Built Up Roof with Gravel | Why Do They Put Gravel on Flat Roofs | Purpose of Gravel on a Flat Roof | Added Benefits of Bur Flat-Roof Gravel

Built-Up Roof with Gravel

Introduction of Built-Up Roof with Gravel

BURs (also known as tar and gravel roofs) are a well-known and popular form of flat roof made composed of alternating layers of roofing felt or fibreglass and asphalt that is placed using heat, resulting in a long-lasting and robust roofing system.

The gravel buried in the flood coat protects the underlying layers from the elements, including ultraviolet rays and natural dangers such as roof hail damage or severe rains.

Depending on the underlying strata, the construction of the building, and the climate of the area, different types and weights of gravel are required for different types of BURs.

Despite the fact that the asphalt waterproofs the roof (this is especially essential for flat roofs where water and moisture can accumulate instead of draining off as it would on a sloping roof), the gravel layer increases the life of the roof.

It’s worth noting that the “gravel” is generally some form of aggregate material, such as pea gravel, slag, or mineral granules that are pea-sized and roughly a quarter-inch thick, and that it’s used to fulfil the Class A surface burning categorization.

There are various advantages to having a tar and gravel roof. They typically have a life expectancy of 20 to 25 years, based on the region as well as the remaining of the homeowner’s building (barring any major natural disasters of course).

The weather resistant properties of the crushed rock embedded in the roof could indeed help to avoid damage such as cracking or blistering, which can ultimately led to leakages or even other problems over time.

Modifiers are got to add to standard roofing asphalt to replace plasticizers deleted during in the distillation process, resulting in bitumen roofing systems.

To boost its strength and durability, it would then be reinforced with fibreglass or polyester fibre matting. SBS (styrene-butadiene-styrene) as well as APP (atactic polypropylene).

SBS increases the roofing membrane’s elasticity, allowing for more contraction and relaxation, whereas APP increases the roofing system’s capacity to remain robust as it matures.

Each type is common in modern climates and purposes, and an expert roofing contractor in the area can help you decide which is best for your home.

There are numerous advantages to choosing a modified bitumen roof. The gravel absorbs as well as heats up and aids in evaporation of water, pushing heat and moisture away from its original layer.

Whenever the team needs to reach the roof or contractors are doing repairs and maintenance on a bitumen roofing system, the looser gravel helps to give a better grip for foot traffic.

It should be noted that the gravel on modified bituminous roofing systems should be maintained reasonably flat on the roof at any and all moments, and part of the gravel must stay loose to avoid damage or punctures from foot activity.

Why Do They Put Gravel on Flat Roofs?

Many flat-roof (low-slope) commercial buildings have gravel on top of their roofs. Have you ever wondered why contractors place gravel on flat roofs?

Gravel is used on flat roofs for three reasons:

  • To safeguard the underlying layer of roofing materials, as is the case with built-up roofs (BURs).
  • To weigh down or secure the roofing material, as with single-ply flat roofs.
  • For these goals, different types and weights of gravel are utilized on flat roofs.

Gravel to Protect Built-Up Roofs

A built-up roof (BUR), often known as a tar-and-gravel roof, is a tried-and-true flat roof type. To build a long-lasting roof system, alternating layers of roofing felt (typically fiberglass) and hot-applied asphalt are used.

To protect the roof from the elements, particularly ultraviolet (UV) radiation and hail, a layer of gravel, or small stones, is applied on top of the final coat of asphalt. The gravel is incorporated in the top coat of asphalt (known as a flood coat), which aids in the retention of the gravel.

The weatherproofing layer of gravel extends the life of the roof’s surface by preventing cracking, blistering, and deterioration, which could lead to leaks or other material failures over time.

Although the asphalt waterproofs the roof (which is critical for flat roofs), the gravel adds a vital, life-extending layer. Although commonly referred to as “gravel,” the top layer is usually some sort of aggregate material (such as pea gravel, slag, or mineral granules).

BUR aggregate is usually pea-sized, about a quarter-inch thick, and is used to impart the Class A surface burning designation in accordance with mandatory ASTM E108, UL790, or CAN/ULC S107M requirements.

Also Read: What Is Pitched Roof | 8 Types of Pitched Roof | Advantages of Pitched Roof

Purpose of Gravel on a Flat Roof

The usage of a ballasted commercial roofing system is primarily motivated by two factors:

Because of the weight given by the gravel, the roof materials are anchored to the decking with much fewer fasteners. Using a specially designed screw and plate fastening arrangement, the gravel may be put in a lot less time.

The ballast keeps the roofing system cool and out of the sun’s damaging rays, reducing energy expenditures. Heavy foot activity and high-wind situations are also no match for the gravel top coat.

Despite the benefits of a ballasted roof system, there are certain drawbacks to be aware of. It is critical to remember that the amount of gravel added to a commercial roof must be precise.

it is determined by the roofing specification utilised and the type of structure. Gravel that is too heavy can cause structural problems. The weight of a gravel-coated roof should be between 10 and 25 pounds per square foot.

Finding a leak amid a sea of gravel can be challenging, especially if the gravel is embedded in a layer of hot asphalt. Because gravel retains dirt and moisture, patching leaks once they’ve been found can be challenging.

Ballasted roof systems are still a viable option for today’s commercial roof demands, even if they aren’t as popular as they once were.

Added Benefits of Bur Flat-Roof Gravel

The coating of gravel on a BUR flat roof may both assist water evaporate and keep heat away from the underlying roof structure since it stores and releases heat. When doing maintenance or repairs, the gravel gives a stronger grip for foot traffic.

The gravel also serves as a barrier to prevent natural material (such as leaves) from moving towards and clogging the flat roof’s drains, retaining them instead.

Modified bitumen roofs are made out of a combination of asphalt and rubber with a coating of gravel placed in the top layer to give UV protection. There is no need for extra gravel on the roof.

Also Read: What Is Damp Proof Course | Types of Damp Proofing Course | Application of Damp Proofing Course | Advantages  Disadvantages of Damp Proofing Course

Gravel on a Ballast Roof System

Ballast is a kind of gravel that is used in single-ply roofing systems. Although the primary function of ballast is to weigh down roofing materials, it also provides the same protective advantages as indicated above.

Ballast is widely used with single-ply flat roofs built of tar-and-gravel replacements such as ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), and thermoplastic polyolefin (TPO).

Single-ply roofing materials are not self-adhering or bonded together in any way. Ballast is required for weight to protect the roof from severe winds since nothing ties the waterproofing membrane to the roofing components beneath.

Ballast is not the same as BUR protecting gravel. Ballast stones are typically one to two inches thick and used more liberally than on a built-up roof. Wind gusts are significantly reduced by the heavier stones.

A ballast system reduces roof system application costs since it takes less time to install because the layers are not sealed together. Ballasted flat roofs are a common choice, particularly for commercial structures.

Additional Benefits of Ballast on a Flat Roof


A ballasted roof’s gravel absorbs heat, keeping the sun from heating the roof materials below and making the roof more energy-efficient.

Although single-ply roofs are naturally sun-protective, ballast adds an extra layer of protection from UV radiation. During repair or maintenance operations, ballast also protects against hail and foot traffic.

Because the ballast stones are “loose-laid,” rather than entrenched in a layer of tar (asphalt), they are easily moved for repairs or maintenance.

1. Open Joints:

To repair split joints or seams, place some cement under the open seam and hold it down so it may stick to the substrate.

If this fails, cut a huge piece of felt and lay it over the open joint. Nail it down, then cover the nails with roofing cement. Finally, put gravel over the cement and allow it to cure.

2. Blisters:

Small blisters can be readily treated by cutting the blister with a knife. Allow as much time as possible for the area to dry. If the top layers are wet, continue cutting down until you reach a dry layer.

Remove the felts (plies) and replace them with new felt. Cover the asphalt with chippings once it has been applied. If chippings aren’t accessible, you can utilise liquid-applied coatings on top of the repaired region.

3. Undulations or Waves:

Repair built-up roofing undulations by simply layering on top of the affected region to level it. Before doing any repairs, make sure the substrate is in good shape.

4. Cracks:

Cracks in the asphalt should be simple to repair. To begin, clear the area of any gravel or debris. Apply an asphalt cement layer to the surface and cover it with roofing felt.

To ensure that you’ve covered the whole area, make sure there’s at least 4 inches of overlap. Apply a final coat of asphalt cement and repeat the process. Cover the cement with gravel.

Also Read: Types of Roof Tiles | Tile Roof Replacement | Tile Installation Cost | Roofing Tile Price | Ceramic Tile Price Per Square Foot | Tile Installation Factors


Do You Need Gravel on a Flat Roof?

Gravel and pea shingle has two primary purposes on a flat roof; they provide a ‘loading coat‘ and they afford UV protection. As ballast, the gravel will help anchor the material underneath and lower the risk of it being blown off in high winds.

Can You Put Gravel on a Roof?

If you have a built-up roof, adding a layer of gravel is a very good idea. Adding gravel over the final layer of roofing mix will protect it against ultraviolet rays, hail and other weather elements. Do not worry; the gravel will not be washed away by rain because it is embedded in the top coat of asphalt

Can a Built-Up Roof Be Repaired?

The Following Method of Repair Is Only Applicable to Roof Systems That Are Asphalt-Based. If Your Roof Assembly Is a Single-Ply Membrane, Such as Epdm or Tpo, the Application of Asphalt Repair Material to the Surface of the Membrane Can Damage the Membrane and Lead to a Much Larger Patch or Even Full Replacement.

How Long Do Built-Up Roofs Last?

The average lifespan of BUR is 20 to 30 years, depending on the climate and the particular materials that it’s made of. Still, there are specific constructions that can last up to 40 years.

Can a Built-Up Roof Be Repaired?

The following method of repair is only applicable to roof systems that are asphalt-based. If your roof assembly is a single-ply membrane, such as EPDM or TPO, the application of asphalt repair material to the surface of the membrane can damage the membrane and lead to a much larger patch or even full replacement.

Area Built-Up Roofs Good?

Built-up roofs tend to provide excellent waterproofing and ultra-violet protection. Thanks to the aggregate top layer, they are also fire-resistant. Built-up roofing is generally low-maintenance and therefore costs little to maintain over its life.

What Is a Built-Up Flat Roof?

A built-up roof, most of the time referred to as BUR, is a time-tested roofing system typically comprised of hot tar and gravel. It is made up of many layers and typically the top layer is where the tar and gravel lie. Of all the flat roof options available today, BUR has been around the longest.

How Much Does It Cost to Put a Roof Up?

According to HomeAdvisor, the typical range for roof replacement costs is between $5,100 and $10,000, but roof replacement can be as low as $1,200 or as high as $30,000. Many roofing companies will charge between $3.50 and $5.00 per square foot.

What Does a Built-Up Roof Mean?

ARMA defines a built-up roofing system as a roof where multiple layers of asphalt alternated with ply sheets (felts) are applied over the roof deck (vapor retarder) and, most often over insulation that is attached to the roof decking.

How Long Does a Built-Up Roof Last?

If properly installed and maintained, a commercial built-up roof can last 40 years. There are a few other benefits of built-up roofing systems: seamless and waterproof – the continuous solid surface does not require joints or seams, removing the most vulnerable area for leaking.

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