Double-Stud Walls Gaining Ground in Cold Climates
Double-stud construction is a modern energy-efficient framing concept that is gaining ground among professional homebuilders.
To get the nitty-gritty on the basics, HIR turned to construction expert Ben Bogie: “Double-stud construction is a type of wall that’s often used in cold climates (zone 4 and above) to gain large amounts of insulation, using common building materials and avoiding environmentally harmful foam. In most versions, the exterior is constructed with a typical 2x4 load-bearing wall just like the ones found in most houses. Then, a second non-load-bearing wall is built to the interior spaced away from the exterior wall. The amount that it’s spaced apart can vary, depending on how much insulation is desired. In Maine, we typically build 10-12-in. walls, but they can range anywhere from 8-16 inches.
“There are a few reasons these walls are favored. First is how well they perform thermally, and that’s not just because they have a lot more insulation, but because they have insulation in the right places. There’s a phenomenon called thermal bridging where you have framing material touching the outside wall surface and the inside drywall. These framing pieces act as a bridge for indoor heat to flow across them to the outside during the winter, and outside heat to flow in during the summer. But if you space the walls apart, you short-circuit this highway of energy loss and end up with a wall that performs dramatically better.
"You can accomplish the same effect by adding continuous insulation to the outside of your wall, stopping the energy flow through the framing, but that requires an additional complicated ‘lap’ all the way around the outside of your building with expensive and potentially not-so-environmentally-friendly materials. (There are more ecologically benign products becoming available, but they are still quite expensive, comparatively).
“Double-stud walls use low-cost, common building materials that any carpenter or handy person is already familiar with and requires no special training. There are some factors to be aware of: These walls perform best with cellulose insulation, and the addition of what’s known as a “rain screen.” They should also be built as airtight as possible, minimizing the accumulation of wintertime humidity in the wall. They are far from complicated to build, the cost is low for their level of performance, and they utilize environmentally friendly and readily available materials.”
NOTE: Always consult your local building codes for specific construction guidance.
Ben Bogie is a second-generation high-performance builder working as a lead carpenter in Portland, Maine, and is an active member of the Northeast Sustainable Energy Association. He specializes in building science, low-energy designs, and high-end custom finishes.