Image Credit: Bensonwood Attaching Huber sheathing to the 9.5-inch-thick I-joist panel at Bensonwood; the panel will be insulated with dense-pack cellulose.
Image Credit: Alex Wilson Jay Lepple, the Building Systems Steward at Bensonwood, showing off a wall panel. The holes in the webs of the I-joist framing members will be used for blowing in cellulose.
Image Credit: Alex Wilson Wall panel suspended by overhead crane for window installation and finishing.
Image Credit: Alex Wilson Illustration of Bensonwood's OBPlusWall system. Not shown here is a rainscreen detail that is incorporated behind the exterior siding.
Image Credit: Bensonwood Bensonwood has developed an R-60 wall detail for Passivhaus performance. Shown here is a mock-up in the company's showroom.
Image Credit: Alex Wilson Passivhaus panels and doors ready for protective wrapping and shipping
Image Credit: Alex Wilson For a recent Passivhaus project, Benson used advanced high-performance windows from Germany.
Image Credit: Alex Wilson Bensonwood uses a baseboard raceway for all electrical and data cabling to minimize penetrations into the wall system. Shown here is a mock-up.
Image Credit: Alex Wilson
I had the good fortune last week to spend a few hours touring the Bensonwood offices and factory in Walpole, New Hampshire. I’ve known Tedd Benson for perhaps 20 years, and knew of him a lot longer than that through his writings. He pretty-much created the modern timber-framing profession, starting back in the early 1970s when he set out to reinvent the craft of timber-frame construction that our New England ancestors used centuries ago. His 1980 book, Building the Timber Frame House, and several others since, have inspired many of us for their vision, beauty, and rugged durability.
In recent years, Benson has shifted his primary focus away from timber framing (though that’s still an important part of what his company, Bensonwood, is all about). His Open-Built¯ construction platform, inspired by the work of Open Building pioneer John Habraken and supported by MIT’s Open Source Building Alliance, has gone a long way toward bringing down the costs of the top-quality homes his company builds.
Unlike the old days, when each of Benson’s homes was custom-designed from scratch, the new Bensonwood Lifestyle series is built on a modular platform with pre-engineered components that can be used to create homes ranging in size from 800 square feet to over 4,000 square feet. This system is called the 3BMatrix (3B for “Bensonwood Building Block”). The company uses advanced Swiss “building information management” (BIM) software to put these 3BMatrix modules together in 3D models. Then fabrication instructions are transmitted to their German Hundegger computer-based machinery that cuts the components to precise dimensions for factory-panelizing.
I’ve visited modular home and panelized construction factories before, but what sets Bensonwood apart for me is the attention to energy performance, green materials, and rigorous building science. At the heart of this system is the OBPlusWall (OB for “Open-Built”). These factory-built (panelized) walls are framed using 9.5-inch-deep I-studs filled with R-35 dense-pack cellulose insulation, then clad with exterior moisture-resistant OSB sheathing (with taped joints). Advanced gasket technology is used for air sealing, detailing is provided to minimize thermal bridging, a drainage plane is installed on the exterior, and integral baseboard raceways are provided on the interior for electrical and data cables to eliminate wall penetrations for wiring.
The computer modeling not only controls the exact design and fabrication of these wall panels, but even identifies the proper placement of nylon straps for hoisting the (heavy) modules into place on the jobsite. All this is done with a minimum of waste through material optimization and factory fabrication. OBPlusWall modules ship to the jobsite with windows installed and sometimes also with siding, though for some projects the builder chooses to handle more of the finish work on-site.
The companion to the R-35 wall system is a standard R-38 roof system, also insulated with cellulose. Where performance goals demand, Bensonwood can go a lot further with energy performance — by using deeper I-joists and including additional insulation components in the wall and roof systems.
When I visited, the company was finishing a house designed to meet the Passivhaus standard. This walls will have an additional 3.5 inches of cellulose on the interior and two inches of polyisocyanurate on the exterior, to achieve approximately R-60 performance. That project was slowed down because advanced Passivhaus windows took some time to arrive from Germany — one of the complications with creating state-of-the-art buildings today.
Bensonwood creates premium homes with costs higher than that of typical tract homes, but the panelized construction allows the company to be cost-competitive with most custom homes today — while offering faster construction, better energy performance, excellent durability, and the addition of timber components to achieve Benson’s signature elegance.
While Benson has been reinventing residential construction for more than 35 years, you wouldn’t know it if you try to keep up with him on a bicycle! After my Bensonwood tour, he and I biked to Walpole for a beer — via a hilly circuit that Tedd uses to keep in shape on his lunchtime rides. It turns out he uses annual biking trips in the Alps to visit high-tech European manufacturers and software companies — some of the tools that keep Bensonwood ahead of the curve in today’s quickly evolving building industry.
In addition to this Energy Solutions blog, Alex writes the weekly blog on BuildingGreen.com: Alex’s Cool Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail — on any blog page enter your e-mail address in the upper right corner. Alex is founder of BuildingGreen, LLC and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.