Well, Jason, in order to answer your question you need to define what you mean by "green" when you say that you want to make a "greener choice."
Are you thinking about
- recycled/sustainable content,
- end-of-life recyclability,
- thermal performance,
- embedded energy,
- carbon footprint,
- health issues, cost, or
- a multitude of other measures?
Once you identify what variables matter, you then have to prioritize them so you know what is most important.
Living roofs and standing seam metal roofs
Depending on your answer to this question, the perfect roofing material will vary greatly. Generally, the choices that will satisfy most of these criteria are living roofs (plants appropriate for your environment) and standing-seam metal roofs (cool roofs).
- Unfortunately, both living roofs and standing seam metal roofs are very expensive options compared to composition shingles, and you clearly said that you want to stay in the same price range as your existing asphalt shingle roof.
- For this reason, we install either 50-year or lifetime warrantied composition shingle roofs on most of our jobs here in California.
- They are relatively inexpensive compared to any other roof material, are extremely durable and long lasting, and can be recycled into roads when their life as a roof is finished.
Cost/benefit depends on your climate
We also have a harder time justifying "cool roof" systems like standing-seam metal here in Northern California due to our mild climate.
However, it may be worth it for you in Phoenix to evaluate the cost/benefit of spending more on this type of roof since you could save significantly on your cooling bills in the summer.
If you choose composite shingle, choose one of the longer life versions
I'm afraid, however, that with the significantly higher cost of metal roofs, you will end up with another composite shingle.
Just make sure you spend a little extra to get the longer-life product (50-year or lifetime) since it is worth a little more to not have to ever worry about your roof again!
For more information:
Read "What type of roof should I choose in a hot climate?" a Q&A answered by Mick Dalrymple.