Asymmetrical Information

The earth's surface area is 1/2 billion square kilometers. There are about 2 billion households. If they average 100 square meters of roof area that's a mere 0.04% of the surface area.

Note that lots of people live in apartments and multistory buldings.

-dk

I used to design and sell steel buildings. I can assure you that Kynar 5000 Polar White is the default and predominate roof color on steel buildings, for said reasons.

mmm, your point on white roofs is well seen, but you can't actually just use paint. It wouldn't last and would flacke off, getting into the environment, by being washed off the roof and into the drains. The use of the older asphalt based materials is based on their ability to shrink/swell and not crack, and because they are dirt cheap. The white roofing materials are very [10-20x more] expensive... A gallon of elastomeric roofing liquid is $85 a gallon, and it would take hundreds of gallons for a building's roof.

The energy savings isn't so much cared about by the building owner, since they only care that their building is undamaged, they don't have to pay the electric... The roofing trade would probably have to get all new equipment, since you don't do the white stuff the same way... etc, and so on.

It's a fabulous idea, very hard to implement based on cost. I used to manage a building where we put in the new roofing [in silver even] and it was very much cooler, but it was a stopgap to avoid putting in a full A/C system in a 100 year old building in Chicago. That A/C would have required a rewire, and expensive permits and...
yeah, nothing is ever as easy as it sounds.

Thing is, I think you could get INDIVIDUALS to do this sort of thing, much easier than getting building codes or laws about it. Kinda like the change to CFL's. But since roofs often last 25 years on houses, without some way of making it cost effective.

So, you're a smartykid [and I mean that], figure out how to make it pay, and the world beats a path to your door.

Green roofs should not be looked at as a savior from Gobal Warming. Heck, they will only have a minimal impact on the urban heat island, which is a micro-climate effect, not global. The problems of urban islands on global warming is minimal.

Which is not to say that urban heat islands cannot be made better. There was a study Lawrence Livermore, I believe, that found that if significanly urbanized metropolitan area decreased their impervious surface coverage by 5% then the urban heat islands would drop by 3-5 degrees. Impervious surfaces include asphalt pavement as well as asphalt roofs. The pavement is the major contributor, but roofs are where the greatest potential lie at increasing green space.

Back to green roofs' benefits. Yes, the contribution to the ambient heat is notable. They are FAR better at reducing the energy usage of the building itself. An asphalt roof in a 90 degree day rises to almost 170 degrees. Try roofing and you'll experience this in person. A green roof, however, is only about 5 degrees warmer than the ambient 90 degrees. This is a tremendous benefit when trying to air condition the building beneath.

The best benefit I've read for green roofs is their ability to absorb runoff water. An asphalt roof washed water off the roof and straight into the stormwater sewers. Prior to development, the rain would have just hit the soil and either soaked in until sautation or run off normally into the watershed. Add impervious roofs and pavement, the water no longer soaks in but is flushed as fast as possible into the watershed. No wonder the old 100-year-flood markers are being hit regularly every 10 years or so lately. Green roofs reduce this flash flood impact that urbanized areas have caused on watersheds. Plus, instead of washing the toxic material off the roof into the streams and rivers, the water stays where it is. We will get cleaner water with more green roofs.

Sorry this went on, I spent much of my university studies for my Geography degree focusing on urban stormwater issues. :)

Uh, D, this guys are smart, and are already making it pay.

(Disclaimer: they are a customer of mine--I developed and maintain some of their internal IT systems.)

Sheesh--it obviously should read "these guys"....

I'm confused. Are we discussing green roofs or white ones?

Triticale,

Yes.

The beauty of the common asphalt shingle is that it is durable, functional, lightweight, low maintenance, and compartively cheap to replace if worn out or damaged. No special construction techniques are required in order to accommodate it, it can be replaced two or three times before the old layers have to be stripped back down to the roofing boards, and the soft surface helps damp out the sound of inclement weather.

Your next-best option has a lot of competition there, no matter what its narrow scope of benefits may be in some other area.

Mature shade trees are probably the best way to keep sun off of a roof AND combat global warming. Unfortunately, few people have that long-term perspective when buying a house these days.

I worked for the largest commercial RE company in our city back in the 80s. Some of the buildings we built had black roofs, some white but all of them had gravel ballast that covered the entire roof so the color of the roofing material didn't matter. We built all types from one story warehouse/showrooms in the suburbs to high rise office buildings downtown. AFAIK all the other developers did the same. Is this just a local thing?

In regards to so-called 'green roofs' two factors must be considered. First is the load factor for your roof. Not only do you have to consider the weight of any greenery and the necessary soil that it requires, you also have to add in the weight of the water that the soil can hold, if say, you get a spring thunderstorm that drops 4 inches in 2 hours or a blizzard that drops 2 feet of snow.

Excessive moisture inside the building is also a problem. One San Fran based company decided to eco-friendlyize a warehouse here by putting some kind of prairie grass on the roof. I am told that by the middle of the first summer it felt and smelt like working in a swamp. The equipment, the product, and the people were all negatively affected. The grass was gone before the next spring.

Plant roots can crack granite. If you put plants on your roof, I really want to know what you're going to use underneath the plants to keep them from shooting roots right through the roof. Metal would hold up for a while, but eventually a seam will gape a bit, a root will get started there, and as it expands it will pry the seam wide open. And asphalt (used at least as a sealant in nearly all roofing systems) would hardly be a barrier to roots at all, unless it can be made sufficiently poisonous to the plants - and in that case, I'd doubt whether you could keep the plants alive.

As for white roofs, either you use metal - with the obvious problems of noise, and the less obvious problem of keeping leaks in check - or AFAIK you'd have to try to somehow whiten asphalt. Asphalt isn't the primary roofing material just because it's cheap, but because it's water-repellent and stays somewhat flexible for at least 20 years. With asphalt, small holes often seal themselves. With anything else, keeping a seal through decades of thermal expansion and contraction, wind pressure, hail, and rain is going to be very difficult.

OTOH, asphalt deteriorates in direct sunlight, so you do have to cover it with something. The most obvious example is the asphalt shingle - a slab of fiber matting (fiberglass for the good ones) to hold the shape and give strength, saturated with asphalt for waterproofing. The top side is covered with fine gravel to block sunlight, one end of each gravel bit embedded in the asphalt.

Usually they use medium to dark colors for the gravel, so sun rays that go down between the bits are absorbed by one or the other. If you used white gravel instead, you would get a cooler, heat-reflecting roof, but sunlight could bounce back and forth between two bits as until it reached the asphalt and caused premature failure. Beyond that, much white rock is actually translucent, that is light passes through a thin slice, and much of the gravel would be that small...

There should be a way around this, but I'm not sure. I suspect it is ultraviolet light that does most of the damage. Materials can have selective reflectivity depending upon the wavelength - for the visible wavelengths, we call that "color". So I think we could get a rock-like material that reflected most of the heat of the sun (which peaks at red to infrared wavelengths) while absorbing the UV. I just don't know what material, if there's a natural rock that fits or it would have to be synthesized, and what it would cost...

Usually they use medium to dark colors for the gravel, so sun rays that go down between the bits are absorbed by one or the other. If you used white gravel instead, you would get a cooler, heat-reflecting roof, but sunlight could bounce back and forth between two bits as until it reached the asphalt and caused premature failure. Beyond that, much white rock is actually translucent, that is light passes through a thin slice, and much of the gravel would be that small...

I would be at least equally worried that if the shingle is too good at reflecting light, it won't heat up enough to properly seal the tar stripes on the underside, or re-seal any holes that develop in the asphalt. Seems this could be particularly problematic in areas like the upper midwest, where summers tend to be cooler and the ambient humidity reduces sunlight intensity at the ground level -- and copious amounts of precipitation fall year-round.

A better solution would be Solar Powered air conditioning.

Most CA, TX, & FL gov't buildings should be getting surveyed about solar panel installation. Rather than reflective roofs (perhaps better than what is now), conversion to energy roofs would be the goal.

CA should be budgeting millions every year, with results being posted (installation & maintenance estimates and real costs, plus energy costs).

I think the shiny new NYC building code mandates white roofs for just this very reason.

I read it in the NYP, so it must be true.

A better solution would be Solar Powered air conditioning.

Another wonderful idea about to be shot down in flames by heartless realities of thermodynamics and material sciences.

You can't get air conditioning on the scale of a mere house, let alone a large a office building, unless you run a refrigeration cycle of some sort -- and the heat is the product you want to get rid of, not keep. That means anything solar powered has to be creating electricity somehow.

Photovoltaic cells can do that, but the efficiency is low and the lifespan is limited. And not only do you need a bank of solar cells, you need a large battery pack (or at least a large capacitor bank) to buffer the power against transients, and a step-up converter to turn it into something a compressor motor can use. When you get done manufacturing and installing all this physical plant, you have an air conditioning system that might pay for itself by the time the first batch of photovoltaic cells expires (15-20 years IIRC) -- assuming you don't have too many cloudy days in your area. Don't forget to incorporate the pollution costs associated with all that manufacturing into your greenhouse calculations; lots of nasty chemicals and energy input are involved.

The other option, which is far more practical and efficient but requires a larger installation location than a typical rooftop, is to use an enormous array of self-adjusting mirrors to focus sunlight against a central elevated boiler chamber, then drive steam turbines the conventional way. In the US, California has experimented with such facilities and Nevada is building one now; something like 100 acres' worth of mirrors installed in a desert climate gets you 10MW of power generation during the peak of the day. This is comparable to what you might get from a modest wind farm.

http://en.wikipedia.org/wiki/Solar_Two

anony-mouse,

The lithium bromide/water absorption refrigeration cycle is thermally activated, though electric power is required for the circulation pumps and the cooling tower. Single-effect LiBr absorption chillers can be operated with ~200F hot water, at an efficiency of ~60%. The Japanese have built residential scale LiBr absorption chillers, but they are far from economical. Large single-effect LiBr absorption chillers are in common use in commercial and institutional buildings in the US. Many are used in heat recovery situations.

When I bicycle in the summer, what I think we really need is white asphalt.

One major disadvantage of planted roofs or solar systems on the roof: someone has to go up there to maintain them. Not dangerous on a commercial building with a flat roof, but it would cause a significant rise in fall injuries from the typical steep pitched roof on a home. Not sure if anyone but hospitals and orthopods would benefit.

The lithium bromide/water absorption refrigeration cycle

Interesting. Off to Google I go.

Later:

Okay, that looks interesting, and I imagine (as you suggest) that the capital cost is high and the maintenance cost is not inconsequential -- although I suppose this could be hybridized into a winter heating system. Seems like you would still be looking at a decade or more to pay it off, though, and at that point the solar plumbing is approaching the need for serious maintenance.

At which point you may wish you had just planted the shade trees...

The old joke was that if global warming turned out to be true, we could just paint Texas white, has now run into reality. We have already lost a Texas sized area of reflective Arctic Ocean permanent ice cap (the kind that's there in the summer when the sun is shining 24 hours a day up north) has melted completely, between 2004 and 2006. It's probably going to get worse before September, and on an accelerating scale.
I've GOT to buy real estate up in Alaska where my cousin lives. Preferably at least thirty feet up a hill someplace where there is low land between me and the hills so I can live on an island and get me some beachfront property.

anony-mouse,

Heating is direct and simple. Maintenance for LiBr systems is minimal. However, economics suck, particularly in small sizes.

When we built, we brow-beat the builder about the trees. He left them and stayed away from their root systems. So far, they are all alive and thriving. And yes, they do make a big difference.

wkwillis,

Yes, get your Alaskan inland-soon-to-be beachfront property. I hope all thouse who believe with the same fervor as you do the same and move up there.

One thing that is NEVER address, at least from the reports I see, is that if the trend does not continue. Everything assumes it will. That's like saying because I rolled 3 sixes in a row, I'll keep rowing sixes for the next 3 or more throws. Now I don't think the weather is as random as a throw of the dice, but the trend may very well not continue, and to assume that it will continue at the same rate or accelerate is probably not correct.

Interesting that most of the people who are deeply concerned with the environment are crowded in big urban cities where they pretty much destroyed their own environments and insist that "we've gotta do something" while ingoring the fact that millions of people like myself live out in relative isolation in/near nature and have managed not to destory our environment by covering it all with concrete, sub-dividing our acreage to sell it off for a few bucks, etc. etc.

As long as "we gotta do something" involves you changing your lifestyle and not forcing mine that's fine.

Here's a summary of some interesting research on green roof technology from Texas A&M:

http://tinyurl.com/2s5ena

Considering that many green roofs add $20/ft. to the cost, some developers are starting to ask that - since the green roof subtracts from impervious surfaces - that Planners allow them a bigger impervious footprint to begin with. If granted, this allows bigger buildings and nullifies any impervious surface reduction due to green roofs.

Why not pave the roads and parking lots white too? Or, for new roads, just use white concrete? (Road lines could then be painted black.) Just guessing here, but I'd bet that the total amount of paved road in the US exceeds the amount of roof space by a wide margin, perhaps an order of magnitude. Virtually every house and building that I see is fronted by road space and/or a parking lot that at least equals the roof space in square footage, and often exceeds it. Then there's plenty of road space (see highways) that isn't fronting any buildings at all.

"If you put plants on your roof, I really want to know what you're going to use underneath the plants to keep them from shooting roots right through the roof. "

A little bit of googling on green roofs would answer this for you. What you do is plant vegetation with shallow roots. Additionally, green roofs have a lifespan roughly twice to triple in length over traditional roofs. That especially includes the membrane that keeps out water.

And with regards to green roofs being an pervious surface, fact it they are not. They only have a capacity to absorb a percentage of the precipitation. At about an inch of rain they aborb about 60–90% of the downfall, the rest goes straight to the normal stormsewers. And the water absorbed doesn't get infiltrated into the soil like pervious surfaces allow. Green roof-topped buildings still prevent infiltration of rainfall like impervious surfaces.

It's not a perfect replacement for natural ground, but it is a bit better than pavement.

The extra cost of green roofs are more than made up over the lifetime of the structure in energy savings and total cost of ownership (less-frequent replacements).

I don't see how bigger buildings topped with green roofs somehow nullifies the gain granted by use of green roofs. Used with liberal amounts of rain gardens and pervious pavers, bigger buildings are a good thing over several smaller distributed buildings. Contain sprawl and all that.

There's another possible way to raise the Earth's albedo: We must increase production of non-biodegradable plastic peanuts.

After a few decades, the plastic peanuts will all wash down to the sea where they will float and reflect the Sun's rays. After the oceans are all covered with styrofoam, the Earth's albedo will be high enough to stop the global warming.

Why not pave the roads and parking lots white too? Or, for new roads, just use white concrete?

Most newer concrete roadways ARE pretty light. The problem is that concrete is far more expensive to implement due to a greater volume of material, the need to stabilize the road base for the additional weight, and the labor required to install it.

In exchange, you get a more durable material...if you don't live in a snowbelt state, where the heavy and regular application of deicing materials during the winter will rapidly destroy almost any plausible paving material, in which case it is cheaper and quicker to re-pave than it is to patch and repair concrete.

Also, asphalt roadways aren't black for more than a few months. Weathering and tire wear quickly removes the thin surface coating, after which the road takes on the color of the embedded rock. (If you ever tour the US by car, you can regularly see noticable changes between grays, reds, and greens.)

There's another problem: a few years ago civil engineers discovered that asphalts blended with a significant proportion of ground-up tires are more durable and create less traffic noise than traditional all-rock mixes, due to the damping effect and more uniform consistency of the material. This is particularly useful in urban and suburban areas as it allows for the reducion or elimination of sound barriers along major highways. Tire rubber does not color-fade much beyond a dark grey, so asphalt roads are likely to become darker, not lighter.

directed here from instapundit, and seeing that you repeat his mistake (disclaimer, I'm in the home design business), how one designs one home is very important, and very dependent upon where one lives. There are hundreds of useful ways to reduce energy consumption that, not surprisingly, utilize the style of construction... as well as the color of construction. Hint: Dark roofs are only bad where the climate (or your social station) dictates that you need air cooling as opposed to an open window.

Astounding how such smart folks cacoon themselves within that with which they are familiar.

And if you really want to rid the society of black-body heating, get rid of shopping malls.

Here in New Mexico many of us have shiny metal roofs that reflect sunlight quite nicely. I am in the process of building a house with metal roof and Solar Panels for elec and some of the hot water.

ok, Bains, I'll bite. What percentage of the population live in areas where you need more than open window cooling? I'm going to bet a lot... it's astounding how smart people make pronouncements like that. 4million people live in Phoenix metro, and it is miserable there w/o A/C... it can be done, sure, I lived in Tucson for a year in college with no A/C, but there were times I napped in the library to avoid heat stroke. It's only 4mil, but what about Vegas, Houston, DFW, Inland Empire California, Atlanta...

Even if you can get your cooling via open window, does a high percentage of dark roofs in one area change the actual air temp of that area? Wouldn't it be a good idea to not do that, all other things equal?

If we choose within reason to do the best we can, isn't that an advantage? How many of these choices are societal inertia? [kentucky bluegrass in the desert? Non-native trees in dry areas?]

Seems like for a lot of this question of roofs, light or green, or energy savings in general, education would be the good swift kick for many people. Of course, no-one wants to pay for that either...