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Instructions for Installing Torch-Down Roofing

John Landers

Torch-down roofing has been used in the commercial roofing industry since the 1970s and more recently in residential applications. Often referred to as modified-bitumen roofing, torch-down roofing is mostly used on flat roofs. The process is not very difficult and takes less time to install than conventional roofing systems, such as built-up tar and gravel roofing.

The modified-bitumen membrane is a polymer-based bitumen (asphalt) that is strengthens with fabrics, such as fiberglass or polyester or both. The material creates very resistant and durable roofing that can last from 15 to 20 years.

Installation Guidelines

Building with a torch down roof

For re-roofing projects, find out what the local building codes are for installing a new roof over existing roofs. Some regulations will not permit new installations over more than two layers of roofing.

Inspect the surface of the roof and make sure that it is structurally sound. The roof also must be free of sharp objects and clean of any debris. Install the roofing on a smooth surface, which requires you to cut out blisters in the existing roofing and fill to even out the surface. Secure flashing along the edges of the roof. Apply primer on the metal so that the roofing material adheres to the flashing.

A three-ply roofing system will give the roof the longest life span. Begin by attaching a fiberglass base sheet to the surface of the roof. Use a 43-pound felt for the base sheet and secure the sheet in place with cap nails placed at fou- to six-inch intervals.

Install the first row of membrane at the low end of the roof. Place the membrane parallel to the slope of the roof. Extend the membrane three inches over the edges. Cut the membrane even with the roof line at the end of the installation process. Pull the sheet tight to remove rumples and wrinkles from the material. Roll the sheet back half way back. Keep the roll tight and maintain the alignment so that the sheet can be rolled back into position as it is heated.

The torch must be positioned about a foot in the front of the roof and between the membrane and the base sheet. Use an "L-shaped" movement of the torch across the material. As the bitumen or asphalt becomes liquefied, push the membrane forward with your foot and allow the membrane to bond with the fiberglass base sheet.

At the ends of the membrane sheets, use a tool to raise the material and apply heat to melt the bitumen. Press the material in place with your foot. If you need to install another sheet of membrane to complete a row, overlap the sheets about six inches. Lap the next row over the bottom sheet about three inches.

Apply an eight-inch wide strip of roofing over metal flashing. If the roof has a ridge, install modified bitumen sheets on both sides of the crest and then overlap both sheets with a single sheet.

Repeat the process for the third layer of a three-ply roofing system.