Will the old roof need to be removed altogether before the new roof is installed?

Contractors are not allowed to add a third layer of any kind of roof covering where another two layers already exist, so if that is the case, the old roof will definitely need to be taken up. If there’s only one layer of shingles, the new roof can be installed over the existing material or the old shingles can be torn off first. The choice depends on financial considerations and on whether the roof deck underneath is in good condition.