House Structure: Systems, Not Just Sticks and Bricks
Wood framing, concrete blocks, and SIPs each have pros and cons. Make sure you understand your options before you start building.
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 Framing: Old and New
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.
Insulating Concrete Forms (ICFs): Light and Tight
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.
This special line of insulating concrete forms from Logix offers even more R-value for walls. Logix Platinum Series features 2 3/4”-thick silver/gray panels made with Neopor GPS (Graphite Polystyrene) by BASF. The graphite resists heat transfer and raises the R-value of the wall from R-24 to R-27.
Lightweight Concrete Blocks: Lasting Value
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.
Structural Insulated Panels (SIPs)Many Strengths
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.
Premier Structural Insulated Panels offer many advantages for homeowners. First, they’re tremendous labor savers, in a time when labor is scarce. Second, they create a strong, tight structure with very little air leakage, and no job site waste of materials. Premier SIPs typically arrive on the site precut, prelabeled, and ready for fast installation.
Since 1990, SIPA has worked to advance energy-efficient construction through the use of structural insulated panels (SIPs). A replacement for wood-frame construction, SIPs are made of foam core sandwiched between two structural facings. SIPs provide builders shorter construction time and less jobsite waste. Homeowners benefit because smaller heating and cooling systems are required with SIP construction.
What is OVE Framing?
Pro Tip: Advanced Framing. The method of framing shown here is called optimum value engineering, or OVE. It saves lumber and allows for better insulating of the home–a win-win for the homeowner and the environment.
DuPont Thermax Sheathing is a nonstructural, rigid board insulation with reflective aluminum facers on both sides. When used on the roof, these facers dramatically reduce unwanted heat gain in your attic space (up to about 30 percent). The glass fiber reinforcement contributes to improved fire performance and dimensional stability. We’re using Thermax in one of our latest VISION House projects in Scottsdale, Ariz.
SIPS on the Roof
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
Glossary of Terms: Know the Lingo
- Dimensional Lumber: Wood that has been cut and shaped from a single tree, typically used for framing.
- Load-Bearing Wall: A wall that helps hold up the house. Interior walls may not be load bearing, but external ones almost always are.
- Engineered Wood Products (EWP): Structural products made in the factory from industrial wood scrap or fast-growing species, assembled with resins under extreme pressure.
- Oriented Strand Board (OSB): A type of engineered wood panel. The thickness of OSB used in most SIPs is 7/16”.
- Fly Ash: Controversial waste by-product from coal-fired power plants. Used as a filler in some—but not all—brands of lightweight concrete blocks.
- Sound Transmission Class (STC): Refers to how well a wall partition attenuates sound. Products such as ICFs have high STC ratings and greatly reduce noise levels inside the home.
Study: Embodied Energy in the Home
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.
Publisher’s Note: This content is made possible by our Today’s Homeowner Campaign Sponsors. These companies take sustainability seriously, in both their products and their operations. Learn more about building and buying homes that are more affordable and less resource intensive.