Interview on Passive House

So, Scott, tell us about Passive House.

‍PassiveHouse is an energy efficiency certification system that takes a deep dive into making buildings as energy efficient as possible and in the process, creating better indoor air quality and thermal comfort. It started in Germany in the mid-90s although many would argue that its principles – maximizing solar gain, building thick walls with good insulation -- have been around for as long as people have been building buildings. One of its greatest potentials is that it puts Net Zero within reach.

Why is it called PassiveHouse? Is it just about residential buildings?

‍It started asa residential program but was quickly applied to small office buildings and schools and other non-residential buildings. Since the focus is energy efficiency there really is no limit.

‍On the projects you've been working on, why have the clients decided to pursue Passive House versus any of the other sustainable standards like LEED? ‍‍

That’s a very good question. We see a range of client motivations. The Hillandale Passive House project that we've been working on in Maryland has a client who is trying to do what's right for the planet and is also a long-term real estate holder that wants things to be durable and of high quality. They did a project inFrederick County where they explored some of the Passive House principles and realized they were leasing up faster than anybody else, so their use of PassiveHouse is also just savvy business practice.

What we're also seeing is the program’s use on affordable housing. Pennsylvania started incentivizing their tax credit program by adding points for PassiveHouse.  Many argue the construction premium for Passive House of 2% is a pretty small up-front cost when compared with the lifetime benefit – to owners and to residents -- of drastically reduced utility costs.

So how different is it to design a PassiveHouse building?

‍What we're finding is that it is different both in process and execution. It requires early collaboration with consultants so that when you're massing the building, you’re talking about whether this is good or bad for Passive House. Early energy modeling done in SketchUp provides a lot of input into major design decisions.

You also need to understand a lot of the exterior wall assemblies to avoid the thermal bridging that compromises a walls thermal performance. Many of the details that connect through or to the facade – such as balcony connections -- are figured out early on. Even when we're in concept for a site plan, we are much further along in understanding the building details.

What is the biggest difference in design of a Passive House?‍

I think the thing that's the most different is how the exterior wall is designed.What we're used to, especially in our market, is to construct a wall with wood or steel studs and stuff the cavity full of insulation. If the energy code requires it, we sometimes add a couple of inches of continuous insulation on the outside. That's the wall.  We take about 15 minutes to think about it.

The PassiveHouse program makes you think about the wall entirely differently. It requires you to go off autopilot. The best Passive House steel stud wall for instance puts the insulation entirely outboard of the studs. This prevents the steel from being a thermal bridge. That's what we've done at Hillandale with four to five inches of insulation outside of the steel structure. When the wall is designed this way many other details – such as windows or balconies – are totally different.

PassiveHouse also makes you think differently about windows and the amount of glass you have in the facade. It is performance based so that is determined by many factors– solar orientation, shading, or the amount of insulation. At Hillandale, for instance, on the southern façade with the living rooms, we are using the balconies as the shading device to permit the expansive glass. In the bedrooms, by contrast, the windows are smaller, and so don't need shades. Those are some of the games you play but you must think about all those things.

So, do we also need to rethink how we build buildings? Is there a whole new group of contractors who are now being trained to do this?

Yes and no. It’s a gradual process. In Pennsylvania, for instance, contractors at first didn't know how to do it so the premium for the first project was maybe double what it is now. But after that another project got built with the same contractor and now their subs know what they're doing, so the cost comes down and the expertise starts to filter into the broader industry.

It is going to be an ongoing struggle to find the contractors that know how to doit and aren't afraid to do it. It will also challenge some trades much more than others. For instance, Passive House requires thermally broken double and triple pane windows, and that now has created a community of Passive House window subcontractors that everyone ends up going to.

‍Is there anyone around here who knows how to build it now?

‍The jobs that have been built around here are small residential buildings, townhouses or single-family houses. Hillandale is the first multifamily building in the area and largest scale of any that has been done. The only similar one I know of is a high-rise dorm in New York City that opened a couple years ago.

It seems like the colder climates – Canada, Germany and Austria – are ahead of the curve on this.‍

Yes, you're exactly right so adapting it to the more temperate Mid-Atlantic climate is interesting, but the principles will work for any climate – cold, hot, temperate.

I think that we're at the front end of a wave of this. Europe, especially Austria and Germany, has been doing this as standard practice for decades. And I understand that Canada is going to be doing Passive House as standard code within the next four or five years. The wave seems to be trickling down from the north.

In the U.S. I do think there’s an incentive for long-term owners, like Housing Authorities or legacy builders, to use the system. Otherwise I don’t think until energy codes change or incentives are provided will it be a widespread standard.  But if we are interested in Net Zero, it is an essential tool in the toolbox.