From our many discussions with contractors over the years, we’ve learned that roof-over installation introduces an increased risk of workmanship errors. Moreover, a tear-off will reveal defects in decking that might otherwise go undetected. We have also learned that a growing number of contractors recommend a tear-off to their customers because they believe that a roof-over installation will “cook-up” and deteriorate the asphalt more quickly than will a clean roof installation.
Of course there are arguments in favour of doing a roof-over as well. For example, two layers of roofing provide redundant protection against leaks. Also, by allowing the original layer of roofing to remain, the cost of the job and the burden on landfills is reduced.
On balance, we are convinced that the argument for tear-offs and clean roof installations is persuasive for ensuring the highest possible quality finished roof system.