for 98 units at that scale properly with the time and the complexity it was taking. After some very last-minute back and forth calculus with the contractor who was, of course, quite uneasy about making a change, we were able to switch to an air barrier that had a lot more simplicity in the installation. I think everybody on the team has been really delighted by the process and the work the carpenters have done.
Zack: That’s powerful—the mockup process. To dive a little bit more into your world, Michelle, with the architecture of the building and the whole process of design iteration and design being informed by energy modeling, could you walk through that a little a bit? How did the Passive House nature of the building inform its architecture? What did you discover in that process?
Michelle: When we started the project, we were just coming off the completion of the Distillery. I had in my mind that we were going to design this as close to Passive House as possible, but the owner had been very clear from the get-go that she wasn’t planning to certify. It just wasn’t in her budget and it wasn’t in her mindset.
It was really great to have the GC on our team early on because I just kept going down the Passive House path with the design and the specifications and the continuous insulation and some extra detailing and the triple-glazed windows, and all of that, and the pricing kept coming back and no one was panicking. So, I felt that we had a strong process in that regard. At a point, during DD, I did start to have concerns that without a model we were shooting a little bit in the dark. We were using intuition, but this building is way different than the Distillery. It’s much taller, it’s a different construction type entirely.
We were looking for someone to do WUFI Passive modeling for us. It wasn’t an extensive cost, thankfully, so the owner was willing to do that. The building has huge facades facing east and west, which is not optimal, and we were very worried about solar gain. We were carrying shading on three of the four facades for that reason. Ultimately the energy modeling proved that it was not beneficial in the east and west, and so we were able to eliminate that, which was awesome. It meant substantial savings for a lot of reasons, partly because it takes a lot to install them structurally—we have structural thermal breaks at every one of those solar shading structures. Ultimately, we only needed shading on the south, and that was really great to hear.
We also used the modeling to test. At the Distillery we had used three inches of insulation on the outside, and I felt like we could get away with two here. The modeling was able to help confirm that for us, as well as other general R values around the envelope. We also tested whether we could get away with double-paned windows, and the answer was no. There were a lot of things that testing just helped us dial in.
Zack: The east and the west shading was not necessary because of the low angle of the sun where the overheating was happening?
Michelle: If you shaded, it did help mitigate heat gain, but it also hurt because it created more of a need for heating.
Zack: Those chilly Cambridge winters.
Michelle: Right. Exactly.
Zack Is there anything else you want to add, something we haven’t talked about regarding the project or the process?
James: Michelle, maybe it’s too fresh still, but I think the heat tracing of sewer and storm is a good lesson learned relating to Passive House. Would you like me to explain that?
Michelle: Sure thing.
James: In a typical multifamily building with parking beneath, in our experience, historically, there’s been no great solution. The industry hasn’t done a particularly good job with that assembly in terms of its thermal performance. Oftentimes we’d see the insulation above an acoustic tile ceiling, or the garage ceiling, and then it created a quasi-heated space that sprinkler piping was in and sanitary waste and storm was in, and oftentimes there would be a unit heater that was used to heat that space. It was kind of a classic example of thermal air barrier or vapor barrier confusion that would happen in that assembly because there was so much going on.
Over the years, we’ve been concerned about that assembly and the lack of attention to it. So, with this job, the thermal barrier went where we thought it should as mechanical engineers: in a place where you could simplify and get rid of a lot of the complexity. Now that the building’s almost complete, it’s clear to us, from an engineering perspective, that we do have a freeze risk where we have exposed lengths of sanitary runs—horizontal runs—and also horizontal storm runs.
And so, this is just within the last week, we’ve been refining our calculations on how we believe it will impact the Passive House energy model, and I think the answer to that question is that it’s a relatively minor impact if we do a good job with the controls of the heat trace. But I think moving forward to the next project, I think we take another fresh look at seeing if there’s a better way to tackle that assembly.
Tom: Related to that, one of my big takeaways from this project, is pushing for getting good data from buildings during operation. We’re installing a remote monitoring and optimization system to collect hourly data on heating and cooling electricity use; solar PV production; domestic hot water, gas, and water use in addition to having whole-building utility data for the owner meters plus the tenant meters. That system will be going in shortly and it’s expandable. In the future, Homeowners Rehab and everybody else on the project is also very interested in the indoor air quality performance of a Passive House versus a conventional building, so we’re looking at additional sensors to add in, but I think this project will be fairly unique—certainly in the region and maybe in the industry—for the granularity of the data that we’ll have from the various systems.
Zack: Thank you for doing that on behalf of the rest of us! Well, thank you so much you guys. I really appreciate you taking the time to talk.
Michelle: No problem. It was great talking to you!
James: Our pleasure.
