WHILE WOOD FRAMING IS THE MOST COMMON AND FAMILIAR TYPE OF HOME STRUCTURE, YOU HAVE OTHER OPTIONS, including insulating concrete forms (ICFs), structural insulated panels (SIPs) and lightweight concrete blocks. Of course, if you’re adventurous, many other systems have been around for decades, including log homes, straw bale, cordwood and even 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. For the purposes of this primer, however, let’s stick to the structural systems your builder is most likely to know and understand.
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”x6” 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.
Virtues:
Renewable (if forest is well managed)
familiar to contractors
Excellent durability
Caveats:
May create unwanted thermal bridging
Requires skilled labor
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.
Virtues:
Very little air infiltration
Lightweight forms assemble easily
Thermal mass of concrete slows termperature swings
Caveats:
Exposed foam may need protection
Some brands require additional furring strips to attach to draywall and siding
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 Cresco Concrete, creator of Liteblok (www.crescoconcrete.com) 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.
Virtues:
Easy to handle
Less energy intensive than concrete
Durable and termite proof
Caveats:
May not be locally manufactured
Contractors/masons may need training
Waste components should be tested/verified
Virtues:
Reduces labor time/cost up to 60%
Excellent insulating and air infiltration barrier
Caveats:
Stoarge on site must be dry and flat
More expensive material costs than stick framing
Skilled installation recommended (for the wall to roof transition especially)
CICFI
Comprised of leading ICF companies, the Council for ICF Industries (CICFI) is a non-profit dedicated to promoting and enhancing the social, environmental and economic value of ICFs in North America. Advantages of ICF construction include versatility, strength, energy efficiency and speed of construction. www.cicfi.org
Norbord Inc. SteadiTred Stair Treads
These sturdy stair treads are available square-edged or bullnosed, and come pre-sized in popular lengths and widths for faster construction. Moisture and wear resistant, SteadiTred stair treads are made from OSB from rapidly renewable aspen trees. www.norbord.com
Structural Insulated Panel Association (SIPA)
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. www.sips.org
The point where wall panels connect to a 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.
Image: www.thermalshellhomes.com
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