Developing Boston’s Tallest Passive House with Brad Mahoney

As we continue our discussions around high-performance buildings, we would be remiss if we did not discuss the laudable endeavor that is MP Boston’s Winthrop Square. Projected to be the fourth tallest building in Boston and the largest Passive House office space in the world, Winthrop Square is a pinnacle of high-performance design.

Although construction for this project has just begun, we were eager to hear about the plans for this immense undertaking. So, we sat down with MP Boston’s Director of Sustainable Development, Brad Mahoney. Brad shares some of the extraordinary energy conservation measures that will be included in the tower and highlights the many benefits that the project is anticipated to achieve, including advanced productivity, wellness, and social engagement.

Episode Guest: Brad Mahoney

Brad Mahoney Head Shot

Brad Mahoney is responsible for all aspects of MP Boston’s commercial development, including design, construction, leasing and tenant coordination. In addition, he is also the sustainability and technology lead on MP Boston’s next Boston project, an iconic 1.5 million square foot project in Winthrop Square.

Brad joined MP Boston in 2012 and oversaw the restoration of the historic Burnham Building, the former Filene’s Building, in Downtown Crossing. He was also on the development team for Millennium Tower, which is Boston’s tallest residential building. Prior to joining MP Boston’s team, Brad worked at Lend Lease as a construction manager where he oversaw a wide variety of projects ranging from large scale residential to historic restorations. He also managed an expansion for a life science client by using an integrated and virtual MEP design assist platform.


Information & Resources

About Winthrop Square:

About Passive House:


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Buildings and Beyond is a production of Steven Winter Associates. We provide energy, green building, and accessibility consulting services to improve the built environment. For more information, visit


Robb Aldrich | Kelly Westby

Production Team

Heather Breslin | Alex Mirabile | Dylan Martello

Next up on Buildings and Beyond…

Carbon Policy with Laurie Kerr

Guest: Laurie Kerr

Laurie Kerr head shot







Episode Transcript

Kelly:                                  00:06                   welcome to buildings and beyond

Robb:                                00:09                   the podcast that explores how we can create a more sustainable built environment

Kelly:                                  00:13                   by focusing on efficiency, accessibility and health.

Robb:                                00:18                   I’m Rob Aldrich

Kelly:                                  00:19                   and I’m Kelly Westby.

Robb:                                00:21                   This week I talked with Brad Mahoney who is the director of sustainable development at MP Boston and we talked about Winthrop center, which is a very large building under construction right in downtown Boston, 691 foot tower. The top 30 stories are residential, 420 apartments, and then below that are 20 stories of office space, 750,000 square feet of office space. And if everything goes as planned, this’ll be the largest passive house certified office building in the world, as far as we know, we talk mostly big picture: why they’re doing what they’re doing, a little bit of how they’re doing what they’re doing. If you want to learn more details and if you can make it to New York City at the end of June, consider coming to the n a p h n conference.

Robb:                                01:15                   That’s the North American passive house network conference. Dylan Martello from SWA will be presenting on some of the details of the curtain wall system and there’s a lot that goes into it, especially for such a big building. I’m looking forward to the conference. I’ll be talking in a session about heat pumps- getting more from air source heat pumps. Lois and Kelly will be talking about the importance of commissioning in high performance buildings. Lots of industry experts really focused on high performance buildings and especially low carbon buildings. So if you can make it June 27th to 28th at Metropolitan Pavilion in New York City. And if you want a discount code, we have one of those for you. If you want 10% off for the regular conference admission rate, use the code naphn19*SWA for 10% off. All this is on our show notes. So you can go there and you can click on it and you can copy the discount code. The conference website is Hope to see you there, and here’s my talk with Brad Mahoney.

Robb:                                02:30                   So the whole building will be certified to LEED?

Brad:                                 02:34                   Correct.

Robb:                                02:35                   But the office and the residential sections are kind of being tackled in a different way?

Brad:                                 02:41                   They are.

Robb:                                02:42                   And it’s the office section that will be passive house and LEED platinum?

Brad:                                 02:51                   Yeah, that’s correct, Robb. It’s exciting. This will be the largest passive house office project in the world. Certainly the largest here in the northeast. And the other thing is we’ve gone through our passive house journey, and we found that there are these inherent synergies that passive house has with other components of the ecosystem that we’re creating here at Winthrop. So we’re certifying the office space to WELL gold. We’re really trying to help create and define the workplace of the future.

Robb:                                03:30                   To a lot of people it may seem curious as why you split it up. I mean, why go for passive house only on the office section? Is this your first foray into passive house?

Brad:                                 03:50                   Yes. This, this is our first passive house venture. And to answer that, I think you really have to look at the market, right? Companies are looking to attract and retain top talent, right? You read about it everywhere and that’s kind of where this conversation starts. So we’re creating a healthy, high performance environment, that’s founded in passive house, right? And we think this project will be where companies want to be. You will have to be at Winthrop Center. There’ll be over 4,000 women and men working in this building every day, and it’s that appeal. The other piece is, you know, if you look at the office component per person, it’s where you can most directly impact carbon reduction, the amount of energy per person, right? So first off, the residential- 400 units, 4,000 employees in and out of this building every day.

Robb:                                05:13                   So there’s many more people using the office sections and there’s a bigger opportunity for energy savings, for comfort, for health. Now and when you’re thinking about the passive house concept, is this something that kind of you championed or did you see a need in the marketplace for efficient, healthy office space? How did you get to be looking at passive house here?

Brad:                                 05:48                   So it really did start at the onset of the project when we started this. How do we make this project truly next generation, right? So when you look at passive house, which is ultimately performance based standard, right? And right now when you hear about performance, you think about energy performance, carbon reduction, long term carbon reduction goals, things that we all, both in our community and at large care very much about, and the desire to express what we’re doing, and make the office user understand that, but feel that they have a play in that- feel that they are able to participate in that solution, participate in this idea of going beyond the things that may be traditional. People understand what sustainability means, when you look at some of the top measures, how do people feel that they’re able to contribute, you know, conserving water and recycling? Well, this goes far beyond that because you’re talking about energy reduction and there are many, many other benefits that have tremendous appeal to the office user. You know, better indoor air quality, right? Thermal Comfort. Noise reduction because the triple glazed windows, long term the quality of construction.

Robb:                                07:38                   So it was really the tenants, when you were toying with this idea, it was really that this is going to be better for the tenants

Brad:                                 07:46                   it’s going to be better for the tenants on many, many levels, on many levels.

Robb:                                07:52                   And obviously the idea is, hey, we’ll be able to lease this quicker. or it might be for a little bit of premium. Was that a tough sell or did that just seem like a next logical step when you’re thinking about going passive house?

Brad:                                 08:15                   So it became clear. I think when any organization is contemplating something new, and this is new, not just to us, but it’s new really to the industry, you take a long hard look at it. And we took a long, long hard look. And the more we studied this, the more it really became clear that this is where we want to go to really set the bar and create a new paradigm because we believe this is where development ultimately will go. And we’re trying to do that in a way that really allows for the best experience for our customer, for our tenants.

Robb:                                09:04                   You don’t want to be obsolete in 10 or 20 years

Brad:                                 09:07                   right, I mean the benefits, the resiliency benefits, right? I mean that alone, you know, you can find that there are pieces and elements of passive house that can appeal to different subsets within each organization. And it really has a broad overall appeal.

Robb:                                09:35                   Are you getting feedback yet from brokers or possible tenants or is there interest yet? Is that resonating with folks yet? First of all, actually, let’s back up. What’s the whole schedule for this?

Brad:                                 09:53                   So we open in three years, 2022. So we are starting those conversations with tenants, with brokers. People want great space, right? That’s number one, right? Views are huge, location, and we have all of that, right? And what we’re doing is we are tremendously enhancing that. Right? So when you think about what are the elements of passive house? You know, triple glazed windows, energy recovery, heat recovery- really understanding the vision spandrel framework, what that vision of wall ratio is and kind of optimizing that. The other thing that obviously appeals are the energy savings, the utility savings. Not only today, but long term. Right.

Robb:                                10:47                   And that does appeal to the tenants?

Brad:                                 10:51                   That does appeal, that does appeal. I mean, you know, the traditional, “let’s sell on utility savings,” that’s maybe what people traditionally start with as the key marker for passive house. And I think in some respects, that’s where it starts. But when you look at everything else, and you look at what I was saying earlier- how to optimize the vision to spandrel framework. You know, we have 10 foot high windows, right? And we’ve optimized those for views, right? Because we know the benefits of daylight. And when you look at the overall floor plan, you know, 95% of the overall floor plan is within 35 feet of one of those windows. It’s so everyone has that opportunity and everyone really plays in that.

Robb:                                11:54                   Cool. Yeah that totally makes sense. Can we talk about those windows in more detail? What are they, how are they constructed? What are the big differences between this construction and past big projects that you’ve worked on?

Brad:                                 12:13                   So I think taking a step back, right? So this idea of integrated design, right? And I think with integrated passive house design, you start the project and you kind of set certain parameters- this is what we’re doing on the project, we are moving forward with a passive house design. So that’s really kind of the baseline, right? And you always need someone that raises their hand and says, this is what we’re doing, this is what we’re driving to. And it’s our job to make sure that everyone’s committed to achieving that mutual goal. Everyone on the team is fully committed to it. And it kind of permeates everything. It permeates the modeling on the MEP side and the integration with the PHPP. It permeates the design and the facade when you get into the procurement of the facade in 80 to a hundred million dollars on a project of this scale and size. And I mean there are very real, commercial, financial aspects to this, you know? Like what premium are you spending on that facade? 10 to 15%? Right? And what does that relate to on the overall? And so, you talk about modeling, talk about the facade, talk about the MEP systems and the commitment in driving through that and flowing it through from initial design into design development, into procurement, then into construction. So integrated- everyone is working towards the same goal. And you look at the differences between another high rise project and this, when you look at the facade, it’s curtain wall, unitized system, third layer of glass, right? And with input from our passive house consultants, Steven Winter Associates, we’ve come up with the optimal solar heat gain, the U value, the R18 spandrel insulation. The R18 is a big driver. That’s a big difference, over a traditional curtain wall. So it’s all of those things. It’s the triple glaze. The R18, the ceiling, the perimeter ceiling. That’s inherent, that’s where a lot of old leaky buildings lose their energy. Right? Well, on this one, that’s where our primary focus is and making sure that within that passive house envelope, the collective envelope, we are sealed.

Robb:                                15:22                   So I mean, yeah those are a few big ticket items. You know, the triple pane glass, the higher R values, the air sealing. And there are some pretty large numbers associated with those features. But would you say the first thing you came to when I asked you about it, what was the coordination, was the integration. In your mind, is that a bigger change or a bigger challenge than any of these line items? Does that make sense?

Brad:                                 15:58                   Well, yeah, in some respects it is, because, you know, we’re talking about something that hasn’t been done before. And so you really need to shepherd that. You know, the supply chains are not there. And supply chain starting from, look, this is in its infancy, right? So Handel has done this before, but when we talk about supply chains, it’s not just the architecture, the engineering, the construction managers, the facade manufacturers, the equipment manufacturers. So you really need to watch through that and make sure that everyone has their eye on the collective goal because, you know, you don’t want to bring it to a point and then have it fall down because someone wasn’t paying attention. Right. It’s more a matter of making sure that everyone’s working together. And so in some respects that is bigger than the upfront capital cost. The ability to say, “we’re committed to this and we’re doing it,” that really got us out of the gate, and now we’re off and running. We’re committed to it. We’ve looked past that and now we’re focused on delivering

Robb:                                17:20                   Right on. Yeah. And obviously in a project that is this big, you need really good coordination and communication. But passive house adds another layer. I guess it’s even more important with passive house.

Brad:                                 17:41                   It definitely is. And that’s why really having the right team members, people that are committed to this and we absolutely have that from top to bottom.

Robb:                                17:54                   I mean you’re asking for some wacky curtain wall, something new, have they have their suppliers ever done that before? Anything like that?

Brad:                                 18:05                   So at this scale, no. And you know, I mean adding a third layer of glass is nothing really that novel, right? I mean you’re just adding, however, when you’re talking about producing this many square feet of current wall, it is a challenge. So Cariss + Cariss and Soda Wall, have been working with us and they understood from the onset that this kind of was the Bible. And they have been excellent. I mean we’ve been working through Design Assist now for a couple months and they’ve been pressing hard on the facade and the facade opportunities and the early signs are very good. I mean, they’re very committed to it and it seems like we’re going to be in production soon.

Robb:                                19:02                   Excellent. So what’s been the biggest challenge? What’s been the biggest nut to crack so far?

Brad:                                 19:12                   I think the biggest nut to crack its really- what is passive house. And when I say that, I mean kind of from top to bottom. You know, you’re starting something new, hasn’t been done before, hasn’t been done before at this scale. Its new to the industry. But you can see beyond all of that, and you can see the outcome, and it’s a matter of getting everyone to feel that. And I think once you do that and you realize that we’re committed to this because sure, maybe the first couple projects in a region that go passive house, maybe they have some cost premiums. Over time, as those supply chains open up, as more construction managers are exposed to it, as more designers in teams realize how to build passive house, those premiums go down, and we’ve seen that in other states, Pennsylvania, the Pittsburgh area, other communities that have been committed to passive house, and we’re starting that here in Boston and we hope and think that others will follow. And we’re fully committed to it.

Robb:                                20:46                   So are you looking ahead to future projects yet?

Brad:                                 20:49                   Not yet. This is a big one. It’s super fun because there’s a lot at stake, right? There’s a real lot at stake when you think about where we are today and where we have to go tomorrow. And that’s a huge part of it. And that’s a huge appeal to tenants, to people that want to be in a space that cares about the tomorrow. Right. All the while bringing them just a greater experience within their work environment.

Robb:                                21:31                   Is there going to be any premium, do you think, compared to other comparable office space in Boston, in downtown? I mean there’s certainly a lot of demand for office space in Boston.

Brad:                                 21:49                   The honest answer is I think it probably remains to be seen. I fully believe in it. When you believe in something, you’re creative with it and you say, look, this is how we’re going to put our money where our mouth is, so to speak. We’re fully invested in this and we believe in the outcome and it’s going to be to your benefit.

Robb:                                22:13                   Who’s going to manage the building? Who’s going to run the building?

Brad:                                 22:16                   So we will manage and run the building. We will hire a team, when we get to that point, which we still have a couple of years, but we’ve already started those conversations, because it doesn’t just start from scratch, that understands what we’re trying to do collectively on this project.

Robb:                                22:45                   Gotcha. Yeah. So you’ll be reaping the benefits down the road of the lower the lower energy bills, the durability, the demand for healthy, a comfortable space.

Brad:                                 23:01                   Absolutely. And this only becomes more and more in demand as every year it goes by. That’s my firm belief. That this is not a blip on the radar. This is something that is going to be the new standard and we’re just, we are helping to define that and helping to usher that in.

Robb:                                23:30                   So, if we were to talk again in five or 10 years, what do you think we’d be talking about? Would this be standard? Would there be something bigger and better?

Brad:                                 23:43                   So I think if we’re talking five to 10 years, let’s see, where does that put us at? Close to 2030. Right. Or 2025. So we know that the direct path to carbon neutrality in the urban core for large downtown projects, it requires passive house, it requires high performance. You can’t get there without this. So I think in five to 10 years we’re really talking about some something else, I think passive house is the talk of the town. It’s something that people are familiar with and integrating into their projects. But I think in five to 10 years, hopefully we’re talking about the next innovation. And that’s what this is. It’s an innovation that is so very simple at its fundamental level, at the scientific level, and it just needs to be brought out and explained in a way that people grasp and understand it.

Robb:                                25:20                   Brad, thanks for coming on.

Heather:                           25:27                   Thank you for listening to buildings and beyond. For more information about the topics discussed today, visit And check out the episode show notes, buildings and beyond is brought to you by Steven Winter Associates. We provide energy, green building and accessibility consulting services to improve the built environment our professionals have led the way since 1972 and the development of best practices to achieve high performance buildings. Our production team for today’s episode includes Dylan Martello, Alex Mirabile, and myself. Heather Breslin, thank you for listening and we’ll see you next week.

Speaker 7:                        26:11                   [inaudible].

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