How Building Envelope Design Impacts Energy Consumption

September 20, 2022

By: Hillary Davidson, P.Eng.

The building envelope significantly affects the energy consumption, efficiency, and overall performance of a building. The building envelope separates the exterior, variable environment from the interior, and controlled environment and includes components such as the walls, roof, windows and doors. Careful consideration of the building envelope design must be made to control air leakage and water penetration and provide a continuous thermal barrier. With a sound building envelope design and quality construction detailing, we can build more comfortable and controlled interior environments that consume less energy and reduce operating costs.

Reducing Energy Consumption and Increasing Resiliency

Being the primary barrier between a building’s interior and exterior, the envelope is one of the most impactful systems on energy consumption and efficiency. Building Science is the study of the performance and interaction between the construction components that comprise a building and includes the structural, mechanical, electrical, and building envelope systems. It is essential to understand these systems and how they work together when considering the building envelope design. The insulation selected for walls and roofs, the type and number of windows, and the materials selected to control air leakage will all affect decisions made about the mechanical, electrical, and structural systems to minimize energy consumption while meeting targets established through evolving code requirements.

Material selection during the design phases of new construction or restorations to existing buildings is increasingly important to ensure resiliency against intensifying weather conditions. Examples of these materials may include selecting impact-resistant siding products that have a higher chance of withstanding storm events, energy-efficient and high-performance windows that maintain seals with heavy wind-driven rain events, investing in durable roof systems that can withstand impact and wind uplift, and protecting foundations with robust waterproofing and water management systems to keep a building water-tight during changing water tables and run-off. Each of these material options provides long-term cost benefits, reducing the need to repair and replace components of the building envelope by investing in durability and strength to withstand extreme weather events, wind uplift and an increasing number of freeze-thaw cycles in our local climate.

Using Energy Modelling for Sustainable Building Envelope Design

Energy modellers build a baseline model that meets current energy codes and any requirements a building owner may be targeting, such as LEED certification. They then create a model of the designed building and compare the two models to determine if codes and targets will be met with the current building design. Energy modelling provides insights early in the design stage that is essential for efficient building envelope design and is a cost-effective method that reduces the risk of having to revise material selection and design at a further stage of the project. For example, a proposed wall assembly or number of windows in a building can be modelled to determine whether the building design will meet the code. If it does not, considerations and conversations can be had early in the design stages with all consultants on measures to reduce energy consumption to bring it down to acceptable levels. These measures may include increasing insulation in the wall assemblies, reducing the number of windows, or adapting the mechanical systems. A cost-benefit analysis of these design decisions early on can assist with providing an energy-efficient building within the project’s budget. In addition, because building envelope consultants are present during a project’s construction phase, they can provide additional insight into construction detailing or decisions being made during the construction process that may impact an energy model and the overall effectiveness of the building envelope’s durability, reliability, and long-term performance.

Meeting Energy Codes and Sustainability Targets

With new requirements from the National Energy Code of Canada for Buildings (NECB) and the desire for more energy-efficient and comfortable buildings, the performance of the building envelope must be a key consideration when designing new infrastructure and improving or altering existing buildings. Building science engineers play a unique role in meeting energy targets and work closely with sustainability experts to provide the critical information, such as effective insulation values and the impact of thermal bridges, that are required to create accurate energy models.  As energy codes are now focusing their efforts on testing the performance of building envelope components, air leakage testing and thermal bridging analysis through thermography have become necessary and sometimes required building commissioning tasks to not only confirm performance targets are met but also confirm the continuity and quality of construction detailing.

Pairing energy modelling and building envelope engineering services provides a beneficial and collaborative approach that brings the building envelope design considerations to the table earlier in the design process and also stimulates meaningful conversations within the integrated project team in considering the impact that certain design decisions have on energy use. As a multi-disciplinary firm, our sustainability and building science team members collaborate to provide innovative energy modelling and design solutions that help meet our clients’ most significant challenges while reducing energy consumption in the communities where we work, live, and play.