A tar and gravel commercial roof is a big part of American roofing heritage. This type of roofing system has been around for over 100 years and has stood the test of time, but like any other roofing system, older or newer, it has its issues. So, what is a tar and gravel commercial roof, anyway?
Tar and Gravel or BUR
Tar and gravel roofs are also called built-up roofs, or BURs. It is a well-known roofing system designed for flat style roofs. They are generally made up of anywhere from three to five layers that are laminated and consist of asphalt sheets, hot tar, and roofing fabric. The layers alternate between roofing felt (or fiberglass) along with other materials, asphalt or tar. Heat is used in applying the various layers. A layer of gravel is ingrained on the asphalt top, or what is called the flood coat. This final layer protects the different layers from weathering effects, (UV) ultraviolet rays, wind damage, hail, and rainstorms.
The final top layer of rock or stone is meant to increase the roof’s life and usability, plus give it a pleasing appearance and added resistance to wind. It also provides waterproofing against pooling water that can accumulate on a flat roof. The number of plies or layers can be designated with a final layer of stone or gravel. The stone or gravel can be a variety of composite materials such as pea-sized gravel, granular mineral material, or slag (non-metallic derivative from iron production).
Any dark-colored asphalt or bitumen (a type of asphalt)is usually covered with lighter colored gravel to disguise any darker underlying layers. The gravel also protects against sun damage, adds extra weight, and protects a roof from piercing from any maintenance and repair work from foot traffic. The gravel finish work also retains heat and releases it. It also helps any water or moisture accumulation on a flat roof to evaporate, which protects any underlying area. In addition, the gravel hinders and traps any collection of airborne debris from getting into drains and creating obstructions.
Average Cost of Tar and Gravel Roof
Tar and gravel or built-up roofing is an economical and budget-friendly option for commercial roofing. Its costs will depend on the roof’s size, its pitch, and its slope. Currently, square footage wise, costs run from $2.50-$4.00 per sq. ft. Prices will fluctuate with different contractors and localities.
Maintenance and Repair of Tar and Gravel Roofings
Consistent maintenance and repair can add to the life of a tar and gravel roof, which can give it a lifespan of up to 30 years. Such a roof can be further reinforced and protected through added layers of fiberglass or foam to optimize the insulation factor. The application of cool roof coatings can further increase weatherproofing.
An older tar and gravel roof can be repaired and enhanced through patching areas of weakness or where leaks have occurred. Correct and proper patching is essential as weak spots can quickly spring up and cause leaks. If a roof has numerous patches, up to a quarter of the roof, the whole roof probably needs to be replaced. An older roof can be further assessed by walking on it and getting a feel for its stability. Watch for cracks, discolorations (which include any mold growth), indentations, loose gravel, and general deterioration.
Issues with Tar and Gravel Roofing
Tar and gravel roofs have issues that you should take into consideration. These include the following:
- When gravel coverage of bare areas is neglected, membranes can suffer deterioration from continual exposure to the elements.
- Unfavorable weather conditions, especially perpetual rain and snow, can make tar and gravel a problematic roofing choice.
- Improper installation of underlayment, flashing, and other roofing materials can cause serious leaks.
- Tar and gravel roofing is susceptible to ponding and roof depressions.
- When water and the weight of it remain in place on a tar and gravel roof, structural roof changes can occur.
- Ongoing pooling can cause mold and other related plant growth to increase on a roof’s surface, which can cause subsequent roof deterioration.
- A tar and gravel roof requires adequate drainage to operate efficiently.
Other Critical Issues with Tar and Gravel Commercial Roofs
Additional Weight –
One problem with a tar and gravel roof is the added weight that the materials bring to a structure. When you have layers of tar along with supporting fabric, and a finishing or top layer of gravel, a roof is going to gain an additional 5-10 pounds for every square, which adds significant weight. The extra weight can significantly overburden a roof, any under layers, and the building as a whole.
Maintenance and Repair –
A gravel roof can present challenges when it comes to locating a leak. With the gravel covering the tar layer, there are going to be difficulties. A whole area of gravel may need to be removed either through slow shoveling or vacuuming to pinpoint the leak. These moves will involve considerable time, effort, and added expense. In comparison to a foam or membrane roof that can be quickly inspected, a gravel and tar roof leak assessment is going to be a much slower process.
Gravel Stone Deterioration –
Gravel stones are going to be a less effective covering when they break down due to weather, sunlight, foot traffic, and the passage of time. When the top layer of gravel becomes worn, the layers of a roof are going to be subject to deterioration and damage.
Walkover Damage –
A commercial roof will eventually be subject to various maintenance personnel working on it. People could be freeing the roof from debris, cleaning nearby windows, maintaining the cooling and heating systems, checking roof projections, or doing other related tasks. Without the utilization of walking paths, individuals or teams of individuals are going to be walking over gravel and causing damage to it. With enough pressure and force, sharp gravel pieces can be forced into layers beneath the gravel and create areas susceptible to leaks. There might not be immediate damage. Still, the degradation of gravel pieces can affect the longevity of a roof through the exposure of the underlayer areas to continued foot traffic, the elements, and ultraviolet rays of the sun.
Tar and gravel may be the answer to your commercial roofing needs, especially if you require a flat roofing alternative that has been around for several years and has proven itself to be a dependable roofing material. If that is your interest, or you have general questions, complete the online contact form and a roofing expert will answer any of those concerns as quickly as possible.