Membrane roofing is used totally on reduced pitched roofs wherever shingles, slate or tiled roofing wouldn't be successful. Universal creating codes allow for for up to 2 layers of shingles on the roof, but there are times It might be superior to tear off the single layer and start refreshing: https://magazinethis.com/the-top-3-roofers-in-oswego-illinois-expert-services-you-can-trust/