Roof color opinions: dark vs. light

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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #32
    Re: Roof color opinions: dark vs. light
    rollandelliott wrote: »
    for other roof types like white metal the savings are dramatically higher.

    Which brings to my mind another question about metal roofs - - - -
    I've seen a few metal roofs where it appears metal expansion and contraction has caused stress cracks and metal fatigue around the fasteners. Might it be that dark color metal roofs would expand and contract both more, and more often, thus exacerbating this problem, compared to white metal? Food for thought.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #33
    Re: Roof color opinions: dark vs. light
    waynefromnscanada wrote: »
    Which brings to my mind another question about metal roofs - - - -
    I've seen a few metal roofs where it appears metal expansion and contraction has caused stress cracks and metal fatigue around the fasteners. Might it be that dark color metal roofs would expand and contract both more, and more often, thus exacerbating this problem, compared to white metal? Food for thought.

    Definitely.
    But even the shiny aluminium ones suffer from this. I suspect they last longer/don't need as frequent repair in a climate with more averaged temperatures, but I've never lived in one of those. :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,658 admin
    #34
    Re: Roof color opinions: dark vs. light

    Boy--You guys are fun. Now I am wondering if I am making a big mistake choosing (dark colored) steel for my new roof in the next couple weeks. :confused::cry::p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #35
    Re: Roof color opinions: dark vs. light
    BB. wrote: »
    Boy--You guys are fun. Now I am wondering if I am making a big mistake choosing (dark colored) steel for my new roof in the next couple weeks. :confused::cry::p

    -Bill

    In California? It never rains there! Why do you even need a roof? :p

    Seriously, Bill; you don't have temperature extremes really (compared to some places). The colour probably isn't going to be so much of a problem as the material. I think a lot of installers make the mistake of not allowing for expansion/contraction when they put the stuff in (even with standing seam). They could learn from the siding installers: "Never nail it tight"!
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #36
    Re: Roof color opinions: dark vs. light

    One of the tricky parts about heat absorbtion vs color is that much of the heat gain is in the infrared region, and what you "see" may not be what you get. While most whites reflect the entire spectrum (that is why it is "white"), some other colors differ. The best example is that green vegetation has a very high reflectance of infrared http://www.seos-project.eu/modules/agriculture/agriculture-c01-s01.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #37
    Re: Roof color opinions: dark vs. light

    Not all green is alike either. I remember back when solar was first becoming popular (1970's) testing showed the best colour for thermal absorption then was not flat black, but an elm leaf green. There's some complex physics behind visible light absorption and conversion to heat energy, some of it having to do with the material that creates the colour (low density radiating the heat off instead of having enough mass to hold it, et cetera).

    If nothing else this thread has proved there's almost no chance anyone in politics understands this stuff. They'd just been told "this is energy efficient; put a rebate on it" and off they go.
    Pardon my cynicism. :roll:
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #38
    Re: Roof color opinions: dark vs. light

    back to the original question, for a second........

    if you are going to shade your roof with solar panels the color is kind of mute.

    I doubt shaded white is any better than shaded black roofing.

    of course for most solar installs the panels only take up 1/3rd or less of the roof, so cool roof advantages are too be looked into.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #39
    Re: Roof color opinions: dark vs. light
    rollandelliott wrote: »
    back to the original question, for a second........

    if you are going to shade your roof with solar panels the color is kind of mute.

    I doubt shaded white is any better than shaded black roofing.

    of course for most solar installs the panels only take up 1/3rd or less of the roof, so cool roof advantages are too be looked into.

    the sun will change angles as it moves across the sky and could illuminate the areas underneath a pv, but it will still heat areas not covered by the pvs as well so it is not totally moot. at this point you can worry if the pvs are being heated an extra degree or 2 or not worry about it and get what you like as it would be splitting hairs at this point. your roof, your decision, and your money.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #40
    Re: Roof color opinions: dark vs. light
    rollandelliott wrote: »

    if you are going to shade your roof with solar panels the color is kind of moot.

    ...of course for most solar installs the panels only take up 1/3rd or less of the roof, so cool roof advantages are too be looked into.

    But the one third that they cover is usually the prime south-facing area where the most solar heating would occur anyway. Not sure that the cool roof treatment helps enough on the north facing part of a pitched roof to justify the cost. (However, there is this strong tendency to want all of the roof to look the same!)
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,658 admin
    #41
    Re: Roof color opinions: dark vs. light

    My array covers much of my main south facing roof and really made the attic cooler.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #42
    Re: Roof color opinions: dark vs. light

    For areas not covered by solar panels you could put in a similar support structure and cover it with white metal panels. You'd then have space ready-made for future solar expansion and in the mean time reflect heat with enough air space beneath to keep the main roof (and thus what's under it) cooler.

    This is probably not a practical/efficient idea either, but it could be done.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #43
    Re: Roof color opinions: dark vs. light

    red light goes on - -
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #44
    Re: Roof color opinions: dark vs. light
    waynefromnscanada wrote: »
    red light goes on - -

    No worries, Wayne; he gone bye-bye. :D
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #45
    Re: Roof color opinions: dark vs. light

    Haha Good to hear Cariboocoot, was pretty sure the direction he was heading :)
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