Ultra Seam recommends that rosin paper not be used as an underlayment separation sheet between the roofing underlayment and the Ultra Seam metal roof panels. With today’s modern underlayments there is no advantage of using, or drawback of not using rosin paper in the assembly of the metal roof system. In fact there is a potentially major drawback to its use.
Rosin paper was originally used to prevent bonding of the panel to heavy asphalt coated felt that was used in prior decades. If that occurred, panel movement could result in tearing of the underlayment. With today’s lighter weight felt, which is not asphalt saturated, and ice shield membranes, which have a non stick surfacing, the panels will not bond to the underlayment.
There are 3 reasons for not wanting to use rosin paper in the roof assembly. The first deals with installation drawbacks. Rosin paper is flimsy and tears easy. Even on mildly breezy days it may become impractical to apply the rosin paper and not have it rip apart and blow away before the panel is installed. Crews may therefore not be able to work on what otherwise would be a day of installation. On taller structures, virtually every day could encounter this problem. With limited construction seasons in many areas of the country, and the tight schedules that most projects have today, this type of delay is not acceptable.
There are also serious safety concerns with the use of rosin paper. Since it tears so easily it is not safe to walk on with a sloped roof surface. Its use greatly increases the chance of a worker slipping and falling. Obviously, on a sloped roof this exposes a worker to unacceptable risks of major injury.
The final reason to avoid rosin paper is that there have been a number of examples of panel failure due to rust through from the underside that was caused by moisture retention of the rosin paper slip sheet. Rosin paper is very porous and absorbs and retains moisture like any other paper product (paper toweling, tissue, etc.). This constant source of moisture on the underside of the panel can eventually attack the integrity of the panel.
Because of the reasons outlined above, Ultra Seam does not recommend the use of rosin paper in the construction of our metal roof systems. Its use may because for voiding system and paint warranties that might otherwise apply to your project.