It's over our heads - Putting that roof to work

Roofs are one of those things one doesn't immediately think of when thinking of helping the environment. But once you do start thinking about it, well, you realise that your roof does more than just keep the rain out and serve as stand for the antenna. It is also a space, which, in some cases can serve more purposes and also, perhaps more importantly, it is something that dramatically affects your house’s energy performance.

Anyone who has lived in an attic studio knows how warm it gets in summer and how cold in winter in comparison to middle of the building flats. When you are in the middle your neighbours insulate you both from cold and heat, so your apartment is nicely averaged. You also leech a bit of the heating or cooling from your neighbours because walls do transfer a bit of the heat or cold, even when they are well insulated.
Anyway, I digress.

Roofs should be insulated. No argument about that. Even if you do not use your attic much, the colder or warmer it gets, the more it will cool or warm up the other floors.

But there is more that can be done, even in houses already built. Usually the outside of the roof is something that gets a bit ignored when thinking of how to improve the energy efficiency of a house. So I thought I would go a bit into what you can do with it and came up with three things to start

Solar panels
White roofs
Green roofs

Solar panels are the most obvious thing, even if they aren't the most basic approach. Solar panels will use the energy hitting your roof for something useful, but besides this, they will also shield the roof, meaning that they indirectly help insulate the top floor. Anyhow, everyone knows about solar panels so I won’t go much into that. Moving on.

The most basic thing one can do is paint one’s roof white (or some other light colour).
That’s right. It isn’t for nothing that traditional houses in the hottest areas in Greece, Spain, Portugal and hot countries around the world are often white.

White reflects more sunlight, and therefore keeps your house cooler. As simple as that and not all that expensive in comparison to other measures.

But besides this decrease in the need for cooling systems, white roofs actually help fight global warming more directly by the so called ‘albedo effect’. In short, everything has a certain albedo effect, ie, it reflects sunlight. But some things reflect more than others. Constructions tend to reflect less and absorb more heat, leading to the so called ‘urban heat island effect’. So, increasing the albedo of towns should help decrease warming (not fix it, but at least contribute in taming it).

I found the following text calculating the theoretical effect on global warming of painting all roofs white on http://www.treehugger.com/files/2005/12/white_roofs_to.php
Please refer to it if you want more information. Or look up white roofs on any search engine for ample information on the subject.

“The Earth has an albedo of 0.29, meaning that it reflects 29 per cent of the sunlight that falls upon it. With an albedo of 0.1, towns absorb more sunlight than the global average. Painting all roofs white could nudge the Earth's albedo from 0.29 towards 0.30. According to a very simple "zero-dimensional" model of the Earth, this would lead to a drop in global temperature of up to 1 °C, almost exactly cancelling out the global warming that has taken place since the start of the industrial revolution. A zero-dimensional model, however, excludes the atmosphere and, crucially, the role of clouds. [But!] It would be interesting to see if more sophisticated models predict a similar magnitude of cooling.”
(Earth Institute at Columbia University in New York – Global Rural Urban Mapping Project)

Just an idea. It will help gain us time though I doubt it will solve anything on the long run, especially since estimates of global warming are now higher than at the time this was written, but the idea stays if you want to try it out.

Independently of the global cooling effect it might have, if will for sure cool your house down during the summer.

The big thing you can do is going for a Green Roof

A green roof is basically a roof with soil and vegetation on it. The idea is actually relatively new to most of us city dwellers but it has been around for a long time. In Norway and Iceland green roofs have been around for centuries.
Might seem mad, but putting vegetation up there is actually the best insulation you can come up with both against heat and cold. Actually, it’s not that mad when you think of how much cooler it is in the summer when you are in a wooded area, or even just surrounded by grass.

Besides insulation, a properly built green cover will also increase the lifespan of the roof and, with a bit of luck and depending on the type of roof you have, you might actually get a garden with flowers or even fruit where you used to have nothing at all.

Green roofs are also very good at retaining water, meaning that the plants there will need little water and the run off from the roof will be drastically decreased helping combat flooding in the adjacent area.

And if you’re a bird or insect watcher and you’re lucky, you might get rewarded by the appearance of wildlife attracted to your ‘roof garden’.

Besides the benefits for the owner, green roofs are quite a benefit for the surrounding areas.
They fight the ‘urban heat island effect’, absorb CO2, contribute to avoid overflowing of drainage and sewage pipes during heavy rain by retaining water and releasing it more gradually, and they filter rainwater, removing some pollutants and heavy metals which then do not end up on water sources. They also help wildlife facing shortages of natural habitat by increasing the green area and by working as stepping stones between green areas for birds, insects, wild plants, etc.

The types of green roof vary wildly, depending on area, slope of the roof (which will imply different levels of drainage and may require making the roof watertight if it is flat), type of of purpose and vegetation desired (you might want a deep cover of soil or simply a thin layer as a result), and amount of maintenance you are willing to provide (from heavy maintenance to virtually self-sustaining green roofs which need at most one visit per year).

There are many firms specializing on green roofs and much information is available online too. Just type green roof on a search engine and it should be easy to find your way.