If the materials become available for this idea, instead of a dial to adjust temperature, a thermostat could adjust to do that automatically. It would probably be expensive, but hinged roofing tiles that could raise or lower like spines to change heat exchange rates might also work.

I believe their are some new dyes that change color with temperature. One that goes from black to white as the temperature rises would do the trick simply and cheaply. I don't know how much they cost but the energy savings would be considerable. Whats more they could be painted on to any suface:- walls; iron; tiles, you name it. With all this talk about greenhouse gases this is exactly the kind of solution that could really work. Well done!

In warmer climates, such as the southern US, roof heat gain in the summer is a problem much greater than any benefit likely to be gained from having darker roofs in the winter. Therefore, it is possible to make most of the gain in efficiency that you are seeking with these color changing roofs by simply painting the roof a lighter color. I believe there are special roof paints and coverings designed to reflect heat. Thermal reflectivity should be considered whenever a roof is being replaced. In hotter climates, a thermal reflective barrier can be attached to the underside of the roof, but better attic insulation and ventilation are often a better deal.

Shingles are expensive enough already, but to coat an entire roof with actively changing shingles would probably be extremely expensive.

A great idea, but if you are going to the expense of using that technology on a roof, why not just include solar collectors, as well. I'm afraid the expense of these technologies in terms of resources, evironmental and economic impact is too great. A more green solution may be a green roof - insulates in the winter and summer, helps collect rainwater runnoff, contributes to CO2 reduction and provides wildlife habitat. We need to rethink our roofs and especially, get away from those asphalt shingles.

Having shingles that change color themselves based on temperature wouldn't work. Even in the winter, the shingles will get hot when the sun shines on them, causing them to turn light. An external thermostat could work, but would require that they be wired together somehow. That would be expensive. I think if you're going to spend the extra money, you should design something to utilize the solar energy hitting the roof year-round. Maybe you could have a dark roof and run tubes along the underside of the roof. Water would run through the tubes to collect the heat. There should be insulation under the tubes, so the heat collected by the roof would be "trapped" around the tubes. The heat could be used for home heating in the winter, cooling in the summer, water heating year-round, or maybe power a generator of some kind.

I live in a flat roofed trailer home. I have made certain adjustments to my landscaping and tree deciduous tree placement to maximize winter sun exposure and minimize summer exposure but while doing this work the idea of a roof coating that would change from black to white based on temperature changes struck me as a relatively simple idea that could have massive energy use implications.

I looked around on the old google and found that the technology exists and paints that change colors (including from black to white and back) are already sold by paint specialty manufacturers.

The objection that the roof would heat up in the winter anyway is not completely relevant because though the roof would heat during the day even in winter it would not heat up as much as it would during the summer (the angle of the sun in the sky is one reason winter is colder - less direct overhead heat, ambient temperature would also contribute slightly to a difference in the amount of heat the roof could retain) - the difference in heating of the roof between summer and winter is evident in the different amount of heat transferred to the home in winter vs summer. The temperature difference would exist but might need to be calibrated to a measurement not immediately apparent (a higher temperature and a smaller spectrum of temperature difference) - the means of calibrating at what temperature difference the color should change would be the challenge.

So far I haven't found any roof coating manufacturers who have attempted to incorporate the temperature sensitive pigments now on the market into their products but I do foresee such a product eventually being offered.

The thin film solar and solar conductive paints being developed also look promising but are not yet "ready for prime time."

So foe now, it looks like natures gift of trees that shade in summer and then drop their leaves to let the sun in during the winter is still the most practical rooftop heat regulator. there is a wealth of information on the internet about optimal placement of deciduous and evergreen trees and shrubs for maximum energy efficiency.

I had the very same idea and have been investigating the practicality of it application. In addition to the thoughts you had on the subject, the use of darker color roofs in cold climates would speed up the melting of snow and relieve some of the weight snow build-up causes. Rather than have a dial that relies on the homeowner to adjust the color, the material, or coating on the roof, would respond to a combination of heat and light. This would remove the necessity of constant intervention, and account for the possibility that a change might be needed when there was no one home to activate the system.

Good!

This is a great idea but another company has already thought of it. You can find them at movingcolor.net.