What is a Tar and Gravel Roof?
Whether referred to as Conventional Built Up Roofing or BUR, tar and gravel roofing is a system of flat roofing protection that is budget-friendly and can last up to 30 years. If you have a home with a flat roof, a tar and gravel roof may be a good option for you.
Tar and gravel roofs are usually made of 3 to 5 laminated layers of asphalt base sheets, hot tar, and roofing felt. A top layer of bitumen and extra top mineral coating is also added. Light colored gravel is used to cover the dark layers. The gravel weighs down the roofing materials, protects the layers against sun damage, and reflects some of the sun’s light. An even layer of gravel must be kept on the roof at all times and some gravel should remain loose to protect your roof from puncturing caused by any foot traffic.
Drains and downspouts are also built in to drain any water from the roof. When new equipment is installed on a tar and gravel roof such as an electrical access or an air conditioning unit, special care needs to be paid to ensure the membrane of the roof isn’t penetrated. Resealing the roof is an effective way to prevent leaks caused by new additions to the roof.
Cost of Tar and Gravel Roof
BUR is inexpensive compared to other roofing products. Generally, it only costs around $2.75 to $7.00 per square foot. However its lifespan is only about 10 to 20 years, depending on installation quality and the climate. Some well maintained tar and gravel roofs may last up to 30 years.
If properly insulated, a tar and gravel roof can help reduce your heating and cooling cost. Just two inches of spray foam installed as sheeting under your tar and gravel roof can reduce the interior temperature of your home by 8-10 degrees during the summer.
Maintenance of Tar and Gravel Roof
With regular maintenance and repair, a tar and gravel roof can last as long as 30 years. You can strengthen your tar and gravel roof by adding additional roofing layers made out of fiberglass or foam to increase insulation. Also, applying a new acrylic/elastomeric “cool roof” coating can further weatherproof a tar and gravel roof. Older tar and gravel roof can be fixed by patching the roofing membrane. However, if you’re evaluating a tar and gravel roof on a prospective home, many patches may indicate past leaks or weak areas.
If the patching has not been done correctly, these areas are likely to leak again. As a general rule, if 25% of the roof is covered with patches, then the roof needs to be replaced. With older roofs the best way to determine how worn out they are, besides obvious signs like excessive patching, is to walk on them and see how they feel under your feet. Look for loose areas, depressions, deteriorated surfaces, cracking, and discoloration.
Common Concerns with Tar and Gravel Roofs
Strong sun exposure can also damage the roofing membrane if left uncovered by the gravel. Tar and gravel roofing is not normally recommended in areas with lots of snow or rain. It is sometimes prone to leaks, especially if the flashing and underlayments are not correctly installed. Flat roofing is prone to ponding, when water stays on a roof surface for more than 48 hours. This excess of water places increased weight on the roof and can change the roof structure. Depressions may also result, affecting the drainage slope and causing the pooling to continue. Continued pooling may result in vegetation growing on the surface of the roof. Vegetation will grow roots, hold moisture, and deteriorate the roof’s surface. A tar and gravel roof must have an adequate drainage system to avoid this problem.