This is the tried-and-true roofing material for flat roofs, and it is exactly what it sounds like. Used for more than 100 years, it involves layering bitumen – usually tar, asphalt and the like – with gravel and other materials. It can be added to over time and is extremely durable, especially if the roof gets a good amount of foot traffic. It is simple to ensure all seams and openings are sealed with built-up roofing. The downside? All those layers and gravel make for a heavy roof, which likely would require additional structural support.
Modified bitumen roofs are somewhat related, in that they involve a layering system that includes an underlayment, a membrane and a granule coating. However, both built-up and modified bitumen roofs are usually dark in color, which can end up creating additional heating and cooling costs for the building down the road.
Instead of a “painted-on” roof coating, many building owners choose to have a membrane applied. A membrane is fantastic for making sure all openings, seams and cracks are covered. The membrane often is white, which can assist in keeping HVAC expenses lower.
The downsides of this choice are the cost – it is usually the most expensive option – and the fact that any sharp objects can easily pierce the membrane, providing the opportunity for water leaks. Here are some of the choices for membrane materials: