Dutch engineer aims high with latest green roof design

September 10, 2017 by Mike Corder
In this photo taken on Tuesday, Sept. 5, 2017, Joris Voeten inspects the rooftop garden he helped develop in Amsterdam. Voeten, an urban engineer in Amsterdam has unveiled a new kind of rooftop garden that he says can store more water than existing roofs and feed it to plants growing on shallow beds of soil. (AP Photo/Michael C Corder)

Standing between raised beds of plants on top of a former naval hospital, Joris Voeten can look across to the garden, cafe and terrace that decorate the sloping roof of Amsterdam's NEMO science museum.

Such productivity is part of the urban engineer's vision for cities worldwide, places where he sees the largely neglected flat tops of buildings doing more than keeping out weather and housing satellite dishes.

Voeten, of Dutch company Urban Roofscapes, says a rooftop system he unveiled Friday on the former hospital roof stores more rainwater than existing green roofs and requires less power by relying on a capillary irrigation system that uses insulation material instead of pumps to water plants.

"You can relax here, you can have meetings here. You could operate a restaurant on your to make it more economically beneficial," Voeten told The Associated Press ahead of the official presentation. "But most of all, we finally get to exploit the last unused square meterage in the urban environment."

Roofs that are adapted so plants can grow on them produce a cooling effect on buildings and the air immediately above them in two ways. The plants reflect heat instead of absorbing it the way traditional roofing sheets do. They also reduce heat by evaporating water.

Voeten said readings taken on a very hot day showed a temperature difference of up to 40 degrees Celsius (72 degrees Fahrenheit) between his hospital garden above the banks of a busy waterway compared with a roof covered in black bitumen.

In this photo taken on Tuesday, Sept. 5, 2017, Joris Voeten shows people around the rooftop garden he helped develop in Amsterdam. Voeten, an urban engineer in Amsterdam has unveiled a new kind of rooftop garden that he says can store more water than existing roofs and feed it to plants growing on shallow beds of soil. (AP Photo/Michael C Corder)

Robbert Snep, a green roof expert from Wageningen University and Research in the central Netherlands, said the cooling effect is well known, but the new roof in Amsterdam is an improvement on existing designs because of the way it stores water and can feed it back to plants.

Sensors in the shallow layer of soil on top of the water storage elements monitor qualities such as temperature and moisture content. If the soil gets too dry, extra water can be added. If there is too much water, it can be released into the drains.

"The smart roof really ensures that there is evaporation during, for example, heatwaves and thereby they cool the surroundings," Snep, who is not involved in the project, said. "People can sleep well and people can work well in such an environment."

Voeten says his system can be laid on any flat with sufficient load-bearing capacity, Voeten said. Costs would likely be around 100-150 euros ($120-180) per square meter (10 square feet), he estimates.

Amsterdam, a city built around water and its World Heritage-listed canals, is keen to have its residents turn their rooftops into gardens where possible. To promote the practice, the city is offers subsidies to help meet the costs.

"We ask citizens of the city to create rooftops like this. We ask companies to create rooftops like this," Vice Mayor Eric van der Burg said. "Not only for storage, not only for helping cooling down our city, but also to create extra gardens, extra green for our inhabitants."

Explore further: Chicago plan would pay for 'green roofs'

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Dug
not rated yet Sep 10, 2017
Works great until you get a roof leak and your start digging to find the leak.
rrrander
not rated yet Sep 10, 2017
Maintaining the integrity of of a flat roof is hard enough without it being filled with soil and plant-life.
Eikka
5 / 5 (2) Sep 11, 2017
Maintaining the integrity of of a flat roof is hard enough without it being filled with soil and plant-life.


The soil does act as a protective layer - flat roofs are an issue because they're exposed to UV and heat which degrade common sealant materials like bitumen. The soil acts as a sponge that locks up the water instead of dripping it straight through any small crack, so that also reduces the sealing problem.

Ultimately, one can design roofs with runoff underneat the flat soil top, so the soil is thinner in the middle and any excess water percolates through to gutters on the side. The structure of such a roof is vaulted, which is stronger.
antialias_physorg
5 / 5 (1) Sep 11, 2017
Maintaining the integrity of of a flat roof is hard enough without it being filled with soil and plant-life

Putting plants on flat rooftops is not a new concept. Nor is it difficult or maintenance intensive. There's plenty of roofs where this is done (I can see two just looking out of my office window).
The new thing here is to optimize it so that you can actually get some productive output (apart from the cooling effect)

Works great until you get a roof leak and your start digging to find the leak.

Flat roofs leak as often as any other kind of roof (which is: basically never). Building non-leaking roofs is pretty much a solved tech.
Eikka
not rated yet Sep 12, 2017
Flat roofs leak as often as any other kind of roof (which is: basically never).


Flat roofs with short awnings are one of the design flaws of the 70's fad "functionalist" style which lead to widespread rot problems. They're generally shunned anywhere where there's considerable amount of rainfall these days.

The issue is that while in theory a flat roof is perfectly serviceable - if properly designed an maintained - the actual build quality and materials quality varies as contractors cut cost and the owners neglect the upkeep. A good flat roof is trouble free, but the average flat roof isn't.

I can point to several houses around my neighborhood where I see pools of water sitting on the bitumen for days and weeks on end, and the effect of this water freezing in the winter erodes the materials. In my building as well, there's a crack in the ceiling caused by water seep through the concrete element, as it got wet thanks to the roof leaking.
Eikka
not rated yet Sep 12, 2017
Another big issue on flat roofs was also the fad to build windows on the roof to let in natural light, because the hole ends up in a pool of water any time it rains and the seals around it eventually leak, and the window itself typically leaks as well because it has all sorts of inconvenient sharp corners that are difficult to close properly.

Fortunately the idea of a house as a "machine for living" has faded and now new buidings are made with aesthetics in mind as well. They're not simply concrete cubes stacked in a pile, so slanted roofs are back.
Eikka
not rated yet Sep 12, 2017
Here's what I'm talking about

http://www.dumpt....h3kd.jpg

All those seams in the tar paper, the rectangular ventilation boxes, and the sunlight and heat eroding the surface until it forms cracks and pores. The water pools on top, seeps in by capillary action, and then comes winter and the ice expands inside the wet roofing material. Repeat year after year and it won't be long before the water gets through and the roof structure itself gets moist. Then the whole house starts to rot.

One common way to protect these roofs is to spread a layer of gravel on top, but that presents the additional trouble when the wind blows the gravel all over the place. A living turf is actually a pretty good solution because it stays in place.

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