How do you repair a built up roof?

flat roofing system in need of repair

How do you install a built up roof?

Before we discuss repairing a built up roof, let’s clarify what does built up roof mean? A built up roof consists of layers called asphalt or tar that are alternated with reinforced fabrics for support. It is installed directly on the roof in as many layers as the building owner chooses or is recommended by the roofing contractor. Once all the layers are installed, a layer of gravel or stone is installed on top. 

A built-up roof is one of the oldest roofing processes still used today. A built up roof is water repellant and leak resistant. It is a durable roof material with a long life span on a commercial structure when maintained and kept up. The basic steps to install a built up roof are: 

  • First: Base sheets are attached to the subsystem with roofing nails.
  • Second:  Adhesive, asphalt, concrete, or tar are applied over the base sheet and alternated to the desired thickness. 
  • Third: Then a final layer of built up roof with gravel is applied. 

How much does built up roofing weight?

A built-up roof typically includes several materials that account for the weight. There is the built-up membrane, insulation, and then the final layer of gravel if the owner chooses.  The thickness of the layers can vary the weight and the thickness of the insulation can affect the weight as well.  

For an existing roof’s weight estimate, it is recommended to do a field verification because of these factors that can alter the weight of built up roof. In addition, when estimating a built up roof weight, the weight of all materials used to build the roof supporting structure should be included. This is the roof rafters and trusses in addition to the built up roof system. 

  • 4-ply Built up Roof with Gravel Surface: Weight (lbs.) per Square Foot 6.3
  • 4-ply Built up Roof with Smooth Surface Weight (lbs.) per Square Foot 2.58

What is the difference between built up roofing and modified bitumen?

Flat roofing is common for commercial and industrial structure. This is where the HVAC system is installed along with electrical and plumbing.  There are several option for roofing materials on a flat roof, with built up roofing and modified bitumen being the most popular. Where they are alike is the reinforcement, surfacing, and weatherproofing layers.  Where they differ is explained as follows: 


Built-up roof system, or BUR system have been used over a century in America. The name is derived from the way it is installed: Layer after layer after layer, typically 4 layers, of asphalt and reinforced fabric or tar and reinforced fabric, then a layer of gravel is the final layer. 

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