Commercial buildings often times have flat roofs, but some modern and historic homes also have roofs with little or no slope. A tar and gravel roof is a type of flat roofing used for some these homes.
A tar and gravel roof is also known as “built up roof” or BUR. Traditionally, a tar and gravel roof is usually made of 3 to 5 laminated layers, which are made from 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 roofing layers. The gravel weighs down the roofing materials, protects the roofing 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. Drains and downspouts are also built in to drain any water from the roof.
Compared to other roofing products, built up roofing is quite inexpensive. However, the lifespan of a tar and gravel roof is only about 10 to 20 years, depending on its installation and the climate. Some well maintained tar and gravel roofs may last up to 25 years.
Strong sun can also damage the roofing membrane if it is exposed and not covered 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. A tar and gravel roof must have an adequate drainage system to avoid this problem.
Fixing an Older Tar and Gravel Roof
An older tar and gravel roof can be fixed by patching the roofing membrane. Adding additional roofing layers made out of fiberglass can add further insulation. Also, applying a new acrylic/elastomeric “cool roof” coating can further weatherproof a tar and gravel roof.
Although these refurbishing measures can extend the roof’s lifespan, it should only be done if the roof is still structurally sound. Otherwise, the entire roof will need to be replaced.
Installing or fixing a tar and gravel roof is very different from installing or fixing conventional roofing shingles. It’s important to find a roofer who has worked extensively with tar and gravel roofing and ask for references.