The building envelope: A driver for energy retrofits

The addition of insulation in exterior walls and roofs, combined with a water-resistive barrier (also acting as part of the air barrier system), is integral to improving building performance, reducing leaks, and creating more comfortable indoor environments.

Office buildings

Evidence shows an office building’s indoor environmental quality (just like office ergonomics) will impact the long-term health and performance of employees; controlling noise with a proper acoustical insulation plan will protect their health and improve productivity.


Student performance is also closely linked to the building’s indoor environment; receiving natural light during the day will help students sleep better at night, and while colder environments tend to improve concentration, once it exceeds a comfortable level, it will create a negative effect on student performance.


A positive guest experience can rely as much on physical comfort and noise control—both in guest rooms as well as common areas—as it does on the building’s esthetics; if design is an important criterion in a hotel’s retrofit, it need not be sacrificed for the sake of thermal or sound performance by the building envelope; new solutions in stone wool insulation products can satisfy both requirements.

In addition to thermal efficiency and occupant comfort, planning for energy retrofits should also factor in the building’s needs for durability and constructability. One of the critical benefits of retrofitting buildings is these projects can increase their lifespan. The added longevity and durability of an enclosure and the energy savings they create are a way to justify the upfront costs. Assessing the primary water, air, and thermal control layers is part of the considerations for a durable enclosure. It is critical to ensure appropriate drainage and drying measures, and vapour diffusion control considerations are in place, as poorly designed retrofits may lead to unintended moisture damage.

The constructability of a retrofit relates to the ease with which the retrofit strategy is installed and executed. Likewise, it also encompasses the total cost of implementation and the amount of occupant disturbance. Therefore, upgrading the building enclosure can bring different constructability challenges, depending on the building site and existing condition. The strategies applied will vary and cannot necessarily be applied on all projects in the same manner.

A building envelope’s thermal efficiency is only as good as the sum of its parts

The various applications within the building envelope each have unique requirements that support the building’s goals for thermal efficiency, durability, and constructability.

Depending on the roof retrofit strategy, thermal performance may be achieved by adding a few additional inches of insulation over the existing roof, or it may require a full re-roof (tear-off).

Exterior wall insulation

Thermal efficiency

Increasingly, architects, specifiers, and builders recognize the superior thermal performance of continuous insulation (ci) on a building’s exterior; it is important to consider the selections for cladding and attachments as they will impact the performance of the ci system. There are numerous generic and proprietary cladding support systems designed for use with exterior insulation, and while each system is different, they generally feature continuous framing, intermittent clip and rail, direct fastening with screws, or other engineered systems. Take for example using 102 mm (4 in.) of exterior stone wool with a nominal RSI value of RSI 3.03 (R-17.2). If installed between continuous galvanized steel vertical Z-girts, a highly thermal conductive material creating a continuous thermal bridge, the thermal efficiency of the insulation will be around 20 to 40 per cent. In comparison, if installed between intermittent stainless steel clips, the thermal efficiency of the insulation increases to 65 to 85 per cent.


Upgrades to the exterior side of the enclosure allow for new water control strategies to be applied. The addition of exterior insulation can improve the thermal gradient of a wall assembly by pushing the dew point towards the exterior side of the assembly. However, the ratio of exterior insulation (dependent on climate) and the type of insulation will play a role in the overall performance of this system. A vapour impermeable insulation may reduce the drying potential of the wall assembly, causing moisture-related concerns. In these cases, take extreme caution to add enough exterior insulation to avoid these problems. When using vapour permeable exterior insulation such as stone wool, increased drying potential and outward drying is possible, as the insulation will not trap moisture within the assembly.

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  1. Construction Canada received the following Letter to the Editor:

    Dear Editor,

    The article was very interesting and informative. Could the author comment on the affect this type of roof energy design has on the design roof snow load? The reason I ask is research in the United States indicates the roof load is significantly higher than for roofs retrofitted with R-30 insulation than older buildings. It has been observed that freezer buildings have significantly greater depths of snow on roofs than on the ground. I have also seen the same condition in my work in Canada. The commonly accepted explanation is the surface of the roofs are cooler than the ground and snow does not melt as normally expected. Up to this time, the ratio between ground to roof snow loads is based on extensive field studies done in the 1960s, so the reduction of snow depth on the roof is based on how roofs were insulated during this period. A discussion of increased snow loads on building roofs is well presented in the article “Snow Thermal Factors for Structural Renovations” in Structure Magazine ( The latest version of ASCE-7-22 has incorporated these factors. Also, for low sloped roofs, structural engineers are now required to calculate the roof deflections when checking for ponding of rain. With more snow on roofs, the roof deflects more which encourages ponding of rain during spring melting. Care needs to be taken to improve drainage off roofs to ensure ponding is less likely.

    David P. Thompson, M.Sc., P.Eng.
    KTA Structural Engineers

  2. David,

    Thank you for the comment and the interesting article that you shared.

    The engineering design of the roof is outside my area of expertise, and generally as an insulation manufacturer. For this application, we always recommend to work with a structural engineer to ensure the roof system can withstand the upgraded insulation. That said, I do believe that we should not compromise energy efficiency due to structural concerns. When dealing with a roof retrofit, different approaches can be taken both in terms of the type and amount of insulation added, and whether updates are required to the structure. For example, if the existing roof structure is not being reinforced and you need to limit the added weight, one can opt for a hybrid retrofit solution where you can use a layer of foam plastic insulation and then add the non-combustible and dimensionally stable stone wool insulation as a cover board. Stone wool roof insulation can also be tapered and available as a cant strip to assist with drainage requirements.

    I would be happy to connect you with our building science team if you have any additional questions, or you can reach our technical service team at .

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