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About Exterior Wall Framing
Determining the basic framing system of your house is a fundamentally important decision. This decision will affect the energy performance of the walls, the resource intensity of the house and the construction cost. When determining exterior wall framing, another consideration is to plan how large your house actually needs to be. The US has been increasingly building ever-larger houses even though family size is shrinking. Space is a resource and sprawl has become a serious environmental problem and so house size should be adequate, not excessive.
| Advanced Framing |
Insulated Concrete
Forms |
Engineered Wood |
Steel |
Structural Insulated
Panels |
Advanced Framing
A method of framing that optimizes wood use by eliminating wood where it is structurally unnecessary. Advanced framing techniques help reduce thermal bridging while also distributing loads more evenly by stacking roof rafters directly over studs.
What Makes It A Green Product
- Advanced Framing can reduce wood use by 30% without compromising the structural design loads of a wall system. This savings translates directly to your bottom line because the strategy uses less material and improves energy performance by dedicating more area to insulation instead of wood.
- Additional sustainability can be achieved by using FSC-Certified lumber
- Reduces thermal bridging (transfer of heat through framing).
- Deeper wall cavities allow for greater amounts of insulation.
Negative Environmental Considerations
- Advanced framing may not work well with salvaged wood.
- Although it is wood-efficient, advanced framing still requires wood use and so alternative structural techniques such as straw bale or structural insulated paneling will place fewer demands on forest resources.
Insulated Concrete Forms (ICF)
CSI Division: 042219 | Residential Category: Insulated Concrete Forms
ICFs are forms for poured concrete walls that stay in place as a permanent part of the wall assembly. The forms, made of foam insulation or other insulating material, are either pre-formed interlocking blocks or separate panels connected with plastic or metal ties. The left-in-place forms not only provide a continuous insulation and sound barrier, but also a backing for drywall on the inside, and stucco, lap siding or brick on the outside.
What Makes It A Green Product
- Has a high thermal mass to buffer the interior of a home from extreme outdoor temperatures, which reduces both the peak and total heating and cooling loads.
- Can result in a 25% to 50% energy savings with an energy bill costing $35 less than that of a wood or steel-framed homes.
- Structure is durable, long lasting and requires little to no maintenance.
- Alternative aggregates, such as recycled concrete, are readily available.
Negative Environmental Considerations
- Because ICF are filled with concrete, additions and expansions to homes can be difficult and require the use of a jackhammer unless pre-planned.
- The production of Portland cement generates significant volumes of CO2, a significant greenhouse gas and so substitutes like fly ash and slag should be used when possible.
Engineered Wood
CSI Division: 061723 | Residential Category: Strand Lumber
For engineered wood framing, wood beams are created with chippings of small dimension, fast growing timber that can easily be replanted such as Aspen and Poplar.
What Makes It A Green Product
- Engineered Wood helps reduce the need for old-growth lumber and provides for a much more sustainable, renewable timber resource. Engineered Wood can be substituted for any traditional lumber and can be cut, nailed and installed using the same tools framing trade contractors use today.
- More and more engineered stud manufacturers are finding ways to use recycled, flawed wood to create Engineered Wood.
Negative Environmental Considerations
- Adhesive binders used in Engineered Lumber can be any of several synthetic resins that pose varying degrees of human health risks.
- Because of adhesive binders, engineered wood framing may be more difficult to recycle than standard, solid sawn lumber.
While steel can be used for framing, precautions must be taken as steel is substantially more conductive of heat than wood. Without these precautions, exterior wall steel framing results in extreme heat loss and is not considered green.
What Makes It A Green Product
- Steel framing is generally made from at least 25% recycled content but is readily available with 100% recycled material.
- Can be easily recycled
Negative Environmental Considerations
- Insulated walls framed out of steel experiences thermal bridging — major heat loss through the studs. Because of thermal bridging, steel framing shouldn't be used for exterior walls unless a layer of eco-friendly insulated-foam sheathing is added.
Structural Insulated Panels (SIP)
CSI Division: 061216 | Residential Category: Stressed Skin Panels
These panels have a foam insulation core surrounded by skins of oriented strand board (OSB). Agriculture fiber cores, such as wheat straw, are widely available and environmentally preferable.
What Makes It A Green Product
- When properly assembled, an SIP house is very tight with very little unintentional air leakage.
- SIPs are very resource efficient and strong.
- Agriboard cores, such as wheat straw, should be used for better indoor air quality.
Negative Environmental Considerations
- Non-formaldehyde polyurethane binders must be used in OSB to prevent offgassing.
- Petrochemical-based foam insulation cores should be avoided.
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