Green Product Category: Structural Systems & Components

The structure of a building should be designed for durability and soundness—unless it’s a temporary structure, in which case it should accommodate disassembly and reuse of the materials. Some structural materials may compromise the building’s energy efficiency by creating thermal bridges from interior to exterior that allow heat to bypass the insulation; these should be addressed during building design.

Framing materials

For houses and small commercial buildings, wood is by far the most common framing material. Even with wood from certified, well-managed forests, measures should be taken to minimize the use of wood framing and maximize the amount of insulation in the building envelope. “Advanced framing” measures include framing at 24 inches on-center instead of 16 inches, using single top plates (and lining up roof framing over the wall studs), using two- or three-stud corners, and insulating headers above openings.

Larger framing members, such as 2x10s and 2x12s, are made from mature trees that often come from scarce old-growth forests; engineered lumber products, such as trusses and I-joists, are preferable. Finger-jointed lumber, which uses short pieces of wood that might otherwise become waste, makes straighter boards that are less prone to warp.

There also are alternatives to wood.

Light-gauge steel framing is used as a piece-for-piece substitute for wood framing. While it does contain some recycled content, the sheet steel used for light-gauge framing generally contains less recycled material than heavier types of steel. Steel is also quite energy-intensive to produce (high in embodied energy). Most important, however, is that steel conducts heat 400 times more readily than wood: steel framing can easily compromise a building’s thermal performance unless insulation is specially designed to block thermal bridging.

Masonry systems

Masonry construction is common in many areas. Hollow-core concrete masonry units (CMUs) are hard to insulate effectively. A special type of masonry block called autoclaved aerated concrete (AAC) insulates much better than standard concrete block. Other types of block should generally be insulated on the exterior, or between the concrete block and the exterior skin.

Concrete wall systems that are more typically used for foundations—including insulated concrete forms (ICFs)—can also be used to form above-grade walls. Making concrete is energy-intensive and polluting: the production of a ton of cement releases up to a ton of carbon dioxide. Admixture components also affect the environmental impact of concrete. Though concrete walls can provide thermal storage, they don’t provide much thermal insulation; concrete walls for conditioned spaces should always be insulated.

Insulated panels

Structural insulated panels (SIPs, which are sometimes called stress-skin or foam-core panels), are usually made with foam insulation sandwiched between oriented-strand board (OSB) skins and are a viable alternative for houses and other small buildings. They insulate well, are usually quite airtight, and go up quickly. Some panels are available with mineral-wool insulation or compressed straw as the core instead of plastic foam.

Foam-core panels are often used to enclose post-and-beam or timber-frame structures. These heavy timber structures use a great deal of wood, but they’re likely to be very durable—the finish materials and exterior skins can be replaced multiple times in the life of a solid timber frame. If the wood is local or from well-managed forests, this construction system can be a good choice. Some timber framers use salvaged timbers from buildings that are being demolished.

Other alternatives

Other alternative structural systems include adobe, rammed earth, straw-bale construction, and cob construction (a hand-formed mixture of sand, clay, and straw). Log homes use a great deal of wood and don’t insulate very well. Like their mainstream cousins, some proponents of alternative materials or methods claim mass-enhanced “effective R-values”—the measure of a wall’s resistance to heat flow—which are relevant only under certain conditions.

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