[Greenbuilding] metal roof colors

[Bruce Donelson]

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org]On Behalf Of LarenCorie
Sent: Monday, August 27, 2007 11:07 AM
To: greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] metal roof colors


> From: "Bruce Donelson" <abetterbuilder at frontiernet.net>

> One advantage of a high-end metal roof is that they have
> darker colors which supposedly reflect the heat. Do you
> believe it?

   I (as well as the Florida Solar Energy Center), not only
do not believe it, I see clearly that it would be the last thing
that we would want a roof to do.  If it reflects heat, it will
also, due to the nature of the surface (low emissivity), not
radiate away heat gained from visible light that it absorbs.
Most all heat gain is from visible light, not radiated heat.
Therefore it will be a far hotter roof, than if it did not have
the coating.  That is what we call a "selective surface"  It is
what is used on the absorbers of Solar collectors, so that
they get HOTTER, not cooler.

> Yes, definitely. There is link from the Energy Star website.
> Cool roofs. They have put some kind of reflective ceramic
> spheres into the paint that reflect more light and keep the
> material cooler.

 That is a very poorly written page with at least one blatant
technical error, and another statement about reflecting heat,
that may arguably be correct, but that will mislead almost
everyone into misunderstanding what is going on.

Let's think about this for a few seconds. Exactly how are these
"spheres" going to reflect light, when they are covered with a
coating of regular paint.  These companies sell this stuff to mix
with regular paint, or they mix it in with thick elastomeric paint.
It makes no sense, and according to testing by the Florida Solar
Energy Center, it is totally useless. Besides, do you really want
a roof with low emissivity?   It will be hotter, not cooler.



I haven't tried the new "cool" metal roofing panels yet. But Elk makes a
composition roof material using the same technology that I have used,
although it doesn't qualify for the tax credit because it isn't as
reflective as is required for the  Energy Star standard. It looks a little
lighter than some comp shingle roofs, but not as light as the lighter
colors. It is WAY cooler to the touch than even the lightest comp shingle
when it sits in direct sunlight. Not just a little. I don't know how it
works, but I installed a roof with the stuff last summer, and we could
easily walk on the stuff in hot weather, and it never burned our hands like
most shingles do, unless they were stacked "wrong side up." Cost about
$95/SQ, delivered, so I won't use them on roofs for lots of customers. I
would guess that they last a while if they stay cooler. I haven't tested the
roof to see if it retains its "coolth" with dust on it, but the customer is
a friend of mine. I gotta go see how cool to the touch it is a year later.
We've still got some hot days left this summer.

Bruce Donelson
A Better builder