Understanding Performance at Air, Water Barrier Penetrations
FRIDAY, APRIL 6, 2018
By Andrew Dunlap and Sarah Flock, Co-Chairs of the Air Barrier Association of America Research Committee
Air and water barriers (AWBs) require continuity to perform successfully. Therefore, consideration of the specific detailing requirements at penetrations is necessary. While items such as mechanical penetrations, structural members and fenestration openings may be more apparent or obvious in their need for attention, the importance of fastener penetrations, such as at cladding attachments, is often overlooked and underestimated. This article will discuss current test methods and limitations related to fastener penetrations, installation practices and industry terminology, as well as future activities to better understand field performance.
INTRODUCTION
The building enclosure is intended to protect the structure and interior spaces from the exterior environment. The enclosure is comprised of many different elements, but one important component integral to building performance success is the air and water barrier. In order for this component to be successful it must be continuous and complete, as well as free of breaches and voids. However, many exterior enclosure assemblies require attachment systems that will inevitably penetrate the AWB. While these intermittent penetrations may be viewed as insignificant and low-risk by some, these discontinuities can create paths for leakage that may contribute to unintended consequences such as increased energy costs, mold formation, condensation, corrosion and premature deterioration of the building systems. Further, the number of fasteners that can penetrate the AWB as a part of these systems can be much more than sporadic, and when considered in aggregate, could impact overall performance.
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| Photos courtesy of the Air Barrier Assocation of America unless otherwise noted |
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Air and water barriers require continuity to perform successfully. Therefore, consideration of the specific detailing requirements at penetrations is necessary. |
To exacerbate this issue, there are many new AWB materials and cladding attachment systems that have not been time-tested to understand long-term durability. Manufacturer guidelines for detailing the AWB can be limited, and installation practices are not consistent from project to project. It is recommended that design and construction professionals consider these issues when dealing with the performance of penetrations through the AWB.
TEST METHODS, EVALUATIONS AND STANDARDS
Current Methodologies
Currently, there are no consensus standards for testing or installing fasteners through an AWB. However, the industry has utilized various testing options to obtain data for fasteners to resist water penetration.
One of the more frequently used standards for the water resistance of fastener penetrations is ASTM D1970, Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection. This test method applies a membrane to a horizontally oriented substrate with two nails penetrating. The nails are backed out 1/4-inch and a 5-inch head of water is applied for a duration of three days. The results are classified as pass or fail and determined based on whether any visible leakage is observed. If a membrane “passes,” it can then be referred to as “self-sealing,” which will be addressed in more detail later. Another similar method is ASTM D7349, Standard Test Method for Determining the Capability of Roofing and Waterproofing Materials to Seal around Fasteners. It is very similar to D1970 but includes a few allowable variables such as test duration, water depth and whether or not an intervening material is used between the fastener and waterproofing material. It also provides guidance on which method can be used based on the specific roofing application. Both of these methods provide limited value with respect to replicating “real-life” conditions of the vertical enclosure and also do not address the many other types of fastener penetrations in the market today.
Another standard used when evaluating sealability of fastener penetrations is AAMA 711, Voluntary Specification for Self-Adhering Flashing Used for the Installation of Exterior Wall Fenestration Products. Specifically, Section 5.2 addresses methods related to nails. Both methods require the testing to be conducted before and after thermal cycling of the samples. The first method incorporates a modified ASTM D1970 with the exception that the water head is adjusted to 1.2 inches for a period of 24 hours and the nail heads are driven within 1/8-inch of the surface of the sample.
The second option for penetration testing incorporates a modified version of ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors and Curtain Walls by Uniform Static Air Pressure Difference and E547 Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors and Curtain Walls by Cyclic Static Air Pressure Difference. After the test specimens are prepared and penetrated with nails in a similar fashion to the first test method, water spray is then applied to the exterior while a differential positive pressure of 1.5 inches of water (7.8 psf) is induced and maintained for a period of five minutes, released for one minute and then repeated a total of four full cycles. Note, this method orients the panel vertically during the testing, which begins to replicate a wall condition.
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It is recommended that design and construction professionals consider these issues when dealing with the performance of penetrations through the AWB. |
After testing, the membrane edges are lifted away from the substrate to reveal the back. At that point, observations are made regarding evidence of water penetration. This procedure is then repeated with a differential test pressure of 5 inches of water (28.9 psf).
Unfortunately, most of the industry does not utilize this second option. In addition, this test method specifies nails and uses a plywood substrate, which is not representative of the materials commonly used.
Other Performance Criteria
The previously mentioned test methods address water penetration, but they do not address air leakage at the fasteners. When it comes to air leakage associated with fastener penetrations, test methods are available that can be utilized, such as ASTM E283 or E2357, however, they are not specific to fastener related leakage.
ASTM E283 was developed to determine the air leakage rate through exterior windows, curtain walls and doors. In this method, a test specimen is sealed against a chamber and an air flow rate is supplied and measured while the chamber is under a pressure differential. This test provides an air leakage rate of the entire fenestration product.
ASTM E2357 is used to determine air leakage of air barrier assemblies. This standard requires three exterior wall specimens for testing. The assemblies are approximately 8 feet by 8 feet and typically include wall framing, exterior sheathing and the AWB. The first wall specimen is free of any penetrations, while the second wall specimen includes several common penetrations such as brick ties, conduits and windows. The third specimen includes the transitions between the wall and foundation, and between the wall and roof. The wall assemblies are preconditioned by being exposed to positive and negative wind loads (sustained, cyclic and gusts).
The results of the testing provide the air leakage rate with and without the various penetrations and to be in compliance with building code provisions, must not exceed 0.2L/(s•m2) @ 75Pa. (0.04 cfm/ft2 @ 1.57 psf). This can provide some understanding of the impact of the penetrations on the overall leakage of the assemblies, but it does not specifically identify the leakage of individual penetration types. While this is valuable information, this test method may not accurately represent actual site construction for most projects and could vary significantly from the jobsite application. This test also does not allow for easy substitution of new or additional fasteners or penetrations that enter the marketplace without retesting the entire assembly.
SELF-SEALING, SELF-HEALING AND SELF-GASKETING
There are three terms that are often discussed in the industry when dealing with fastener penetrations: self-sealing, self-healing and self-gasketing. These terms have been used interchangeably, but they have very different meanings.
As discussed, ASTM D1970 can be used to designate a material as “self-sealing” around a nail. Some people extrapolate these results to believe that it is also self-healing. Experience has shown that there are no materials that are truly self-healing and few materials that are self-sealing. This situation has created confusion throughout the profession.
The term “self-gasketing” is often suggested as a more appropriate term to describe what happens when a membrane is reported to create a closure around the head of a correctly installed fastener that can help to resist air and water transfer. However, one primary difference between terms may lie in how a fastener is installed. Membranes that are “self-sealing” may provide some air and moisture control with various levels of fastener engagement, but membranes that provide self-gasketing properties likely rely on fully setting on the fastener head to produce compression on the surface of the membrane for an air or water tight condition.
GENERAL RECOMMENDATIONS BASED ON WHAT?
Industry groups, such as the ABAA, recognize the risk of both air and water transfer through fasteners. However, there are multiple approaches on how fasteners can be treated and, at times, they can be at odds with each other. The primary issue is that there is no consensus on a standard method or methods for practitioners to specify. Some AWB manufacturers provide guidance on the detailing of fasteners, which may establish minimum requirements, but may not produce durable long-term installations. These differences in practices can create problems related to bidding projects, inspecting installations and the durability of the wall assembly.
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| Tremco Commercial Sealant and Waterproofing |
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Some AWB manufacturers provide guidance on the detailing of fasteners, which may establish minimum requirements, but may not produce durable long-term installations. |
Here are some common recommendations found in the industry that are not requirements in many projects:
- Use self-tapping screws (i.e., makes its own hole as it is installed);
- Use fasteners with heads larger than the diameter of the shank;
- Use fasteners with the point no larger than the diameter of the shank;
- Install the fastener into a solid substrate;
- Install the fastener perpendicular to the surface—variances in this can create a larger hole than the fastener, creating avenues for air and moisture as the membrane may not have the ability to seal around the fastener;
- Completely set the fastener so the head is compressed against the membrane, resulting in a gasketing effect as mentioned previously;
- Set fasteners and cladding accessories in sealant; and
- Apply sealant over fastener head.
To this point, most of the testing and terminology discussed describes the fastener’s performance upon installation, rather than the long-term durability of the installed condition. A building can experience significant movement while in service, which can affect the fasteners that secure exterior claddings and penetrate the AWB. Further, these fasteners are concealed within the wall and cannot be maintained or repaired easily.
Given these concerns, there is a need to develop installation methods that will provide durable and resilient solutions. In order to determine those methods, new specific test methods also need to be developed in order to validate the proposed installation methods. These test methods also need to address long-term performance.
CONCLUSIONS AND NEW STUDIES
The ABAA Research Committee and ASTM have initiated efforts to address these issues and are in the process of developing new test methods to evaluate air/water leakage through fasteners and cladding attachments. The committees include participation with representation from manufacturers, architects, researchers and industry professionals.
Under development within ABAA is a multi-step process that may include a large-scale wall assembly test similar to ASTM E2357, but with the inclusion of a water penetration test similar to ASTM E331. A “sub-assembly” test that can isolate individual fasteners or attachment devices in a singular test is also being discussed, with the goal intended to produce product specific results that can be substituted into the large-scale wall assembly test.
These tests will include variations on fastener installation methods, various types of preconditioning of the specimens and testing at various pressure differential levels.
With the information learned from this study, penetrations through enclosure elements can be better addressed to provide air and moisture management. ABAA and its Research Committee endeavor to continue to further study this issue to produce meaningful data that will assist the design and construction community.
Tagged categories: Air Barrier Association of America (ABAA); Air barriers; Building envelope; Building Envelope
