Mod Bit Attachment Methods
What is not to love about modified bitumen roofing systems? They are incredibly tough, durable and weather-resistant. They are budget-friendly and easy to maintain. And the variety of cap sheet and attachment methods available mean that a system can be designed for virtually any low-slope roof. But how to select from among those options?
The recent post, “Mod Bit – So Many Choices (Part 1),” discussed the two types of mod bit membrane – APP and SBS. Parts 2 and 3 will tackle the other key question – how the membrane will be attached.
Four Attachment Methods
Mod bit cap sheets can be self-adhering, torch-applied, attached using a cold-process adhesive, or mopped in with hot asphalt. Adhesive and asphalt installations are messy, are often smelly, require a well-trained crew to complete properly and, in the case of asphalt, involve having kettles of hot asphalt on the roof.
The focus here will, therefore, be on the far more installer-friendly self-adhering and torch-applied systems. Each has advantages and characteristics that make it ideally suited to certain applications. This post will discuss self-adhering systems and a future post will address torch-applied systems.
Self-Adhering Cap Sheets
Self-adhering mod bit cap sheets go on quick, clean and torch-free. They have an aggressive adhesive on the bottom and an APP or SBS weathering surface on top. Simply position the sheet, let the membrane relax, peel away the release liner, press the membrane into place, and roll the membrane to ensure adhesion.
Any torch-applied roofing installation comes with an inherent risk of fire. Self-adhering membranes eliminate that risk, making them ideally suited for projects in which that risk is unacceptable. For example, when reroofing an occupied building with a wood roof deck. They also are the perfect solution in the growing number of communities that have banned the use of torches on rooftops.
Self-adhering membranes are installed using roofing knives, brooms, trowels, rollers and other tools and equipment that are inexpensive, readily obtained and easy to use. There is no need to purchase – and then become proficient in the proper use of – heat welding equipment.
Careful attention must be paid to the thermometer during installation of any mod bit system, but particularly when working with self-adhering membranes. When asphalt products get cold, they become less pliable and their ability to retain tack lessens. Therefore, self-adhering mod bit cap sheets should only be installed when ambient temperatures have been at least 40 F and rising for 48 consecutive hours. The rolls themselves must be room temperature – between 60 F and 80 F – at the time of application and must not be stored outside overnight in cool weather, so having a heated storage area on site is recommended during cold-weather work.
These temperature-related considerations mean that, in many parts of the country, self-adhering modified bitumen membranes are best thought of as a three-season solution that can be used roughly six months of the year. But when the weather is right, they are a quick, crew-friendly option that keeps torches off the rooftop.
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