Browse Forums Building A New House 1 Mar 25, 2007 1:31 pm Have you noticed how a white car stays much cooler than a black car? Makes sense when you think about. White reflects light, black absorbs it.
Doesn't it then stand to reason that the roof on your typical Aussie home, should be a light color? If a roof was white or at least a light color, and possibly reflective to boot, wouldn't it be MUCH easier to keep the roof cavity cooler? Couldn't that save you a packet on insulation?? Does the color or the roof come into the equation when selecting insulation for a roof? Re: Roof color in the thermal equation 2Mar 25, 2007 6:03 pm Dobly , your spot on there mate. When you get out in the country, take notice. Most tin roofed homes are a lighter colour, usually Silver or white. As you say darker colours draw and hold the heat. But depending where you live ? that may be an advantage to some ? People still go for Reds/Greens etc But i reckon the lighter colours are the way to go. Best wishes "MO" Its better to regret things you,ve done, than things you haven't. BUT Never regret growing old because some people never have the privilege. Re: Roof color in the thermal equation 3Mar 25, 2007 6:21 pm I agree, I have answered a couple of these questions before….
Not only are they cooler, they FADE slower after a period of time. Internal and External Building and Colour Consultant Online - Worldwide http://www.denovoconcepts.com Re: Roof color in the thermal equation 4Mar 25, 2007 10:00 pm I've actually been thinking the same over this last summer that has just started to turn into autumn, and did some experiments. We were looking at extending & redoing the whole roof in colorbond, but we bought another house instead!
I have 6 colorbond samples - the sample bits you get that are about the size of a playing card. I have pegged them all up on the clothesline - between the lines, so the steel wire doesn't act as a heatsink. Pegged on with the colour upwards, horizontally, facing the sun. I then checked them (on the underside) with the infrared thermometer at various times. The dark blue was regularly pulling 37-39 degrees C, while the cream was 33 degrees, and off-white & white were both 32. I was amazed that the blue wasn't a lot higher, so did it a few more times on really hot days, and got similar percentage differences. So yes, dark colours do soak in more heat, but possibly not as much as you would think. I also choose the colour of my work cars based on the heat-soak, which is why I always end up with silver or very pale colours - the car is so much nicer to get into of an arvo, after being in the sun, and the aircon kicks in & cools it down a lot sooner. Re: Roof color in the thermal equation 7Mar 26, 2007 12:05 pm I am personally not willing to give up roof colour for lower energy use. I prefer to use other options to achieve the same thing and more.
1. In roof extractor vents that can be opened in summer and closed in winter. 2. High R-value insulation in ceiling. 3. Sarking At the end of the day, I guess it is just a personal choice. 3xb Re: Roof color in the thermal equation 8Mar 26, 2007 1:16 pm commodorenut,
Your experiment on different colour metals is interesting. However, I think it may not well represent the actual situation. A roof has one side that heats up from solar radiation, but the other side is not ventilated (the roof to ceiling space). Therefore a roof will get hotter than a sheet that is exposed on both sides. From www.colormatters.com/energymatters.html we have that on a 32 C day: White roof: 43 C Aluminium roof: 60 C Black roof: 88 C What your experiment shows is the value in venting the roof space. As 3timesbuilda said, roof extractor vents that can be opened in summer and closed in winter may be the best solution. Then you can choose whatever roof colour you prefer. (Remember to include inlet vents in your eaves to allow air flow to happen.) From memory, BASIX promotes a light colour roof. This however, when you think about it, may not be the best solution. I would think that a dark roof is better as long as you do the three things that 3timesbuilda mentioned. This way you stay (almost) just as cool in summer, but get some free heating in winter. (Now, if only you could turn the insulation off and on just like the roof extractors, that would be something!) By the way, I’ll be designing and building soon and hope to use a dark roof to provide heating during winter days and cooling during summer nights. The idea would be to use conventional hydronic pipes (used for heating) in the slab to circulate through the roof panels. The water pump is only run during winter days and summer nights. Here is little known fact, a black metal sheet will not only go above the ambient temperature when the sun is shining, but will go below the ambient temperature at night (by about 5 degrees Celsius). This means that even on the hottest of summer nights (20 C in Sydney) you have a source of 15 C cooling to “charge” your slab during the night. Haven’t heard of it being used anywhere, but I’ll give it a go. Can’t see any reason why it won’t work. Cheers, Casa Re: Roof color in the thermal equation 10Mar 26, 2007 6:53 pm devank,
I will need a water pump (or fan if you want to use air) to circulate the water between the roof and the floor slab. This pump will be required to push the water against the thermosiphoning action during winter days. During summer nights thermosiphoning means that I just let the water naturally flow through the system. Of course, during winter nights I need to close a valve to stop water flow. During summer days no valve or motor is required (would be nice to divert the water to a hot water system - but that's a whole different story). Cheers, Casa Re: Roof color in the thermal equation 11Mar 27, 2007 9:08 am perryr So logically, a house with a dark roof would be cheaper to heat in winter? It would be interesting to see some results with a thermometer in a roof cavity. Perry Perry With all the news about global warming and climate change, I sure hope there is such a thing as a cold winter in the future. The world is getting hotter. I'll not get on my soapbox about it, but suffice to say, I am very concerned about keeping the heat out. More so then letting it in. As for "dark roof would be cheaper to heat in winter?" I would think that the idea is to have sufficient insulation that your house it not getting cold, through the roof. Re: Roof color in the thermal equation 12Mar 27, 2007 10:42 am Dobly,
I think you are missing the point. If you ceiling insulation is good enough to keep 100% of the heat out in summer then what you say would be true in winter. However, in winter (as in summer) insualtion only provides part of the answer as it is not 100% effective. Having a warm roof space would act as a buffer to the cold and so improve the effectiveness of your insulation. A while back, I read about a company that was basically pumping the warm roofspace air into the home and selling it as a heating system. Not a bad idea and very cheap to run - only a few fans and some ducting needed. Not sure how they are getting on. Regards 3xb Re: Roof color in the thermal equation 13Mar 27, 2007 11:14 am One of the things that I may live to regret is ordering a Bluescope steel Night Sky (almost black)colorbond roof for my new place over here in perth.
http://www.bluescopesteel.com.au/index. ... DB357747A3 The things that i would ask are: You see plenty of black tile roofs, but not many black tin ones, why is this so? (this is the main reason I went for black, something a little different. Do clay/concrete whatever roof tiles are made of hold the heat longer? Ie I would asume that a steel roof can absorb and dissapate heat quicker than a tile (is it called thermal mass?) Obviously being in Perth my main concern is the heat factor, more so than the cold, so armed with the 3 cooling tips provided earlier, hopefully the black tin roof wont cause me to many issues. Re: Roof color in the thermal equation 14Mar 27, 2007 11:27 am Another thing to consider is the material as well as the color.
With my black terracotta roof tiling, warmer days tend to heat the tile throughout, not just the surface. Even with good ventilation, it can take some time for the tile temperature to decline due to the "core heat" With Steel, tin or other, the thickness of the material means it can dicipate heat faster than a 1/2 inch tile, so the roof will cool faster than tiles. When wiring some speakers in Friday night, I got into the roof at about 11pm, figuring that the 35 degree day was over and with a few showers and a cool change would cool the cavity down. The roof cavity was still quite warm and the tiles equally warm to touch on the inside. As mentioned air flow plays a big part of this. The inside of the house was pleasant though, so the insulation is definately doing its job. Adrian B Re: Roof color in the thermal equation 15Mar 27, 2007 2:18 pm 3timesbuilda Dobly, I think you are missing the point. If you ceiling insulation is good enough to keep 100% of the heat out in summer then what you say would be true in winter. However, in winter (as in summer) insualtion only provides part of the answer as it is not 100% effective. Having a warm roof space would act as a buffer to the cold and so improve the effectiveness of your insulation. Regards 3xb Thereby making ventalation in the roof, like those spinning things that replace a typical concrete tile, a bad thing for this 'buffer' you speak of.. I don't doubt you are right.. (you have 3 stars and I have but 2) but back to my first questions.. "Doesn't it then stand to reason that the roof on your typical Aussie home, should be a light color?" "Does the color or the roof come into the equation when selecting insulation for a roof?" From what I have seen so far, yes it would.. At least, it 'should' be considered in relation to the climate you are going to live in. If you live in the snowy mountains you might have a dark roof with no ventalation (to keep the heat in). Where if you live in central Australia you may have a white or silver roof, that is ventalated lots. For the rest of us, it is somewhere in between. Sound about right? Re: Roof color in the thermal equation 16Mar 27, 2007 3:27 pm Dobly wrote:
"Thereby making ventalation in the roof, like those spinning things that replace a typical concrete tile, a bad thing for this 'buffer' you speak of.. " Wrong, The spinny things have a lever with which to close them during the winter months. It is a 6 monthly job but well worth it in my opinion. Roof colour on the other hand cannot be switched off. Maybe oneday.... 3xb Re: Roof color in the thermal equation 17Mar 27, 2007 8:47 pm Interesting discussion...
When I spoke to the lady at Austral about roof tiles, she informed me that the colour of the roof has little to no affect on the house temperature (I'm assuming with decent insulation). I have also wondered if the roof colour would affect the house, and after her telling me that it doesn't matter, I'm now starting to rethink... To add to the discussion, which holds the heat more - concrete or terracotta? My logic would tell me that the concrete would get hotter as it doesn't have the same glaze as terracotta to reflect the heat, but then terracotta is a baked product and may get very hot??? Back to roof ventilation, I saw these nifty things the other day (don't for the life of me know where... maybe on TV?) but they replaced a roof tile (same shape and layed flat), and had a vent that allowed air to pass through. The idea was that you fit 4-6 to your roof - 2-3 on each side, so that the air flows in one side and out the other... They came in a range of tile colours from memory. ~Ray. Second Time 'Round Re: Roof color in the thermal equation 18Mar 27, 2007 8:49 pm Ding! It was on the Better Homes and Gardens show where they showed the energy saving tips... there might be something on their website about it.
~Ray. Second Time 'Round Re: Roof color in the thermal equation 19Mar 27, 2007 10:37 pm I saw that roof vent - replacement roof tile thing - it wasn't obvious though whether they are available for all the different shapes of tile. I got the impression it was only for one or two flat styles.
Anyone happen to catch the brand? Re: Roof color in the thermal equation 20Apr 10, 2007 7:36 pm 3timesbuilda I am personally not willing to give up roof colour for lower energy use. I prefer to use other options to achieve the same thing and more. 1. In roof extractor vents that can be opened in summer and closed in winter. 2. High R-value insulation in ceiling. 3. Sarking At the end of the day, I guess it is just a personal choice. 3xb I agree I would rather spend more money on insulation etc than have an albino looking house I would probably definitely consider contrasting out garage door (e.g. light ash would look great) and make downpipes and fascia same colour as your walls, not as your… 1 3569 Suggestions please for acrylic rendering Color to match austral brick urban one pepper. Pic for reference. Thanks 0 5067 Were struck with: Colorbond Ironstone Grey roof and cream windows. What color should we render and paint the garage door to tone down the cream windows? Farm House, will… 0 26817 |