metal roof color

What color metal roof reflects the most heat in summer, white, bare silver or something else?

Great question and topic. A huge energy factor effecting most climates on earth yet is routinely ignored. Reflectance and Emmisivity are the two measurements that are used for ratings.

The cool roof rating council is a great resource for learning the science and some of the specific products that they have tested under lab conditions. http://coolroofs.org/resources/articles-presentations-and-links

Painted, Bright White Metal seems to be the highest performing cool roof cladding. While the bare and silver products have high reflectance values, their emmisivity lacks far behind the painted products. Another benefit is that white paint seems to better resist UV degradation.

Most research suggests that adding a vented airspace directly below the metal increases performance but its a tricky detail and difficult to make pay off IMO. Choosing bright white metal (with exposed fasteners) is comparable in up-front costs to high-end shingles in our area yet represents a huge jump in durability and energy performance. I feel most metal roofing systems tend to vent a little on their own compared to shingles.

Shawn Dunseith : If you are planning any type of peaked roof as compared to a shed roof, you with want both air vents at the peak of your roof and at the soffet/fassia.
Make sure the insulation in the attic does not block them ! Big AL

I think Big Al is referring to the traditional ventilated attic with insulation usually at the flat ceiling plane. The insulation tends to block the soffit vents where there is little room between the roof deck and exterior walls. This can also contribute to ice dams in the north. Cheap cardboard and foam vent chutes are a good product that allows insulation to be stuffed in this weak spot. When building new, specify "raised heel" trusses or increase the depth of the rafter to make more room for insulation.

The venting method I mentioned above takes place above the roof deck. Very few people do it but its increasing in popularity.

The current trend in much of the US is to insulate up the roof deck creating an un-vented attic. This method makes the most sense when taller vaults are wanted or there is HVAC equipment in the attic.