While wood framing is the most common and familiar type of home structure, the term can refer to many other types of building systems. These include insulating concrete forms (ICFs), structural insulated panels (SIPs) and lightweight concrete.
In addition, if you’re adventurous, many other systems have been around for decades, including log homes, straw bale, cordwood and Earthships.
Not every method of construction may be right for your geography, but most technologies can be modified to accommodate your taste and your region. Ultimately, any structural system must be engineered to support the loads your home will encounter over its lifespan.
Wood, by its very nature, is a green product. If forests are managed properly, trees grow back. How do you know if forests are being treated with respect? Look for lumber that is certified by the
Forest Stewardship Council or the Sustainable Forestry Initiative. Typically, energy-efficient builders prefer 2” x 6” lumber for vertical studs in wall cavities, because the wider space allows for more insulation.
Another more recent wood framing technology is called engineered wood products (EWP). Products such as studs and joists are created in a factory with special water-resistant glues and fibers from leftover mill lumber or fast-growing tree species. They are pressed and glued into lightweight floor joists, rafters or other structural pieces.
The green advantages? First, engineered products use more of the tree—there’s virtually no waste. Second, they tend to be more stable and straight than dimensional lumber.
The downside? Certain products need to be stored carefully and installed exactly as intended, or they can lose their structural integrity. Also, EWP joists require gypsum covering or other detailing to improve their fire safety.
Poured concrete walls alone have very little insulating value. Yet concrete can last forever, or nearly so, if it’s protected from erratic moisture changes and freeze-thaw cycles. That’s what makes ICFs an excellent structural system.
They enclose both sides of a poured cement wall within a water-resistant cocoon of rigid foam. Another advantage to ICFs is that their assembly is quite simple, and the completed walls have an average insulating value of about R-22.
Lightweight concrete is a structural material that’s been around since at least the 1920s. To create these blocks, the manufacturer replaces a portion of the concrete with something lighter and better insulating, such as an industrial waste product like fly ash or petroleum-based polystyrene.
Some companies such as LiteBlock, based in the Phillipines, use a temporary agent that leaves nothing but air gaps behind. If a product does include fly ash, make sure the manufacturer provides data showing that they have carefully tested and screened the material to keep heavy metals and other toxins out of the end product.
The concept here is simple. Two sturdy panels—typically oriented strand board (OSB)—are glued under pressure to a super-insulating layer of plastic-based rigid foam (either polystyrene or polyisocyanurate).
SIPs address air infiltration, R-value and vapor permeability, while at the same time creating the home’s structure and providing a nailing surface for siding and drywall. So why aren’t they seen everywhere? Because they tend to cost more up front than stick framing and aren’t widely understood by contractors.
But if you figure in the benefits in labor savings (up to 60 percent in some cases), plus the ongoing energy payback to homeowners, you can make the case that SIPs come out on par with or lower in cost than wood framing. This is especially true in recent years, due to disruption in many material supply chains.
The point where wall panels connect to an SIP roof is one of the trickier details when building a complete home shell with these pre-made panels. Get it right, and you’ll have a super-strong, super-insulated structure. Courtesy www.thermalshellhomes.com
Materials with higher embodied energy need to last longer to justify their cost to the environment. This study from the University of Michigan compared an energy-efficient house (EEH) with a standard house (SH)—and measured the energy costs for construction, maintenance and improvement of a home within a 50-year lifespan. The EEH does slightly better on these measurements, but greater savings (not shown) will come from energy savings in the more efficient structure.
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