Tar & Gravel Flat Roofs

Roger watching over the hot tar kettle, a crucial aspect of tar and gravel roofing 

Here a staff member embeds crushed stone in a layer of hot tar - the second last phase of the tar and gravel roof, the last being installing the perimeter metal 

Built-Up Roofing (BUR) or more commonly known to the layman as “tar & gravel” roofing, consists of several plies of #15 Asphalt felt paper (usually 4-5), adhered together with hot bitumen. Another layer of hot asphalt is poured on top and clean crushed stone is embedded into the hot asphalt. The stone is simply there to prevent the sun’s UV rays from deteriorating the asphalt. BUR is heavy and is the most rugged of flat roofing systems. It is not easy to damage a BUR system. Usually we have to take an axe to them to start the removal of and old BUR.

However, it has disadvantages too. Most modern BUR roofs are made of asphalt from crude oil rather than from coal tar as in the old days. Coal tar was a longer lasting product (up to 30 years) with some self-healing properties if damaged. BUR using asphalt from crude oil lasts only about 12-15 years. However, the fact that coal tar is so terribly irritating to the skin and eyes means it has long since passed as a product of any favour with roofers. Asphalt from crude oil is also a labour intensive roof system, and dangerous for the fact that one is working with cauldrons of a liquid that is heated to between 400F – 500F degrees. As such, its popularity is also waning. A disadvantage of going with a BUR system is that essentially the roofing contractor is the manufacturer of the roof system on site. There is no manufacturer warranty on the roof system, just on the component products. There is no manufacturer training or certification of the installers of BUR systems. So it is buyer beware. Typically, BUR warranties are from the roofing contractor and range from 2 to 10 years – but usually 5.

This is an inverted tar & gravel roof, meaning, the felt & asphalt membranes are under the insulation, then covered with tarps & stone ballast 

Embedding gravel is the last step in tar and gravel applications 

Here Jeremy finishes piecing together the puzzle of a cricket which will prevent water pooling in a low spot on the roof 

Another shot of the cricket which will be covered over with 4 plies of felt and asphalt like the rest of the roof 

Another shot of the cricket which will be covered over with 4 plies of felt and asphalt like the rest of the roof 

Starting to adhere the cricket onto the 4 ply and then covering over with another 4 layers of felt paper and asphalt 

Another shot of the cricket adhered in place 

Eventually the tar and gravel roof makes for a rugged roof system like on this new Shoppers Drugmart in Ottawa 

Patching and repairing tar and gravel roofs is not pleasant work. Here Kevin retrofits a small curb on an existing roof 

Modified bitumen can also be applied to tar and gravel roofs for repair purposes, but again, a roof replacement would be preferable