What are the trade-offs regarding home roofing reflectance. I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob

x-no-archive:

Is there a down side to this. *Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob

when the roof is covered w/ snow, it does not matter what color the
roof is?

Mark

Rob wrote:
What are the trade-offs regarding home roofing reflectance. I ask
because I'm considering using a 40% R roof for most of my home
(mostly for asthetic reasons) and a 60% R for a south facing (and not
ground visible) large dormer we have -- mainly to reduce heat load in
the summer which has been a problem.

Is there a down side to this. Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but
only a moderate amount of snow usually.


There's at least one other consideration: Looks.

Light-colored roofs discolor from the crap in the air and show unsightly
streaks downstream from vents, chimneys, and other protrusions.

I don't see how snow melt can be affected by the roof color. True, dark
roofs absorb more sunlight and get warmer, but if the roof is covered with
snow, the sunlight's not reaching the roof...

But, I admit, I don't know much about snow. We get snow - maybe a
quarter-inch - once every ten years. 'Course that's cause for panic: they
close the schools, drivers collides with as many other cars as they can
because that's what you're supposed to do when it snows, people stock up on
canned goods and huddle in their family, preachers inform us that the end is
nigh, there are the obligatory news reports of kids making one-foot tall
snowpeople with film of goofy dogs and perplexed cats trying to make sense
of the phenomenon.

Snow in Houston is a truly remarkable experience.

On Feb 9, 9:20*am, Rob wrote:
What are the trade-offs regarding home roofing reflectance. *I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. *Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob

A high reflectance roof on a south exposure is always a good idea. A
metal roof on a south exposure is even better. Given the installation
methods for standing seam, the extra ventilation possible between roof
and deck should markedly lower AC loads in summer. The downside in
northern states is snow sliding off the roof and landing in driveways,
on bushes and other places that you'd rather not have it. Something to
consider for lowering operating costs of the palace.

Joe

"Rob" wrote in message
news
What are the trade-offs regarding home roofing reflectance. I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

The US National Bureau of Standards was working 80 years
ago on insulation problems (as understood in 1920.) The
NBS still exists and it is hard to believe they have given up
building research.

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)

On Feb 9, 9:20*am, Rob wrote:
What are the trade-offs regarding home roofing reflectance. *I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. *Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob

What is a 40% R or 60% R roof. By defanition that might mean a 0.6 R".
There is no 40R roof except 6" of R 7" Foam insulation as roofing. Are
you talking foam.

There's at least one other consideration: Looks.

Yes looks. That's one reason I don't think we'll go more than 40% R max
on the visible portion of the roof -- especially on the street side.

Light-colored roofs discolor from the crap in the air and show unsightly
streaks downstream from vents, chimneys, and other protrusions.

Is this also true of metal roofs as well.

Also one good thing for my house, the visible portions of the roof don't
have any major protrusions -- through it does have 4 roof vents. All of
the stacks and the chimney etc. are on the dormer which is on the back of
the house and not easily visible from ground level.

Thanks,
Rob

when the roof is covered w/ snow, it does not matter what color the
roof is?

I have not paid a much attention to this though people have told me it
does -- but I'm not certain how much I believe that. That is why I ask.

Several ways it could make a difference --usually snow pack is not thick
or may be none around edges and so I suspect a dark roof starts melting
faster there. Also snow must be quite thick in order that there be no
penetration through to the roof -- so it'd expect the roof to be a bit
warmer under even a modest snow layer. The other potential issue is that
the emissivity of a black and a white roof are probably quite different,
meaning perhaps you get more thermal radiation from below for the black
roof case.

I don't know if any of this matters in practice, or if it's a bad thing to
leave snow on the roof as long as possible. I'm personally leaning toward
using as light a roof as possible while still looking good -- unless there
are some issues with that thinking.

Thanks,
Rob

"Rob" wrote in message
news
when the roof is covered w/ snow, it does not matter what color the
roof is?

I have not paid a much attention to this though people have told me it
does -- but I'm not certain how much I believe that. That is why I ask.

Several ways it could make a difference --usually snow pack is not thick
or may be none around edges and so I suspect a dark roof starts melting
faster there. Also snow must be quite thick in order that there be no
penetration through to the roof -- so it'd expect the roof to be a bit
warmer under even a modest snow layer. The other potential issue is that
the emissivity of a black and a white roof are probably quite different,
meaning perhaps you get more thermal radiation from below for the black
roof case.

I don't know if any of this matters in practice, or if it's a bad thing
to
leave snow on the roof as long as possible. I'm personally leaning
toward
using as light a roof as possible while still looking good -- unless
there
are some issues with that thinking.

Thanks,
Rob

Rob,

A shingle roof's color is determined by the shingle granule. Granules cover
97% of the exposed area. Opacity of the granule is 100% on a shingle,
meaning no UV rays penetrate regardless of color (on 97% of the exposed
area).

When talking about heat radiation from below, the issue is resolved through
better insulating factors, & or ventilation. All fiberglass/asphalt
shingles are black on the under side, plus you have or should have black
felt paper.

Apparently a roof is up to 60% of the home's curb appeal, this of course
will vary with the pitch of a roof. Go for the aesthetics, don't get stuck
with an ugly roof, you'll lose money in the long run.

On 2/9/2009 7:20 AM Rob spake thus:

What are the trade-offs regarding home roofing reflectance. I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Let's look at it analytically.

Ideally, one would want a roof to be totally reflective in the
summertime and totally thermally absorbent in the wintertime. Until they
make roofs coated with magic crystals, this will remain an unattainable
dream.

You need to balance the need for summer reflectance against winter
absorption.

Let's look at the worst-case results of having the "wrong" roof surface.

In the winter:
- snow may build up deeper than if roof were absorbent

In the summer:
- more heat may enter the house

Consider the consequences of each. You say you only get a moderate
amount of snow. So long as the roof structure is adequate for the
maximum snow load, having more snow sitting on the roof isn't going to
hurt you. In fact, it may actually help to insulate the house (think igloo).

On the other hand, having a dark roof absorb heat in the summer will
definitely affect you, both in terms of comfort and financially, as
you'll need to spend $$$ to get rid of it.

Therefore, I'd go with as light-colored a roof as possible.

Other comments here about appearance were pertinent. Choose a light
color that doesn't look ugly and won't reduce the house's "curb appeal".


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair

"Rob" wrote in message
news
What are the trade-offs regarding home roofing reflectance. I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.


If your roof heats up and a melts the snow, it may re-freeze in the gutters,
then it will start to build an ice jam and backup. This often happens with
homes that have poor ventilation/insulation in the attic. I would go with
the lightest color that looks good.

If you have proper ventilation/insulation then I would GUESS that the color
would have minimal influence on the roof temperature in the winter but
slightly more in summer. Ask a shingle manufacturer.

Cheers,
Jim


I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob

Jim2009 wrote:

If your roof heats up and a melts the snow, it may re-freeze in the
gutters, then it will start to build an ice jam and backup. This
often happens with homes that have poor ventilation/insulation in the
attic. I would go with the lightest color that looks good.

If you have proper ventilation/insulation then I would GUESS that the
color would have minimal influence on the roof temperature in the
winter but slightly more in summer. Ask a shingle manufacturer.


Good advice, but what looks good NOW may be horrid in a few months due to
discoloration from airborne particles.

If considering a light-colored roof, drive around the neighborhood (city,
maybe even state) looking for a something similar. This will tell you
whether your choice might turn ghastly with time. If you can't FIND a
light-colored roof, that might also be a clue.

Rob wrote:
What are the trade-offs regarding home roofing reflectance. I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons) and a 60% R for a south facing (and not ground visible)
large dormer we have -- mainly to reduce heat load in the summer which has
been a problem.

Is there a down side to this. Some people seem to want to use darker
roofs so the snow melts faster -- others say it's good for snow not to
melt and a cooler roof is better in both the winter and summer.

I live in minnesota -- so we get both very cold and quite warm -- but only
a moderate amount of snow usually.

Thoughts?

Rob
It's been six or seven years since I did much research about roofing
problems. I did run across info about the heat on the surface of light
vs. dark roofs. Dark=hotter, of course. I'm in FL, so the fact that
cooler light roofs grew more mold was of interest. One thought that I
believe I read but can't be sure, is that the surface temp didn't
transfer to an important degree to the attic temp; i.e., didn't make
much difference in the attic temp on the basis of light/dark shingles alone.

From doing a quick Google search, I think the answer is "It depends" )
Climate, orientation, roof style, underlayment, insulation, etc.

Search on 'roofing color heat attic'.

Here is a pretty good link:
http://www.peaktoprairie.com/?D=206

On Feb 9, 9:20*am, Rob wrote:
What are the trade-offs regarding home roofing reflectance. *I ask because
I'm considering using a 40% R roof for most of my home (mostly for
asthetic reasons)

snip

If appearance is important to you, then choose what looks good.
However, there is some prattle in these posts about 'curb appeal'
which in my view is nonsense. If you're into 'flipping' houses or
peddling real estate then curb appeal is like auto detailing,
something to move the product. But if you intend to live in a house
for some years (which may be mandatory given the economy) then paying
attention to details that lower the bottom line operating cost will
trump curb appeal every time for anyone with common sense. The Mc
Mansion mindset is history and we all need to get over it. Change is
on the way and it looks very austere.

Joe