The National Geographic news has written about another San Francisco first:
This week, San Francisco became the first U.S. city to require that certain new buildings be built with a green roof—an eco-friendly design technique that sows plants above a roofline. This latest action builds on a growing trend that has taken root around the world, and which boosters say offers significant benefits for the planet.
The new by-law enacted in January 2016 will mean that 15 to 30 per cent of roof space on new office construction projects must incorporate solar, green roofs, or both. An earlier by-law requires new residential and commercial buildings under ten storeys to install solar panels or a solar heating system with fifteen per cent roof coverage.
Green roofs reduce stormwater runoff, improve air quality, and help mitigate the urban heat island effect. For building tenants and owners, green roofs reduce the need for heating and cooling. They also can provide food and a recreational area for residents. Combining solar panels and green roofs can actually make each component work better. Solar panels can provide shade for plants and grasses, reducing the need for watering, while the panels work best when they are cool (green roofs can help lower temperatures compared to conventional ones).
Other cities such as Chicago has already planted their city hall roof, lowering summer temperatures in the building. Bonn Germany has led the green roof innovation and been an early adapter to this roof form in Europe.
Green roof legislation is being passed around the world. Cordoba became the first city in Argentina to require green roofs in July. France’s new legislation mandates at least partial coverage of green roof or solar technology on all new construction and goes into effect next March. In 2009, Toronto mandated green roofs on industrial and residential buildings. Germany’s green roof industry has been legislated and supported by the government in various ways since the 1970s.
There are approximately 25 North American cities that support green roofs to some extent, from bigger cities to medium and smaller communities like Syracuse and Port Coquitlam in British Columbia. Washington D.C. has a de facto requirement for large buildings through its stormwater regulations. New York City has tax abatements.
Valuable green building certifications, such as LEED, also award points for green roofs, so they are popping up across the country even without legislation. Green roofs offer an environmental solution and provide a range of benefits as regional climates become hotter and populations in cities continue to grow. Kudos to San Francisco for showing the way forward.
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Reblogged this on Sandy James Planner.
There have been “Green Roofs” in BC for many years, primarily at ground level over basement garages of multi-tenanted commercial, strata and apartment buildings.
When leaks have occurred in the waterproofing membrane,tracing the source(s) of the leak(s) is almost always costly and difficult.Leaks over cars in a garage are irritating but leaks from a green roof on to business equipment and/or personal belongings are a much greater problem
Although roofing product technology and application procedures have improved in recent years, roof membranes eventually leak.The costs of excavating soil, shrubs and vegetation on a multi storey building, and repairing or replacing roof membranes will be very expensive indeed.
No one seems to be discussing the life cycle performance and waterproof integrity of the green roof systems.The focus appears to be limited to the environmental benefits, which are obviously important, but society is not well served by ignoring technical issues
I beg to differ. It is discussed and analysed and has withstood the test of time. Poor workmanship is always an issue. Don’t blame the vegetation.
A quick look on line:
“A properly installed and maintained green roof should extend the life of the roof 2-3 times its normal life. 30 to 50 years is not an unusual lifespan for green roofs in Europe.”
Also
http://www.forbes.com/sites/houzz/2013/12/30/6-busted-green-roof-myths/#781bcbc45c7e
There are other factors besides poor workmanship (RV said “Poor workmanship is always an issue. Don’t blame the vegetation”)
Poor roof design, particularly inadequate roof slope and often an inadequate number of roof drains seems to be as common as poor workmanship.And despite the improvements in roofing material technology and quality ,premature material breakdowns do sometimes occur.
The European scenario is often given by the promoters of green roofs.in 2014 Germany had +-85% of the green roofs in Europe,England 4%.No European country is even close to Germany in green roof inventory.Obviously ,we should be talking to the Germans.How do they avoid problems with the waterproof integrity of the green roof assemblies?
The objective is to raise the issue that if large traditional ,roofing projects, such as schools and recreation centre roofs can need replacement prematurely despite the inputs of well established roofing contractors, roofing consultants and prominent roof membrane suppliers, why can problems and premature failures not happen on green roofs?
As the rectification costs for the latter would be considerably more than the former surely there should be widespread discussion on designing green roof assemblies that are serviceable if and when they leak? .
Obviously the Germans have made it work.We need to hear from German sources about any green roof problems they have experienced or how they prevent problems before they occur
The Forbes article on green roof myths seems promotional rather than informative.
If we can install trouble free green roofs ,it would be an economical and environmental success, but let’s get it right.
Bring in the Germans!
Kevin has some very good points. It is not wise to import green roof success stories from drier climates to a rain forest. Even when a green roof is successful given our metre++ of rain in winter, we’re still not quite in business given the cost of the re-engineered structure below to support the additional weight of saturated growing medium, plants and containers, unless it’s a big commercial or public building with a stout framework.
Faulty workmanship may just mean the on-site workers are on a learning curve after an experienced foreman gets the flu, or the architect / landscape architect is placing a portfolio shot and arbitrary green philosophy ahead of a career better performed as a practicum. On the latter point, green roof technology has changed, but still needs work where thousands of kg of rainfall are retained and suspended way up in the air on the roof.
A faulty roof is quite easily repaired and is covered by insurance with few questions asked. A green roof placed on a membrane with a deficient joint can be extremely onerous because water flows horizontally over roof support members and ceiling panels and can pop through tens of metres away from the actual leak. Peeling back the obscuring greenery and soil will add thousands to the repair bill and weeks to the schedule.
Ask insurers what their criteria are with respect to green roofs, and about their worst cases — how many months were the apartment units and offices below rendered uninhabitable with what financial and personal costs imposed on people?
Given our high rainfall I suggest the most successful green roofs will be planted in irrigated pallets that are quickly movable over a level deck suspended over the membrane. There should be no contact whatsoever with the membrane. Still, this doesn’t mitigate the additional cost of beefed-up structural elements in smaller buildings to take the weight. Alternatively, superinsulation and light coloured roof surfaces work wonders with energy conservation and remediating the urban heat island effect, and are much more affordable and easily maintainable.
I believe the statement that green roofs “reduce” stormwater runoff is half correct, but misleading. Intense storm events and overall rainfall are increasing here with climate change. While green roofs only regulate the stormwater flow by storing a certain volume in their structure and slowing the flow, they do not reduce the overall amount except what little is transpired in winter. They quickly reach a saturation point during storms where retention is no longer possible, and nearly full flows occur. These roofs still need drainage. The storm water control is a purely mechanical function. You can attain the same flow-reducing and storage capacity with AstroTurf on a lightweight synthetic drainage profile. And it’s even green and recyclable! (Tongue in cheek here.)
Green roofs, bioswales and small infiltration trenches are only as good as their adjacent receiving environments, engineering and overall surface area. There is nothing that should substitute for a good quality storm water system that, if possible, empties into large downstream self-sustaining artificial wetlands. These are far more effective at slowing stormwater and removing contaminants (or trapping toxic spills) before the water enters high quality habitat-rich environments.
MAB’s comments should be mandatory reading for all parties interested in Green Roofs.
Architects,politicians and environmental planners would benefit greatly from studying MAB’s commentary.
There was strong push in the 80’s for watertight buildings for environmental reasons, which were supposedly properly engineered, but eventually broke down in the leaky condo mess of the 90’s and 2000’s.This resulted in incredible expense to many strata owners. And a problem that a number of experienced builders in the 80’s foresaw.
Vancouver has average annual rainfall of 1457mm.Manchester,England receives 810mm and Berlin,Germany 591mm.So we have a unique rainfall situation as MAB pointed out.It seems prudent to retract my “Bring in the Germans” call because their climatic situation is so different.
We should proceed very carefully and do a critical analysis every step of the way.To date that does not appear to be happening.
Can we achieve the environmental objectives in other ways besides green roofs?
Are green roofs suitable for the BC climate?
E-valueBC has a photo of a prototypical Vancouver green roof at 342 23rd Ave E.