What is a Modified Bitumen?
Question: I have an old tar-and-gravel roof that I am getting re-done. My contractor is suggesting a “Modified bitumen” roof. What is this? (John, San Mateo CA)
Answer: Modified bitumen roofing is made of asphalt that has been modified with polyester. A conventional tar and gravel roof can tear as it expands and contracts with changes in climate and temperature. Modified bitumen is far more flexible and therefore less likely to crack or tear. There’s a single-ply version, but you will be much better of with more than a single layer.