by arslan_ahmed | August 11, 2023 8:00 pm
By Aaron Blom
A weathertight building enclosure is critical when it comes to preventing air leakage and water penetration. It also significantly impacts energy efficiency, indoor air quality (IAQ), and occupant comfort. Therefore, properly specifying and detailing the transitions between fenestration products and the surrounding wall conditions is extremely important.
Flashing is what enables the fenestration product to be integrated with the exterior facing material, sheathing, and the water-resistive barrier (WRB) to ensure the integrity of the drainage plane and prevent unintended water penetration.
To help designers specify and detail the correct flashing products, the Fenestration and Glazing Industry Alliance (FGIA) recently updated two flashing standards: AAMA 711, Specification for Self-Adhering Flashing Used for Installation of Exterior Wall Fenestration Products and AAMA 714, Specification for Liquid Applied Flashing Used to Create a Water-Resistive Seal Around Exterior Wall Openings in Buildings.
Self-adhering flashing
In addition to providing the minimum performance requirements of self-adhering flashing for common exterior fenestration products, AAMA 711 offers a method for determining the flashing product’s minimum width and evaluating environmental factors when installing the flashing under typical field conditions.
Applicable for new construction as well as replacement installations, this standard provides guidance on properly evaluating, selecting, and installing flashing for durable adhesion around the perimeter of exterior fenestration systems. Due to the importance of proper adhesion, testing of these products for adhesion to specific substrates is included. However, AAMA 711 does not address chemical compatibility, and this should be verified by the flashing manufacturer. AAMA 713, Voluntary Test Method to Determine Chemical Compatibility of Sealants and Self-Adhered Flexible Flashings, could be used to assess the chemical compatibility of self-adhering flashing with liquid applied sealants.
Before reviewing the test requirements and installation guidance provided in this standard, it is important to better define what qualifies as self-adhering flashing. These products are flexible facing materials coated completely or partially on at least one side with an adhesive material and are not dependent on mechanical fasteners for attachment.
Testing requirements
AAMA 711 provides testing requirements for the following performance characteristics:
Throughout the testing process, any objectionable appearance such as wrinkling, distortion, blistering, delamination, expansion, shrinkage, or warpage of the self-adhering flashing facing material or adhesive layer must be noted.
Installation considerations
To ensure the flashing will perform as intended, it must be installed correctly. Proper installation is critical for performance and the flashing manufacturer’s installation guidelines should be carefully followed.
First, the flashing should be suitable for the regional climate, installation conditions, and expected long-term environmental exposure. Flashing installation should always follow the standard sequencing of components (commonly referred to as “shiplap” or “weatherboard fashion”) as addressed in ASTM E2112-23, Standard Practice for Installation of Exterior Windows, Doors and Skylights.
The flashing should extend a minimum of 50.8 mm (2 in.) beyond the critical interface and the minimum flashing width should be 76.2 mm (3 in.). This is based on using a window with an integral mounting flange as the baseline example incorporating a 25.4 mm (1 in.) mounting flange with a 50.8 mm (2 in.) minimum adhesion onto the wall substrate. In all cases, care must be taken to allow enough width for good adhesion and potential field installation errors.
To ensure adequate performance, the use of a clean, dry substrate surface is highly recommended. If the flashing comes in contact with different building surfaces (sheathing, WRB, concrete block, etc.), care must be taken to ensure full adhesion to all surfaces.
Installers should anticipate that temperature, moisture content, and surface cleanliness will impact adhesion. Further, certain types of sheathing materials present special challenges; therefore, the flashing manufacturer should be consulted for recommendations on adhering to specific substrates.
The following are important considerations for common sheathing/substrate types:
Since the outdoor temperature at the time of installation can affect performance and adhesion levels, manufacturer-provided installation temperature ranges should be followed. If the installer must work outside of the recommended range, the flashing manufacturer must be consulted.
Many manufacturers recommend primers compatible with their products and specify how they should be used. For less-than-ideal conditions such as very low temperatures, dusty conditions, or rough surfaces, primers are an effective way to enhance the adhesion of self-adhering flashing.
Bubbles, wrinkles, and blisters all increase the risk of water intrusion. Many manufacturers recommend using rollers to help installers avoid these application inconsistencies.
The release liner backing should be removed immediately prior to installation to avoid contamination of the adhesive surface and loss of its properties. As best practice, the number of penetrations through the flashing should be minimized.
Self-adhering flashing products can also be used as sill pans to divert incidental moisture that enters the rough opening cavity to the exterior drainage plane. In this situation, it is possible that standing water can collect on the self-adhering product. Care must be taken to ensure proper damming at the jambs and interior portion of the sill (rear upturned leg) to direct the standing water to the exterior. Sloping the sill to the exterior is recommended. Installers should ensure the sill pan is integrated continuously with the WRB and that penetrations, seams, or other discontinuities do not allow water intrusion through the sill pan.
Liquid-applied flashing
Like all FGIA published standards, AAMA 714 was developed in an open and consensus process. It establishes the minimum performance requirements for liquid-applied flashing, which is used to create water-resistive seals around exterior wall openings in buildings. This includes fenestration products such as windows, doors, and skylights as well as other through-wall penetrations.
Specifiers can use this information to evaluate and select the appropriate liquid-applied flashing materials for their project, based on three different levels of heat exposure classification.
AAMA 714 recognizes that certain local codes and regulations may take precedence. All products must meet regulatory volatile organic compound (VOC) content requirements and other environmental considerations. In addition, proper personal protection equipment (PPE) should be used when handling liquid applied flashing.
Prior to performing any tests, the liquid applied flashing must be allowed to fully cure per the manufacturer’s instructions.
Testing requirements
Tests used in this standard are based on recognized AAMA, ASTM, or other industry-standard tests, which may have been modified. Test procedures and pass/fail requirements discussed in this article are based on laboratory-controlled conditions. AAMA 714 delineates testing requirements for the following performance characteristics:
Sealants, adhesives, and other building materials that come in to contact with liquid-applied flashing must be chemically compatible. Always check with the product manufacturer(s) to confirm compatibility. This could also be confirmed through testing in accordance with AAMA 713 where necessary.
Installation guidelines
Successful flashing performance depends on adequate adhesion between the flashing and the substrate it is adhered to, as well as the installation conditions. The flashing product must be used in a way that allows it to remain attached to the substrate while maintaining a moisture seal throughout its service life. AAMA 714 includes optional recommendations for field applications. The information in Appendix A should be considered optional and are intended to address field application, not laboratory.
When using a liquid-applied flashing product, the following issues should be considered:
AAMA 714 Appendix A provides a table which the flashing manufacturer can fill out to indicate the lowest temperature at which the specific liquid-applied flashing product provides an adhesive bond strength of at least 0.9 newtons per mm2 (5 lb per linear in.) to the substrates indicated. If a product must be installed at temperatures lower than what is recorded in the table, then an adhesive/primer should be used as an aid.
When an adequate adhesion is not achieved at any temperature, which is often the case for loosely bonded surfaces such as fiberglass-coated gypsum board, the flashing manufacturer is permitted to indicate “use adhesive primer” in the table, in place of a minimum temperature. If this is provided in the table, users of liquid-applied flashing are advised to take caution as the effectiveness of the flashing depends on the temperature at which it is applied. AAMA 714 Table A1 provides a means to request the lowest temperature to achieve minimum adhesion for the following substrates:
As noted previously, OSB and fiberglass can provide a highly variable or loosely bonded surface, resulting in difficult adhesion conditions without the use of a primer. For liquid-applied flashing, the same applies to fiberboard. As a highly variable substrate, it is difficult to predict the adhesion performance of liquid-applied flashing products to OSB. Although adequate adhesion is often achievable on warm, dry OSB, it is generally advisable to use an adhesive/primer.
Common in the southeast U.S., exterior stucco facade is often directly applied to CMU walls without the use of a drainage cavity (surface barrier wall system). For these applications, it is essential to have a strong bond between the stucco and the CMU wall. When a liquid-applied flashing is used, it should not act as a bond break to the stucco. Consequently, provisions are made either in the formulation of the liquid-applied flashing or with a secondary application of an adhesion promoting substance for the direct applied stucco.
Meeting a growing need
With the increased application of self-adhering and liquid-applied flashing for water protection, these updated standards come at an opportune time.
“Liquid-applied flashing products are realizing increasing application for sealing building interfaces, including flashing around windows and doors,” says Jim Katsaros, chair of the FGIA Flashing Committee.
AAMA 711-22 and AAMA 714-22 are referenced in both the International Residential Code (IRC) and the International Building Code (IBC) as a requirement for using these materials in door and window flashing applications.
Author
Aaron Blom joined the Fenestration and Glazing Industry Alliance (FGIA) in 2021 and is responsible for conducting and developing the association’s professional education programs. He began his career in 2007, as a technical representative for an aluminum framing systems manufacturer, and represented a major fenestration producer, where he focused on the specification and sale of fenestration systems for monumental commercial construction projects. Blom also has worked for a multidivisional specialty subcontractor. He can be reached at ablom@fgiaonline.org.
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