JLC's Coastal Connection has been following the progress of Maine building company EcoCor, LLC, since 2011, when we connected on site with EcoCor owner, Chris Corson, to document an affordable Passive House project (see "An Affordable Passive House, Part 1" and "An Affordable Passive House, Part 2," JLC 5/12 and 6/12).

In the years since he completed that first Passive House, Corson has built several more examples using the same wall and roof system concepts. The system has evolved from one house to the next—in particular, EcoCor has introduced more advanced European-made materials and components as the new products became available in the U.S. market. Now, Corson is making the leap to factory production: EcoCor has rented a warehouse shop space in Searsmont, Maine, geared up with panelizing hardware, and begun panelization of wall and floor assemblies. This month, Corson will set the first of six houses on his schedule for 2014 and 2015. Coastal Connection traveled to the EcoCor shop this month to tour the facility with Portland, Maine, architect Rachel Conly and to watch a wall panel being constructed (see slideshow: "A Visit to a Passive House Panelizing Shop").

EcoCor carpenter George Reefer screws a wood I-joist to the outside of an existing stud wall for a field-constructed EcoCor deep energy retrofit in Newcastle, Maine.

EcoCor carpenter George Reefer screws a wood I-joist to the outside of an existing stud wall for a field-constructed EcoCor deep energy retrofit in Newcastle, Maine.

Reefer places an I-joist for the same type of wall system for a new home package under construction in controlled factory conditions at EcoCor's Searsmont, Maine, shop facility.

Reefer places an I-joist for the same type of wall system for a new home package under construction in controlled factory conditions at EcoCor's Searsmont, Maine, shop facility.

Says Corson: "This is basically a panelized iteration of seven projects that we've built in the field, adapting those lessons learned, and then trying to re-engineer that into a product that increases our scalability as a company, and also the capacity for us to proliferate Passive House on a larger scale."

Compared to a simple double stud wall system, or an insulated stick frame with exterior applied rigid insulation, Corson admits, his wall system is complicated to build. He's chosen his methods not because they're easy, he says, but because they're high-performance—not just in terms of thermal insulation, but in terms of moisture management.

"We've got three projects data-logged," he says. "We've been doing the hygrothermal data-logging of the wall system for the last couple of years, and it's pretty impressive. The surface area of our sheathing on both sides is staying around 8% moisture content. The walls are staying extremely dry."

But the multi-layer walls are labor-intensive to construct. That's where panelization comes in. Corson is hoping that his factory process will make achieving Passive House—including the robust moisture management of an advanced wall system—easy for builders in the field.

The details matter, Corson says: "It comes down to implementation. There's a way to get it to a level where it's going to perform well. But it's like that with anything you build, including a simple conventional stick frame. You put one nail in the end of a top plate instead of three, then the wall's gonna fail. You have to do things right."

That's where the factory process comes in, says Corson. "You can watch us build stuff on the framing table. There's no eighth of an inch of slop. Everything is framed exactly, sheathed exactly. It's cabinet-quality wall assemblies. And that's partially because I think that's the standard of quality that we should hold ourselves to. The idea is we want to produce a product that's affordable, but at the same time, a premium product. To make the automobile analogy, I don't know if we're there yet, but my goal is for this to be sort of like the Toyota Prius of wall assemblies. The Prius was built on the Corolla platform. There are millions and millions of cars that were built. From an engineering standpoint it's the best engineered production vehicle on the planet right now ... with the exception of maybe a Tesla."

Cabinet quality in the shop is one thing. Precision in the field is another. Making sure that foundations are square, level, and accurate will be a big challenge, Corson notes. "Our panels are perfectly square," he says. "I've told my crew — if I come out there and measure it and it's not square, I'm coming back with the chain saw and cutting it in half and you're going to build it again. However, we build each panel one eighth inch short. That way, if there's some issue with the marriage plates when we build it in the field, and the wall grows a little, the house won't be too long. If I have to pack the wall out a half inch in the field with a piece of plywood, no problem. But if I'm hanging off the foundation a half inch, that's a big problem."

At present rates of production, it takes one shop worker all day to construct a 12- or 14-foot section of wall panel. Panelizing a whole house might take two weeks. That has to speed up, says Corson, but for now it's okay: Accuracy is job one. "We're taking it slow," he says. "I don't need production now; I need it in six months. What we need now is to spend the time refining and dialing in the process, the system. Only when everything is perfect every time, a total no-brainer, with all the guys trained and cross-trained—then we can crank. All the tools are in place."

Once the panels are built, Corson expects field assembly to take only a few days—but the proof will be in the pudding. In coming issues, Coastal Connection will report from the field on EcoCor panel sets.