I call BS to those of you who insist on tearing down to deck in every case for no good reason. If you happen to be a sales person it's just another gimmick to make money.
I did NOT say anything about stacking on a 3rd level either.
I grew up in Amarillo - which is about as hail country as you can get - and worked in a Lumber Yard through JrH/HS and in summers from A&M and sold/delivered/installed many - MANY - doubled up comp roofs. And insurance was not a problem either way so far as I know. And yes, "Certainteed" flat 3-tab 210's were the cheapest we had for sale and the easiest to double up with. I can understand switching from say Architectural Timberline 3-D's and trying to put a Certainteed flat straight over would be an issue but Timberline over timberline just makes it look more like a shake roof.
For my own houses through the years as a new roof has been required I have switched to either Standing Seam or Aluminum Shake look-alikes - applied over a single comp roof both times - and got a nice reduction in insurance rates..
The cost difference saved by not tearing off the old comp roof vs the cost of the new metal roof over was then essentially cancelled out and negligible. And this occurred when Iived in Austin.
In every case of which I am aware where original old cedar shake roofs are being replaced they are becoming more and more scarce as not only do they cost more, higher labor costs, etc, but the insurance rates are sky high to keep/replace that type of roof. And obviously, they would HAVE to be removed to replace with either comp or metal roof - or tile, etc. Granted these were typically on very high dollar houses to begin with, but the option to replace with tile, or concrete, or slate, etc., is much preferable over comp or Timberline or standing seam, etc., on high dollar houses. But again,, to put that much weight on a roof requires close inspection of the structural loading capabilities.
AAAAAAAAAAg - Air Force Aggie Architect and Hospital Administrator fm Amarillo, Altus, Austin, Arabia, Arkansas, Africa, Seoul, Bahrain, Amman, Kuwait, Iraq, Iran, Saudi, DFW-Fairview, Ramstein, San Antonio, Pentagon, OKC, JCAHO/JCR - '65, '69, '73 - A&M Letterman (ret).
Winston Churchill: “If you’re not a socialist in your twenties, you have no heart. But if you’re not a capitalist in your thirties, you have no mind.”