Does cool roof paint actually work on Metal buildings? RESULTS POSTED,

[AV8R4AA]

Hello Garage men,
I have a 50 X 30 metal building. It has a low slope pitch roof. The color is the very
popular light tan. I have well insulated spray foam on the walls and ceiling. The doors
And windows are all well insulated also. I have installed a 4 Ton Mr. Cool minisplit.
i have 2 heads that are on the 50 foot wall. Each head unit is 2 ton. i live in Dallas Texas.
for those not familiar with this area, it’s about a 45 minute drive to the center of the Sun.
it gets VERY hot here. My question is I am interested in using a heat resistant white paint
for the roof of the building. It’s the Tan color now. My shop stays relatively cool in the Summer.
by that, it’s about the same temperature as you keep your home at. In the late afternoon, the temperature
will begin to rise. The AC unit is maxed out and can not keep up with the heat load.

it’s usually very hot and sunny here. Has anyone painted their metal building with a modern
”cool roof” paint. I have seen in the desert Southwest, many building have white color on their roofs.


thanks

 

[BurtEggley]

basic physics is black absorbs most heat and gives it back off quickly at night. White absorbs less heat and gives it off slower. A white roof will be cooler than a tan roof but I don't know if it is worth the cost. Before I'd spend the money I would either have an energy audit done, or get a thermal camera and see where the heat is actually coming from.

 

[dscheidt]

when you need a new roof, get a white one. It won't cost extra. In the meantime, spend your money on insulating the roof. how thick is your foam?

 

[gte718p]

If your roof was black, you would see a substantial difference. Going from tan to white I doubt you will see a significant difference.

 

[nbpt100]

You can do a small test that will cost you very little. Get a piece of metal roofing or a piece of steel similar to your metal roofing. Cut it in half so you have 2 equal sizes. Paint one the tan color of your roof. Paint the other piece white or get some of that special roofing paint you mentioned to be more accurate. It may have reflective properties that impact the heat absorption. Maybe you can get a free or cheap sample from the vendor. Put them next to each other so they get the same Sun exposure. Measure the temperature with a non contact thermometer every several hours through the day. A day with no wind would be the best test case. If you get a 8+ degree delta for several 4 or more, it seems it would be very worth it to me. However, I am not sure where the benefit diminishes. I am assuming this, but it seems to me that painting the roof would be much cheaper than adding insulation. Maybe someone with direct experience building energy savings can chime in on this.

 

[rlitman]

basic physics is black absorbs most heat and gives it back off quickly at night. White absorbs less heat and gives it off slower...

Not really, and we don't care about what's happening at night. Black is going to absorb more heat during the day, and both black and white are going to emit it at similar rates. Anyway, emissivity is less about color and more about chemical makeup of the paint, and if a coating manufacturer want's to upcharge for a special color's energy savings, they'd better back that up with real numbers. So we need to know the coating in question to compare, because not all white paint is created equal.

My own personal experience with this:
At work, we have a highly energy efficient white PVC roof. All good, though you NEED sunglasses to be up there or expect to be snow blind. But the metal hatch door was red, and in the summer, the top edge of the hatch sill (which is in the shade of the hatch) would get hot enough to burn your hands. Not so fun when you need to hold onto that edge to climb onto or off of the roof ladder. A few years back we painted the hatch with Bus-Kote paint. It's a rubberized white paint designed to apply to the roof of motor-homes to reduce interior temperatures in the sun, and man has that worked to keep that steel edge down to comfortably grippable temperatures.

 

[nbpt100]

I have noticed that many of the Brown UPS truck have painted the roof white. For obvious reasons. It would be interesting to know what paint they used. Right on Rifleman, there is more to emmisivity and heat absorption from the Sun than color but I think color has to be pretty dominant. They always seem to choose some shade of white or light silver.

 

[rlitman]

I have noticed that many of the Brown UPS truck have painted the roof white...

I think those are a translucent fiberglass so they don't need interior lights during the day. Not actually painted (at least, they didn't used to be).

Metallic silver tends to have a low emissivity. Good on the underside of a roof (or interior coating of a window), but terrible on the top. Though aluminum is great for UV protection. Reflectivity isn't a very helpful property. If you've been to a garage sale and picked up a mirror or anything shiny sheet metal sitting in the sun, you'd notice how hot it gets, while a white sheet of paper (or even black paper for that matter) stays much cooler.

The problem with "white" is that IR is outside of the visible spectrum, so what appears to be white to our eyes isn't necessarily thermally white. Different pigments have different emissivities as well as costs, plus there's the fact that your eyes can't really tell how much pigment is in the coating, so if one coating has double the barium sulfate, it might appear exactly the same as one with half as much.

 

[readhead]

For the last 10-15 years pretty much all of the metal panel manufacturers have been using a reflective component in their coatings. It isn’t noticeable to the eye but it is there.

If you know who provided the panels you should be able to look at the specs for the coating. I don’t believe that you will see a difference.

 

[AV8R4AA]

Here is my shop. The tan color is the same color as the roof. The side you are looking at,
is West facing sunset side. For clarification, the garage
to the left is fully insulated. There is a mirror image garage on the other end.
both of those DO NOT get AC. The 30 foot wide dimension is from the wall of the lean to,
to about 2 feet LEFT of the white man door. There is no insulation on the lean to.
The AC is Mr. Cool 4 ton twin compressor.
i have 3 inches spray foam on ceiling and 2 inches on the walls.
The other pictures show the inside of my shop.

 

[rust in the eye]

No expertise to offer on roof color but I'm diggin' your E39 touring!

 

[nbpt100]

I think those are a translucent fiberglass so they don't need interior lights during the day. Not actually painted (at least, they didn't used to be).

Google has produced this answer below...... I have also seen other articles that contradict the cooling effect. Maybe that is why some have the Flettner Ventilator. How ever that works?

UPS Truck Roof Color​

UPS trucks have white roofs, but they are not painted in the traditional sense. Instead, the roofs are made from a translucent material that appears white.

Purpose of the White Roofs​

• Temperature Control: The translucent roofs help reduce the need for cooling inside the truck. This is important because the cargo area can get extremely hot, sometimes exceeding 120 degrees Fahrenheit.
• Natural Light: The white roofs allow natural light to enter the cargo area, which helps drivers locate packages without needing additional lighting during the day.

Additional Features​

• Flettner Ventilator: UPS trucks are equipped with a wind-powered ventilator on the roof. This device helps circulate air within the cabin, keeping the drivers cool, especially since the trucks do not have air conditioning.

The design choices for UPS trucks, including the white roofs, are part of the company's strategy to enhance efficiency and reduce operational costs.

 

[rlitman]

...Maybe that is why some have the Flettner Ventilator. How ever that works?...

It's just a turbine that pulls hot air from under the roof as the truck drives. I'd expect them to have some sort of intake scoop that directs fresh air onto the driver too.

 

[BurtEggley]

rlitman, let me share from a physics journal:

Black surfaces emit more heat (radiation) than white surfaces. According to Kirchhoff’s laws of thermal radiation, good absorbers are also good emitters, and black objects absorb more heat and light energy, causing them to radiate that energy faster than white objects.
Physics Stack Exchange +2

Key details regarding black vs. white heat emission:

• Emission Rate: Black materials radiate heat faster, meaning they cool down more quickly in the dark compared to white.
• Absorption: Black absorbs all visible light and converts it to heat, while white reflects it, leading to higher temperatures on black surfaces.
• Context: While black surfaces heat up more in the sun, they are also more efficient at releasing that heat, making them superior for cooling if they are not in direct sunlight.
  Physics Stack Exchange +6

 

[rlitman]

rlitman, let me share from a physics journal:

In physics, "black" has a definition. It is NOT a paint color.

 

[bonneyman]

OP, I don't have any experience painting metal roofs, but did paint alot of roof mounted ductwork. (Any little bit to help reduce heat infiltration helps with the A/C, right?)

I found that all of the "Kool Coat" type roof coatings had inferior adhesion to galvanized metal duct. The only way I found was to "etch" the surface with an acid - that helped adhesion. But it also made the underlying sheet steel susceptible to rust. The best compromise I found was wiping the galvanized ducts with vinegar, and let them thoroughly dry before paining. The mild acid did etch the surface, wasn't strong enough to penetrate all the way though the zinc, and gave better adhesion. One job I did with new ductwork and the above procedure was still intact about 5 years later. Anecdotal evidence, I know. But worth a look see.

 

[Racer_X]

I have well insulated spray foam on the walls and ceiling.

I am interested in using a heat resistant white paint
for the roof of the building.

Perhaps some clarification is due here.
Did you actually insulate the ceiling, or do you not have a ceiling and what you actually insulated was the underside of the roof?
If the former, in most cases you would be better off using a vapor barrier on top of the ceiling with a lot of blown-in insulation on top of it.
If the latter, you would gain a lot more by installing and insulating a ceiling than trying to make the roof more reflective.

But, to address your original question: I believe you will get much better energy efficiency from an elastomeric coating than a simple paint.

 

[readhead]

The pictures don’t show a ceiling. The underside of the roof was sprayed.

 

[rsparks64]

Is the garage door dark brown like the one on the right? Paint that for sure if it is facing west.

 

[BurtEggley]

In physics, "black" has a definition. It is NOT a paint color.

yes, black is considered a lack of color and white all the colors. An artist will still call black and white colors.

 

[Racer_X]

The pictures don’t show a ceiling. The underside of the roof was sprayed.

Thanks. Somehow I blew right on past those photos. No room for a ceiling in that garage.

 

[DGersic]

Totally different environment here. My garage has a “flat” roof (very slight pitch). Wood framed, with styrofoam insulation in the walls, ceiling is not insulated. Northern Illinois, so temperature swings from -20F winter to 110F summer. Roof is torched down rolled material.

The guy that put the roof in told me that it would last longer if I painted it about every five years with the aluminized trailer roofing paint. So I’ve been doing that. Roof is about 25 years old now, holding up well.

i do notice some reduction in summer heat after painting. Not a lot.

I actually get a bigger reduction by sticking silver bubble foil in the south facing garage door windows.

Whether you’d see any difference on your roof, I don’t know. I’d guess a slight reduction, maybe enough to notice, but probably not a huge change.

 

[AV8R4AA]

Well, it’s all done with 2 coats of Elastomeric..

35 gallons of coating later, it’s done. I was expecting a white out up there. Actually it looks very nice.
Been windy AF here. Low 70 degree w low humidity. Tonight is a freeze warning. No real tests done.
it does look very nice and I know by testing on 5be inside its cooler. Used to be just under 10 degrees
Warmer on the ceiling on a sunnny day. Now it’s 2 to three degrees COOLER than the walls .
it won’t be long till the Sun comes in with a Vengeance. With the AC minisplit running will be the
better test. So far, I feel I is going to give a modest improvement. AC should recover faster and use less power to stay cooler.

 

[tinmanwpk]

Love your longroof! Longroofs Rule!

 

[AV8R4AA]

Pics from the neighborhood

 

[bluedog225]

Well, it’s all done with 2 coats of Elastomeric..

35 gallons of coating later, it’s done. I was expecting a white out up there. Actually it looks very nice.
Been windy AF here. Low 70 degree w low humidity. Tonight is a freeze warning. No real tests done.
it does look very nice and I know by testing on 5be inside its cooler. Used to be just under 10 degrees
Warmer on the ceiling on a sunnny day. Now it’s 2 to three degrees COOLER than the walls .
it won’t be long till the Sun comes in with a Vengeance. With the AC minisplit running will be the
better test. So far, I feel I is going to give a modest improvement. AC should recover faster and use less power to stay cooler.

Late to this post. In Austin. I’ve painted a metal roof 20 years ago with Henry’s cool roof. It’s been great. Scrubbed with dawn and floor broom first. No peeling.

You can put a hand down in the stuff when it’s 105 eff. Also painted top of convex boxes. No regrets.

It will get spotty black with lichen? Or some stuff. Bleach might take care of it, but I haven’t bothered.

 

[AV8R4AA]

Today’s readings. Outside air temp solid 88 degrees. Zero clouds Sun knee
all day. I started the AC on when the inside air temp was 73. Without much effort
The mini splits easily held an inside temp of. 64.
needless to say. EXTREMELY satisfied with this modification.

 

[ipgenie]

It is surprising the difference a lighter color makes. My pole barn was 20yrs old when I added onto it. The existing roof metal was galvalume, same as the new roof, but was a little dull and slightly darker due to exposure.

Working on the roof installing solar panels, I couldn't leave a bare hand on the older roof because it was so hot. The newer shiner side was warm but much cooler and not a problem to touch for any length of time.