Built Up Roofs
The technology that is used in a built up roof, or BUR, has been in use in the United States for well over 100 years. Much like the name suggests, a BUR is one that is made of layers of a material and a fabric that holds the materials together. This is why these types of roofs are commonly referred to as “tar and gravel” roofs. Here are some of the basics of how a BUR is built as well as some of the common terms that are associated with BUR materials.
The Basics of a BUR
A BUR called built up because that is exactly how it is constructed. A base of some sort of fabric is laid, then a layer of bitumen is placed on top. These layers of fabric and bitumen are what make up the roof membrane and create the finished roof. Then a surfacing material is placed on top of the BUR in order to finish it.
One term you might run across when talking about a BUR is how many plies it has. This refers to the number of layers of membrane that are contained in the BUR. This means that if someone references a roof with “four plies,” there would be four membranes that make up that roof.
The Fabric Layer
Typically the fabric that is laid down is called roofing felt or ply sheets. They can be reinforced with mats that are made up of either glass fibers or organic felt materials. They are generally in rolls of about 36 inches.
The first layer of fabric, or the base sheet, can be applied directly to the insulation of the roof or the roof decking. It typically mechanically fastened by the use of roofing nails. This results in a roof that is referred to as fully adhere.
Another type of fabric that can be used is called a cap. This cap is generally the top most membrane placed on the roof. Instead of being made of roofing felt like the other layers, it is typically some type of modified polymers. When this type of cap sheet is used, the roof is referred to as a hybrid system.
The Bitumen Layer
Bitumen refers to the type of adhesive that is placed on top of each of the felt layers. There are three main types of bitumen that is used with a BUR:
- Coal Tar
- Cold-applied Adhesive
Asphalt is a byproduct of the process that is used to break down crude oil into gasoline. Coal Tar is likewise made by a process that is used to distill coal. Both of these materials must be heated in order to be used as the adhesive between felt layers. Asphalt and coal tar are typically heated on the job site in large kettles and then lifted up to the roof in buckets. Once they arrive on the roof, they are applied by machines that spray them in place or mops.
Cold adhesives, by contrast, do not need to be heated to be used. They are typically applied to the roof and then have a solvent applied to them to make them adhesive.
Nashville Built Up Roof Experts
Years of experience means that the craftsmen at Antebellum Roofworks Co Inc are experts at installing built up roofs. If you have questions or would like a quote on a new BUR, please contact us at (615) 794-9111 today or fill out our form!