Painting the roof white (improve home comfort and save energy)

Would this even make that much of a difference? Attics usually have an insulation value between R-40 and R-60 on new builds... Even if it did, you'd have the opposite impact in the Winter?

Assuming you have asphalt shingles, I wouldnt paint them. Colour does affect radiative absorption and reflection to an extent, but the rough surface texture of asphalt shingles makes them automatically ~75% emissive. The difference between the darkest black and whitest white is maybe 15-20%. Between grey and white is way less, closer to 5-7% [1]. Bringing the emissivity of your roof down helps, but the change in roof temperature doesnt end up being linear with emissivity. You have a roof thats being heated by radiation, and then rejecting that heat through re-radiation and backside convective cooling from your attic. At the end of the day, you might be looking at 2-3% difference in the total heat gained through the roof, assuming your attic is properly ventilated.

The downside to painting will be that youll have to find a high temperature paint, because keep in mind your white roof is still 75% absorptive. Youll also want to make sure the paint doesnt clog any of the passages between the layers of shingles, or the paint could trap water. Ultimately Im not sure theres much benefit for what will probably be a lot of work (youll probably want to powerwash and prime everything if you want the paint to stick), and youll probably have to redo every few years. Next time you go to do the roof though, you could go with a lighter colour and maybe see some benefit

Hope that helps

[1] http://azcoolroof.com/downloads/Resourc ... Materi.pdf

The only way is to completely cover your roof in solar panels.

Benefits aside I think that painting them white would look terrible. I imagine your neighbors would not be happy, particularly those that live across from you and have to look at it everyday.

I think its fair (I sure as heck hope anyway) to assume this is a flat roof. Lighter colors are very common on flat roofs.

Lots of debate about any actual benefits tho. I trust Fast Company, FWIW.

https://www.fastcompany.com/1790991/pai ... oesnt-work

torontotim wrote: ↑ I think its fair (I sure as heck hope anyway) to assume this is a flat roof. Lighter colors are very common on flat roofs.

Lots of debate about any actual benefits tho. I trust Fast Company, FWIW.

https://www.fastcompany.com/1790991/pai ... oesnt-work

The article was discussing methods of dealing with climate change. Not keeping your 2nd floor from overheating.

To the OP, I think it would look like crap in a season or two. Solar panels would likely be the most effective (both in terms of reducing heat buildup as well as subsidizing your electricity costs), but also most expensive. New shingles in a light color might be effective, but just an additional cost.

C

The_Professor wrote: ↑ Benefits aside I think that painting them white would look terrible. I imagine your neighbors would not be happy, particularly those that live across from you and have to look at it everyday.

Maybe... and its a fair question...
When was the last time you looked or cared about your neighbors roof? ._.

ProjectPixelation wrote: ↑ Maybe... and its a fair question...
When was the last time you looked or cared about your neighbors roof? ._.

I don't particularly recall ever really looking at any of the roofs across from us, but I know that if one were white in my neighborhood which is all dark colours it would stick out like a sore thumb (which is fine, it's your house to do with as you please).

The_Professor wrote: ↑ I don't particularly recall ever really looking at any of the roofs across from us, but I know that if one were white in my neighborhood which is all dark colours it would stick out like a sore thumb (which is fine, it's your house to do with as you please).

Next time we replace the roof shingles (probably in a decade) - I'd go for a ash gray or something... will probably still stick out but people will eventually forget it >_>

CNeufeld wrote: ↑ The article was discussing methods of dealing with climate change. Not keeping your 2nd floor from overheating.

To the OP, I think it would look like crap in a season or two. Solar panels would likely be the most effective (both in terms of reducing heat buildup as well as subsidizing your electricity costs), but also most expensive. New shingles in a light color might be effective, but just an additional cost.

C

Great till its winter and you're heating the 2nd floor.

Cheapo-Findo wrote: ↑

This is way more impact than I would've guessed, do they say somewhere (maybe I'm missing it) where they're measuring the inside temperature? Is it in the attic or second floor, etc?

look at sources

barqers wrote: ↑ This is way more impact than I would've guessed, do they say somewhere (maybe I'm missing it) where they're measuring the inside temperature? Is it in the attic or second floor, etc?

Cheapo-Findo wrote: ↑ look at sources

I did! Maybe I'm having an off day but I didn't see anywhere where they measured internal temperature or over what length of time etc. I also think that llbl site should be just lbl.gov.

OP in winter: Painting the roof black (improve home comfort and save heating cost)

torontotim wrote: ↑ Great till its winter and you're heating the 2nd floor.

Wait... are you really expecting the sun in winter to be reliable? We average less than 3 hours of sun a day in Ontario during winter months. See link below:
https://www.livingin-canada.com/sunshin ... anada.html

Plus, I stand by the logic (and personal) experience that you can put on extra layers to stay warm in a cold room... but you can never take off enough layers to stay cool in a hot room

barqers wrote: ↑ This is way more impact than I would've guessed, do they say somewhere (maybe I'm missing it) where they're measuring the inside temperature? Is it in the attic or second floor, etc?

Have you ever stepped in a hot car in the summer? You'd be surprised at the temperature difference inside a white vs black car under the sun (same model, etc). I was pretty shocked the first time i experienced myself...
I thought this would likely translate to lower temperatures in housing too; just not as dramatic as there is air flow and better circulation.

blackn54 wrote: ↑ OP in winter: Painting the roof black (improve home comfort and save heating cost)

Nice try...
We all know the snow is out to get our roofs in winter! It's a conspiracy!
But what if we could paint the snow black!!?!?!?! O.O

/s

I think this sums it up if you have a whole 3.5mins to watch:



Probably more info has come out recently, however this guy is a great professor at Waterloo and basically wrote the book on building science, so most of this probably holds true.

ProjectPixelation wrote: ↑
Have you ever stepped in a hot car in the summer? You'd be surprised at the temperature difference inside a white vs black car under the sun (same model, etc). I was pretty shocked the first time i experienced myself...
I thought this would likely translate to lower temperatures in housing too; just not as dramatic as there is air flow and better circulation.

I know I was just thinking the insulation in the attic was way better at keeping that heat out! I stand corrected lol

barqers wrote: ↑ I know I was just thinking the insulation in the attic was way better at keeping that heat out! I stand corrected lol

IR heat from the sun is real... wait until you experience the "magic" of ceramic car window films xD

I love reliable long-term passive solutions that require little to no maintenance... cause savings (profits).