High-Performance Walls

Not long ago, 2-by-4 walls insulated with R-13 fiberglass were standard in North American homes, even in regions where winter temperatures fall well below freezing. But residential construction has taken tremendous strides forward. Researchers are helping builders understand much more clearly how heat and moisture move through walls, roofs, and floors. Now, there are a variety of options for building more efficient, comfortable, and durable houses. Tougher building codes promoting energy efficiency and a clamor for lower energy costs have helped advance the technologies, too.

This article will explain some wall-building technologies and techniques in a range of high- and low-tech options. These wall systems come with different price tags and require different construction techniques, some more specialized than others. But all of them are aimed at providing better thermal barriers, fewer air leaks, and lower costs for heating and cooling than conventional stick-frame construction.

One caveat: As houses get tighter, whole-house mechanical ventilation gets more important. If you’re planning a super-insulated house with very low air leakage, make room in your budget for a heat recovery ventilator or its equivalent.

Advanced Framing
Less Lumber, More Insulation

Advanced framing (aka optimum value engineering) boils down to less wood and more insulation. This method of framing structurally sound houses with less lumber—saving time and materials—grew out of a partnership between the U.S. Department of Housing and Urban Development and the National Association of Home Builders Research Foundation in the 1970s. Walls built with fewer sticks of wood allow more space for insulation and help reduce thermal bridging—the movement of heat through relatively dense framing members.

Advanced framing technique relies on standard building materials and is relatively easy to adopt, yet yields big returns—30% fewer pieces of lumber and 60% more room for insulation compared to conventional 2-by-4 walls on 16-inch centers. Some of advanced framing’s major differences over conventional wood-framed construction:

• 2-by-6 studs, on 24-inch centers.
• Single top plates and in-line or stack framing—joists are located directly over studs, and studs are located directly over each other on adjacent floors.
• Eliminating door and window headers without loads and using single headers for load-bearing openings.
• Two-stud corners.
• Fewer studs around door and window openings.
• Raised-heel roof trusses, allowing more insulation where the roof intersects with the walls.

Some builders haven’t liked some elements of advanced framing. Two-stud outside corners made hanging drywall seem problematic, although drywall clips proved an easy fix. Eliminating one of the top plates on the wall also required that studs be 1 1/2 inches longer to maintain the same ceiling height.

There also was a perception that a house framed this way wouldn’t be strong enough. Builders who learned traditional framing techniques could see the value of using 2-by-6 studs (more room for insulation) but might balk at the 24-inch on-center (o.c.) spacing and fall back on 16-inch o.c. framing.

But once convinced to try, builders could see the improvements in building performance and ease of assembly, as well as lower labor and material costs. The Building Science Corp. estimates that advanced framing saves 13% in space-conditioning costs compared to conventional construction.