Commercial roofs do a lot more than just keep the elements out. They are an essential working part of a building’s thermal envelope. Sometimes roof performance and energy efficiency can be sidelined by issues going on behind the scenes. One such issue that can contribute to rising energy costs and moisture concerns pertains to thermal bridging in commercial roofing.
Thermal bridging is the unintended transfer of heat through materials such as metal fasteners, creating weak points in a commercial roof’s insulation. This concept becomes even more critical in Canada’s climate with its extreme seasonal temperature swings. Knowing where thermal bridging occurs and how to prevent it makes a big difference in a commercial roof’s efficiency, durability, and overall performance.
What Is Thermal Bridging in Commercial Roofing?
Thermal bridging occurs when heat travels through highly conductive materials in a roof assembly, reducing insulation performance and increasing energy loss. In commercial roofing systems, steel fasteners, metal decking, and poorly insulated roof details forge pathways where heat can escape during winter or enter the building in summer.
Common sources of thermal bridging in commercial roofing include:
- Metal fasteners: Screws used in mechanically attached roofing systems can transfer heat through insulation layers.
- Metal decking: Steel components can reduce the overall effectiveness of insulation if thermal breaks are not considered.
- Roof details: Areas such as parapet walls, HSS posts, and elevation changes can become weak points if they are not properly insulated.
Thermal bridging and air leakage both cause energy loss, but through completely different mechanisms. A thermal bridge acts as a fast-track for heat to conduct straight through uninsulated structural materials, whereas air leaks are physical drafts escaping through gaps in the envelope. Fixing one won’t fix the other.
Why is Thermal Bridging Important in Canada’s Climate?
Thermal bridging is a big consideration for commercial buildings that regularly face the challenges of extreme seasonal temperature swings in this climate. From freezing winters to hot summers, temperature changes greatly impact energy efficiency and roof performance. Here’s how:
Winter: Heat Loss and Increased Stress
In winter, warm air naturally rises toward the roof. Thermal bridges allow that heat to escape through conductive materials such as metal fasteners and steel decking, which in turn reduces the effectiveness of the insulation. As a result, buildings experience:
- Higher heating costs due to overworked HVAC systems compensating for the heat loss
- Reduced effective R-value of the overall roof assembly
- Increased stress on roofing materials, exacerbated by freeze-thaw cycles that cause moisture movement and material degradation
Summer: Heat Gain and Expansion
In summer, thermal bridges can allow exterior heat to transfer into the building, which increases cooling demands and energy costs. Repeated heating and cooling cycles can also cause roofing materials to expand and contract more frequently, adding even more stress to the system.
With proper insulation design and installation, commercial buildings in the Greater Toronto Area will be more energy efficient with better and longer roof performance.
How Temperature Changes Affect Commercial Roofing Systems
It all comes down to the natural process of expansion and contraction.
- Every roofing material responds to temperature changes by moving slightly as it heats up and cools down. Over time, repeated temperature cycles impact the ways in which various layers of a roof assembly fit together.
- Polyisocyanurate (ISO) insulation is widely used in commercial roofing because it offers excellent thermal performance. However, compared to materials like mineral wool or wood fibre, ISO insulation brings more dimensional movement as a result of temperature changes.
- Though the movement is minimal, shrinkage can occur over time. If insulation joints separate, gaps may form between boards, allowing heat to bypass the insulation layer. This can reduce energy efficiency and impact the overall performance of the roofing system.
- This is why modern commercial roof assemblies now include multiple insulation layers and staggered joints so as to maintain better thermal protection over the life of the roof.
Why Modern Commercial Roof Assemblies Perform Better
Older roof assemblies often feature just one layer of insulation whereby the joints between boards line up directly with one another. With shrinkage, these gaps create direct pathways for heat loss.
Modern commercial roofing systems now feature multiple layers of insulation, with a base insulation layer and a cover board installed above. These layers are placed with staggered joints, which keeps heat from bypassing the insulation system.
This layered approach offers distinct advantages:
- Thermal Continuity: Staggered joints block the direct pathway for heat to escape, maintaining thermal protection even if minor shrinkage occurs
- Enhanced Durability: Cover boards provide a stable, impact-resistant surface that protects and supports the waterproofing membrane above it.
This layered approach helps address thermal performance while improving system durability.
Mechanical Fasteners: A Common Source of Thermal Bridging
Many commercial roofs today use mechanically attached systems, where long metal fasteners secure the membrane and insulation directly into the steel or wood deck substrate.
While these fasteners provide vital structural support, metal is a highly conductive material. Rather than being stopped by the insulation, heat travels straight down the fastener shaft.
Building interior → metal fastener → insulation → metal fastener → exterior roofing system
This thermal bridge not only reduces insulation performance and boosts energy loss, it places a lot of stress on the roofing system. Proper installation methods can minimize these thermal pathways while improving long-term performance.
Research from the National Research Council Canada (NRC) has shown that fastener thermal bridging can reduce the effective R-value of commercial roof assemblies by up to 20% in some tested systems.
The Hidden Risks of Thermal Bridging
Thermal bridging doesn’t just affect energy efficiency. Over time, these weak points in a commercial roof can lead to:
- Higher energy costs: Heat loss in winter and heat gain in summer can elevate heating and cooling demands.
- Roof membrane stress: Repeated temperature changes cause expansion and contraction, prematurely wearing down the membrane.
- Reduced insulation performance: Even insulation with a high R-value may not be as efficient when heat is allowed to bypass the insulation layer.
- Condensation and moisture damage: When highly conductive metal fasteners draw heat outward in the winter, the interior-facing side of the fastener becomes cold. When warm, humid indoor air hits this cold metal, condensation forms, leading to hidden moisture damage and corrosion within the roof assembly.
- Premature membrane wear: Localized temperature extremes around thermal bridges cause uneven expansion and contraction, wearing down the roof membrane prematurely.
- Compromised insulation: Moisture from condensation can drip into the insulation layer, severely degrading its thermal resistance and structural integrity.
Parapet Walls: Another Overlooked Thermal Bridge
Parapet walls are a notorious area for thermal bridging, particularly in older commercial buildings. If a parapet wall lacks a continuous vapour retardant and insulation layer tying into the roof, heat conducts straight up and out through the wall assembly.
Failing to insulate parapets and vertical roof transitions leads to interior condensation, elevated energy costs, and increased stress on the perimeter roofing membrane.
Proper insulation of parapet walls and vertical roof transitions maintains a continuous thermal barrier and protects long-term roof performance.
How Proper Installation Minimizes Thermal Bridging
Reducing thermal bridging in commercial roofing requires careful roof design and quality installation practices. While some thermal bridges can’t be eliminated completely, experienced roofing contractors in the Greater Toronto Area know how to limit their impact and maintain better energy performance.
At Elite Roofing, best practices include:
- Installing fasteners beneath the cover board whenever possible to reduce direct heat pathways through exposed metal.
- Staggering insulation joints between layers to help prevent gaps and improve thermal continuity.
- Properly insulating parapet walls and vertical upturns to maintain a continuous thermal barrier.
- Limiting unnecessary thermal bridges through proper material selection and installation methods.
Cutting corners during installation may save time upfront, but it can lead to higher energy costs, moisture concerns, and reduced roof performance over the long term.
The Elite Advantage
Our team understands that proper installation is critical in reducing thermal bridging and improving commercial roof performance. That’s why we follow industry best practices when it comes to thermal bridging in commercial roofing, including strategic insulation placement, staggered insulation joints, and careful attention to fasteners and roof details. We also prioritize properly insulated parapet walls and transitions to help maintain a continuous thermal barrier. With a focus on quality workmanship and long-term performance, we help commercial building owners not only improve energy efficiency but protect their investment for years to come. That’s the Elite Advantage!
Contact Elite Roofing
Contact Elite Roofing today to discuss your roofing needs and learn how proper installation practices can help reduce thermal bridging in commercial roofing and improve long-term performance.
