Two years ago, Tim Eian, a German architect who has lived in Minnesota for 12 years and operates TE Studio there, was hired by Paul and Desiree Brazelton to design the remodel of their 1,200-square-foot 1935 mock-Tudor home in Minneapolis, adding a two-story 800-square-foot addition in the process . In the course of that Eian, who several years ago designed Passive House in the Woods, in Hudson, Wis., the first Passive House in that state, ended up creating the MinnePHit, the first remodel in the U.S. constructed to the EnerPHit standards set by the Passivhaus Institut, “Passive House Institute,” in Darmstadt, Germany.
REMODELING: What’s the difference between Passive House and the MinnePHit remodel?
Tim Eian: The Passive House Institute’s EnerPHit code is specifically created for retrofits rather than new construction. I became aware of the EnerPHit code through my involvement in several Passive House groups. EnerPHit emulates some Passive House standards but not all of them. It’s a little more lenient.
RM: The idea of this ultra-snug energy retrofit was not your clients’ original intention?
TE: They weren’t in the market for a Passive House retrofit. They had a house they wanted to remodel, and the house had some serious architectural shortcomings. A family of five lived in this small space, which had only one bathroom, and that was on the second floor. They came to me knowing that we could combine architectural work with performance enhancement. But that wasn’t their priority.
RM: At what point did you bring up EnerPHit?
TE: Here in our office we made some assembly designs. That appealed to the Brazeltons. I said: Let’s run an energy model on it and see where we are. It wasn’t originally part of the scope. When we did that, we found we were within 10% of the energy limits of the EnerPHit standard. I called them and said: It’s looking like if you want to go down that path, we’re pretty close. They thought about it briefly and said they were “all in.”
RM: What are the challenges of applying this kind of standard to remodeling versus new construction?
TE: It hinges on climate to some extent. Passive House technology is least difficult in a place where heating loads are modest. In colder climates it’s much harder to do. And it’s a big departure from the status quo. Minnesota has a decent building code, but there’s no air tightness requirement and R-values are very low. So you’re constantly comparing apples to oranges. It’s also the case that when you’re retrofitting, you have the added challenge of thermal bridges you may not be able to eliminate.
RM: What would be an example of that with the MinnePHit?
TE: The basement. It’s virtually impossible to completely insulate it. Ideally, you want to outsulate, which is the same as insulating, only you do it on the outside. Even then, you can’t get completely around the footings. We had access to two walls outside, which we dug out and insulated. The other two were insulated from inside. We removed the slab, excavated 6 inches deeper, insulated with EPS [expanded polystyrene] foam and put a new slab back.
RM: How did the walls change?
TE: In a retrofit, you have to work with what you find. And there are setback requirements and code regulations. We sheathed the entire building in OSB, then taped it. We built out from there with I-joists, then packed the cavities with cellulose insulation for an R-45–rated finished wall. The new walls for the 800-square-foot addition were similar. We started with walls that were about 7 inches thick and ended up with walls that were 17 inches thick. The I-joists were 9.5 inches. The house has Hardie lap siding.
RM: You removed an existing chimney?
TE: The chimney really made the façade. But I don’t think [the clients] used the fireplace or that it even worked. There was some backdrafting and it reeked of creosote. And in an airtight situation, you can’t have open flame. Here we have the paradox of building for 21st-century performance in a house with the open fire of the 18th century. Besides that, the house was designed for a heat load such that any wood stove or fireplace would have overpowered it. So the original brick chimney was completely torn off. It would have presented a major thermal bridge and it wasn’t structurally sound anyway. But the [clients] didn’t want to lose the façade.
RM: How did you solve that?
TE: We designed a replica [chimney] and clad it with stone veneer.
RM: Can just any remodeler or crew do this type of Passive House work?
TE: That was the biggest challenge of all; finding a team that could execute it properly. We had done this before and understood assemblies well. It’s not a technical or a design problem, nor is it a product challenge. It’s a matter of finding a team on the execution side that can be diligent about air tightness and moisture management. We can solve part of it from the office by making pragmatic designs that define the air barrier and the insulation barrier; by making sure that they’re continuous and connected. On the execution side, you have to have people you can count on who won’t cut corners on that.
RM: How much more expensive does that make the project?
TE: There are, inherently, up-front costs to a building that uses quality craftsmanship and where you make a structure where air and water are properly managed. When you take this to the Passive House level, you increase it yet again, both with new construction and, in this case, a retrofit. Of course, getting anything off the ground in this economy is an issue in construction generally right now. That these projects are being commissioned and completed is a testament to the people who see the value in this method. Ultimately, if you look at this over the lifecycle, it costs more on day one but over time it achieves a lower lifecycle cost. That’s what you’re paying for. And the comfort.
RM: Are you seeing a lot of interest in Passive House technology and the kind of retrofits built to the EnerPHit standard?
TE: We have been busy for five years with different projects, but the number that got built is small compared to the ones we started. It usually comes down to financing. Consumers are confused, Realtors don’t know anything about it, and neither do bankers. There are too many green standards out there, and it’s difficult to see this through. So when homeowners go to the bank to get these projects financed, the bankers look only at the comps. There’s little understanding or acceptance that this kind of retrofit is a different sort of animal. We’re saying: Let’s put some additional dollars on the table to buy the lifecycle performance.
But most people want to get in cheap and deal with the problems later.
RM: Is that attitude changing?
TE: First, there’s a lot of curiosity. People think Passive House is all about fat walls and expensive windows. On the other hand, we’re seeing an effort in Minnesota to put air tightness in the building code. I see moisture issues being addressed. It’s having a huge impact now. We just started a design a few months ago and we’re working with the contractor on pricing. The owners are having these same discussions with their bank, and we’re hoping they will emerge victorious.