Dusty Gedge, founder of Livingroofs.org, explains the benefits of installing a green roof, how it can be simple and why lots of people get swayed by commercial systems.
Interview with Dusty Gedge
Dusty Gedge got into green roofs because of a rare bird! When its habitat was about to be built upon he wondered whether it could be re-created on the roof. Despite a lot of opposition he found out how it could be done and things naturally progressed from there.
A Green Roof is Essentially Vegetation and Soil on a Roof
Although there are different types of green roofs, most self-builders will be interested in ‘extensive' green roofs. These are quite thin and in the range of 2 to 6 inches in depth.
It is Important that Excess Rainwater Can Get Off the Roof
Much like any roof, a green roof mustn't collapse or leak but it must also have the capability to drain away excess water.
Green Roofs Can Ameliorate Against Flash Floods
As the climate changes, intense summer rain storms are becoming more common which in turn causes flash floods.
Soil and vegetation on a roof absorbs a certain amount of the rainwater and therefore slows the rate at which it leaves the roof.
Dusty says that a green roof can often take four to five hours before it even starts draining, thus reducing the likelihood of flash flooding.
More Vegetation in Our Cities Will Help Cool Them
Having more green roofs in our urban environments would counter the heat island effect. Vegetation and soil evapotranspirates and therefore can help cool the city.
Dusty says: “In periods of heat excesses where buildings can get quite hot, especially in cities, the ambient temperature can increase and become very uncomfortable. Having a vegetation and soil level can keep buildings incredibly cool.”
When Dry, the Thermal Mass of the Soil and Vegetation Insulates the Building
A green roof insulates the building beneath it when it's dry, but building science shows it's not as effective when it's wet. However, Dusty says that most people who install a green roof find their fuel bills reduce significantly in the winter.
Natural Systems Should Need Little Maintenance
For the green roofs that Dusty advocates, which are relatively natural systems, maintenance should be the same as for any roof. In other words the drainage outlets should be checked once a year to see that they're free from vegetation and soil, etc.
Highly Decorative Roofs Require Much More Maintenance
While it is possible to have a decorative roof, it must be treated and maintained like a garden.
In reality few people, even gardeners, go down this route. Instead they go with a self-maintaining roof that will change with the seasons.
Industry Favours Thin and Light Roofs, But They May Not Be a Good Choice
A lot of lightweight systems are sold commercially which also makes life easier for architects and engineers.
Despite being promoted as low maintenance though, these systems are often so shallow that when there's a drought they would need to be irrigated almost daily.
Changing an Existing Flat Roof to a Green Roof is Relatively Simple
Dusty answers Ben's question on how to upgrade an existing flat roof of a single storey extension into a green roof.
The first step would be to consider how to make the roof stronger. This will clearly be different for each building but in Dusty's experience, for most small extensions doubling up the rafters will suffice. Putting down the marine ply deck will also add lateral strength.
Although this would be a bit of work, it would not cost a massive amount of money.
Pond Liners Can Be Great Waterproofing Treatment
While there are high-end waterproofing treatments, Dusty is an advocate of the Walter Segal method of waterproofing which makes use of a pond liner.
Dusty says: “The great thing about a pond liner is you can get it prefabricated how you want it from the pond liner manufacturer and it rolls up. You can then loose lay it. So there’s no technical heavy waterproofing.”
A puncture resistant textile can also be used to protect the pond liner from impact. After that the soils and vegetation go on.
Having a Slight Pitch to Your Roof is the Best Way to Drain Off Excess Water
While there are plenty of products that the green roof industry will try to sell you, keeping things simple will make a lot of them unnecessary. For example, having a slight pitch to your roof means that water will naturally drain down hill. Dry river beds can then meander through the soil and provide an outlet to drain the roof.
Ceramic waste in a dry river bed
Keep the Nutrients Low
Most people want a self-sustaining green roof and in a natural environment, wildflowers do best when there is as little top soil as possible.
So by selecting a substrate (the term used for the soil) that is very poor in organic material, the grasses don’t like it but the wildflowers thrive. Wildflowers will also be much more resilient to the changes in weather.
The other advantage of starting with very little organic material (perhaps 10%), is that more can be added as required. However, if there's too much organic material the whole lot has to be taken off.
A Green Roof isn't Always Green in Colour!
Everyone seems to associate green roofs with Sedums but you can get a lot more creative than that!
Instead of buying pre-grown ‘instant' blankets and ‘instant' meadows, create a green roof that reflects where you live. This will also mean that it will change with the seasons, evolving before your eyes.
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