A built-up roof system, also known as BURS, is a multi-tiered roofing system for flat roofs. Built-up roof systems provide roof protection against the elements with multiple layers of protective systems.
A built-up roof system is also known as a tar and gravel roof. The number of layers in the system will depend on the owner’s preferences and usage of the building. Typically, it is installed in 3-5 layers. The more layers, or plies, the stronger the BUR system and the longer it will last.
The first layer of a built-up roof system is typically a base felt paper. This prevents the BUR system from being adhered directly to the structural decking, making removal down the road difficult to impossible. Then, alternating layers of asphalt/tar are applied between additional layers of felt paper. Install felt sheet, mop on a layer of asphalt, repeat.
The top layer of a built-up roof system usually consists of gravel. In a built-up roof system, gravel acts as UV protection, which will prevent the asphalt roof system from cracking and breaking apart over time. In some cases, coatings are applied instead of P-stone. This serves the same purpose, UV protection. However, in some cases, they also serve as a heat-reflective top layer that reflects sunlight and heat away from a building to help keep it cool and lower energy bills.
Built-up roof systems were first conceptualized 100 years ago, and the method has endured.
They provide multiple layers of redundancy protection to prevent leaky roofs or roof damage caused by the elements.
Most built-up roofing systems are also fire resistant, adding another layer of protection.
Still, installing a flat roof does not come without its drawbacks.
Here are four reasons why you should avoid built-up roof systems.
Related: Ballasted Roof Repair
Having a built-up roof system installed is a time-consuming and expensive process. Installing 3-5 plys means that the roof system is essentially installed 3-5 times. In comparison, single-ply roof systems, like EPDM, TPO, and PVC, are installed in one layer. And, single ply roofs are installed in 100’ long rolls, which is a lot quicker than mopping on every square foot of asphalt in a built-up system.
All in, a built-up roof system is usually at least double the cost of a single-ply roof system.
Leak Detection Becomes Difficult
It is always much harder to find a leak on a roof system that is covered in stone or granules. Any time the roof system is covered, it means defects are also covered as well. In addition, stone traps dirt and moisture, meaning that, when a defect is found, a lot more work needs to be done to create a clean, workable surface to install a patch onto.
Built-up roofs are also difficult to diagnose leaks on because so many layers exist. Leaks can travel between layers or, in some cases, get trapped in between layers. So, a leak on the north side of the building may be coming from the south side of the building and traveling.
It takes an experienced service crew to diagnose a leak in a built-up roof. The best built-up service crews have either installed built-up roofing themselves or have been trained expensively by someone that installed built-up.
Built-up roof systems are very heavy. The more layers added to the system, the more weight will be added and potentially stress the roof’s integrity. Plus, p-stone adds a decent amount of weight to a roof system as well. Typically, a built-up roof weighs between 5-7 pounds per square foot. A comparative single-ply roof system is usually less than 1 pound per square foot.
Ensure that your roof’s weight load limits are exactingly calculated before installing a built-up roof system.
Still, the stress of weight layers can affect a roof’s integrity over years or decades, even then.
The built-up roof system has been in use for over a century.
However, roofing methods change with time and innovation.
BURS may incrementally become phased out in the comic decades in favor of low-slope roof systems and other emerging roofing methods. As a result, there will be fewer crews to service and flash these roofs systems, and fewer materials and equipment to service these roof systems with.
Need help considering if a built-up roof system is right for you?
Contact Chaffee Roofing for professional guidance.
The expert roofing professionals at Chaffee Roofing have decades of experience and know-how to assist you.
Schedule a roof inspection with Chaffee Roofing today.