Walker, the first place to check is your local city & county code regulations. If your area has no codes then you may overlay the 3-tab with a metal roof system. IBC- International Building Code does allow for two roof systems. I would provide a tear off to inspect the deck and provide a clean substrate for a water tight system. Given the cost of underlayment, I would recommend you use it if you choose to overlay the shingle.
Thanks TripleDub, I'm a ways from taking action but that sounds like great advice. Particularly the tear off. I imagine in my wet climate I'll need the best protection I can get.
That's right...forgot about those fish already! Let's see now...Wild Brown huh? Sounds like a squatch!
Farmhand, my company installs just about everything except hot asphalt. We install truckloads of membrane roofing, PVC, TPO, EPDM and Modified. Lots of asphalt laminated shingles, metal, tile, coatings, etc.
