Thank you for all the comments on the blog post:
We believe a lot of people in North America agree with the comment that in some areas Green Roofs can't thrive without irrigation. We at Green Roof Technology don’t disagree nor agree. Allow us to bring the discussion into a fundamental perspective:
Before you built a structure, you have to remove nature or simpler living plants that nobody watered before. Modern green roof technology is able to mimic this type of environment and allows to promote exactly this drought tolerant and hardy vegetation. With a little more understanding of this technology, it is even possible to increase the plant varieties or the plants density.
Nevertheless the attractivity might not meet the expectations of us (humans). Our picture in mind of a roof garden is a lush green vegetation form that is created with plants that please us (humans), that are not poison or dangerous. In some areas we can achieve this goal by utilizing resources that haven’t been available at this location before the structure was built.
By using natural resources (and water is the most valuable) we start changing our environment (we take water away from somewhere – from plants somewhere) just for our own comfort. Understanding that and the value of water should create an awareness to green roof professionals or engineers to design modern green roof technology in a way that no water or super highly restricted amounts of water are utilized.
Unfortunately, the irrigation industry and most of the green roof designers grew up in an environment where resources are endless. With that said the current waste of water on green roofs is simply not acceptable to me and in these cases green roofs are an environmental nightmare - just for our pleasure (and cash) and that things look “nice and green”.
When I drive around in neighborhoods in San Francisco in the morning, my car is being washed by all the sprinklers and nobody has a problem with that…..
Simple and efficient technology is here since many decades but not in the interest of the industry, nor “re-invented” in the US or there is a lack of common sense – maybe it is a combination of all.
Most issues I am confronted with, are a result of high tech irrigation that is just not doing what it is supposed to do, there is not the right app, poorly designed and installed, too complicated for facility people etc. or simply drains the budget of building owners over time this water costs are going up.
Let’s discuss further and email us directly: firstname.lastname@example.org
Comment by Jure Šumi ((LinkedIn):
Interesting input Jorg. Yes, extensive roofs should be self-sufficient where they can be. But in my mind this is not possible in really arid areas like Jim is saying. With our partners in Abu Dhabi we are now investigating what plants should be used there, where top temperatures are regularly reaching 120 F in summer months (with no rain for years). If you use local plants that are surviving in desert than they are surviving only due to the fact that the roots are extremely long and go deep in to the ground to find some moisture (not possible on the roof). Limited irrigation is still needed but the roof needs design with minimised ET, so also irrigation is as low as possible.
Maybe another thing to consider. Yes or no irrigation is also a question of what someone wants from green roof. Nice look is one aspect, stormwater managment is another. We should not forget Energy efficiency. According to our investigation and perfromance tests, evaporation has big effect on energy efficiency in the summer due to cooling effect. If moisture in the green roof system drops below certain level, the cooling effect is limited. So to have best energy perfromance of the roof, than you need irrigation.
Response Jörg Breuning:
Thank you Jure.
My starting point of thoughts about irrigation on extensive green roofs goes back to a fundamental point and only a handful people make these considerations.
Humans are capable to replace nature with a manmade structure on any location on Earth and they make it suitable for people to live there. In these fundamental thoughts, I expect that humans are also able to create this lost part of nature on top of these structures.
I agree this is not always cheap and not everybody is blessed with creativity or experience. Nevertheless, it is possible and it is our responsibility if we respect nature.
The rooting depth of plants is certainly a key element - it isn’t a road block. It seems it is the preferred excuse that we don’t need to feel responsible in what we re doing and that we don’t feel guilty.
I also think it using water for cooling buildings in an open system (what any green roof is) is considered - in my world - using elementary, limited and precious resources for our convenience. In the case that producing water (in dessert states) for the wasteful irrigation of plants (to make our close environment nice) might be a problem to justify to more than 100 million people that have no access to dependable water resources.
What I am saying is, that growing plants even in areas where plants would hardly grow can be done with extremely low impact on natural, precious resources at costs that are lower in the short or long term. The current hype for green roofs can create significant drawbacks in 15 or 20 years from now to building owners if the costs of water continue to rise. Keep in mind a 20 year old green roof is not even the half of the life span of a green roof (at least that is what I know from experience).
Professionals need to start thinking long term and not for quick profit, they should disregard fancy fashions or get away from desperate LEED point collecting terms if they seriously respect nature.
Picture: Deep rooting plant on roof with hardly any soil and never intentially planted (in Texas at the border to Mexico).