How to Choose the Right Framing Materials for a Sustainable Home

Many discussions about sustainable homes are misguided. Instead of first considering the structural frame of a house, which is responsible for around 20% of the heat loss, other elements such as solar panels, energy-efficient appliances, and low-VOC paints take precedence. We should first focus on the part of a home where it is easiest to reduce emissions.

Why Framing Material Determines Energy Performance

Heat moves through walls in two ways: through the insulation and around it. The second path is the problem. Thermal bridging happens when a highly conductive material, typically light-gauge steel, runs continuously through the wall cavity, bypassing the insulation entirely. Steel has a thermal conductivity roughly 400 times higher than timber, so a steel-framed wall can lose a significant portion of its rated R-value in practice, even with excellent insulation installed between the studs. Timber doesn’t behave that way. Wood has natural insulating properties that keep thermal bridging to a minimum, so the insulation you install actually performs close to its rated value.

Carbon Isn’t Just About What You Burn

When assessing a material’s environmental impact, it’s insufficient to evaluate only its operational performance. We must also consider the embodied carbon, which is the emissions produced during the extraction, processing, and transportation of a material.

The production of steel results in high carbon emissions, regardless of the phase considered. In contrast, timber, if responsibly sourced, has a cooling effect. Timber is the exclusive fundamental material for structures that actively sequesters carbon dioxide throughout its lifecycle. A 2009 study in the Journal of Sustainable Forestry estimated that the replacement of wood with other GHG intensive materials in building construction and materials production would result in a 14% to 31% increase in global GHG emissions.

A Life Cycle Assessment of a timber compared to a steel-framed home consistently reveals timber to have a lower overall environmental impact, not only at point of manufacture, but also at end of life as it may be repurposed, composted, or used for energy recovery. Structural steel recycling requires tremendous heat and processing energy. Neither end-of-life option is landfill, but one is notably less energy intense than the other.

Choosing Timber With Structural Integrity in Mind

Not all timber frames are created equal. The choice between green, air-dried, and kiln-dried timber materials exerts a real influence on the quality and performance of your build over time.

Green timber continues to lose moisture after installation, as it does so, it shrinks. Shrinking timber can pull wall sections out of alignment, while also leaving gaps in the building envelope that undermine the whole-home airtightness you’ve made an investment in.

Kiln-dried or seasoned timber arrives on-site at stable moisture levels, so the sections stabilize after installation and you know what you’re getting. For truly high-efficiency homes, this kind of stable timber won’t be optional. Timber Wall Frames made from properly seasoned stock give accurately sized, stable sections that can be relied on to stay in alignment over the life of the building, necessary for delivering on your energy expectations in the real world.

Species Selection Matters in High-Risk Environments

Standard framing pine is a great option for protected, low-moisture environments. But exceed those parameters and it all starts to fall apart.

If you are in a high-humidity area with regular moisture exposure, or you know you are in termite territory, then that is no longer a "preference" question but a structural one in terms of your species selection. For example, Western Red Cedar’s natural tannins and oils make it resistant to both rot and insect infestation, and it requires no or low VOC treatment. Hardwood treated with tannins and other naturally occurring substances can also do the job just as well, and they are the best option if your local species can fill the gap and is a natural choice given your climate.

But the broader point here is that the most sustainable frame is usually the one that lasts the longest. A frame that fails early, or requires extensive remediation over the course of its life, has a big environmental cost that never makes its way into the brochure comparisons. So, in fact, choosing the species that works best with your set of actual site conditions is really just as much a sustainability decision as going out and sourcing certified timber.

Hygroscopic Properties and Indoor Air Quality

There’s another way in which timber is a no-brainer that generally doesn’t get talked about enough. If you’ve been paying attention to the discourse on biophilic design and healthy homes, though, you’ll already be there: wood’s hygroscopic qualities.

Put simply, timber absorbs and releases moisture from the air, which helps buffer humidity swings inside the building envelope. That means less work, and lower loads, on mechanical ventilation systems hashing up and down all day long. Which typically leads to more stable indoor air quality, and a bit of energy saved too.

Steel or concrete framing does absolutely nothing in this space. They’re more or less inert for humidity change, meaning any kind of moisture management is 100% the job of mechanical systems. Or, if you’re kidding yourself for any reason, the airtightness detailing.