Sometimes you just have to wonder. Found a post about how to “refinish a metal roof” and really have to wonder if all the work was worth it.
Sure, metal roofs can last 100 years or more- and their roof may still have some life in it, but the amount of work they describe- sounds like a replacement would have cost less by the time you add in all the labor. As someone who has “painted” a metal roof that’s been coated with asphalt, I can tell you that standing on top of a metal roof with a paint roller and a bucket isn’t a barrel of monkeys.
If you read this post- here’s the beginning, you can start to get a feel for how much time is involved:
The first job was to scrape all of the loose rust, dried paint chunks, and roof cement which should not be used on a terne metal roof. The roof was power washed and a metal putty knife was used to scrape the rust and old paint. Although it isn't recommended to use a metal implement to scrape the roof, it was the only way to remove the loose rust and old paint. You have to be extremely careful not to pierce the metal. Photo B shows an area that has been scraped. During the scraping, straighten up any bent seams.
After the scraping, the roof was power washed and a strong solution of TSP brushed on. This TSP solution was then removed using the power washer. A hose with a nozzle probably would have worked as well as the power washer since the scraping and TSP solution took off all of the loose material. Finally, a chlorine solution was washed on to remove any remaining moss that was growing on some of the roof panels.
via Painting a metal roof on an historic home – Fixing Our Historic House.
I’d also be a bit careful about scraping and pressure washing an old metal roof which may have high concentrations of lead. Washing a roof with chlorine also may cause some runoff issues.
However, if you’ve got a modern metal standing seam roof, some of these hints may come in handy in 30+ years as your roof starts to oxidize and rust.