Sustainability 101: Building Shell / by Sustainable

Written by: Kelsey Saunders

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Welcome back to the Sustainability 101 educational blog series! Our blog today will focus on the building shell.


The building shell is a system that includes all of the components that separate us and our comfortable indoor spaces from the unpredictable weather outside. The building shell is responsible for protecting the indoors from extreme temperatures, wind, and rain.


Depending on the location of the building, climates can vary widely and so the requirements of the building shell will be different as well. However, there are some guiding principles of a good building shell that are important in every climate:

1. Structure

The first element of the shell in a typical building is the structure. The structure act as the bones of the building and can be composed of many different materials, for example, masonry (like brick or concrete), wood, or steel.

The structure of a building must remain for the building’s lifetime (or certainly while the building is still in use!), and therefore, it needs to be well protected from the environment to prevent degradation or compromise in its strength to hold up.

2. Membrane

In order to protect the structure, a good building shell needs a membrane material that will shield and also control the movement of air, water and vapour toward the structure and into the building. If the structure gets wet, either through rain or from water vapour, this can cause serious issues. Some of the effects of the intrusion of moisture into the structure include rot and mold that occurs in wood frame construction, corrosion in steel-frame construction, or freeze-thaw damage in masonry construction.


The membrane thus needs to be continuous to create an air-tight building shell. We want to prevent unwanted air from leaking into the building through the building shell for two reasons: first, warm air during the summer months carry a lot of moisture with it and can cause some of the issues we mentioned above. Second, air carries a lot of heat with it, resulting in an increase energy demand to make the indoor space comfortable (ie. to cool interior air during the summer).

3. Insulation

The next component of a good building shell is insulation. Placing insulation on top of the membrane, outside of the building structure, keeps the membrane protected and keeps the structure at a consistent temperature.


We recommend using rigid rock wool insulation such as ROXUL, which essentially acts as a big wool sweater surrounding the building shell to keep the heat in, or out, depending on the season. The amount of insulation that is ideal for a building shell will vary depending on the climate and geographic location of the building.

4. Rain-Screen Cladding

The final component of a good building shell is the rain-screen cladding. A rain-screen can be made up of any siding material, but we recommend something lightweight since lightweight cladding is easier to install through insulation and results in less heat loss.

The cladding protects all of the components mentioned above of the building shell from rain, wind and other extreme weather. Behind the cladding, there is a ventilation space that helps the building shell to stay dry.


Stay tuned for our next blog in the Sustainability 101 series!

*The Sustainability 101 lecture series is made as a supplemental learning initiative for high school students across Ontario