My current house had Forrest Green metal put on the roof 8 years ago. I noticed darker colors fade more in hard sun. That might be okay but if you put on an addition the colors will be way off. My original roof vs. the new addition last year was noticeable but not terrible. To correct that I would have to replace all the old tin, so I took a closer look at it matched perfectly:laughing:
Around here, they went right over the shingles with the tin and worked out fine. For the addition I built it like a pole shed roof but used a thin insulation under the tin for condensation. I put in a foot or so insulation in the attic so noise isn't a problem.
Similar issues, but in our case, we had 3 year old pole barn with forest green metal roof and a 25 y/o house with a really badly sun degraded, rolled, cracked, stoneless asphalt roof, which we had replaced after a full 2years of interviewing roofers with small and large companies/crews.
We also ende up with a complete tear-off, which in our case revealed some big problems which had been atcleast partly camoflaged by the roofing materials.
That led to some repairs and then as was said by the OP, underlayment with a synthetic replacement for asphalt felt paper, which is significantly more waterproof and resilient.
Our local codes call for the ice dam barrier membrane for the bottom 3' or 4' of the roof above the edge.
Our house roof is standing seam, which is also synonymous with hidden fastener roofing.
I considered getting a crimped seam roof but my wife was worried about how hard it would make any future repairs.
Funny thing, we went driviing around looking for houses with metal roofs for months before we got ours done, so we coul ask the owners who did their roofs nnd would they use them again, and we actually found very few to compare.
Now about 4 or 5 months later, we see them everywhere.
God luck, now that we finally have ours, we love it.
BTW, for all those saying that metal roofs are hotter than asphalt, you couldn't be more wrong.
Metal roofs have a higher albedo, which means that they are more reflective, therefore there is less heat gain.
Also because they are raised off of the roof deck on batten boards or purlins, so that there is air flow under them, they actually create a convective air flow, which further helps to cool them.
Although we did have one yutz who called himself a roofer, who wanted to screw the metal panels directly to the roof deck, violating every principle of metal roof installation- we told him to go spit, and he was outraged that we didn't think he was doing us a favor by bidding on our job.
PPS: For barn and shed roofs, installing a vapor barrier and even a nominal 1" of fiberglass or foam board insulation goes a long way to prevent condensation from forming and raining down on the inside of it.
We have had a devil of a time keeping it from occurring in our wood shed, especially in midwinter thaws when the air temps get into the 40's or 50's but there is a foot or more of snow sitting up on top of the roof cooling it.
Our wood shed has a lean-to roof, but it isn't very steep, so snow sits on it for months...
