I only know what people have told me... and that is developing into a problem. I am told there are two kinds of tar. Coal tar (used in the 50's) and asphalt. The roof on this low slope (told it is 2/12 and OK for tight lock standing seam) 1958 house which I have owned since 1980 has no gravel on top. It appears to be rolls of fiberglass saturated heavy tar fabric with a MOSTLY level layer of hot asphalt mopped over it. Twenty years ago, you could not see the seams of the fabric as clearly as you can now. There is little tar material covering the rolls and the seams are not only visible but can be seen to be separating... clearly at the end of it's life but no leaks visible within house. At the bottom of the eaves, and near rake end, tar is slightly "globbing" and is irregular in height. No insulation over eaves or garage area creates another 2" height variation over the intact, old roof which was NOT budgeted to be removed.
I have contradictory opinions on how perfectly level this existing roof must be since the insulation and accumulation of tar creates variable height. Complicating this system is the built in gutters. The 2x 8 fascia on the eaves creates a dam which is also tarred and I have five 3" round holes drilled in the last 2x6 Tongue & Groove nearest the fascia to accept the tarred in metal downspouts. These have leaked over time creating isolated dry rot mostly very near the downspouts and limited to first or second 2x6 nearest fascia but now the contractor states he does not intend to remove the fascia but merely CUT OFF the top 3 inches (not TEAR OFF) to enable a conventional gutter.
The written proposal which I've agreed to addresses costs of possible HIDDEN rot repairs over ONLY the flat roof section (for which I purchased ALL materials since NONE was delivered with installers) and is silent on the VISIBLE rot under the eaves at the built in scuppers. There are no visible leaks or rot INSIDE the house with the exposed 2 x 6 T&G. The flat roof section is now repaired & finished except for the gutters... I hope.
The contractor now volunteers IF I want a complete tear off (bid is for roofing over tar) ... he can do that for ANOTHER $ 3,500 for a total of $ 26,000 for 2250 sq ft of metal (no dormers, one brick chimney) & the 750 sq ft. of flat PVC (nearly done).
My head's exploding and with the ambiguities regarding material descriptions, I feel like I'm getting the old bait & switch.
Too much information?
Thanks again to all that have replied.