Scientists Reveal Roof Coating That Can Reduce Surface Temperatures Up To 6C On Hot Days (theguardian.com)
- Reference: 0179918980
- News link: https://science.slashdot.org/story/25/10/31/014230/scientists-reveal-roof-coating-that-can-reduce-surface-temperatures-up-to-6c-on-hot-days
- Source link: https://www.theguardian.com/environment/2025/oct/31/scientists-invent-roof-coating-reduce-indoor-temperatures-hot-days
> Australian scientists have developed roof coatings that [1]can passively cool surfaces up to 6C below ambient temperature , as well as extract water from the atmosphere, which they say could reduce indoor temperatures during extreme heat events. One coating made from a porous film, which can be painted on to existing roofs, works by reflecting 96% of incoming solar radiation, rather than absorbing the sun's energy. It also has a high thermal emittance, meaning it effectively dissipates heat to outer space when the sky is clear. Its properties are known as passive radiative cooling. [...]
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> In a study, published in the journal Advanced Functional Materials, the researchers tested a prototype for six months on the roof of the Sydney Nanoscience Hub, pairing the cool paint with a UV-resistant topcoat that encouraged dew droplets to roll down into a receptacle. As much as 390 milliliters per sq meter per day could be collected for about a third of the year, the scientists found. Based on that water capture rate, an average Australian roof -- about 200 sq meters -- could provide up to 70 liters on days favorable for collecting dew, they estimate. [...]
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> In well-insulated buildings, a 6C decrease in roof temperature "might result in a smaller fraction of that cooling being reflected in the top level of the house," [said the study's lead author, Prof Chiara Neto of the University of Sydney], but greater temperature reductions would be expected in most Australian houses, "where insulation is quite poor." She said the coating could also help reduce the urban heat island effect, in which hard surfaces absorb more heat than natural surfaces, resulting in urban centers being 1C to 13C warmer than rural areas.
The researchers found that the prototype coating was comprised of poly(vinylidene fluoride-co-hexafluoropropene), which is used in the building industry but was "not a scalable technology going forward" due to its environmental issues. However, they are now commercializing a water-based paint with similar performance that is affordable and environmentally safer, costing about the same as standard premium paints.
[1] https://www.theguardian.com/environment/2025/oct/31/scientists-invent-roof-coating-reduce-indoor-temperatures-hot-days
Removable for the winter? (Score:2)
This sounds great in the summer. Am I going to pay way more to heat my house in the winter?
Re: (Score:2)
Right, that's the problem. I believe it takes more energy to heat a house from 30 to 70 degrees in the winter than it does to cool one from 85 to 70 in the summer. Obviously there are more variables at play.
Re: Removable for the winter? (Score:2)
You don't like heat in the summer, why use it in the winter. I'm sure you can sell the ice from all the condensation to offset the costs. You should probably disclose it will cause some form of awfulness in 20 years time what we weren't aware of today.
Re: (Score:2)
If that's the concern, you may want to invest in insulation.
Prior Art (Score:5, Funny)
"White paint"
Re: (Score:1)
I know, right? In my last house, I got the lightest shingles I could; they were a light grey. I believe it saved me a significant amount in cooling costs. I never saw the point of black roofs in the high desert but ... folks have to have their 'eastern style farmhouses' even in wildly different climates.
Re: (Score:1)
Fair enough, fancy white paint .
Re: (Score:2)
That raises a fun question - what impact on global temperatures would each have? It sounds like this coating would reduce the amount of solar heating the planet experiences, whereas solar panels might increase it.
A word of warning about "roof paint" (Score:5, Informative)
A word of warning about roof paint.
Years ago Florida Power and Light (FPL) offered rebates and encouraged people to paint their roofs white to reflect sunlight and lower bills. Many gullible people took the bait.
Then the problems started. The paint would shrink, damaging the roof, letting water in. it was a disaster. Even tile roofs were affected. Water leaks. Disaster. Ruined houses. Lawsuits.
I'd be very leery about doing any such thing to a house. Maybe if the material is engineered from birth to be reflective, but as a coating? Fuck that.
There's always someone (or large groups of someones) trying to gyp people using "The Environment" as bait.
[1]https://www.palmbeachpost.com/... [palmbeachpost.com]
[1] https://www.palmbeachpost.com/story/business/2010/12/31/fpl-sued-over-roof-painting/7321023007/
Re: (Score:3)
You can get light-colored shingles instead of white shingles to get most of the way there.
Re: (Score:2)
*instead of black shingles.
Re:A word of warning about "roof paint" (Score:4, Informative)
For those of you confused about how a thin coating of paint could possible damage shingles, it wasn't standard paint. It was a stretchy elastometric paint that's specifically banned by the state's building codes for use on asphalt roofs. It damages them in multiple ways. First when the paint shrinks it's apparently strong enough to cup/curl the shingles. Second, when water gets under the paint it becomes trapped and rusts away the roofing nails far, far faster than normal.
Re: (Score:2)
There are rubberized coatings with aluminum in them which don't shrink and are fine on a roof. I would imagine the coating would go on something like this rather than on shingles
Re: (Score:2)
As always, get the right paint for the job. There are reflective paints specifically designed for a variety of roofs. I painted the roof of my bedroom (a large dormer set in a tiled slanted roof) with the stuff, and it did help bring the temperature in the room down in summers. The biggest problem: on a flat roof, the paint gets dirty, and fast, losing a lot of its heat reflecting properties. Waste of €150 and an afternoon of work.
oh I've heard of that (Score:2)
it's called WHITE PAINT
it's an incredible new innovation, you should try it!
Re: (Score:2)
It's not just white paint. Being highly reflective is only 1/2 the equation. There are certain materials with extremely high IR emmissivity which will actively cool the structure they are applied to. Not only that, but it must be a frequency of IR that the atmosphere is transparent to. Whether such coatings are ready for widespread use is up in the air.
This guy has several videos about trying to homebrew such a coating [1]Making Infrared Cooling Paint From Grocery Store Items (w/Novel CaCO Microsphere Syn [youtube.com]
[1] https://www.youtube.com/watch?v=KDRnEm-B3AI
Re: oh I've heard of that (Score:2)
Sorry, FANCY white paint
Sounds great but.... (Score:1)
Let me guess, it will have an ROI of 30 yrs, voids your roof warranty, and legally requires a licensed installer. No thanks, no excuse me while I go burn some tires. Maybe whatever is after us will do better. Maybe their governments will be helpful.
boat (Score:2)
a poorly insulated structure that could use passive cooling and needs to make fresh water - sounds like a boat could use this.
6C is ok but not amazing (Score:2)
Worth bearing in mind that solar panels reduce roof temperatures by 20C+, and cause materially larger drops in heat flow into the building and HVAC use.
Obviously, the paint can cover the whole of a building's roof, and potentially its entire surface, while solar only covers a portion.
And I'm all for both-and. But it's important to understand that this 6C is helpful but not earth shattering
Metal Roofing (Score:3)
Years ago I owned a highly renovated one room brick schoolhouse (ground-source geothermal heat pump, radiant floor heating, two stories). The attic was cooled with a power vent (at some temp (I think it was like 115f) a central fan would come on and push hot air through a single top vent and pull it up through the eves). In the summer almost every afternoon when it was sunny you could hear the power vent come on.
About 10 years into ownership I installed a [1]metal roof [edcoproducts.com] with a slate-like look. The company claimed that the roof would make the schoolhouse more energy efficient by reflecting a lot of the incoming solar heat. Well, the power vent *never* came on again in the 3 years after I installed the roof. At one point I even checked to make sure it was still working. In fact the A/C would only come on maybe a couple of times per summer instead of almost every day.
The install cost was about double what shingles would be, but next time I have to install a roof I'm doing the same thing. These things have a lifetime non-prorated warranty unlike shingles which are prorated. I don't have the house anymore and I'm not affiliated with the company in any way.
[1] https://www.edcoproducts.com/
So,... (Score:2)
So, in other words, um, paint the roof white.
So if I make the shape of a parabolic reflector (Score:2)
out of fiberglass and paint it with this paint, then 96% of the incoming solar radiation will go to the focus. I can boil water at the focus and run a steam turbine. Right? Didn't Sandia come up with a catalyst from which a block of metallic foam could be made that, at a couple thousand degrees, would split water? So, if I pump the limp steam from my turbine through the focus of a second reflector...
Does it also make julian fries? (Score:2)
I would have been fine with a highly reflective roof coating, but once they start adding the water condensation, it begins to sound like an infomercial for tons of other failed "solar-based water recovery" projects.
Re: (Score:2)
Speaking of solar, it seems like it would make more sense to cover as much of the roof as possible with it. Use reflection where you can't install PV or water heating.
If it's cheap and durable enough, maybe it could be used with solar as a reflector.
Re: (Score:2)
Yup, you're adding a thermal control system (TCS) that generates power as a side-effect of its shielding your roof panels. Seems like a better way to do things than a fancier way of painting your roof white.
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There's a huge difference between the cost of installing panels on your roof and tying them into your electricity vs. just painting it.
If I could snap my fingers and get rooftop solar I would, but I think, what if some of all those new holes in my roof were to leak? And my roof is 20 years old, I guess you have to un-do all the solar to replace the shingles?
Re: (Score:2)
What's wrong with collecting condensation? Seems like the challenge is making it cheap enough to be commercially viable, a big hurdle, but it's not like pseudoscience or something.
The Man in the White Suit (Score:2)
Have they done any long-term testing yet? How long does this paint last, is it cost-effective?
More details omitted by The Guradian -
[1]The company created to commercialize the technology [dewpointinnov.com]
[2]Press Release from the University of Sydney [sydney.edu.au]
[1] https://www.dewpointinnov.com/technology
[2] https://sucs.sydney.edu.au/stories-from-our-research-themes-self-assembled-nanomaterials-san/