Premium underlayment products are especially attractive to contractors who install metal roofing, tile roofing and premium asphalt shingles (also known as designer or architectural shingles). For these roofing systems, there is an expectation that the primary roof may last for many decades.
For residential roofing, Tarco developed no less than twelve types of premium underlayment products for various applications as outlined in its Quick Reference Product Guide. This new category of underlayment is now well established among residential roofing contractors.
Premium underlayment is typically made from specialized formulations of modified bitumen. These are usually blends of asphalt and polymeric modifiers, such as styrene-butadiene-styrene (SBS) or atactic polypropylene (APP), as well as stabilizers, such as limestone, talc and other materials. These blends primarily consist of asphalt but the polymer forms a sort of molecular fishnet that limits the flow of the asphalt and shapes the form of the membrane.
Given the UV protection afforded by the primary roof, the life expectancy of a mod bit underlayment is quite long. These underlayment products are cousins to commercial roofing membranes and are typically made with fiberglass or polyester reinforcement. In the case of metal roofing, the modified bitumen compound is formulated to withstand high temperatures.
Premium self-adhering underlayment products offer many advantages. Most allow for relatively long exposure times and they also self-seal around fasteners. They do not suffer from the wicking of moisture through nail holes. When a fastener is driven through the modified bitumen layer, the material flows around the nail, adheres to it and fully seals the membrane.
For more information, see our numerous case studies on particular tile, metal and shingle applications.