The Importance of Building Science and the Building Envelope / by Sustainable


Architects are in a key position to ensure that buildings well built and that they operate well -well into the future. Buildings are known to contribute too many greenhouse gas emissions to the earth’s atmosphere - allegedly more than any other major economic sector in the industrialized world. Developers, owners, financiers, builders, lawyers and engineers all play a role - but it is architects who stand at centre stage.

An architect may be compared to a director of a play, or, better still, to an orchestra conductor. The architect does not need to know how to play all of the instruments (although this may help) but he certainly needs to know how every instrument should sound - both on its own and as part of the ensemble, However, where an orchestra must be judged solely on the quality of its sound, a building’s appearance is only one of its many important functions. The building envelope determines both how the building looks, and how well it functions to keep the outside out and the inside in.

Understanding the importance of the building envelope to the successful construction and operation of a building is to simultaneously acknowledge the importance of building science. Understanding and employing building science ensures that the external and internal forces acting on a building can be turned from negative to (at least) neutral, to (at best) positive agents - aiding in the successful construction and operation of the building.

Architects represent part of a long tradition of building science. As with most sciences, many early lessons were learned through iterations of trial, observation, improvement, re-trial and re-observation. Today, again as with most sciences, building science has available the help of computer programs to model the trial, observation and improvement. It is of paramount importance for architects to embrace these new energy modelling tools, just as they have embraced the power of the computer to aid with drafting, 3D rendering, and quantity take-offs. The earlier in the design process that energy-modelling trials and improvements can be implemented, the better the resulting building will be.

The work that I am involved in exemplifies this approach: energy-modelling is applied to the earliest possible concept designs. At this stage, many assumptions are made about the building envelope. At each subsequent iteration, those assumptions that improve buildability and performance are retained as strategies. The final design is the result of the best combination of these tested strategies.

A successful building enclosure must achieve the following five functions:

1. Exterior moisture control
It’s most important to design under the assumption that free water will always find a way into the enclosure from the outside; it’s critical to design for adequate drainage and drying to the outside.

2. Thermal control
Not only must a building be highly insulated, but careful attention must also be paid to thermal bridging in order to prevent. “short-circuiting” of the insulation investment. It has been shown that an inch of exterior, continuous insulation can be expected to perform almost 20 per cent better than an inch of interior batt insulation, simply because it is not compromised by thermal bridging through the framing.

3. Air control
Air leakage not only reduces energy performance and durability, but it also worsens indoor air quality, because it can introduce air from dirty locations. Air barriers must be continuous and should be well protected, with redundancies wherever possible.

4. Interior moisture control
While not often a cause for as major a concern as the building code would have us believe, vapour diffusion must be analyzed and managed appropriately, to reduce the risk of interstitial condensation within the wall assembly.

5. Aesthetic excellence
The building envelope is most often the presentation face of the building. This fact must be appreciated in order to create an interesting, pleasant experience for users and viewers alike.

As architects, we need to continually remind ourselves about the physical phenomena that govern the optimal solutions for these functions. Sometimes it takes an elementary school-style demonstration involving balloons, trash bags and spray bottles to teach us about the differences between air control and moisture control. And maybe the best way to comprehend thermal bridging and the importance of conductivity is to try to hold the end of a piece of steel that has been bent around a chunk of insulation, while the other end is heated. Furthermore, we should be proud when this fundamental learning has a positive effect on the design of our buildings.

Learning resources exist all around us; Canadian building science has earned an enviable reputation on the world stage. We consistently produce excellent research and establish progressive design precedents for high performance designs that our neighbours to the south often scramble to incorporate into their codes. Canada has an impressive portfolio of sustainable buildings that boast excellent attention to building envelope design and the embodied building science.

We conclude with three recommendations for all players, or in the spirit of the 2030 Challenge, with three challenges to the building design and construction community: 

1. Continue learning
There is a wealth of information from such resources as the ASHRAf Journal, Green Building Advisor,, and DETAIL Magazine, all of which can be good places to start. Don’t be afraid to drop in on a Passive House meeting, or even on the final student presentations of a building science studio. Keep an open mind about the information you absorb, and it’s almost certain that the quality of our buildings will improve with respect to both sustainability and architectural aesthetics.

2. Take a more active role in the construction process
Keep in mind that the word “architect” continues to mean “chief builder”. Visually inspect all building envelope details, and work with contractors to design them right the first time around. Conduct air-testing (using a blower door and thermal camera) throughout the stages of the construction process, because even the best designed envelope won’t perform if it is leaking. And be open to suggestions from contractors and tradespeople, because even the best design is only as good as its ultimate execution. I have found that when the tradesperson collaborates on the solutions, the result is superior.

3. Use building science tools in concert with architecture tools
The most successful approach includes energy-modelling iteratively on projects, in order to estimate the energy-impact of different design strategies and thus move towards an optimal balance of architectural quality and energy-efficiency. Hygrothermal simulation with a program such as WUFI and heat transfer analysis with a program such as THERM or HEAT3 can be used to develop project-specific enclosures that will not be as negatively compromised due to exposure or poor workmanship. It is, of course, critical to consistently validate simulations using field measurements, to ensure accuracy and predictive value.

This building science-based design mindset must continue to be paired with architectural excellence to ensure that the entire design process creates “durable, energy-efficient, and beautiful architecture”, as a 21st-century update on Vitruvius’s still famous maxim, “firmness, commodity and delight”.

Paul Dowsett is the Principal Architect at Sustainable in Toronto. Paul may be contacted at

OAA Perspectives Fall 2014