Sonya Newenhouse, Ph.D. is an eco-entrepreneur who enjoys providing practical and creative solutions to help individuals and organizations live and manage green. Her firm, Madison Environmental Group, provides LEED green building and sustainability consulting services. She is also founder and president of Community Car, a car sharing organization in Madison Wisconsin. Currently she is developing NewenHouse, a business that will provide super-insulated sustainable kit homes.
Sometimes, like today, when it’s particularly cold and windy this winter, I wonder how our NewenHouse will perform without a furnace. I try to imagine myself sitting in our new living room next year with the sun pouring into the windows and warming up the room. But how will it feel at night, after the sun sets? Our Passive House model suggests that we will be very comfortable and will only need to turn on our two little eco-heater wall units every now and then. I look forward to sharing with you how it really functions next winter. Our home will only need about 2,000 watts of heat (equivalent to two hair dryers). I learned recently that each person emits approximately 100 watts, so if we have an extremely chilly cloudy day we could invite 20 people over and have a house warming party! Luckily Cecil and I love to entertain and Bjorn, our roommate, is always open to having visitors too.
Now we are at the stage whereby I have multiple subcontractors on the job at the same time. It’s fun. The electricians, roofers and plumber have completed much work, but today I’ll share with you the process of building the Larsen Trusses. For our purposes, these are a wooden framework that provides a way to create a secondary wall which hangs off of the structural 2-by-4 wall. Larsen Trusses were invented by John Larsen of Canada, who wanted a way to super-insulate existing homes. His truss system is a little different than ours but uses the same principles of creating a 12-inch-deep wall. This remote wall system is an effective way to create depth for the insulation values (R-57) we need to meet Passive House certification standards in Wisconsin, where it’s colder than most parts of the U.S. Once the trusses are completed, the insulation will be blown in from the attic and held in place by insulation fabric.
The Larsen Truss system on the east wall of the home. Photo By Sonya Newenhouse.
The traditional Larsen Truss uses two 2-by-4s that are connected with a 12-inch horizontal piece of wood, creating what looks like a ladder. The Larsen Truss version we’re building uses less wood as we are attaching the truss to the OSB with blocking rather than using two 2-by-4s. We are further reducing lumber by balloon framing the Larsen Trusses from the base of the house to the roof trusses—attached to the taped OSB air barrier with an 8-inch piece of OSB every 4 feet—hanging like a curtain wall.
Originally we had planned to create two walls, but the Larsen Truss method uses less lumber, thereby reducing the heat lost to “thermal bridging.” A thermal bridge is created when materials that are poor insulators (such as wood or metal) come in contact with each other, allowing heat to flow through the path created.
David Romary and Dan Johnson framed the house, the 2-by-4 structural walls, the inner room walls, the roof trusses, and now they’ve finished building and fastening the remote Larsen Truss walls. To build the Larsen Trusses, David made a pattern so he didn’t have to measure over and over again the distance to attach OSB gussets to the 2-by-4s. He was very pleased that we used two-thirds of our small scrap lumber pieces to create the 8-inch OSB gussets and 8-inch blocking. Before attaching the Larsen Trusses to the OSB, Dan taped the OSB seams with Siga Tape. This tape, made in Switzerland, sticks effectively to the OSB and is known to be a very good quality tape. Since creating an air tight barrier is of utmost importance in the performance of the home, we wanted to use a product that has been used on many Passive Houses. Most of our building products are made in North America, but two European items—the tape and the HRV (Heat Recovery Ventilation) unit—were chosen for their exceptional performance and quality.
Thank you Thorsten Chlupp (Reina, LLC) for sharing the details of your arctic wall Larsen Truss system to help guide us on this project. Thorsten lives in Alaska with his family and builds super insulated sustainable passive homes there. I’d also like to share David Romary’s web page. David and Dan are part of the Kickapoo Green Building Guild in Vernon County Wisconsin.