The Basics of Metal Roofing Underlayment

Metal roofing is becoming one of the most popular roofing systems for new construction and replacement applications. But there’s an essential component of a metal roof that can’t be overlooked: the underlayment.

What Is Underlayment?

Underlayment, sometimes referred to as roofing felts, is the barrier between the outer roofing and decking. Traditional felts are made of sheets of paper soaked in asphalt and are hand-nailed to the roof. This type of underlayment is still sold today as tar paper or “organic” felts, and are still used for new installations because of its stiffness. However, complete roofing systems offered by manufacturers typically have synthetic ones.

Underlayment on Metal Roofs

Sloped metal roofs are constructed with a similar layered approach as traditional shake, tile or asphalt shingle roofs. For example, structural components like trusses and fascia boards – the latter being the part where gutters are fastened to – are the same or similar.

The underlayment, on the other hand, isn’t. A standard metal roof underlayment consists of a layer of ice guard (also referred to as ice or water shield) installed using a peel-and-stick adhesive backing. This layer covers breaks in the roof – areas where flashing is usually needed. The rest of the roof is covered with a combination of mechanically fastened or peel-and-stick underlayment. An extra layer of red rosin paper may be installed between metal and underlayment to keep the metal layer from sticking.

Why the DIfferences?

Building codes require a minimum weight for underlayments, usually in the 30-pound stock range. The added weight is offset by the comparatively lighter weight of sheet metal roofing. As a conducting roofing material, metal readily conducts heat to underlying layers. Therefore, thicker underlayment creates a thermal cushion between metal and decking, which helps minimize the heat that would be absorbed through the roof. It complements the cooling airflow created by the standing seams.

Thompson Roofing and Construction is your leading provider of roofing and siding installation services. Give us a call at (256) 952-3309, or fill out our contact form. We serve customers in Huntsville, AL, and nearby areas.