The building enclosure is a crucial set of assemblies and components that separate the interior conditioned space from the elements outside. The building enclosure covers the entire exterior surface area and therefore has a critical role in controlling heat loss and gain, air infiltration, and moisture. Together, these attributes can significantly affect the energy-efficiency of commercial buildings.
For the building enclosure to be effective it has to be continuous at all of the assembly interfaces across the entire building. The roof-to-wall transition is a pivotal part of the building enclosure. The infiltration of air and moisture at this junction can impact efficiency and occupant comfort, affecting overall building energy loads.
Several best practices in design and implementation can help prevent this infiltration and preserve the integrity of roof-to-wall transitions. Here are the key details to know.
Thermal Continuity Matters
In addition to water tightness and air barrier performance, continuous insulation is a prominent strategy for minimizing thermal bridging of structural framing components. Energy codes support this method by including prescriptive requirements to specify continuous insulation where feasible, because cavity insulation is not nearly as effective.
Furthermore, if a project utilizes the performance path to comply with the energy code, enclosure components that contribute to heat loss through thermal bridging must be accounted for. This includes derating insulation effectiveness where cavity insulation has been specified. Attachments made of metal, such as metal fasteners and plates used for roofing and metal Z-channels used for facade attachment, can be significant thermal bridges.
Continuous insulation is important in roof-to-parapet wall conditions, which may facilitate heat loss in commercial buildings. This is mainly because both faces of the parapet are inherently exposed to exterior conditions. A recent study by BC Housing concerning a high-rise building found that nearly one-third of rooftop heat flow is lost through the parapet. Losses occur because some buildings terminate their wall insulation at the parapet, creating a thermal boundary interruption at the roof-to-wall condition.
Other buildings extend the wall's cavity insulation into the parapet, exposing the structural studs to the exterior and reducing the value of the wall assembly insulation. In the latter case, the exterior surfaces may also attract condensation in winter due to the exterior's cold surface and warm interior. These pitfalls can be avoided by employing continuous insulation in one of several ways.
Wrapping the Parapet
One option is to wrap the exposed parapet surface areas by installing insulation along the roof face of the parapet wall, extending it horizontally below the coping cap, and then down the opposite face of the parapet wall. This technique works well on short parapets and where the building is insulated on the exterior.
However, full wrapping of the parapet may not be feasible in tall parapets, depending on coping blocking attachment requirements, or designs with an exposed structure or masonry coping.
Using a Thermal Break
Where structural framing extends into the parapet from the wall below the roof, condensation can be problematic, and where there is increased parapet height, the thermal bridging effect increases. Accordingly, a solution beneath the parapet can be implemented by transitioning the roof insulation and air barrier continuity directly into the wall insulation or utilizing a thermal break where the top of the wall connects to the roof. Thanks to its low thermal conductivity, the thermal break reduces heat losses effectively.
Keep in mind that the 2024 IECC specifically addresses parapet insulation in a designated section, so it's essential to consult local energy codes for guidance.
Minimize Exterior Wall Penetrations
Consider simplifying the roof-to-wall assembly detail wherever feasible. Exterior insulation will work best with a simple enclosure assembly. Work with a structural engineer to minimize the number of components and avoid a complex enclosure support system, so gaps in connections between materials can be easily insulated. For instance, exterior cladding systems and their fasteners, which penetrate the exterior wall's continuous insulation, provide a pathway for heat loss.
During the design stage, select thermally efficient cladding attachments that act as thermal breaks. Fiberglass or stainless steel clips and rails perform better than a thermally conductive material like aluminum or steel. Additionally, specifying a wood-based roof edge blocking can help limit conductive losses.
In addition to the thermal performance at roof-to-wall transitions, consider how the insulation is specified on the remainder of the roof deck. Detailing multiple layers of insulation at the roof is required and can offset convective heat loss that may occur at the insulation joints. Multiple layers of insulation can significantly reduce re-entrant air intrusion, thereby helping to prevent heat loss. Reducing air intrusion also helps minimize the potential for moisture intrusion, reducing the potential for condensation in the cavity or at the underside of the membrane.
Coordinate Building Layers
In addition to the best practices for insulation detailed above, it's crucial to understand that the overall performance of building enclosures relies on the successful integration of all building layers. A continuous air barrier layer is required by the energy code and can help maintain the overall roof-to-wall connection integrity. Since several critical layers interface at the roof-to-walls junction, designing and installing all the components to minimize air leakage is a challenge. Where a vapor barrier is determined to be necessary by the design professional, ensure that the vapor barrier layer is maintained to prevent possible moisture degradation. Condensation can reduce the insulation's effectiveness. Conducting a hygrothermal analysis in the design stage can identify how the assembly design performs over time to manage or resist moisture accumulation.
Maintaining Integrity Through Construction
Equally important as designing the transition is the construction implementation. To reinforce the roof-to-wall transition integrity, the air barrier installation must ensure that the membrane is carefully sealed and that there are no gaps. Construction sequencing is also critical. For example, installing the air barrier after the parapet wall has been built can make it more challenging to maintain continuity. The air barrier layer should be wrapped from the roof side of the wall and be continuous under or around the roof edge blocking to connect to the air barrier layer on the opposite wall.
Additional on-site issues may arise. For example, attaching a guardrail for fall protection or other rooftop accessories to the parapet wall creates additional opportunities for thermal bridging or air leakage, especially where insulation may be penetrated. Rooftop penetrations and structures, such as mounting curbs, drains, vents, etc., can also cause thermal bridging. Insulation and air sealing must be performed on these components. In some instances, using sealant as a component of the air barrier will be required to maintain continuity.
Keeping the Focus on Efficiency
In the design phase, it's important to target these key construction details in the drawings to substantially improve the insulating value of the enclosure. Oftentimes, parapet or roof-to-wall transition details are overlooked in construction documents because standard details are carried over from project to project. Calling out these key details on plans, wall sections, elevations, and 3D details draws attention to these pivotal areas.
During the construction phase, coordinating trades on site is necessary to ensure that the architect's original specifications are not overlooked. Thermal, air, moisture, and vapor layers will need to be installed with proper sequencing to preserve the roof-to-wall intended performance.
Ensuring Efficient, High-Performance Roof-to-Wall Transitions
With sustainability now a driving force in modern architecture and commercial construction, the need for efficient, high-performance building enclosures is top of mind for many. Working with a leading brand with expertise across the entire building enclosure can help during the design stage and provide peace of mind once construction begins.
When premium roofing, waterproofing, commercial wall systems, continuous insulation, or vegetated roof solutions are needed, Siplast can help. Explore the available systems and services to learn more.
