bil

Desert birds are often black because feathers with melanin in are stronger.

There's a lot of to-ing and fro-ing about why black would be cooler or hotter.

Bear in mind a couple of other elements. Multiple layers of fabric by and large make the eternal colour irrelevant, and desert arabs often had to hide from attackers or hide to attack.

There is no way you can hide as effectively in a white robe, as in black.

Econ

Mine is solid and not an air space, it is concrete, tarred felt, roof tiles, sand and poly, of what %'s I don't know as the only reason I know this is I put a chimney in about 15 years back.

I only know of one complex that has white roofs on the buildings and it looked a bit run down and dirty even 3 months after it was painted and it's not a cheap complex, maybe that has something to do with it. In fact it was the colour of clay after several months so why even bother painting.

Clay has been used since Roman days for the same, even before.

Econ

It's to do with air flow JDR, there is none through a solid surface.

The other thing is it will probably also depend on the dress of the robe, for example, put on a black T-Shirt and see the difference in the heat when you are out and about, ware a white one and it is a lot easier to suffer than a black one.

During the day in summer try and find a white surface that is flat and a black surface near by where the sun is baking down, try placing you hand on the white surface and then the black one... but beware to take your hand off the black one very quick before you apply any pressure. BTW, don't do it if the surfaces are metal as the metal will absorb the heat more.

bil

My solid one is much the same construction. Plaster, racilliones, concrete and then on the top it was tarpaper painted red. We ripped that off, and recovered with glassfibre cloth and white rubber paint.

That was at least two years ago and it is still pretty white. Obviously you have to use a paint that is suitable for the job.

Clay comes in a wide range of colours, from white to a deep red. There's a hell of a difference in heat absorbtion there!

wrto the arabs, cloth has little to compare with solid surfaces. read my post below.

jdr

Yeah I found out about the airflow when I read it, seems crazy but must work for them. ;-))

Econ

So from what I can see... that's about 0% of urbanisations then!

Don't know what they painted it with but it is the only complex/building I know of on the CDS that has a white roof.

bil

Airflow possibly, multiple layers DEFINITELY, camouflage essential.

Black wins hands down.

Fair comment on the Urbs tho.

bokeh

Paint the roof white. Bahh! Just grow some trees. They work wonders.

bil

Shade the house with trees and vines, fine, but painting the roof white works well to lower house temps.

bokeh

Painting the house white will make it colder in winter. Having trees that drop the leaves in winter allows the house to get some sun in winter and lots of shade in summer. If you want to measure the temp of interior walls, ceiling, etc. use an infra-red thermometer. It's warmest in my house about midnight, but rarely get over 25 even when it's been in the 30's all day long outside.

bil

It's harder to cool a house than warm it, and 30C isn't the problem. It's when it is 40 plus for long spells.

Trees take a long time to grow, painting is quick and immediate. If you are so worried about the heat shortfall in the winter and have a flat roof, you could lay a black tarp over it.

It's far more sensible to wear more clothes in winter and be more comfortable in summer.

Then again, there are situations where it's often neither sensible or possible to plant trees too close to the house, and for me, planting shade trees would rob me of space I need for other things. I certainly physically couldn't shade the house for 2/3 of the day because there is nowhere I could plant a tree.

The infra red thermometer is a good idea. Thanks for that.

bil

It's always fun when someone comes on in a snit telling you bah humbug.

I listen to a lot of people complaining about the heat on here, but no-one talking about how to solve the problem. I post the suggestion about painting the roof white, which is nothing new, it's been suggested as a valuable and cost effective way of keeping houses cooler in the summer on many a scientific thread.

On comes Bokeh with the bah humbug how stupid, the way to shade houses is with trees.

Well, I went away and had a little think about this, and as soon as I thought it through, I came up against a couple of problems.

My house is about 20 feet wide, 50 - 60 feet long, and 10 - 12 feet high Let's overlook that there is no physical way I can plant trees on the sun side and do the math.

A tree or other object in mid summer, in Spain casts a shadow only half as long as the tree is high. In other words, a 40 foot high tree will cast 20 feet worth of shade. So, to cast the 20 foot shadow needed to shade the house, I need a 40 foot tree at least, plus the extra height needed to get to roof leve, means I need a 50 foot tree. I can't plant that up against the house, that would be madness! The roots would do a lot of damage. So the tree has to be moved away by a distance of half its diameter. Say half the height, thats another 12 or 15 feet away. Trouble is, the top is now that far away too, so it will need to grow another 30 odd feet to compensate.

So in all I will need a row of 80 foot high trees along two sides of my house which will make a strip of land some 20 - 30 feet wide totally unusable for fruit trees and the like. That's a row almost 100 feet long, which is x 30 wide, 3,000 square, which is bigger than my garden and would take forever to grow.

Or I can buy a couple of tubs of white rubberised paint and a roll of glass fibre and tell Bokeh to stick it.

I'll leave it to any structural engineers on here to point out the damage that a row of trees like that would do to the average house.

bokeh

Reading your post really has given me a good laugh. I love the maths too.

Here are some figures for you too (re: 5 July 2008, a day when shadows are near their shortest):

• 06:47; Sun altitude: 0 degrees; Shadow length: infinite
• 07:46; Sun altitude: 10 degrees; Shadow length: 5.7:1
• 08:40; Sun altitude: 20 degrees; Shadow length: 2.75:1
• 09:32; Sun altitude: 30 degrees; Shadow length: 1.75:1
• 10:24; Sun altitude: 40 degrees; Shadow length: 1.2:1
• 10:49; Sun altitude: 45 degrees; Shadow length: 1:1
• 11:15; Sun altitude: 50 degrees; Shadow length: 0.84:1
• 12:08; Sun altitude: 60 degrees; Shadow length: 0.58:1
• 12:08; Sun altitude: 63.4 degrees; Shadow length: 0.5:1
• 13:10; Sun altitude: 70 degrees; Shadow length: 0.36:1
• 14:08; Sun altitude: 74 degrees; Shadow length: 0.29:1
• 15:07; Sun altitude: 70 degrees; Shadow length: 0.36:1
• 15:49; Sun altitude: 63.4 degrees; Shadow length: 0.5:1
• 16:08; Sun altitude: 60 degrees; Shadow length: 0.58:1
• 17:01; Sun altitude: 50 degrees; Shadow length: 0.84:1
• 17:27; Sun altitude: 45 degrees; Shadow length: 1:1
• 17:53; Sun altitude: 40 degrees; Shadow length: 1.2:1
• 18:44; Sun altitude: 30 degrees; Shadow length: 1.75:1
• 19:36; Sun altitude: 20 degrees; Shadow length: 2.75:1
• 20:30; Sun altitude: 10 degrees; Shadow length: 5.7:1
• 21:29; Sun altitude: 0 degrees; Shadow length: infinite

i.e. there are only 4 hours where the shadow is half the length of the casting body, and only 6 hours where the shadow is shorter than the casting body. The rest of the time the shadow is longer.

Here's my situation: Several small palms and a large pepper shade the east facing porch in the morning. South-east large memosa. South three large olives (5/6 metres) plus a couple of smaller trees shade 90% of the south facing wall and part of the roof through the hottest part of the day. Roof is insulated apex. Then to the south-west and west there is a row of 12 metre pines and a row of figs between them and the house.

You don't need to completely cover your house under an umbrella of vegetation to notice the effect. If you manage to keep the sun off 70% of the surface area for 70% of the day that is really going to be noticeable and you don't need anything like what you are talking about to do that. Also the trees are a mini ecosystem and the continual evaporation from them sets up a cooling/refrigeration effect that no amount of white paint ever could.

One other thing regarding the white paint (apart from it looking hideous): just because it may be quite reflective in the visible range doesn't prove in any way that it offers any defence against heat, only visible light. And also if it were to lower absorption of heat it would also lower re-radiation of any heat that had been absorbed.

EsuriJohn

Why are the white villiages white?

bil

Beats me. Apparantly black would be fine as long as we planted trees round them. White is now officially hideous. Shame, I always thought they looked rather nice. Still, once I get my Screen of 40 foot trees round the house, I won't be able to see all those ugly white houses anyway. I'll have them up in a day or so which will be a lot cheaper that that awful white paint for the roof.

Of course if you have oodles of land and want big trees up close to your house, then trees are an option. Trouble is, I don't have a huge spread where I can sacrifice so much land to shade trees, and besides, there isn't enough space between my house and my sun side boundary.

Plus I prefer fruit trees that cool the air, and give me free fresh fruit too.