Roof Report

Installation Guideline Tips For Modified Roofing Part II: Torch Applied Membranes featured image

Installation Guideline Tips For Modified Roofing Part II: Torch Applied Membranes


Part I of this series focused on asphalt and adhesive applied modified membranes. We covered an overview of the history of modified roofing membranes in the global market. Also, we discussed proper roof deck preparation, which should be utilized in this section as well.

In Part II, we are focusing on torch-applied roofing, also referred to as torch down in the industry. Part III will include the considerations, evaluations, and procedures for a roof over an existing system left in place as well as reflectivity, ECO-friendly options, and future of laminates in modified installations.

Below are some guidelines and tips from manufacturers, contractors, and my observations over the years to assure a successful and long performing installation.

Membrane Types

SBS (Styrene-Butadiene-Styrene) has a rubber modifier additive combined with a premium asphalt flux, providing an asphalt-blended coating that has elongation and recovery properties. SBS modifiers can deal with the stresses created by wind, temperature fluctuation, and normal roof-top expansion and contraction. The coating is applied to a reinforcing carrier of fiberglass for high tensile strength and dimensional stability; polyester is used for superior elongation and tear strength, or a composite of the two. SBS membranes offer excellent flexibility, especially in cold weather. While these products are typically applied with hot-asphalt, they also can be heat-welded (torched down), applied with cold adhesive, and some products are available in self-adhered options.

APP (Atactic Polypropolyene) has a plastic modifier additive combined with the asphalt to provide a more robust, better weathering asphalt coating that can be heat-welded or applied with cold adhesive. The APP blend is more plastomeric than the elastomeric SBS blend, so it will not have the recovery properties associated with the SBS products. The coating is usually applied to a polyester carrier mat, but a small amount of fiberglass products also exist. APP was designed to be a heat-welded (torched down) and are also found specified with cold adhesive applications. APP self-adhered cap sheets are an option that is growing with popularity.

Common Applications

The two most common types of torch-applied roofing systems are two-ply systems and three-ply systems. Both systems utilize a base and cap sheet, but in the three-ply system, it will consist of a base sheet, then a smooth cap sheet (mid-ply), and finished with a granule cap sheet. It is noted that with APP applications, the final cap can also be smooth, with or without a coating applied. SBS is not well protected against the exposure of a lot of UV radiation and requires a protective surface such as granules provide. Both APP and SBS are available with a foil surfaced for both UV and reflectivity.

Roof Layout

As was discussed in part I, torch-applied modified bitumen roof installation also starts at the low point of the roof with each successive ply or rolls installed so that no laps are against the flow of water. APP modified membranes can be installed with sidelaps perpendicular to the slope where roof slope is 2″ (5 cm) per foot (30.48 cm) or less. Over 2″(5 cm) install sidelaps parallel to roof slope direction). Where roof slope exceeds 1″ (2.5cm) per foot (0.31 m) for SBS modified or 2″ (5 cm) per foot for APP modified “back-nailing” of the membrane is required.

Endlaps are to be staggered. While different details of endlap staggering are permitted and used by manufacturers and installers, I have always preferred the endlaps staggered three feet apart from each other. In multi-ply applications, membrane sidelaps must also be staggered.

Torch Applied Application

The following recommendations are standard professional practices. Always refer to your manufacturer’s specifications for any specific requirements.

Unroll the roll and align the sidelaps. Re-roll the roll halfway. Stand on the unrolled portion to prevent shifting, begin torching the exposed polyethylene side of the rolled portion. Walk forward as you torch, pushing the heated roll forward and into place with your boot or roll hook. Proper torching procedure involves passing the torch flame in an “L” pattern across the rolled portion of the roll and up the sidelap area. As subsequent rolls are installed, heat is applied to both the roll and the exposed laps of the membrane that it is being overlapped onto.

As it is heated, the roll becomes shiny, and the polyethylene film melts away. Visual confirmation of adequate heating (torching) is confirmed when a uniform flow of melted bitumen compound flows evenly in a 1/4″ to 1/2″ (0.64 cm to 1.28 cm) uniform bead that oozes from the applied membrane’s edges. Make sure you heat the entire roll evenly, not just the lap areas, with extra concentration at the laps. Once at the end of the roll, you repeat the procedure.

Other Tips:

  • Trim the lower outside corner of the roll at an angle. Overlap subsequent rolls 3″ (7.62 cm) at sidelaps or as specified, but always a minimum of min. 3″ (7.62 cm). Endlaps should overlap 6″ (15.24 cm)
  • It is critical, especially at the lap areas, to apply the proper amount of heat to both the membrane being installed and the area of the membrane being overlapped onto. Granulated membranes require treatment of the underlying lap granules by heating and removal or heating and pressing granules to ensure a proper end lap weld. A warm trowel should be used to check laps for an adequate seal. Any unbonded areas must be lifted and re-torched. Do not attempt to reseal by torching the top surface of the membrane, which will result in unfavorable and unacceptable results.

Torch Safety

NRCA, other Roofing Associations and Manufacturers that I researched, recommend that professional applicators receive the CERTA torch safety training before installing torch down applications. Torch applications are a hot open flame process, and proper safety precautions and procedures must always be followed.

Personnel Protection – Proper clothing must be worn at all times, including work boots, long pants, long-sleeved shirts, and gloves. Other than the torch operator, all other crew members should be no closer than 3 feet to the torch flame.

Jobsite Firewatch – Your own plan should include, at a minimum, the following items. A designated trained supervisor in fire safety that should remain on the Jobsite a minimum of 4 hours after torching has ceased to check for any signs of smoke, smoldering, or fire. The safety check should also utilize infra-red thermometers, and if access is available to the facility, including a thorough interior inspection in addition to the roof area where torches have been used. Before leaving the Jobsite, you must be sure that all chance of fire, including smoldering fire, has been eliminated.

Following these guidelines for SBS and APP torch-applied membrane roof systems and referring to manufacturers, NRCA, CRCA, and CERTA recommendations on proper installation and safety procedures for the application of open flame torch-applied roofing installations will lead to a successful project.

In Part III of this series, we will include the considerations, evaluations, and procedures for a roof over an existing system left in place as well as cap sheet reflectivity, ECO-friendly options, and future of laminates in modified installations.

John Kenney has over 45 years’ experience in the roofing industry. John started his career by working as a roofing apprentice at a family business in the Northeast to operating multiple Top 100 Roofing Contractors. As Chief Operating Officer, John is intimately familiar with all aspects of roofing production, estimating, and operations. During his tenure in the industry, John ran business units associated with delivering great workmanship and unparalleled customer service while ensuring strong net profits for his company prior to joining Cotney Consulting Group. If you would like any further information on this or another subject, you can contact John at