I've always wanted to install a metal roof on the Mill Creek NetZero Home. The installation is almost complete now, and I'm very pleased with the sharp look of the roof. Style wasn't our main motivation for choosing to go with metal though.
Durability is our primary reason for wanting the roof - the most important component of the house - to be metal.
Metal roofs are reputed to last fifty years and more. In fact, I am confident that this roof will outlive me. I believe that economic resources of all kinds will be much scarcer in the years to come, with that scarcity increasing every year. So it makes sense for us to invest in a super-durable roof now, when there is relative abundance. In the future, it will be much more difficult to acquire the resources (economic or otherwise) to put a new roof on the home.
We intend to use collected rainwater as the primary means by which to water our garden, so another consideration for choosing a metal roof is the rainwater that will wash off of it. Asphalt roofs are made from petroleum products that leach chemicals throughout much of their lifespan - who wants to pour rainbow-coloured water on their organic tomatoes?
The possibility also exists that we will need to harvest drinking water off of the roof someday. The water washing off of the metal roof will be squeaky clean, and we'll be confident about drinking it or eating the vegetables that have been watered with it.
Metal roofs with recycled content (which ours has) qualify for LEED points (LEED is a certification program for green buildings). However, I have my doubts about whether a metal roof is a clear-cut winner over an asphalt one.
Metal is very energy-intensive to manufacture. Plus, it is imported from somewhere other than Edmonton. Asphalt shingles, on the other hand, are made right here, from a local product (yes, we Edmontonians, for better or for worse, can claim oil as "local"). Plus, asphalt shingles are much more durable than they used to be - they can come with 35-50 year warranties.
Overall, given the durability and recyclability of a metal roof, I think that it narrowly beats an asphalt roof for "greenility". That fact, combined with the clean water washing off of it and the financial security that comes with such a long-lasting roof, made a metal roof an obvious choice for the Mill Creek NetZero Home.