On Tuesday, April 4, 2017 at 11:44:06 AM UTC-4, Bobby wrote:
replying to JT, Bobby wrote:
It may be against code to ut more than two layers of roofing even though it is
metal. May look like crap too if the base is not right. Your house is
probbly a big investment so protect it by doing the job right.

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It's against code to do more than two layers here.

Another factor is that 2 layers of shingles means the roof is typically
50+ years old. The only way to accurately assess the condition of the
decking is by removing the shingles. If there is some rotted decking,
he'd be putting a new, expensive metal roof over rotted wood. I'd
run from any roofer that offered to do the job that way. I would not
even do a second layer, let alone three.