As trendy as they are for green building and demonstrably beneficial for energy savings
through daylighting, skylights are sometimes viewed with a certain trepidation by roofing
contractors. After all, skylights are essentially holes in the roof with the potential to compromise roofing workers’ handiwork by providing unintended leakage paths.
Proper installation is essential to realizing designed-in leak-free performance and can vary by type of roofing involved and the type of skylight. It is recommended to always refer to and use the skylight manufacturer’s instructions that are specific to the roof system being installed. Of course, applicable code requirements supersede any instructions to the contrary.AAMA 1607-14, “Installation Guidelines for Unit Skylights”, which is an industry consensus guideline published by the Schaumburg, Ill.-based American Architectural Manufacturers Association, intended for use when manufacturer instructions are absent or incomplete, provides basic step- by-step installation instructions for 19 different ways to integrate various roofing materials, underlayment, flashing and skylight-mounting configurations to preserve the drainage plane. This must be the overriding intent of any installation protocols.
Note that some roofing contractors warrant their work against leakage, and skylight installation should not compromise or void such warranties. When in doubt, independent installers should confer with the roofing contractor.
Proper installation begins with selection and use of the proper supplies—notably sealants, fasteners and flashing.
If sealants are recommended by the manufacturer, follow the manufacturer’s specifications. When the manufacturer is silent about the use of sealants and the installation guidelines dictate their use, the following recommendations should be observed:
- Compatibility—The sealant must not adversely react with or weaken the material it contacts.
- Adhesion—The sealant must have good long-term adhesion. Surface preparation, cleaning procedures and, in some cases, primers are recommended by the sealant manufacturer.
- Service Temperature—If the installation location involves elevated ambient temperatures, the sealant should exhibit corresponding service temperature performance.
- Durability—The sealant must be capable of maintaining the required flexibility and integrity over time.
- Application—Proper bead size and other application details should be followed to ensure a well-performing joint. Improper use of sealants can dam water pathways, so an important rule of thumb is not to block any weep holes that may be in the skylight system.
Typically, sealant or roofing cement is applied around the perimeter of the rough opening (deck mount) or the flange of self-flashing units or the top edge of a mounting frame. However, some skylights are designed with integral flashing flanges to be installed without the need for sealants.
It is also possible to utilize rolled roofing membranes as a substitute for sealants or plastic roofing cement.