Exterior Walls: 4 Elements to Consider



Category:   -  Published by: Alejandro Camalda

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As you know, the number of key factors to keep in mind when designing building envelope assemblies can make the task quite arduous. Components, such as the structure, roof and windows, each come with their share of challenges and are governed by specific standards. Exterior walls are no exception for steel buildings or any other type of construction!


Here are our tips on how to deal with efficiency and durability issues and avoid disputes caused by design flaws. In a nutshell, costly errors caused by a poor choice of materials and faulty installation.


1. Thermal resistance value

Before the introduction of energy codes, building designers were mainly preoccupied with the nominal thermal resistance value of building assemblies based on insulating materials. Today, energy codes evolved and take effective thermal resistance into account, paying attention to the manner in which various building components work together.


Fifty years ago, building standards were primarily focused on the comfort of occupants; today, their main goal is to achieve energy efficiency. North American design standards, as defined by modern energy codes, are now adapted to the different climate regions of each province or state, requiring minimum efficiency benchmarks, including the effective thermal resistance of building envelopes.


This more comprehensive approach includes thermal bridges, among other factors, when calculating thermal resistance. Since steel buildings often contain several thermal bridges, thermal resistance can be difficult to evaluate. Because of their conductivity, steel elements easily allow energy to pass through assemblies, which can result in significant heat loss and contribute to the formation of condensation on surfaces within the building envelope.


The good news is that by factoring in a building’s energy efficiency as a whole, it is possible to compensate for the weaknesses of one component by focusing on greater efficiency elsewhere. The goal here is to find a balance between building costs and energy savings.  

2. Combustible and non-combustible materials

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It is important to bear in mind the standards concerning the use of combustible and non-combustible materials according to building codes. Location, usage, area, height, street facing and sprinklers are just some of the factors that influence the selection of building materials as early as the design stage.   


In order to contain potential fires and ensure the safety of the building and its occupants, chosen materials must prevent the spread of flames and smoke to varying degrees according to the type of building. According to the National Building Code of Canada (NBC), materials used  in a non-combustible construction must meet the requirements of CAN/ULC-S114, “STANDARD METHOD OF TEST FOR DETERMINATION OF NON-COMBUSTIBILITY IN BUILDING MATERIALS.”

3. Fire resistance


When it comes to exterior walls, fire resistance standards, as required by building codes, ensure that neighbors are protected from the spread of flames. Fire resistance ratings are expressed in hours and are determined by the distance from building to property lines and the distance between building faces of neighboring buildings.


Fire resistance is measured on the entirety of the exterior wall assembly, not on individual components. Unidirectional tests are performed using thermocouples to evaluate the temperature of the exterior face of walls, during which the interior surface is exposed to a fire over a determined period of time. Fire resistance ratings vary according to the intended occupancy of a building, thereby influencing the choice of materials and several other elements, such as the number and location of windows and other openings in the envelope.

4. Condensation risks

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Certain buildings, such as aquaculture facilities, public pools and those that use misting systems, have high interior moisture levels. 


Breaches in walls allow humidity to penetrate, which may lead to condensation build-up on the cold surfaces of the envelope’s components. During winter, humidity condenses and freezes. Once it thaws, it can be absorbed by the insulation, which then loses its effectiveness. Well-designed walls breathe and dry out over time, preventing mould and maintaining their efficiency.


Opting for exterior continuous insulation helps avoid these types of problems, as it prevents structural elements inside the cavity from reaching the dew point, thus significantly reducing the risk of condensation. Using inorganic components will also help avoid the spread of mould.

Say goodbye to dilemmas thanks to prefabricated solutions

Building requirements can be difficult to reconcile, especially when attempting to stay true to your architectural vision while juggling budget constraints and multiple requirements to conform. For example, in the case of building envelopes, fire resistance standards can hamper the building’s thermal efficiency, making it difficult to find an effective and economically viable compromise.


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Prefabricated Murox wall panels being installed onsite


After years of research and development during which we thoroughly examined numerous wall assemblies, we found a number of beneficial combinations. One less thing for you to worry about! Our Murox products are tested in laboratories and designed to meet numerous building codes requirements. Some of our options combine high effective thermal resistance with a fire-resistance rating of one to two hours.


The Murox building system also has the advantage of being manufactured in a controlled environment according to high quality standards. Results are therefore consistent because they depend on fewer variables encountered on a construction site, say, during winter months.


Choosing an exterior wall is no easy task. The good news is that opting for a prefabricated exterior wall can make your life easier. Get ready to find solutions tailored to your needs!


To find out more about the authors, we invite you to view Alejandro Camalda and George-Étienne Bouffard LinkedIn profiles.


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