Everything you need to know about built-up roofs!

Defining a built-up roof

As the name suggests, a built-up roof is a technique of roofing that entails building up multiple layers of roofing membranes and other types of materials in an alternating pattern that are installed in a sequence that binds all the layers together to the bottom-most layer. This common technique of roofing is used for roofs that have very low pitches and cannot be shingled. 

A Built-up roof,  commonly referred to as BUR, is a long-lasting roofing system that is mostly made up of gravel and hot tar, which typically are located in the top layer. This system has been popular throughout the ages for its aesthetically pleasing looks and sturdiness that allow it to handle more foot traffic and structures on the roof surface. 

Advantages of Built-up roof

Built-up roofs have the following advantages that make it a popular choice among all other roofing systems,

• They are economical: Unlike the other high-performance roofing systems, built-up roofing is a  great investment due to its inexpensive pricing and longevity. 
• Multi-layered protection: BUR provides long-lasting protection from the elements owing to the watertight barrier that the multiple layers of bitumen and bitumen saturated “felt” create.
• Resistant to fire: The Factory Mutual Research Corporation tests every BUR system thoroughly, where each BUR system has to meet strict fire resistance requirements before installation, ensuring that the BUR system is extremely fire resistant. It also provides sufficient wind resistance. 
• Great Insulators: The many layers of the BUR make them great insulators and save their consumers a lot of electricity by keeping the hot and cold air inside the room longer. 

Disadvantages of Built-up Roof

• The multiple layers of built-up roofs that make them such great insulators, also make them extremely heavy which can cause issues if not supported properly. 
• Requires a significant number of reinforcements to be added to the structure of your roof before installing BUR systems, which can end up being a costly exercise if you want to replace your pre-existing flat roofs with BUR systems. 
• BUR systems require the building to be completely empty of inhabitants before it can be installed, which can significantly increase delays in your operations if its a commercial or an industrial building.

Components of a  built-up roof system

A built-up roofing system is made up of the following components,

• Membrane
• The roof deck
• Surfacing material
• Insulation
• A vapor retarder

The core of the BUR system is the roofing membrane that is made up of roofing bitumen. Bitumen is the main agent of waterproofing that is applied between the roofing plies, along with a number of reinforcing plies of roofing felt.

The multiple reinforcing plies are made up of roofing felts or sheets that are coated with asphalt. To give strength and to stabilize the BUR membrane, multiple layers of these plies are installed.  

Embedding gravel in the bitumen and applying a surface coating or a granular surfaced cap-sheet protects the BUR roofing membranes. Surfacing materials, especially the light-colored ones, can help reflect heat away from the building and can also provide extra protection from fire.  

Easy Fixes of BUR systems

As it is with all structures, Built-up roofing systems also require some repairs from time to time. Any damage to the BUR should be addressed quickly before further damage destroys the roofing or the materials below the roofing. A few common problems that can be easily remedied are as follows, 

• Blisters: Blisters can be easily handled with a knife that can cut the blisters. Keep cutting the blisters down till you find a dry layer and allow the spot to dry up as much as possible. Replace the felts with new ones over that area. Cover the area with chippings after applying asphalt to it. Chippings, if unavailable,  can also be replaced with liquid-applied coatings. 
• Cracks: Cracks on the asphalt are the easiest to fix. Simply clean all the gravel and debris away from the affected area and apply a coat of asphalt cement to it. Top it off by installing some roofing felt. Ensure the entire area is covered and has an overlap of at least 4 inches. Repeat the whole process once more before applying some asphalt cement and gravel. 
• Waves: To fix undulations or waves in a built-up roof, simply level the area by adding more layers. Before starting any repairs, however, ensure that the condition of the substrate is good. 
• Open joints or seams: Simply add some cement to the open seam and hold it down to allow it to adhere to the substrate. Alternatively, you can also secure a large piece of felt with nails over the open joint and top it off with some roofing cement. Add to this some gravel and allow it to dry. 

To conclude,

Installing a built-up roofing system is detailed work. If proper attention is paid to the details, the resulting roofing system will be an aesthetically pleasing, efficient, quality, and cost-effective product that will last you a long time.