Friend - you got a lousy metal roof if it only lasts 30years. And if your roof slope was too low, then you probably needed a different type of roof, or the proper metal roof with taller seams, and proper detailing.
First, you don’t paint anything that you want to last an extended time because paint will always wear out/ugly out well before the substrate. If you want it to last the most affordable option is unpainted galvalume coated steel. It does not need to be cleaned, not any more than rain provides. If you have trees and debris that does not wash off, then yes - you should clean that away, but this is likely a symptom of your roof not being steep enough.
That roof will cost 2-3 times more than an asphalt impregnated shingle roof, and will cost less over the service life of the roof. IT COSTS LESS TO USE A GOOD ROOF.
I’m not attacking metal roofs (or any other kind of roof). If you read my comment you will note that I like the roof, it saves on Heat Pump/AC use in the summer and looks nice on the house. I like that I won’t have to plan on replacing it since I inherited it from the previous owner with plenty of life left on it. On the question of painting, I will take the advice of the company that installed the roof in 1998, they’re coming to clean it this spring (to the tune of $1200, by the way).
I was simply trying to point out that a single product will never be a golden bullet to solve all problems. There are a number of roofing materials available to the interested homeowner, all of which have advantages and drawbacks. You’re only considering one factor - cost over the life of the home. Everything is more complex than that, and I tend to thrill at the complexity rather than reduce decisions to black or white. What about the homeowner who wishes to work on his or her own home? A composite roof will be easier to penetrate and reliably seal to install vents, etc. A cedar shake roof is absolutely beautiful and will weather and age over time, as will a copper roof. A tile roof fits a certain style of home like nothing else, and I assume the tiles are less likely to blow away (although not sure about that). A slate roof fits a different style of home and is beautiful in an entirely different way.
I have an interest in architecture - why do you think there are so many different options when building or remodeling a home? I don’t care for granite or tile countertops, so have specified solid surface countertops for my upcoming kitchen remodel. Would you disapprove if I had chosen formica? It would save me a bundle and might allow me to put more budget into the cabinets, which will be re-used plywood cabinets from the existing kitchen.
What I’m trying to get across is, no one makes decisions for the same reason that you make decisions, and every homeowner makes choices (sometimes irrationally) based on their assessment of their situation. As an architect (as reflected in your profile) don’t you work with your clients to design the best home for them, or do you specify your own preferences and tell them to take it or leave it?
