PHlex Is a PHabulous Idea - A Prefab Custom Wall Built to Passive House Standards

Bensonwood Factory

These days, a wall is a sophisticated and complex product that shouldn't be thrown together in a field.

Over a decade ago, Architect James Timberlake wrote that mass production was the "the ideal of the early twentieth century" and that mass customization is "the recently emerged reality of the twenty-first century." He also noted that "to uphold a true return to craft, construction needs to embrace new technologies and methods for making."

I was reminded of this when I read about prefab builder Bensonwood's new product, PHlex, a prefabricated wall panel for Passive House buildings that builders can buy and use to assemble custom homes on site. It's a PHascinating concept; meeting the Passive House standard for air tightness is easier to do in a factory than on site. But this is where the Mass Customization comes in to play; every Passive House design has to hit certain numbers for heat loss or gain, so the amount of insulation can vary significantly. So the walls are not only customized for clients in terms of length and height, but also thickness. Hans Porschitz of Bensonwood explains: "Our PHlex system adapts to each building's parameters to achieve Passive House performance, including the local climate, the orientation of the home, occupancy, square footage and budget."

PHlex wall detail section

© Bensonwood PHlex wall section

This is not easy, especially with the American PHIUS system, which has a different target for each of a zillion different climate zones. As Porschitz notes, "Passive House design is not one-size-fits-all. Cooling and heating requirements for a particular building depend on where you live, microclimates, floorplans, and many other factors."

This requires very sophisticated mass customization.

wall display

Lloyd Alter/ open building electric wiring/CC BY 2.0

The wall panels are built according to Bensonwood's OpenBuilt principles, where services like electric outlets are in a Service Layer inside the air and vapour control layer, so that it is less likely that anyone will punch a hole through the air control layer, and so services can be upgraded over time without ruining the wall. It has continuous insulation on the exterior so that there is no thermal bridging through the studs, and a proper rain screen to keep the wall dry.

hand made windows by Brad Johnson

Handmade windows by Portico Timberframe/ Photo Lloyd Alter/CC BY 2.0

It is really a logical evolution in building; contractors don't build their own windows anymore because they are complicated and the work is precise. I was in a cabin last week where the owner/builder spent an entire winter just making the windows; they were beautiful and he wanted the look of old single-glazed windows, but it made absolutely no sense and they are thermally pretty awful.

In the twenty-first century, a wall is like a window; it is a complicated and precise assembly that should not leak air, water vapour or heat. It is made with sophisticated tapes and membranes and should last a hundred years. It makes total sense that one should buy it, assembled carefully in controlled conditions with sophisticated tools, instead of trying to slap it together in a field.

Hans Porschitz with wall

Hans Porschitz with wall/ Photo Lloyd Alter/CC BY 2.0

With panelized walls, construction on site is also much faster and easier.

"A team of skilled builders, with the assistance of a crane and/or forklift, construct the weather-tight efficient building shell in a matter of days," explained Porschitz. This efficient production method reduces the onsite waste of building materials and reduces the time it takes to erect the building. "A general contractor can complete the project with the confidence that the many building envelope details required by Passive House standards have already been addressed," Porschitz continued. "PHlex helps make building to Passive House specifications more realistic, achievable and affordable."

Every wall should be built this way. And of course, they won't be; a lot of builders want to keep the profits and markups that might go to Bensonwood and would rather hire their own carpenters, and are happy to build to the Building Code minimum standards instead of the far more rigorous Passive House standard.

In my recent post, Five radical steps we can take to fight climate change, Number One was Radical Efficiency – Make every building Passivhaus. To do this without it costing a fortune will take massive change and innovation in the industry, and the kind of thinking going on at Bensonwood, and walls like these. Last word to founder Tedd Benson:

Off-site fabrication of homes and buildings brings much-needed high technology into the building trades. It introduces career paths for the next generation of the construction workforce. It also fosters new levels of respect for the building trades by introducing sophisticated machinery and processes to an industry that hasn’t seen much real innovation.