In the push towards carbon neutrality, mass timber structures provide significant advantages over steel and concrete because of the carbon sequestration benefits realized in the formation of wood. Wood is unique in its ability as a structural material to store carbon. Roughly half of wood’s weight is made up of carbon, making this natural resource an ideal carbon keeper.
But carbon storage gets us only partway towards our goal of truly sustainably-designed buildings. Although a high performance envelope can be designed using steel or concrete, mass timber certainly gives us a head start in that quest. But if you wrap a mass timber structure with a low performance envelope, you lose the race. In order for a building to entertain the notion of true sustainability, carbon neutrality or net zero energy, a high performance envelope is essential.
A number of factors favor mass timber structures for high performance envelopes. For example, if your design includes a thermal bridge (e.g., if you have a structural cantilever that protrudes through a high performance envelope), it’s better to start with a wood structure, because wood’s thermal resistance is far superior to that of steel or concrete. So if you can’t design away from a thermal bridge, then a wood structure is a better choice.
Another advantage of mass timber structures is the fact that cross laminated timber (CLT) panels are continuous and precise, and systems are factory- fabricated in a controlled environment with tolerances far more exact than a field-assembled structure. By using CLT, you provide an excellent first line of defense with air-tight roof, exterior wall and floor assemblies.
Once you’ve created the envelope, take care with the details.
The high performance envelope prototypes we’re developing include numerous features, such as:
- Minimal thermal bridging throughout the envelope by fully enclosing the structure with thick layers of continuous exterior insulation
- Thermally broken and insulated windows and doors
- Exterior cladding materials supported by thermally efficient attachment methods
- Extremely air tight assemblies, tested at various stages of construction to verify and isolate deficiencies
- Superior thermal insulation values
- Exterior solar shading devices to control thermal gain
- Highly durable materials, substrates and fastening systems to ensure longevity
A timber structure with a high-performance envelope has a head-start when it comes to designing the remaining parts of the building that actually consume the energy, such as heating, cooling, ventilation, lighting, elevating devices and others.
For example, if we look at a building designed to Passivhaus standards, the energy consumption of the building ends up being about one-tenth that of a comparable building built to the minimum code requirements. Thermal insulation values are critically important; a high performance envelope needs to go beyond minimum code requirements—in some cases, even doubling the minimum required insulated values.
And, when you consider the life cycle cost of a building, the cost of adding extra insulation is minimal. There is a direct correlation between the up-front capital costs of adding insulation and the on-going operating costs of a building. Our goal is not to build buildings that last for decades but centuries. By adding extra insulation to the envelope from the beginning, you reap the value through the life of the building.
We think our quest for sustainability can be likened to that of Christopher Columbus crossing the Atlantic to discover the New World. Once Columbus and his crew realized there was no turning back, they chose to push forward; they had faith and knew in their minds that land was ahead somewhere. But at the moment, it must have felt like a mirage. Throughout their difficult voyage, they battled scurvy and other ailments; a mutiny was in the works, and many were left feeling that the voyage was a waste of time with no purpose… that their efforts were in vain. But they persevered, they arrived, and they reached their destination.
We’re collectively on a similar journey, and are at our own tipping point.
It’s time for a monumental shift away from our current resource-intensive building path and instead toward a decision to use durable materials and systems that will last centuries instead of just decades.
While there are many ways to proceed, we know it is possible to achieve carbon neutrality, net zero energy and true sustainability. Mass timber structures with high performance envelopes are a good place to start.
An exciting time-lapse video of one of our newest projects!
William Dewson Architects Inc./Element5 Co.