Guiding Principles of Fenestration Installation
Because of the many complexities involved in the installation of various types of fenestration products in all the possible wall systems and expected environmental exposures, it is impossible to maintain prescriptive installation details that cover all of the potential installation configurations. However, if the installer follows a set of guiding principles for installation, which can be applied to any configuration, the likelihood for success of the installation dramatically increases. These basic principles can be summarized in the following list, followed by some supporting comments:
Guiding Principles for Installation:
1)Maintain continuity between flashing and the window-wall interface
2)Ensure correct shingling / lapping of flashing and other water resistive membranes and materials
3)Provide a drainage path for leaks
4)Test the window-wall system as a complete installation
5)Installation conditions that promote adhesion of sealants and flashing
6)Materials that have adequate durability for the anticipated exposure
7)Risk Assessment
1) Continuity: Continuity is defined in the ASTM E2112 standard as follows:
“5.1 Continuity —Continuity shall be maintained between elements in the fenestration product and the water resistant barrier that provides weather protection, air leakage control, and resistance to heat flow and vapor diffusion….”
The continuity between the fenestration product and the water resistant barrier is best provided by the flashing products, and self-adhering flashing products provide the greatest water resistant seal over this interface if used properly. Lack of continuity at this interface is a source for leaks causing air and moisture intrusion, which is unfortunately a very common occurrence found in actual field installations. Figure 1 provides an example of insufficient continuity in actual installations observed in the field.
Figure 1: Example of lack of continuity between the WRB and Fenestration Product
2)Correct Shingling / Lapping of materials: The application of flashing in correct shingle fashion is now required by the ICC Code, Section 703.8, but this is one of the most common flaws found in the field. Figure 2 illustrates the basic principle of applying building materials in correct shingle fashion.
Figure 2: Application of Materials in Correct Shingle fashion
The picture below in Figure 3 shows typical shingling errors, where the flashing at the head of the window is installed under the flange of the window. The other picture shows another common flaw, where the head flashing is applied over the WRB, rather than the WRB lapped over the flashing. In both of these cases, water that gets behind the WRB and/or the flashing product (which is not self-adhering), is likely to travel behind the head of the window and enter into the wall cavity or interior of the building. This is often depicted as a ‘window leak’, but is actually a flawed installation.
Figure 3: Examples of incorrect shingling of flashing at the window head
3) Provide a drainage path for leaks, “Barrier versus Drainage Installation Methods”: The original ASTM E2112 document also detailed a ‘barrier’ installation method, in that sealant was applied around the entire perimeter of the integral flange of the fenestration product to create a full barrier at the external interface between the window and the wall system. Thus, both the air and water seal existed at the external interface. The shortcoming with this method, importantly, is that if at any time during the life of the installed fenestration product any leakage occurs either at the interface between the window or wall, which could be due to sealant failure, insufficient sealant coverage, or cracks and bends in the flanges themselves, or through the joinery of the window, which includes corner welds, frame cracks, or any other mechanical or welded joint in the window, then the water leakage into a barrier installation system will be trapped in the wall cavity or directed to the interior, since there is no reliable means for drainage to the exterior.
This is a key defining risk with using a barrier installation method, since leakage in windows through the entry paths noted above is a common occurrence that should be expected and anticipated. Figure 4 provides a schematic to describe the potential for water entrapment in a barrier installation, where any water intrusion that penetrates the external barrier will have no outlet to the exterior.
Since the original launch of ASTM E2112 in 2001, the committee has developed significant upgrades to the document, which will be published as a revision of ASTM E2112 in 2007. These upgrades include the recommendation for the use of “sill pans” under all windows and doors. Details on the types and specific installation considerations for sill pans are defined in Section XX.XX of ASTM E2112.
Figure 4: Side view schematic of water entrapment potential for barrier installation methods
The sill pan system, as explained in Section XX.XX of ASTM E2112, enables the installation to manage any water intrusion that will inevitably occur through the life of the fenestration product installation. This is accomplished by leaving openings in the seal between the window flange and the sill pan flashing at the sill of the window, to allow drainage. The 2007 version of ASTM E2112 calls for at least two discontinuities in the sealant that are each at least two inches (50 mm) wide. Many drainage installation methods do not call for any sealant at the sill of the window. In this drainage system, a robust air and water seal at the interior perimeter joint between the fenestration product and the wall cavity is essential. This seal must be continuous and of adequate adhesion & durability to withstand any pressures that will be imparted through the ‘open’ sill at the exterior interface.
A schematic of the drainage installation with a sill pan system is given on Figure 5. Note that the discontinuous sealant at the exterior flange is left open to enable drainage, while the interior perimeter seal now acts as the primary barrier to air and water intrusion. It is important to note that this internal seal will not be subject to the external environmental cycles that the external seals are, resulting in less joint movement over time, and thus should be a more durable joint.
Figure 5: Side view schematic of drainage installation system
4) Test the Window Wall System as a Complete Installation: Window manufactures are very diligent at testing window performance for thermal, wind, and water resistance. In addition, much testing is done on wall assemblies to measure energy efficiency and water management performance. However, there is relatively little testing required or reported on the performance of the window-wall assembly as installed. The American Architectural Manufacturers Association (AAMA) has developed a lab test protocol, AAMA 504, which is used to qualify installation methods outside the conventional standard as detailed in ASTM E2112 or the InstallationMasters Training course. The general principle of the installation testing is to mock up the installation in the lab, subject the installation to wind load, water load, and structural loading, and do the testing before and after the installation is subject to thermal cycling. A flow chart of a suggested protocol is given in Figure 6. It is also critical that a tear down ‘inspection’ of the installation is done after the protocol is completed to assess any moisture intrusion that occurred behind the components of the installation, which was not readily apparent during the wall testing.
Figure 6: Suggested Flow Chart for Installation Test Protocol
While this lab test protocol of the installation greatly enhances the ability to evaluate the performance of any given installation, it is very difficult to adequately predict and simulate actual field installation flaws that will occur. Purposely flawed installations have been tested through this protocol to evaluate the robustness of the installation and the materials, but it is questions whether this adequately covers the multitude of issues found in the field. In addition, the thermal cycling provides some indication of durability of the installation through joint movement and thermal history, but it is not expected that this will adequately simulate the real exposure that the materials and installation will see in actual used.
Therefore, while the lab wall testing is an essential component to successful installation performance, it cannot fully replace specific installation guidelines as the only performance measurement for a successful installation.
5)Installation Conditions that Promote Adhesion:The fifth principle of installation addresses the need for the materials used to seal the fenestration interface with the wall, including self-adhered flashing, mechanically attached flashing, and building sealants will perform in the field as required based on the initial conditions for installation – specifically, will it adequately adhere to the surface to promote a durable moisture seal? This ability to achieve a durable moisture seal is typically measured through peel adhesion between the flashing or sealant and the substrate, which is subject to a number of special challenges.
In typical industrial sealant and adhesive applications, the conditions of the substrate surface and exterior environment are specified and tightly controlled. This is essential to achieve reproducible results and a reliable bond between substrates. In the case of self-adhering flashings and building sealants, this type of substrate and condition control is not possible. First, the products are applied on widely varying substrates: these include vinyl flanges of windows (which can be of various composition), water resistive barriers (which can range from polymeric films, nonwoven substrates, to asphalt impregnated building paper), or the exterior sheathing of the building, which is the highest source of variation. Building sheathing can include Oriented Strand Board (OSB), which itself is a highly variable substrate, plywood, fiberglass coated gypsum board, poured concrete or concrete block, metal frame, and various other fibrous or film coated materials.
While the substrate type is highly variable, the other main source of variability lies with the environmental and surface conditions in application. Building sealants and flashings are applied in an exterior environment that is exposed to a continuous source of contamination and debris – it’s a building site! In addition, the external exposure includes a full range of environmental conditions: wet, dry, hot, and cold are all expected states. Thus, substrate variability, surface contamination, and a full range of environmental conditions make the application of building sealants and self-adhering flashing a unique challenge to achieve a reliable, water tight seal at the interface between the fenestration and the wall. Flashing and sealant manufacturers typically specify a minimum installation temperature where their products maintain adequate adhesion to building substrates, but it is critical that all of these conditions are carefully considered to achieve a successful installation.
6) Material Durability: Whereas the previous principle of installation addressed the initial conditions for installation, it is equally important that the materials used to seal the fenestration interface with the wallwill perform in the field as required over the life of the installation, i.e. will it maintain integrity through UV exposure, heat exposure, thermal cycling, water immersion, etc. It is possible for temperatures behind building facades or on the window flanges to reach 80° C or higher on warm sunny days, or if exposed to reflective materials. Are the materials used suitable for these exposures or will this heat exposure cause degradation and loss of moisture seal? These critical elements are currently being addressed by committees developing material property standards, such as the AAMA-711 standard for “Voluntary Specification for Self-Adhering Flashing Used for Installation of Exterior Wall Fenestration Products”, the AAMA-800 standard for “Voluntary Specification and Test Methods for Sealants”, per section 808.3, as well as the ICC-ES Acceptance Criteria for Flexible Flashing Materials, AC-148. It is essential that the installer and manufacturer ensure that materials used for the installations meet the criteria specified in these standards to ensure adequate durability.
7) Risk Assessment: While the 2007 version of ASTM E2112 ‘recommends’ the drainage method featuring a sill pan, this system is not mandated by code or any Industry Standard. This, along with much of the installation details, remains the decision of the design professional, installation contractor, or window manufacturer. The decision as to what installation method to use is actually an assessment of risk tolerance, bringing together a number of factors. The EEBA Water Management Guide has developed a set of risk factors, including water resistance rating of the fenestration product, moisture tolerance of the assembly, exposure to the environment, rainfall amount, drying potential, and workmanship. All these factors need to be taken into account when determining the installation practice to be utilized.