Flat Roof Systems

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Introduction to Roofing Membranes.

A roofing membrane layer makes a roofing system water tight. It is fitted over the insulating material (see image). In some methods, a roofing membrane may be mounted right above a deck.


Numerous kinds of membranes will be identified in this class. You will understand later on that membrane types are quite unique. For instance, just one of the much more popular roofing membranes is a built-up roof (BUR). BUR is a mixture of components. They are set jointly at a job site to form a full roof membrane. An additional frequently used roof membrane is in a single-ply sheet. It is constructed as a single sheet. It is also fitted as one sheet. It can be installed in a number of various ways.

Built-Up Roofs A built-up roof (BUR) system is constructed of about three components. The three components are bitumen, felts and surfacing. It is called a built-up roof because it is made (or built up) at a job site.


The first part of a BUR membrane is bitu-men. Bitumen is what helps make a membrane water tight. There are two types of bitumen. One type is asphalt and the other coal tar. Coal tar is also referred to as pitch.


Asphalt is a petrol product. It is processed from crude oil. There are four kinds of asphalt (see image). Just about every kind of asphalt softens at a distinct temperature. What this usually means is that just about every kind of asphalt will become softer into a thicker liquid at a various temperature.


Type I (one) has the smallest softening point. Type IV (four) has the greatest softening point and is referred to as special steep asphalt. The most typical kind for roof methods is Type III (three). It is known as large asphalt.

The higher the softening point, the steeper the incline on which it can be utilized. Steep asphalts have to be used on steep-slope roofs simply because they will not get soft and slip when they get too hot.

Asphalt types with the lowest softening points are called dead-level asphalt. They can only be used on surfaces without much slope.

Coal Tar

The 2nd kind of bitumen is called coal tar. As you may possibly believe, it is made from coal. It is only applied on roofs with minimal inclines. Its softening point is even lower than Type I asphalt. There are 2 varieties of coal tar utilized in roofing. They are Types I and III. Type III is called coal tar bitumen. Both work well, but Type III does not give off as much coal tar fume as Type 1.

The two types of bitumen are heated up in kettles or tankers. Kettles are trailers that are transported by trucks. Tankers are trucks that can be driven to a job site. Both are massive heating tanks for melting bitumen. The materials are normally pumped up to a roof by means of a supply line. It is crucial that bitumen is maintained at the proper temperatures in the kettle. If it is too hot, the quality will not be as beneficial. Over heated bitumen can also catch fire. If it is to cool, it will not flow well when it is used. If it does not flow properly, it will also not adhere correctly. If this happens, the roof system will have a short life span.

A BUR system is made up of layers of felts and bitumen. When the layers are properly installed, they will create a very strong, water tight membrane.