BUR & Mod-Bit Roofing Experts: Install & Repairs

The quality you deserve, from the roofers you trust.

BUR: Built-Up Roof
Mod-Bit: Modified Bitumen

How to Choose Your BUR and Mod-Bit Roofing Contractor Wisely

For over 25 years, Pacific Roofing Systems has proven to be Orange County’s premier commercial roofing company and is often considered the best roofer for built-up and modified bitumen roofing applications throughout Southern California. Contact us for the highest quality roofing contractor you can trust to complete your project with great care and expertise.

Built-Up roof membranes (BUR) and Modified Bitumen (Mod-Bit) are generally composed of alternating layers of bitumen and reinforcing fabrics that create a finished membrane.

Built-Up Roof (BUR)

Built-up roof membranes have been used in the U.S. for over 100 years. These roof systems are called “tar and gravel” roofs. BUR systems generally comprise alternating bitumen layers and reinforcing fabrics that create a finished membrane. The number of plies in a cross-section is the number on a roof. The term “four plies” denotes a four-ply roof membrane construction. Sometimes, a base sheet, used as the bottommost ply, is mechanically fastened. Built-up roofs are generally considered fully adhered if applied directly to roof decks or insulation.

Typically, bitumen-built-up roofing systems have three or more component layers. They consist of the base asphalt layer with modifiers, ply sheets, and top surface. Modified bitumen roofs use asphalt, which acts as primary waterproofing protection, but is modified with agents like synthetic rubber to create a uniform matrix. This improves the puncture resistance and strength of the asphalt, increasing its resistance to permanent deformation during stretching under loads.

The multiple layers of ply sheets can be of reinforced fabric, felt, fiberglass, polyester, or, in some cases, plastic core materials. These internal sheets offer tensile strength, weather resistance, and stability to the final finished roofing structure. The top surface protects the lower layers from damage due to harsh sunlight and rain or debris. This layer also holds and releases heat, thereby keeping moisture and heat from damaging the underlying layers of your commercial built-up roof.

Modified Bitumen (Mod-Bit or MB)

Modified Bitumen (MB), also called Cap Sheet roofing, is an asphalt-based, close cousin of the Built-up-Roof (BUR) designed for buildings with low-slope or flat roof structures.

Modified bitumen is “modified” when a polymer (a synthetic rubber or plastic) is mixed into the asphalt (“bitumen”) during the manufacturing process. Modified bitumen is also known as polymer-modified bitumen or rubberized asphalt. It is usually called “mod bit” in the roofing industry.

Bitumen is the first adhesive layer, and roofing felt is installed in multiple plies over the base layer of a commercial roof. The top layer consists of stone, gravel, crushed slag, or other aggregates.

Modified Bitumen roofs give designers and installers a broader array of options than BUR. MB may be installed by the torch-application method, or hot-mopped like BUR, or applied with cold-process adhesives. The latest innovation with MB is the self-adhering sheet. The installer removes the release paper, and as the sheet is rolled out, it adheres to the substrate. This method eliminates the risks associated with torches and hot asphalt and is completely free of VOC (volatile organic chemicals) fumes during and after application.

Whether you’re trying to find the right commercial roofing solution for a new building or replacing an old commercial roofing system in Orange County, California, contact Pacific Roofing Systems and talk to one of our specialists about BUR and Mod-Bit roofing. Homeowners and businesses can enjoy the benefits of a well-maintained and reliable flat roof backed by quality workmanship and a commitment to customer satisfaction.

Pacific Roofing Systems flat roof specialists in Orange County are vital in providing expert solutions for installing, repairing, and maintaining flat roofs. Our specialized knowledge, experience, and dedication ensure that your flat roof is installed correctly, remains in optimal condition, and stands the test of time.