BY BRIAN LIBBY
In recent years the US Green Building Council's LEED rating system has been joined by a number of other green design verification and certifications, such as the Living Building Challenge, Green Globes and Passive House. But the latter has almost never been applied to a scale beyond that of the single-family home. An apartment building project on North Williams Avenue in Portland now under construction, the Kiln Apartments (formerly called the Payne Apartments), seeks to become one of the first to do so. Recently Agustin Enriquez of GBD Architects, the project's designer, discussed the challenge of applying Passive House standards to multi-tenant housing.PORTLAND ARCHITECTURE: How is Passive House more challenging to meet than other certification systems?
AGUSTIN ENRIQUEZ: With LEED, there are a lot of points to assess, so you can pick and choose a strategy. Generally speaking, if you do a thoughtful job it’s relatively straightforward. With the checklist, it’s kind of easy to do because there are so many options and approaches.
Passive House is different. Passive House has two or three things you’ve got to do. If you do them, you’re done. If you don’t do them, you don’t receive certification. There aren’t silver, gold or platinum [levels]. It’s yes or no. It’s very black and white in that sense.How do you accomplish the ambitious energy-efficiency goals?
Generally speaking, you end up with a building that’s very highly insulated with very high performing windows.
You insulate everywhere: not just the exterior walls. You’re literally insulating, if you think about it, like a thermos. In our case we have insulation under the slab and under the footings, which adds a layer of complexity. In a house, it’s not a big deal [to insulate under the slab]. It doesn’t weigh that much. In a bigger building, that’s a much more significant challenge. You’ve got a lot of weight that’s sitting down on those footings. It also meant a whole lot more insulation on the roof than we’d usually have: R70. It’s literally a thermos with a bunch of holes (windows) poked into it that are sealed very, very well to bring in fresh air and keep it temperate.
And with a high performing skin, you tend to get a lot less windows, because windows are leaking energy through the glazing. If you look at other Passive Houses buildings, they just don’t have a lot of glazing. The rule of thumb in our climate for every day, code-compliant buildings is 30 percent, give or take, and up to 40 percent if you have really high performing glazing. In a house that tends to be easier because you just don’t need a lot of windows on all sides. In an apartment building, you’ve got apartments fronting every direction. If you’re on the backside facing north, you still want to have the same amount of windows. It’s just a whole series of challenges on that side, which I think we knew about but didn’t actually understand the magnitude of prior to the energy modeling. We’re using triple-glazed, super-high-performing, metal-clad wood windows, and they perform unbelievably well. But they’re expensive, a lot more expensive than a typical window.
In addition, you have 24-hour ventilation being provided through an energy recovery ventilator. We’ve done that before but not to this level. But we knew that going into it.
What we didn’t necessarily fully grasp was that the way the metric works is it’s basically energy per square foot as opposed to energy per person. Our owner in this case and those in most of our projects tend to try and make the units as efficient as possible and as small as possible. That way you can spend more money on the quality of other things. So we have the smallest units we’ve ever really done for a market-rate apartment project. We thought that was going to be really useful and valuable. In LEED you get bonus points for that.
In this case, that is a significant penalty, because if you think about having a 1,000-square-foot apartment, with two people living there the amount of energy that apartment is using is basically the same: the same number of TVs, of refrigerators, the same number of showers being taken. You’re heating a little more atmosphere, a little bit more volume. But you’re losing very little of the energy that’s in there. So you’re not spending that much of your energy budget on heating and cooling, for example. If you go from 1,000 to 500 square feet, you’re using the same amount of energy but your denominator changed. We didn’t, or at least I didn’t, understand the magnitude of that when we got into it. It turned out to be a significant challenge. We worked through it, but it’s very challenging. I think maybe the deal is because it was developed in Europe, maybe the size of the units tends to be smaller. Maybe it’s not as big of a deal – I’m not sure. But here in our market the difference between a 700-square-foot unit and a 500-square-unit is a big deal. That’s a big market difference. Shaving off that much more energy is just really challenging. It was fun, but more challenging than we grasped.How did the site figure into those energy calculations and goals?
To be honest, we probably wouldn’t do it on a site that was long and skinny like this in the future. It’s a 50x120-foot site. So the building’s only 45 feet wide. We’d not done a 45-foot wide apartment building because that poses some financial and efficiency challenges. And we overlaid it with this very aggressive and aspirational goal on the energy side. We know enough now to say, ‘We should probably attempt this on a different site.’ This particular client was really interested in figuring out what the next step in reducing energy consumption might be. They’re super interested in energy efficiency. Certification wasn’t as important, but this gave us a metric to address. They said, ‘We’d love to be part of this experiment.’
We now have learned an awful lot about how to do this more cost effectively. The first thing is we’d probably avoid a site this constricted. You’d be helped out a lot because the typical units, which I really like and are really cool, are these long, skinny, wide units as opposed to long, skinny and deep. You pay an energy penalty for that because you’ve got a lot more skin, which is where you’re losing all your energy, than if you had a typical shotgun or just a deeper unit. In other projects you’re not thinking about penalties on the energy side per se. And there were a lot of steps in it, because we had a whole series of conceptual frameworks of why we were doing that. And we were also really trying to fit this large building into a neighborhood of single-story and single-family homes. How can we reduce the mass in some ways? We had these stepping ideas. That’s all good. But you typically wouldn’t do that in a Passive House building. Ideally, you would have a rectangular box and you would just find the most efficient way to skin the building. Not necessarily very creative, but that is certainly the most straight forward approach to an efficient building skin.
These units are long and skinny, but placed along the perimeter of the building instead of the way so many condos are like bowling alley lanes. We’re getting a lot of the light and solar energy deep into the space because the building just isn’t that deep. Our building is 45 feet wide. If you walked to the Pearl and looked at a lot of the shotgun units, a lot are 45 feet wide. That’s our entire building width.
How did you decide the best way to heat the building?
We honestly looked at a wood pellet boiler. The energy model actually takes into account where the energy is coming from, so if you’re delivering it onsite, there’s some advantages to that. And this would have made the building a little easier on the energy side. But it was really hard to wrap our head’s around burning wood in the summertime to heat water. It might be a hundred-degree day but you need warm water and you’re burning wood. It just seemed real odd.
We’ve got solar thermal up on the roof that preheats domestic hot water. The heating is delivered through radiant wall panels; so we’ve got hot water that’s basically running around the building. The solar thermal heats it to a certain level preheating it, and gas boilers heat the water that little bit more for washing hands, taking showers, and supplying the water for the radiant heat. The building is so well insulated that we don’t have to provide a lot of space heating. Most Passive Houses don’t have space cooling, either, so there’s no cooling system here. We could have done, say, the radiant in the slab. We wanted to have wood floors and it was a little more efficient and cost effective to do it in the walls. Down on the ground floor we’ve got slab heating where we’re exposing the concrete. We’ve also got ceiling fans to create air movement in the apartments. The building won’t fluctuate in temperature very much throughout the year. It probably hovers around 70 degrees, give or take 10 degrees, and then that’s when the space heating or cooling kicks on. I live in a house with no air conditioning and it works for me and my family. I like that. And this building will perform much better than that.
What about people using operable windows? Won’t they disrupt the tight Passive House envelope?
That’s a good question. We asked that question immediately: are we going to lose an awful lot of energy right away? Probably not. The building itself will retain so much of the energy that you won’t lose a ton. It’s kind of like your refrigerator – when you open the refrigerator to grab a pitcher of orange juice, all the cool air doesn’t immediately leave. If you were to leave the door open accidentally and take off for the weekend, then the refrigerator is going to be working like crazy. Same thing in a Passive House. And the times of year where someone will likely want to open a window, will be the times of the year that the temperature is mild to hot and it shouldn’t be a significant issue. The Passive Houses we’ve toured, people have opened the windows to bring fresh air in the summertime, but the anecdotal feedback is they don’t necessarily need a ton of breeze.
We worked very diligently with them. I think we came up with a lot of solutions I think ultimately they were very appreciative of. The height of the building, from a neighborhood size, I think they would have preferred a smaller building. We didn’t ask for modifications or adjustments on the height. It’s allowed outright. But I think we had a really good working relationship with the neighborhood association. And it’s still a tough conversation. We got letters back that said, ‘We really appreciate the quality. We like the building. We understand you’re trying to build a building that’s going to be here in 100 years. Could it be smaller?’ Ultimately we ended up moving the mass of the building around from the neighborhood side to other locations.
How much more efficient than code is it?
The real conservative estimate would be 65, 70 percent better. And that’s Portland code, which is really aspirational anyway. In another part of the country that is really conventional, it could be 80 percent [more efficient]. Now, we have a lot of advantages. You don’t have to heat and cool to the same degree. But in Portland, our rough, conservative metrics are that it’s 65 to 70 percent better than a code compliant building.
How unique or unprecedented is a multi-family housing project designed and built to Passive House scale?
We’re hearing that there are only a handful of these in the country, and they’re not this scale. There’s a dorm that’s under construction that is larger. There is also a building in the planning stages here in town that is larger. Its still very new and cutting edge for multi-family.
How does this project and its energy goals differ from some of the LEED Platinum projects GBD has designed?
On the Passive House side, the systems are low-tech. We’re piping around hot water. That’s not a complicated system. The insulation is what it is, and the windows. We don’t have a bunch of complicated systems turning on and turning off, really finely tuned, which was one of the attractive things to this owner: low tech and a lot less maintenance. We did OHSU’s Center for Health and Healing, for example. That requires a building manager that really understands the building. It’s a very complicated system. It works: it’s performing the way we expected. But it took a year to fine tune it. Passive Houses really shouldn’t. There just aren’t that many levers to switch or dials to dial in. Which for us was really exciting. Low tech is really interesting.
Low-tech sustainable buildings existed a millennium or more ago: holding thermal mass and oriented for the best natural light.
The site orientation, how much glazing, all those things: that’s the way a farmer would deal with his farm. He would site his house and his crops in a way that took advantage of the prevailing winds, the location of the sun and how it moves across his field. Here the site is very constricted but it has the right orientation. It’s long and skinny in the east-west directions, you have broad faces for the south, small faces for the east and west. If you were to flip this 90 degrees, we wouldn’t be able to have this much glazing, so you just wouldn’t have units that were this attractive—if you could even meet the metric.
When we were going through the design phase, there were other people tackling similar issues on the home side. To be honest, I don’t think we understood the magnitude of what we were trying to accomplish. This is a project that at the end of the day really needs to make financial sense. It’s not a single family home where you can kind of absorb those costs and rationalize it as, ‘It’s my dream house.’
Is there incentive for owners to do this if the renters pay for the electricity?
In this case, it’s something the owner wants to do. I think there is definitely a marketing and branding opportunity. I think the units themselves are going to be nice and very interesting. If this wasn’t Passive House, the quality of the units and the location are still awesome. At the end of the day, does someone move in here because it’s super energy efficient? Hopefully, though, I’m not sure. My ultimate goal would be for the project to be full of great apartments that happen to be extraordinarily energy efficient.
I think the effort here is to learn everything you can learn about how to make a building more energy efficient and then take the good ideas that are cost effective and export those to larger projects—not necessarily even larger Passive House projects. For example, we have four inches of exterior insulation because we were really working hard to get under our energy threshold. Does it make financial sense to go from three inches to four? Should we have gone to five? At what point does it not make financial sense to do that? We have a significant amount insulation under the slab. If you weren’t doing Passive House, but wanted to do an almost Passive House quality building, would it make more sense to halve the amount of insulation under the slab and apply those cost savings somewhere else?