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Built-up roofing systems are also known as gravel and tar roofs, and they are popular types of flat roofs made from alternating layers of fiberglass, roofing felt, and asphalt. The resulting system is a robust and long-lasting roofing system.

The gravel is buried in the roof, and this helps to protect flat roofing materials from natural dangers like severe rain, roof hail, and ultraviolet rays. The main factors that influence the type and weight of gravel used include the area's climate, building construction, and underlying strata.

It's worth mentioning that having a tar and gravel roof comes with many advantages. This type of roofing system is specifically designed to last up to 25 years, as they possess weather-resistant properties.

Putting rocks or gravel on flat roofs has many other benefits, but the big question is why you should do this to your roofs. Keep reading to find out more.

Why Do They Put Gravel or Rocks on Flat Roofs?

Flat roofs are primarily used as commercial roofs on commercial buildings and are used with gravel on top of these roofs. This is done for two main reasons:

  • For the safety of the roofing materials
  • To secure the roofing materials

To protect built-up roofs

As mentioned earlier, built-up roofs are mostly known as tar and gravel roofs and are mainly used on flat roofing systems. The ultimate aim is to build a long-lasting roofing system with different hot-applied asphalt and roofing felt layers.

This is done to protect the roofing from different elements, especially small stones, layers of gravel, hail, and ultraviolet radiation. It's worth noting that the gravel is applied to the asphalt coat, and this is to ensure that they are firmly held.

They also feature a weatherproofing layer of gravel that extends the life of the roofing surface. This prevents deterioration, blistering, and cracking that can cause leakages or failure over time. Even though asphalt helps to waterproof the roof, it's worth noting that the gravel top layer also enhances the strength of the roofing system.

Gravel on Flat Roofs

People use ballasted roofs for many reasons. One of the main reasons is the weight offered by gravel. The roofing materials are held firmly to the decking, and this is with very minimal fasteners. The ballasts can keep the roofing system cool and prevent damage from sun rays.

In addition, it also helps to minimize energy expenses. A ballasted roof system offers many additional benefits, but despite these benefits, it's important to note that they also have drawbacks. The amount of gravel to add to a flat roofing system must be precise.

The amount of gravel to be added is determined by the specifications of your roofing system and the type of structure. If the gravel is too heavy, it can cause issues with the structural integrity of the building.

The ideal specification is for the weight to be between 10 to 25 pounds per square foot. Another drawback is that if there's a leak, detecting the leak may be challenging. Also, fixing the leaks after detection can be difficult.

Additional benefits of BUR flat roof gravel

Gravel on BUR (Built-up Roofing) flat roofs also offers a range of benefits. This includes enhancing water evaporation and keeping heat from the underlying roof structure. Gravel also provides a firmer grip for foot traffic, which is vital, especially when performing roof repairs or roof maintenance.

The gravel acts as a barrier that helps prevent natural materials like leaves from clogging the roof surfaces. Modified bitumen roofs are designed from a combination of rubber and asphalt, and this is also done with gravel to confer UV protection properties on the roofing system.

Gravel on Ballast Roof System

Another gravel roofing system type is ballast, used chiefly as a single-ply roofing system. The primary function of this option is to reduce the weight of the roofing material, in addition to protection. This popular single-ply roofing option is built from tar and gravel replacements like thermoplastic polyolefin, polyvinyl chloride, and propylene diene monomer.

Another thing to note is that single-ply roofing materials are not bonded or self-adhering. Ballast helps to provide the weight needed to keep the roofing firm during severe storms or wind.

More benefits of ballast on a flat roof

Besides the protection they offer, ballasted roofs also help absorb heat, making them more energy efficient. In general, single-ply roofs provide sun protection. However, the added layer of ballasts helps to increase the protection against UV radiation. Ballast stones are loose-laid, which makes them easy to be repaired or maintained.

Repairing seams or split joints is done by placing cement under the open seam and holding it down so the substrate can stick properly. Blisters, on the other hand, are treated by using a knife to cut the blisters and allowing them to dry, after which it is covered with asphalt.

Cracks within the asphalt are also straightforward to repair, and this is done by clearing debris and gravel out of the area before applying a layer of cement onto the surface. In general, gravel in ballast roofs enhances heat absorption, and this is done by preventing the sun from heating the roofing materials, making it energy efficient.

The ballast also offers protection against hails and foot traffic, especially during roof repairs and other maintenance work. The ballast system is designed to help you cut down costs in many ways. It is easy to install and energy-saving, all of which are features people look out for in roofing systems.

Frequently Asked Questions

Here are the answers to a few frequently asked questions concerning rocks on flat roofs:

Do you need gravel on flat roofs?

Gravels are designed to serve two main functions, primarily when used on flat roofing systems. They offer UV protection and a loading coat, which are helpful features for a sound roofing system.

Gravel is an anchor for the materials underneath the roofing system, which helps reduce the risk of the roof getting blown away by strong winds or other potentially similar hazards.

Can you put gravel on a roof?

Adding a gravel layer to your roofing system is a great idea, especially if it's a built-up roofing system. When you add gravel over the last layer of your roofing system, you protect it against hail, ultraviolet rays, and other adverse weather elements. You have nothing to worry about because gravel cannot be washed off by rain.

Can built-up roofs be repaired?

You can repair built-up roofs; you only need to know the right approach. If the type of roof assembly you use is that of a single-ply membrane like Tpo or Epdm, applying repair materials like asphalt can cause damage to the membrane. This can ultimately lead to more extensive patches on your roofing system, making it harder to fix.

How long do built-up roofs last?

Generally, built-up roofs are designed to last between 20 and 30 years. However, this depends on different factors, like the material used in making the roofs and climate conditions. In addition, some can last up to 40 years, but this is with adequate maintenance.

It is because of this ability to last long that they are considered to be a great roofing option. They also offer excellent UV protection, and roof waterproofing, all of which help to make the roofing systems last long. Another thing to note is that the aggregate top layer is resistant to fire, which is an important quality that roofing systems require.

DIY Isn't Always the Best Idea

Regarding roofing, there are better ideas than trying to handle the installation yourself. While it may seem straightforward to put rocks on flat roofs, this process is best left to professional roofers to avoid any issues with your roofing in the future.

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