Modified Bitumen Roofing
Since the time Pacific Sheet Metal (PSMR) was a young company until the present we have seen the evolution of MBR products and its multiple uses. This product was developed in Europe for low or no-slope roofing. Bitumen sheet membranes were being modified with the addition of polymers. These modified membranes are constructed by using strength—enhancing fabrics that have the ability to hold heated modified bitumen (MB) as it is manufactured into a roll of roofing material.
By the middle of the 1970s, the polymer-modified bitumen membranes were being applied to commercial roofs in the United States. These membranes consist of several layers that are amalgamated with polymer and bitumen making a cohesive roofing material. The MB rolls are constructed in much the same manner as basic Built-Up Roofs (BURs) membranes, but have different protective values. Installed as a two-ply system, the MB material is generally fully adhered.
Currently Pacific Sheet Metal uses two types of MB membranes for roofing, the SBS or Styrene Butadiene Styrene and the APP or Atactic Polypropylene. When an APP or SBS membrane is applied on top of two or three plies of a typical BUR, it is referred to as a hybrid roof and is recognized by the National Roofing Contractors Association as a polymer—modified membrane system.
SBS membranes can be installed using three different methods. The rolls can be laid out in hot mopped asphalt, cold adhered or have a built in adhesive backing. With the SBS modification, the bitumen takes on a rubber—like quality, hence its nickname, rubber roof. This product can be handled in colder temperatures without cracking.
APP membranes are installed using heat that fuses the seams together. Installed using a heat weld or a torch, this thermo-fusing provides an impervious seam. APP membranes give a plastic nature to the bitumen creating a flexible material that retains high tensile strength.
Both the SBS and the APP modified bitumen membranes can be surfaced with different products. Surfacing refers to the uppermost layer that protects the membrane from UV rays and overall weather conditions. Surfacing can be a smooth liquid-application, metal foil—lamination, or an aggregate or mineral topical.
PSMC requires all MB used in our installations to meet the American Society of Testing and Materials (ASTM) standards.
1) The ASTM Standard Specifications for APP or Atactic Polypropylene Modified Bituminous Sheet Materials must meet:
- ASTM D6222 for "sheet materials using polyester reinforcements"
- ASTM D6223 for "sheet materials using a combination of polyester and glass fiber reinforcements"
2) The ASTM Standard Specifications for SBS or Styrene Butadiene Styrene Modified Bituminous Sheet Materials must meet:
- ASTM D6162 for "sheet materials using a combination of polyester and glass reinforcements"
- ASTM D6163 for "sheet materials using glass fiber reinforcements"
- ASTM D6164 for "sheet materials using polyester reinforcements"
- ASTM D6298 for "sheet materials with a factory applied metal surface"
All our MB roof system will come from the material manufacturer warranty to assure the product is free of defects. Pacific Sheet Metal Company will supply a manufacturer's certificate explaining the terms. Pacific Sheet Metal & Roofing Company of Seattle also warrants our labor to assure that the installation process was properly executed.
For over fifty years, Pacific Sheet Metal & Roofing of Seattle has offered high quality commercial roofing solutions to Northwest commercial, industrial, and public properties. We provide a full range of installation and re—roofing services including a variety of materials and brands. Please take a look at our Gallery to see why we are the company of choice in Seattle.
We are bonded and insured, and a member of Roofers Local 54.
