Heat Reflective Roof Paint

[chiang mai]

I've become very confused about roof paint properties regarding what will work and what will not and the paint companies are no help. I tagged some of the following onto a year old thread in another forum but am hoping to attract wider input by posting here, here's the scenario:

My house has a steeply pitched roof that's covered in concrete roof tiles that are about eight years old, they're a very dark brown in colour.

My roof space gets very hot because of its positioning, I've done lots of work to reduce the heat such as increased ventilation, radiant barrier and insulated bats, I'm also in the process of installing an exhaust fan.

But it seems to me there's a quick win to be had, if the paint manufacturers blurb is to be believed, by painting my roof with a modern heat resistant paint, "ceramic paint blocks 95% of UV" and "paint reduces internal heat by up to 5 degrees", and so on. Given that the forecast for next year is that Thailand will be even hotter, this seems worth exploring.

I'm certain that if I changed my roof colour from dark to light using any light coloured paint I'd achieve a huge benefit in heat reduction, if I used ceramic paint the reduction would probably be even greater..

But painting an old dark roof with modern light colored paint almost certainly wont work out well, most people report such a thing looks pretty crap after six months plus light colored roofs show mildew deposits very quickly - primarily, the case against doing this is the poor workmanship aspect..

So what that sensibly leaves is repainting an old dark coloured roof with a modern dark coloured paint, question is, will that provide any real benefit?

FWIW the cost of painting the roof is quite low, about 7k for the paint and 9k for the labour.

Any helpful input, gratefully received.

[wpcoe]

I could be totally off base, but isn't UV blocking more for reducing color fading than for heat reduction? I thought infra-red (IR --the opposite end of the color spectrum from UV) was the heat producer.

[chiang mai]

I could be totally off base, but isn't UV blocking more for reducing color fading than for heat reduction? I thought infra-red (IR --the opposite end of the color spectrum from UV) was the heat producer.

Very possibly, I don't know, that's why I'm asking the questions here and trying to get to the bottom of what is marketing BS and what is actually useful to the consumer.

[BuaBS]

Heat reflective paint ? Why does a mirror or shiny Aluminium/steel or even a highly reflective Silver coin and glass get very hot in the sun ? Aren't they supposed to reflect the whole range from infra red to ultra violet ? ( or let it all through , in the case of glass).

Why would paint be different ? A white car in the sun may not get as hot as a black one , but not that much difference.

I have 2 roofs over my head , and can still feel the sun's radiant heat.

[chiang mai]

As far as I can tell, UV does not generate heat but it's still important to reflect it because it can penetrate the roof and it is harmful to humans.

Long range IR however does however appear to store heat in roof tiles which then radiates heat.

An interesting conclusion on this here:

"Ceramics are used on the shuttle because they absorb heat and evenly distribute it, not because they are a good insulator. What keeps the interior of the shuttle from becoming an oven during reentry is a blanket made of Nomex fibers between ceramic tile and the interior of the shuttle. The Nomex fibered blanket is the actual insulation, not the ceramic tiles. This was never more apparent than with the Columbia shuttle disaster.

When Columbia shuttle lifted off, a piece of foam from the external fuel tank broke off and damaged a protective ceramic tile on the leading edge of the left wing. When the shuttle reentered Earth’s atmosphere the heat was not evenly distributed over the ceramic tile surface of the shuttle. This heat imbalance caused reentry plasma (super heated gas) to penetrate the protective ceramic tile and caused the explosion.

When it comes to roofing, the darker the surfaces color the more resistance to solar radiation, the more the resistance the greater the heat gain. The only “magic” in an energy efficient “cool roof” coating/ paint is the color, period! A white colored surface reflects maximum amount of solar radiation, second to a gold mirror.

What makes a roof coating/ paint different from a standard latex paint is the resin. Elastomeric resins are designed to be extremely flexible. This flexibility is very important on a roof because the coating/ paint must expand and contract with the roof surface. If it did not expand and contract with the roof, it would crack and eventually peel off.

The only “magic” in an energy efficient “cool roof” coating/ paint is the color, period! A white surface reflects a very large amount of solar radiation. Ceramics offer very little if any insulative value.
Still not convinced? Here what the experts have to say:

Do ceramic modified roof and or wall coating offer any additional “insulative” value to a paint or coating"?

“No way can solar reflectance be converted into an equivalent

R-value.”
T.W. Petrie
Sr. Research Engineer
Oak Ridge National Laboratories

“I don’t believe that a 20 mil thick material would provide an

R-value.”
Gordon Hart
Consultant with Artek, Inc.

“A coatings thermal resistance is negligible.”
Heinz Poppendick
Geoscience, LTD

“The reflection of heat has nothing to do with the real insulation

R-value.”
Dr. Ray Taylor
Perdue University

“In side-by-side tests of white coatings with and without ceramic beads, where the coatings were roller applied on smooth surfaces, we have not seen any significant differences in performance of the two types.”
Ceramic Coatings Installed on Federal Buildings at Tyndall Air Force Base

United States FTC vs. Kryton Coatings International

The

Federal Trade Commission

took legal action against a coatings manufacturer that made outlandish claims about its ceramic coatings “insulative value”.

• Perdue ceramic report
• Ceramic coatings
• FTC vs. Kryton
• T.W. Petrie
• Gordon Hart
• Geoscience

http://energy-seal.com/ceramic-coatings/

You might argue that the above is simply a bun fight between the paint companies and the solar insulation business, dunno.

[chiang mai]

Heat reflective paint ? Why does a mirror or shiny Aluminium/steel or even a highly reflective Silver coin and glass get very hot in the sun ? Aren't they supposed to reflect the whole range from infra red to ultra violet ? ( or let it all through , in the case of glass).

Why would paint be different ? A white car in the sun may not get as hot as a black one , but not that much difference.

I have 2 roofs over my head , and can still feel the sun's radiant heat.

When we talk about heat reflective paint we intend to mean paint that reduces heat levels, not eliminates them.

[Naam]

I could be totally off base, but isn't UV blocking more for reducing color fading than for heat reduction? I thought infra-red (IR --the opposite end of the color spectrum from UV) was the heat producer.

we have a winner!

[Naam]

As far as I can tell, UV does not generate heat but it's still important to reflect it because it can penetrate the roof and it is harmful to humans.

UV can't penetrate any concrete tiles nor any other dense medium no matter how thin (e.g. metal foil as thin as 1µm). moreover, a certain amount of UV is required for the body to produce Vitamin D. overdoses can cause skin cancer.

[Naam]

FWIW the cost of painting the roof is quite low, about 7k for the paint and 9k for the labour.

16k Baht wasted!

[chiang mai]

I think that pretty much nails that one, for me at least, the answer seems to be, no heat reduction benefit to be gained by painting my roof.

Thanks to all for your input.

[Naam]

I think that pretty much nails that one, for me at least, the answer seems to be, no heat reduction benefit to be gained by painting my roof.

Thanks to all for your input.

what about inviting those who have saved you 16,000 Baht for an icecold beer?

[chiang mai]

I think that pretty much nails that one, for me at least, the answer seems to be, no heat reduction benefit to be gained by painting my roof.

Thanks to all for your input.

what about inviting those who have saved you 16,000 Baht for an icecold beer?

That's a great idea, you're all welcome for as much free ice cold beer as you can drink, tomorrow.

[Pacificperson]

I would suggest a simple experiment. Buy three cement tiles. Paint one white, paint one dark and leave one unpainted. Put them in in a sunny spot in your yard and go out at about 2pm and check their temperatures. The barefoot test works well.

[chiang mai]

I would suggest a simple experiment. Buy three cement tiles. Paint one white, paint one dark and leave one unpainted. Put them in in a sunny spot in your yard and go out at about 2pm and check their temperatures. The barefoot test works well.

A reasonable test although you may wish to read the OP again, the issue is paint attributes not paint colour.

[passingas]

We have 2 of those very large umbrellas....one dark blue and the other one white (cream colored now) and being hair folically challenged, I can certainly tell when I am under the lighter colored one! Why do you think all the robes the men wear in the middle east are white? But then....why the hell are most of the womens clothing black???? Oh....right. pg

[Pacificperson]

I would suggest a simple experiment. Buy three cement tiles. Paint one white, paint one dark and leave one unpainted. Put them in in a sunny spot in your yard and go out at about 2pm and check their temperatures. The barefoot test works well.

A reasonable test although you may wish to read the OP again, the issue is paint attributes not paint colour.

I am sorry, but I was responding to this in the OP "So what that sensibly leaves is repainting an old dark coloured roof with a modern dark coloured paint, question is, will that provide any real benefit?" The short answer is no.

If you want to cool your roof paint it white, but realize that the paint will be nowhere as durable as your cement tiles.

[55Jay]

On Guam, my roof was flat, concrete, and it had the black algae growth, and the house was very hot. Had it cleaned and painted white again, and the difference inside was very noticeable.