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Four Commonly Used Commercial Flat Roofing Systems

An Explanation of Four Commonly Used Commercial Flat Roofing Systems

Flat roofing systems commonly installed in commercial buildings can be of four types. Our specialization is the highly durable 2-ply Modified Bitumen Torch Down system. Our services are available in Fairfield CT, Stamford, White Plains, Harrisburg, and Pittsburgh.

What are these four commonly used systems? They are:

* BUR or Built Up Roof also called “Hot Tar and Gravel” roofs
* Roofing systems using Metal panels
* Modified Bitumen Membranes
* Single Ply Membrane. PVC, TPO, and EPDM

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Built-Up Roof Systems (BUR)

This is a system that has been used in the United States for more than a century. It is also called the “Tar and Gravel” roof. These roofs are made up of asphalt paper layers that are each mopped down with hot liquid tar. This is the reason why it is called a “built-up roof”. The layers of paper are laid down in a criss-cross pattern, and depending on the contractor, the installation can consist of as many as 12 layers of both paper and tar.

Thus asphalt layer can be saturated and form a felt or a ply sheet. Fiberglass matting is used to reinforce these roofing felts.

Solid cold blocks of coal tar are used to make the tar. This asphalt gets heated by propane gas in a kettle, and is then pumped up to where the work is being done on the roof. The heated tar is spread over the surface that is being worked on and then felt paper is rolled over it.

Crude oil is refined into the petroleum product, asphalt. Distillation of coal forms the basis for coal tar. Both coal tar or asphalt act as the adhesive between the layers of felt paper to form the roof membrane.

Once the required number of layers have been built up into the roof membrane, a further layer of asphalt is spread over the entire roof membrane and 1/2 ” aggregate or gravel is spread over all parts of the membrane. This stone acts to protect the roof form the ill effects of ultra violet light.

BUR roofs can last for many decades, but ultimately will show some signs of degradation. Drying of the petroleum based products causes them to become brittle, leads to cracking from evaporation, and this further results in leaks in the roof.

A BUR roofing system becomes expensive because it involves a lot of labor. Roofs with many layers can last for over 50 years. Roofs have been noticed by us that have 15 layers, but there are also contractors who will reduce the number of layers to just 3 or 5.

Metal Panel Roof Systems

Where roofs have low slopes, many of them use a structural metal panel roof system. You will see them quite widely used in warehouses and factories.

Metal panels are laid over rafters that can have a spacing of as much as four feet, and be able to support the weight of a person.

Metal panels will have seams and overlapping joints and these need to be sealed with special sealants. Bolts are used with neoprene washers to fasten the metal panels to the rafters.

Properly maintained metal roofs can last from forty to fifty years, and make for excellent barriers against water leakage if they are properly installed.

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Modified Bitumen Membranes

Commercial Flat Roof Repair ContractorsThis system, the Modified Bitumen Torch Down Membrane is a development pioneered by the Italians in the 60s, and then made its appearance in the United States. It consists of a 2 ply membrane that is made up of asphalt with modifiers that cover reinforced fabrics. It is these modifiers that give the asphalt elastic properties on both the sides. This modified asphalt gives the material a feeling of rubber, and is manufactured in rolls that are 36″ wide. This has led to the membranes being called as rubber roofs, because of the rubberized technology used.

MB or rubber membranes come in two types:

APP – Polymer – Modified Bitumen Membrane. The seams of this membrane are welded together with a torch, leading to their being named as torch down membranes.

SBS – This Modified Bitumen membrane is installed cold or hot with asphalt or tar adhesives. SBS membranes can be self adhesive, and these have a sticky backing that will allow it to adhere to any surface that it is rolled on to.

In the MB roof system, the installation is meant to be a two-ply system, but some contractors will use just a single ply. Our specialization is the two-ply system as this prevents premature failure, as thinner membranes are vulnerable to both ultra violet rays and precipitation.

These MB membranes can have three different types of surfaces. They are those with a smooth surface, those that have a mineral surface, or those that have a foil laminate surface. A ceramic type of material is used in mineral surfaces that gives it protection against ultra violet rays.

In the business of roofing installation, we specialize in using the best materials in the systems we use and only use 2 ply membranes with ceramic surfaces, with the equipment used for the torch down being one that will give the best result for your commercial roofs. This system can last for thirty years more than any single ply system. This system, the Modified 2 Ply Bitumen Torch Down Roof System needs practically no maintenance.

Single-Ply Membranes – TPO, PVC, ad EPDM

These are generally referred to as TPO and PVC and are factory made wide sheets of vinyl or synthetic rubber. They are very thin and rolls can be anywhere between eight to twenty feet wide.

These membranes have no protective surfacing. Their top layers have a composition that allows them to withstand ultra violet rays for a limited period of time.

The use is made of an adhesive to allow the membrane to adhere to the substrate that has to be properly cleaned. If this substrate is not prepared as per the instructions of the manufacturer by removal of all dust and particles, its adherence can get compromised and lead to a reduced life of the roof.

Seams in TPO ad PVC membranes are sealed with the use of hot air, using solvents as a primer.

EPDM is material that is made from two compounds that come from natural gas and oil. This is the same material that you will see being used in the inner tubes of tires. Seams in EPDM are sealed with liquid adhesives or special self adhering tapes.

EPDM, during its short time after introduction has been plagued with problems. The adhesives used do not have the ability to withstand the extreme heat that roofs are often subjected to. This single ply membrane degrades with ultra violet light and is prone to punctures.

Armadillo Roofing & Exteriors (512) 333-7663, provides commercial flat roof repair, commercial flat roof replacement and commercial flat roof installation services to Austin, Texas and the surrounding communities. We have been providing commercial roofing services to the area for over 15 years. When ypu have concerns or questions about any commercial flat roofing system, we can help.

You can also visit our sister site,, if you have questions or need need help with commercial metal roof restoration or repair.

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