Sheet metal roofing is gaining ground in my area (USA Southeast). There's a little catalog of colors available from every supplier, they all cost the same so just pick one! ... most people seem to like dark red, dark brown, and black; still. I cannot comprehend it.
15 years ago I put a white, metal roof on my house, my summer cooling costs are half or less my neighbors' with the shingled roofs, and they've replaced their shingles in that time frame.
The crop duster aircraft also use my house as a navigation marker and we get to see them frequently.
I don't think most people are going to retrofit metal roofs onto asphalt shingle houses because the house are 30+ years old and no one is sure how long they are going to live there and what the house is going to be worth. A metal roof on a million dollar house is no big deal but on 200-300k structure with unknown lifespan to the owner? hardly makes sense. Same cost benefit as solar panels really. The benefit is over 15-20+ years usually where many people can't even justify spending a point on their mortgage because they'll be out in less than 6 on average.
I'm struggling with the same decision right now. I have a small (2k sqft is small in this area) 300k structure and I don't know whether it will be worth lot value in 10-15 years or still worth 300k+inflation+value additions. The surrounding neighborhood with 1-2million dollar structures says "lot value" even if it's pristinely maintained.
I'm talking mobile homes and an area with an average home value of under $100k. One of the big selling points of metal roofing here is durability, i can point to another neighbor (3mi down the road) whose house was built sometime in the 30s but is now a more valuable redneck shotgun shack because of the (burgundy) metal roof. Edit: come to think of it, it may have been tin roofing originally; it had been shingled before the metal tho.
It sounds like your area is one where the location and the market determine value far more than anything on the land, so treat it as "build to suit" commercial property and assume anything built on it is disposable.
Older rural houses are getting new metal roofs out here all the time. It's actually a really common trend out this way.
It is one of those upgrades you can add to a house that actually retains its value when you go to resell... Most metal roofs have lifespans that are minimum double that of shingles and, per your example, solar panels.
Of course, most people buying in the countryside aren't intending on moving out in fewer than 6 years; 7 minimum is generally considered the break even point around here.
How loud is it in your house when it rains/hails? I have a metal awning covering my back porch, and it is painfully loud during hail (granted not that frequently). Does the attic insulation help deaden/dampen the sound?
I have a metal roof and it's no louder than the shingle roof in my childhood home. I think the big difference vs your awning is that my roof is fully supported by the home's sheathing and is screwed down in many places. This limits the opportunity for the metal to resonate.
It's noticeable; not much louder than a shingle etc roof tho because we have a "R9" fiberglass insulation layer between the roof studs and the metal. A retrofit roof would have roof decking to help with that, and you could probably arrange similar insulation too.
Its nowhere near as loud as an aluminum skinned mobile home.
Speaking as a person presently engaged in roof repair.
Not just black. Dark, fractulate, nigh-furry extremely light-absorbing black.
It's like they designed it to soak up sun and get hot. So hot that it starts to melt. So hot that you need to use special nails so they don't pull through the half-melted black goo.
Farther north in Ontario, the heating season is way longer than the cooling one, so it does kind of make sense to optimize for heat retention.
The other side is that having a roof which warms itself in winter is better for reducing snow accumulation. Though that’s also less of a consideration for a slippery metal roof.
> Farther north in Ontario, the heating season is way longer than the cooling one, so it does kind of make sense to optimize for heat retention. The other side is that having a roof which warms itself in winter is better for reducing snow accumulation.
So much wrong here. Asphalt shingles neither "retain heat" nor "warm themselves." You really do not want either property in a roof covering in a climate where it snows because that will cause the formation of ice dams. If you have snow on your roof, it obviously covers the black shingles - now you have a white roof anyway. If it is winter and you do not have snow on your roof, it is still not worth it - solar irradiance at 50° latitude (approximately Timmins, Ontario) is going to be about a factor of 7 less in January than in June. You are much better off with a white roof in northern Canada to reduce peak heat stress in the summer, which will continue to get worse and worse due to greenhouse gasses.
Yes, plus while every Canadian home has heating, not all homes have air conditioning. Optimizing the roof for the summer makes a lot of sense.
We had a steep roof in the Okanagan which rose about 20ft to the peak. That extra room was problematic in winter for heating but a life saver in the hot, sunny summer. The loft was unbearable during the summer.
A neighbor with a low roof would run a sprinkler on his roof all summer long, that's how bad the heat would get.
Interesting, that's a good point about the height of the sun in the sky!
My previous house already had a light colored metal roof, and my current one is shingles that are not due to be replaced for another ten years or so, but these are good things to think on.
Low sun angle in the winter vs summer means a bit more thought needs to go in to making the decision of whether net retention or net reflection is preferable. My strategy is to cover the entire roof in solar panels and to try to find useful things to do with the electricity. Sadly that does not send much power back into space, and my panels are only 22% efficient.
Plus, in practice, you'll want a ton of insulation between the interior space and the roof anyway. So if you've done a good job there it's kind of a moot point wrt/interior comfort. But sending that power back into space rather than absorbing it can reduce thermal cycle stress on the roof and keep the outdoor space nearby cooler.
Commercial buildings have white membranes on the roof. They’re flat so you can’t see it from the ground.
Residential buildings usually have sloped roofs visible from the ground so the roof color is an architectural choice. Depending on the locale, current building codes can require enough roof insulation that very little heat flows through the roof in either direction. The insulation has an added benefit of preventing heat loss in the winter.
I live in Florida and see black and dark brown tar shingles installed at least 95% of the time. I even live in a hurricane-prone area and it's surprisingly rare to see a metal roof installed.
Tar is black. (Zinc-)Titanium dioxide paint is an extra expense; using barium sulfate is crazy as barium is toxic. Problem of dirt. The money would be better spent on alternative sources of power besides fossil fuels.
Soluble barium compounds are toxic. Barium sulfate is nearly insoluble and has very low toxicity. People routinely drink the stuff as a radiocontrast agent before getting an x-ray.
Even if some of the sulfate will be reduced to sulfide, making the barium soluble, the sulfide will be oxidized again by the air after some time, immobilizing any remaining barium.
The barium that might have leached will be precipitated by the carbon dioxide from the air into barium carbonate.
Any form of soluble barium left in the environment will end soon as either barium sulfate or barium carbonate, which are insoluble, thus non-poisonous.
Barium is one of the least dangerous metals with high atomic number. You have to do something really stupid and deliberate with it in order to be able to poison anyone.
Titanium dioxide a.k.a. titanium white is a different white pigment.
Most white paints used nowadays contain titanium white.
Nevertheless, many white plastics contain other white pigments instead of titanium white. Titanium white itself is inert, but when it is exposed to the sun light it can catalyze the destruction of organic substances like plastics or paint binders that have not been selected to be resistant to this.
So when using titanium white outdoors, the white paint must be specified as UV resistant.
I have not heard about paper that uses titanium white.
That might be due to the higher cost of titanium white, which might be too much compared to the cost of paper.
Barium Sulphate is nothing new. It's used widely on integrating spheres, and I have painted some myself. The video that they show painting it on a piece of glass and comparing that to commercial paint is very misleading. It is not the easiest thing to work with, and is not at all durable. Once on a surface, it dries to a white chalky texture and just touching it will get it dirty and diminish its reflective properties. You would have to have so many additives to make it weatherproof and durable enough for outside that it would end up being no better than standard white paint. When I used it to coat an integrating sphere, it had to be thinned with 100% alcohol (impossible to obtain unless your a pharmacist because all non-drinking alcohol is poisoned so you can't get drunk without paying a liquor tax) so that all the thinning agent would dry out without leaving any residue behind. Anything left in the Barium Sulphate will diminish its reflectivity.
That's too dismissive take of the paper. The whole innovation here is the formulation of BaSO4 based acrylic paint that retains most of the reflective properties while being practical as a paint instead of using pure BaSO4 which would be too fragile.
Select quotes:
> Overall, the BaSO4 film reached a solar reflectance of 97.6% and an emissivity of 0.96 in the sky window (Figure 2b). Its solar reflectance is significantly higher than that of the commercial white paint (400 μm thickness), especially in the UV and NIR ranges. [...] For the BaSO4 paint, a standalone paint sample of 400 μm reached similar optical properties (98.1% solar reflectance, 0.95 sky window emissivity)
> To demonstrate the reliability of our BaSO4 paint, we conducted abrasion test, outdoor weathering, and viscosity characterizations. [...] The BaSO4 paint reached a wear index of 150, comparable to the commercial exterior paint with a wear index of 104. The weathering test was conducted by exposing the BaSO4 paint outdoors for 3 weeks (Figure 4b). The solar reflectance remained the same within the experimental uncertainty.
3 weeks of outdoor exposure means absolutely nothing. The minimum for most paint manufacturers is at least 2 years in a sub tropical area like Florida.
> Barium Sulphate is nothing new (…) It is not the easiest thing to work with, and is not at all durable
I only read the abstract, but it seems like they’ve considered your stated limitations.
“we experimentally demonstrate remarkable full-daytime subambient cooling performance with both BaSO4 nanoparticle films and BaSO4 nanocomposite paints”
“providing great reliability, convenient paint form, ease of use, and compatibility with the commercial paint fabrication process.”
Also, you can always get commercial licenses for restricted substances like ethanol; that’s not an actual problem for house paint jobs.
In many (most?) other countries pure ethanol can be bought easily over the counter, and where I live even at any gas station. Yes, you could drink the ethanol from the gas station here (it has no additives, but better dilute it first), but nobody does because the cheapest cachaça isn't any more expensive.
It's a peeve of mine. One of those inconvenient truths of history that people don't like to talk about or don't know about. We (the US government) started poisoning alcohol WITHOUT TELLING PEOPLE. The fact that the practice continues is ridiculous.
My father worked for Saudi petrochemical company SABIC in the 80s. Some bright spark decided to go to the ethanol factory and get some high purity hooch from a tap and make an end run around Saudi alcohol restrictions. Unfortunately he made a wrong turn and went to the methanol factory instead…
I can't talk for all countries, but in Austria the cheapest alcohol you can buy is "Spiritus", and they add something to make it taste bitter. You can use it as fuel, for degreasing, cleaning, etc.
You can get pure, food grade ethanol at the pharmacy.
> 100% alcohol (impossible to obtain unless your a pharmacist because all non-drinking alcohol is poisoned so you can't get drunk without paying a liquor tax)
Only ethanol needs to be denatured. You can easily get 99.953% pure isopropyl on Amazon, and it isn't poisoned because isopropanol is already poison.
I mean ethanol is denatured by adding methanol, which is also an alcohol, so technically the mixture is still 100% alcohol :-) Except for drawing water due to being hydrophilic etc.
They don't add methanol. You can check this easily by looking up a Safety Data Sheet. They will add a bittering agent to make it extremely unpalatable.
> 100% alcohol (impossible to obtain unless your a pharmacist because all non-drinking alcohol is poisoned so you can't get drunk without paying a liquor tax
Actually, its because ethanol is a aziotroph with water at about 95%. To distill it further, you need to add dangerous and toxic organic compounds. 95% ethanol is the highest that is still safe to drink.
Possibly, possibly not. One thing they really like with this is that it radiates heat photons in wavelengths that go through the sky rather than being reflected back to the ground by the greenhouse effect.
I wonder how Teflon (PTFE) compares to this stuff. In the DIY multispectral photography community, a lot of people use it as a reference material because not only is it pure white to our eyes, it also reflects (diffusely) UV-A, UV-B, and SWIR very well. I found a chart and paper[1] showing that a proprietary variation of it called Tetratex continued that theme well into the SWIR range, but unfortunately the authors didn't measure it into the MWIR or LWIR ranges.
It's easiest to find at the hardware store as very thin tape for wrapping pipe threads, but I bought a few bars of it (about 5mm x 30mm x 300mm) on eBay years ago, so I know it comes in a form that would be more convenient for making into roofing or siding material. I don't know how it holds up to weather, though. According to that paper, it needs to be at least 0.5mm thick to reflect longer wavelengths, so anyone who's curious about testing it should find the thicker stuff like I did.
> I don't know how it holds up to weather, though.
It does very well. The main terminal of Denver International Airport has an enormous PTFE-coated fiberglass fabric roof. It's decades old now and has weathered hail, high winds, and Colorado sun without any significant wear that I know of.
EDIT:
The same product has since been used in a bunch of other stadiums and other large structures, including the Georgia Dome where it survived a near-miss by a tornado with only minor tears:
> "The material is pound-for-pound stronger than steel while weighing less than 5 ounces per square foot. It offers up to 24 percent solar translucency while providing as much as 75 percent solar reflectance"
But for teflon to passively cool, it would have to be strongly absorbent in the IR.
The way it works is this: the sun’s rays are at 5500 K. So you pick the set of materials that reflect light in the visible gap (the atmosphere takes care of the rest).
This keeps the material from getting heat.
Then, from this set, you pick a material that is strongly absorbent in IR.
If it absorbs in IR, itll emit there too, there y cooling itself
Specifically, it needs to absorb/emit in a frequency range called the “sky window”, where the atmosphere is transparent. In this range, the object is basically seeing the cold of space at a few Kelvin, so that almost no energy is absorbed and a lot is emitted.
The trick is to design a system where the total power absorbed across the solar irradiance spectrum is less than the power that is emitted in the sky window, so that the system is a net power sink (in this case to the tune of 100W per sq. meter or so).
Isn't that going to be absolutely blinding, especially when wet? In Denmark some cities already have rules about glazed tiles, disallowing its use in many areas because it blinds neighbors and potentially traffic.
Came here with the same question, but there’s a good answer elsewhere in the thread that it’s about wavelengths: reflect where the sun is bright, and among those materials find one that is the most absorbent/emissive in the IR.
Absorption spectra and emission spectra are identical for thermodynamic reasons. But emissions happen in the infrared and absorption from sunlight happens at visible frequencies. So if you reflect visible light and absorb infrared light, you can stay cool in the Sun. Conversely, applying ultra-thin metal coatings to carbon-black objects can make them reflect infrared and absorb visible light, which is ideal for solar-thermal collectors.
Black is both best radiator and best absorber. So it works perfectly in space (where you minimize incoming energy by turning it perpendicular to sun), and not so good on surface.
This material works by being reflective in spectrum, where most of sunlight energy is (which makes it white, as visible spectrum ~= sunlight on earth surface), and being 'black' (good radiator and absorber) in other spectra.
Retroreflectors focus their reflection specifically in the direction of the light sources using reflection and/or refraction, which involves some losses. I'd expect retroreflectors to sacrifice total brightness/emissivity in favour of directionality. Probably better to just have a reflective surface (mirror finish perhaps?)
Does it get even whiter by using a fabric detergent with a whitening agent? ;-) Then again, will these white fabrics still glow blue in blacklight since they don't need these whitening agents? Pure white in blacklight would be cool.
It seems almost cheating to simply change their reflectivity for a huge cooling power savings.