Balancing construction realities with ideal fenestration design

by arslan_ahmed | December 22, 2023 11:00 am

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By Bradford J. Antes, PE, and Erin E. Regan, PE

Providing a comfortable and attractive interior space for the building’s inhabitants is a primary concern of the design team. A large component of this is preventing water leaks to the interior of the building. The recommendations and considerations in The Construction Specifier feature, “Key considerations for designing fenestration systems for success[2]” serve as Part 1 of this article (the article can be found in the August 2023 print issue of The Construction Specifier), and they discuss what will help prevent water leakage into new buildings. This article will discuss what can happen when some of those recommendations are not followed due to the nature of construction.

Sometimes these changes may be due to value-engineering decisions communicated between the owner and contractor to reduce the project budget, which, unfortunately, the design team may not know about until construction is underway. Other times, changes may occur due to incomplete shop drawings, unknown or unforeseen site conditions, construction sequencing, or supply chain issues which can lead to the construction team figuring it out and making changes at the time of installation.

Submittals process

During construction, the first place the design team will review information for the project is during the submittal process. Some of the most important submittals for the fenestration system include product data, lab test reports, and shop drawings.

The most important and often most complex part for the fenestration submittal process is the shop drawings. The shop drawings should show all relevant information for the product, flashing, waterproofing, anchorage, and tie-ins to the surrounding construction (for coordination, even if it is not in the fenestration contractor’s scope).

All too often, a set of shop drawings will be submitted several times and will not include the surrounding detailing, making it difficult to accurately depict the adjacent construction and intent for how to drain incidental water that travels through the fenestration system. This is when the language included in the specifications in the design phase, requiring project-specific shop drawings and fully coordinated drawings including adjacent trades, can be referenced.

Usually, a submittal will require reviews from multiple parties, resulting in a rushed review if one or more parties are not on schedule. This can lead to problems with reviews being incomplete or submittals being approved, despite missing critical information, just to keep the project on schedule.

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Approving the shop drawings during the submittal process, with the mentality of figuring it out in the field, can lead to owners requesting the design team to complete the review, in order to not hold up production or ordering materials, both of which could result in costly delays. However, an incomplete shop drawing package, which is rushed through the review process, may ultimately cause a longer delay, due to possible window leaks discovered during field testing due to the original design details not being followed.

Coming up with a solution to address the leakage and implementing it may cost the project more time than if the shop drawings were complete and followed from the start. Further, a ‘figure it out on the fly’ mentality can result in inadequate field details that can put the project at risk for condensation or water leakage and no paper trail to hold the correct party accountable.

There is a balance between holding firm on the correct detailing in a set of shop drawings, versus accepting a manufacturer’s typical package without any project-specific detailing to keep the project moving. When it comes to reviewing project submittals and shop drawings, the goal is to provide helpful and actionable reviews without derailing the project budget and schedule with extreme requests. A designer who takes an uncompromising position may end up causing more problems (e.g. delays, costs, or an owner who overrides them) than one who can identify and accept reasonable compromises to the design.

Window testing

The proof test of all the thorough detailing in the design and reflected in the shop drawings is the first window test. This is when the fenestration is put to the test for air and water leakage. However, if conducting a performance mock-up (PMU), additional tests may also include structural components, such as inter-story drift and load testing or condensation resistance modeling.

Ideally, this first test happens during a PMU, but for simple configurations using off-the-shelf (i.e. pre-tested) windows, the first test may be completed in situ. For field testing, only air and water leakage are tested. Another window test that may be done at, or ideally sometime before, the start of the construction phase is a lab test at the manufacturer’s facility to confirm that its internal assembly procedures results in a sound system, or that a particular manufacturing line is producing windows with the same performance as an originally tested sample.

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Prior to testing any units on the job, a field-testing protocol inclusive of all the fenestration systems should be documented and agreed upon by the project team. This ensures everyone is on the same page, and that the contractor is aware of all testing requirements early in the construction phase. More importantly, it helps avoid disputes over test results if the passing criteria and test procedures are clearly laid out and agreed to by the relevant parties.

Laboratory testing is a hybrid solution between a fully constructed, project-specific PMU and in situ field testing. A lab test on the window unit can be done for semi-custom systems that may have a unique size or atypical framing/glazing conditions, but are based on a previously tested assembly, where the budget cannot accommodate a PMU; typically, these tests are done at the manufacturer’s facility. This would include air, water, and structural testing of the window unit.

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Lab tests can be performed on units pulled directly off the assembly line as quality control (QC) during fenestration production to ensure the manufacturing, assembly, gasket, and sealant installation are all done properly prior to the windows arriving on site. This provides additional confidence that the windows will pass the field testing, or at least not have systemic manufacturing issues within the system.

Testing without all parties present

Whenever the window testing is performed, ideally at the start of the project, all parties must be present to observe the window test, including the installer and manufacturer’s representative. When one of the parties is not there to witness the test, there are several problems that may arise if a leak is discovered during testing.

If it is the fenestration system, and the manufacturer’s representative is not present, the installer may not understand the system well enough to diagnose the issue. If the installer is not present and there is a leak at a perimeter condition, then no remedial action or investigation into the leak can take place. If neither party is there and a leak occurs, it is the responsibility of the general contractor (usually after receiving the testing report) to communicate with both parties.

However, if both the installer and manufacturer’s representative witness the leak during the test, the diagnosis and remediation can start immediately. If the unit can be repaired on the spot, a retest may be done while all parties and equipment are already on site. If the manufacturer needs to come out to visit the site, make the repairs, and then reschedule another test, the testing schedule will be extended, which sometimes does not agree with the project timeline.

Testing when installation is (almost) complete

Postponing testing until the window installation is almost complete happens far too often. If something is discovered during testing, or a leak occurs, what does this mean for the project? The first field window test should always be done during the early stages of installation. Even if there are no resultant leaks, it confirms the installation and production methods are sound.

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Conversely, if there is a product leak or an installation issue, it is better to know early on, before more units from that production run (which may also include a potential systemic issue) or too many units with the same installation defect are installed. Referencing explicit language in the project specifications can ensure windows are tested at appropriate project milestones and can be incorporated into the project schedule.

Without any specific milestones listed, the contractor may set up the testing when it is most convenient for the project schedule, which is usually when the installation is complete, as to not cause a delay for the installer. However, it is in the best interest of the project and all parties to perform a test early on, before installation gets too far along, so any design, manufacturing, or installation issues can be caught before more work is performed and the cost of remediation becomes significant.

Inswing windows

If a project has elected to use inswing operable windows, there is a higher chance the window may leak under negative pressure when tested to ASTM E1105, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. Leaks are often discovered at the operable sash when testing due to negative pressure, pulling the window slightly open and pulling water through any minor gaps in the operable sash gaskets. This is certainly a window type where it is important for the manufacturer and installer to witness testing and make any adjustments to the window operability, should a leak occur. If improvements to operability are made, the design team must ensure the same protocols are done to all windows on the project to reduce the risk of leakage.

Non-domestic windows

As discussed in Part 1, quality standards and testing requirements are different for domestically made windows when compared to non-domestic windows (e.g. European-made). Leaks resulting from field testing a foreign-made window to U.S. standards can cause confusion on a project due to the “passing” criteria being different.

A non-domestic window also means it is far more difficult to make repairs to the windows in the event of a systemic failure as the manufacturer is not local to the site. If the windows passed their respective European (EN) or similar window testing standards, there is not much recourse with the manufacturer to address the leaks observed during the field testing to U.S. standards.

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In some instances, with smaller non-domestic manufacturers, addressing leaks can be limited to additional sealant to frame joints, which are not required per the manufacturer’s installation instructions. This makes it even more difficult for the owner to hold the contractor responsible for these repairs since it is not standard protocol. These repairs may also affect the warranty provided by that manufacturer. Larger-scale non-domestic manufacturers have better support and repair options and may have local representatives to figure out the issue.

Unexpected site conditions 

Some level of change during construction or unexpected site conditions that vary from the design are inevitable. These can be due to owner-directed or contractor-led changes, or because of unforeseen conditions as the building is constructed. Another potential scenario is where a detail is installed, but it is not similar to the drawings, and the owner is now seeking the design team to come up with solutions—working with what is installed without compromising performance. This results in the design team needing to document the changes and how the field conditions differ from the design in case the change leads to a lower performance of previously approved systems or details. In some cases, it is also on the shoulders of the design team to work with the changes that occur and offer constructive recommendations that will still benefit the project. It is imperative for the design and construction teams to work together to detail surprise conditions effectively and efficiently.

Sill flashing

One detail which is constantly under the threat of being value-engineered out of the project is the fenestration sill flashing. Ideally, the design includes a membrane sill pan with an upturned leg and end dams and a metal sill pan with an upturned leg, end dams, and fully soldered corners. When it is time to price this and the value-engineering process is underway for the fenestration systems, the metal sill pan is often the first thing to go. Common reasoning includes the installer saying they have not used sill pans in the past and have not had problems or the manufacturer not requiring a sill pan. Both arguments can sound very convincing to an owner who needs to reduce their budget, although owners who have experienced window leaks on past projects will be much more hesitant to make this change. The following will describe alternative options in the field in lieu of the metal sill pan flashing.

Membrane sill pan 

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If the metal sill pan flashing is removed from scope due to cost issues or coordination concerns, then the next best option is a standalone sheet membrane sill pan with an upturned leg and end dams. This will still capture any leaks through the window system and prevent them from migrating to the interior as long as the inside corners are properly sealed. This installation is more favorable as the window installer or waterproofing professional can install the membrane sill pan without having to potentially introduce another trade (roofer/sheet metal worker). This can also be installed in the field and is easier to cut and fit in the rough opening compared to a sheet metal sill pan.

Fluid-applied membrane sill pan

Another sill pan configuration often used is a fluid-applied membrane. This is common in exterior insulation finish systems (EIFS) as they regularly use a fluid-applied weather barrier as part of their proprietary system. A caveat to using fluid-applied membrane sill pan flashing is that its installation is very sensitive to workmanship, especially at the inside and outside corners of the sill, and in maintaining the required membrane thickness.

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Some sort of reinforcement, (e.g. fiberglass scrim) is a good option to help with durability and consistent thickness, as the mesh needs to be fully embedded and covered by the fluid-applied membrane. The back dam for these can also be made of plywood or continuous blocking, depending on the window attachment, with the membrane turned up onto that surface. Fluid-applied sill pan flashing is also common below window wall systems within a slab depression as discussed in Part 1. Here, the membrane will extend up the backside of the depression, creating a bathtub effect below the window wall system. In either case, all fasteners and penetrations going through the fluid-applied sill pan need to be sealed to prevent leaks to the interior.

Membrane wrapping rough opening

One of the most common sill flashing details in construction does not even include a dedicated sill pan. It simply consists of the sheet membrane (i.e. sheet membrane flashing) wrapping the rough opening of a punched window and terminating horizontally on the rough opening surface.

Contractors often suggest this as it is shown in the manufacturer’s typical detailing, with the addition of interior and exterior sealant joints (note: the waterproofing surrounding the fenestration is not warranted by the window manufacturer and therefore, they do not own that trade or responsibility). This relies only on an interior sealant joint to act as a back dam and prevent any water or air that leaks through the window from getting to the interior. This setup will likely pass an initial window water and air test, but sealant joints will not be as durable as a flashing (metal or membrane) and are more workmanship sensitive. Over time, the sealant may debond or become damaged, eventually allowing leaks to the interior. This method does not have any backup measure compared to other methods which include a dedicated sill pan below the entire window unit.

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Fastening through sill

If the project makes it through design and into construction and a metal sill pan is installed as part of the fenestration installation, considerations need to be made to not have the window anchors fastened down through it. If the metal sill pan is part of the installation, an alternate method of window anchorage needs to be reviewed, approved, and ultimately installed independent of the horizontal sill surface to maintain the integrity of the sill pan flashing. It is recommended the window be anchored through the vertical leg of the sill frame to avoid horizontal penetrations, with tapered shims for dead load support.

In a typical curtain wall system, anchors are installed in the dry zone, therefore not requiring a sill pan to extend the full depth of the system. Installing flashing inboard of the wet zone provides no benefit, both because of the lack of exposure to water and the multiple penetrations that occur at each vertical mullion anchor. The sill pan should be made an integral part of the drainage system and does not need to extend beyond the glazing pocket.

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Storefront tie-in

As discussed in Part 1, one of the most challenging transitions is between a storefront system and foundation waterproofing. This transition is often difficult due to site conditions and damage that occurs during typical construction activities. If a curb is not installed, the eventual tie-in will be significantly more difficult, given foundation waterproofing will be covered up at the time the storefront is installed.

If there is no curb, some removal of fill may be required to install a transition membrane between the storefront system and foundation waterproofing. Foundation waterproofing that is damaged during construction needs to be repaired prior to the storefront installation (whether at curb or at grade). In addition, if the transition is at grade, care needs to be taken to protect all repairs. To avoid damage to the foundation waterproofing, temporary protection should be installed to protect the waterproofing until the storefront tie-in can be done and the storefront system is installed, and then backfilling can take place.

Conclusion

All the effort put into the design means nothing if it is not built properly. How unforeseen circumstances are handled during construction can make or break a project’s success—whether this is a part of the sill flashing details or the testing procedures. Fenestration systems and their associated installations remain a hotly contested item for new buildings and require a healthy mix of field experience, testing knowledge, and sometimes creative detailing to accommodate changes that occur that stray away from the original design, in order to still achieve the desired aesthetic and performance.

Authors

Bradford J. Antes, PE, is a consulting engineer within the building technology division in the Simpson, Gumpertz & Heger Inc. (SGH) New York office. He is experienced in the design and investigation of new and existing building enclosure systems. He regularly collaborates with owners, architects, and contractors during design and construction of the building enclosure systems. He can be reached at bjantes@sgh.com.

Erin E. Regan, PE, is a senior consulting engineer within the building technology division in the Simpson, Gumpertz & Heger Inc. (SGH) New York office. She focuses on building energy analysis, finite element analysis, roof design, window and curtain wall systems, and below-grade waterproofing. Regan has experience in design, investigation, rehabilitation, commissioning, and construction administration of historic and contemporary buildings. She can be reached at eeregan@sgh.com.

Source URL: https://www.constructionspecifier.com/balancing-construction-realities-with-ideal-fenestration-design/

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