Learn the secrets for durable building envelope details

The overall performance of any building enclosure relies on well-designed and well-installed details. These are the interfaces between systems, at changes of plane, and at penetrations of otherwise continuous assemblies. After careful research and selection of materials, it is imperative to plan an approach to construction and detailing that minimizes requests for more information and ensures constructability. A change required in the field can result in lower realized building performance. This article discusses key considerations for designing robust interfaces and details. 

Robust details are where continuous control layers actually become continuous. Figure 1 shows a parapet detail for a roof-to-wall interface where the four control layers are highlighted: water’s layer is in blue, air’s layer is in red, thermal’s layer is in yellow, and vapor’s layer is in dashed green.

When highlighted, it is easy to see where each of the control layers occur, but it can be much more complicated when the colors are gone and only material callouts remain, as is the case in Figure 2. In this example, the air control layer consists of a single-ply roof membrane (labeled A1) that wraps over the top of the parapet. A transition flashing (labeled with a hashed light blue line, N8, and Sheet 2.1) connects the roof membrane to the air and water-resistive barrier on the wall (labeled with a hashed dark blue line and B5). Additionally, there are sealants that seal the lap joints to provide additional durability and robustness, as shown in the blow-up directing to detail 4.1 and labeled with N7. More parapet detailing information is available in GAF's parapet guide. 

This process should be completed for all details throughout the building enclosure, especially for the water, air, and thermal control layers to prevent moisture issues within the assemblies. The design and specification callouts in the details should be specific to both material and, where required, function, as shown in Figure 3. The extra effort for this step is necessary for clear communication with everyone involved in the project and is required by code (IECC C402.6.1.1). It sets expectations for the different materials and components and how they must be detailed to operate effectively. 

4 Considerations for robust details

To reduce late changes and maintain quality, here are four considerations for details: 

1. Select materials that are compatible and will adhere to each other where needed. This often requires communication with manufacturers during the design process to understand where known issues may arise. Figure 5 shows a material interface less than a year after installation where there was a known, avoidable compatibility issue between PVC roof membranes and asphaltic materials (flashing, in this case).
2. Understand the detail’s installation process. This does not require getting into means and methods, but it does require evaluation of the order in which the team installs the materials. Which material is installed first may impact both adhesion and compatibility, especially when it comes to materials installed by different trades. One example is self-adhered membranes that have high-density polyethylene facers: Sealants and other materials may not adhere to them, but a membrane may adhere to them.
3. Determine if the detail can be simplified. Oftentimes, by using the same product in multiple locations, teams can require fewer materials. Other times, a team can complete the installation in fewer steps by eliminating the need for primer or additional sealants at interfaces. Working with one manufacturer that produces materials for multiple systems, such as both the roof and the wall, can reduce the work for designers in creating simplified details like the one in Figure 4.
4. Engage the whole project team in the communication of project requirements. This includes setting expectations for end performance, such as limits for whole building airtightness testing or sustainability certifications.
    

Considerations for project communication

Designers can include a few fundamental items in their specifications to help ensure teams don’t miss critical interface details. 

First, specifications should set up communication among all parties throughout a project. For instance, defining the complete scope of work for the contractors installing the different assemblies assigns responsibility and allows for easier scheduling and quality assurance in the field. The same goes for specifying the party responsible for installing flashing and transitions between systems. People with questions should seek clarification during a pre-construction meeting where attendance is mandatory for all parties.

Second, it is good practice to require shop drawing submissions that include details at the interfaces around the building enclosure. This will confirm that all participants understand how the materials are to be installed and who will install them. This will also highlight areas that specifications may have missed and clarifies which trade is responsible for which part of a specific detail. Designers need to define any items labeled “by others” during the review phase. 

It is also advisable to specify mockups and require performance testing to confirm interfaces are functioning as intended. This helps validate the constructability of the design, anticipate issues that may arise during construction, and help installation crews train with agreed-upon methods prior to the start of work. 

Finally, quality control and operational maintenance ensure long-term performance of the building enclosure. It is important for quality assurance and quality control to occur throughout the project rather than just during a final walk-through in the field. Fixing issues or missed details at the “almost done” stage is difficult. Maintenance plans for after construction can also be required to be submitted for all major systems in the building enclosure. Some manufacturers offer extended guarantees for systems when operational maintenance is completed during the life of the building. 

Conclusion

Designing robust details takes care and attention. It requires careful selection of materials, understanding the order of installation, and quality control during construction. Working with manufacturers and trusted technical resources, such as the GAF/Siplast Building and Roofing Science Team, can provide extra confidence that the many project interfaces and details will perform as intended. 

For more information, contact your local GAF building and roofing science resource. 

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