Roman Mars:
This is 99% Invisible. I’m Roman Mars.
Roman Mars:
Last October, the mayor of LA, Eric Garcetti gave a speech about one of the biggest issues facing his city. It’s just way too hot.
Eric Garcetti:
“We know that climate change is not an abstract crisis. This is the fight of our lives.”
News Anchor:
“Mayor Eric Garcetti in South Los Angeles today, rolling out key elements of his Cool Streets Program.”
Eric Garcetti:
“This is the first of five neighborhoods across the city where we’re rolling out new features that’ll help us lower our temperatures.”
Roman Mars:
The city is trying lots of things to cool down temperatures like painting sidewalks white. But the easiest way to solve this problem is shade, just creating shade. Lots of neighborhoods in LA don’t have tree coverage or high rise buildings, and because of city bylaws, it’s really difficult to build features like shade sails or canopies. Journalist Sam Bloch has spent a lot of time looking into shade so I sat down to talk with him about why shade is actually a matter of life or death for people living in really sunny places.
Roman Mars:
So you used to live in Los Angeles and what did you notice about Los Angeles when you started walking around the city?
Sam Bloch:
What did I notice? I noticed that there was no one around. I noticed that the people who were around would have to position themselves in such a way to protect themselves from the sunlight.
Roman Mars:
What do you mean?
Sam Bloch:
I noticed people waiting for the buses behind telephone poles, and I noticed people waiting behind the people waiting behind telephone poles because there was only that small sliver of shade that people were protected from the sunlight.
Roman Mars:
Why is shade so important?
Sam Bloch:
Los Angeles, like almost every city in the world, is heating up. There are some scientists who I speak to who have found that in hot, dry, arid environments like Los Angeles, but also Phoenix, that shade is the most important factor when it comes to human comfort – more than air temperature, more than humidity, more than wind speed, and there’s a close relationship between human thermal comfort and mortality and illness and heat stroke. If you don’t have shade, if you’re not protected from the sun, you can become dizzy, you can become disoriented, you can become confused, lethargic, dehydrated. If you are obese or elderly or pregnant, that can tip into more dangerous things like heart attack or organ failure.
Roman Mars:
And so what is the magnitude of the problem in LA?
Sam Bloch:
There are a few different ways of thinking about it. We can talk about shade in terms of tree canopy, which is a very serious problem. Los Angeles has terribly unequal tree canopy and by tree canopy I just mean coverage. Let’s say you’re an outer space looking down on LA, you’ll see parts of the city that are covered in green, and you’ll see parts of the city that are not, that are baking in asphalt, and those, to a tee, follow lines of wealth. It’s a problem with tree canopy. It’s a problem in terms of the built urban form. Los Angeles is notoriously anti-density. Los Angeles has this image of itself as not being New York City. In fact, being the anti-New York City. So sunlight and open space is a part of the culture, and that’s not necessarily a problem, but it becomes a problem when you can’t escape it.
Roman Mars:
Right. So there are no tall buildings to provide some measure of shade?
Sam Bloch:
I wouldn’t go as far as to say there are no tall buildings. However, there are a few tall buildings-
Roman Mars:
And they are spaced pretty far apart.
Sam Bloch:
Correct. They’re located in certain height districts, Downtown being one of them. And even some areas that city planners have designated to be taller neighborhoods. Even today, there’s still fought and contested by neighborhood activists.
Roman Mars:
So I’ve seen old pictures and I get a sense that Los Angeles used to be greener, like there was a lot of shade. So tell me how the city was designed and how it developed into this.
Sam Bloch:
So was Los Angeles was a Prairie. If you look at photos of LA from 150 years ago, it’s all grasslands. And when it was settled by the Spanish, downtown – which was the original settlement – was laid out according to the ‘Law of the Indies’. The city would roughly conform to a 45-degree angle, so you could have sunlight in the winter and shade and shadow in the summer.
Roman Mars:
So explain the Law of the Indies. What does this mean?
Sam Bloch:
The Law of the Indies means build your cities at 45 degrees basically – completely unlike the way we think of most American cities, which have this North-South-East-West, very rigid grid. So you have these original settlements that are laid out in such a way as to be able to create shadow when you need it and also to bestow sunlight also when you need it. Spanish architecture tends to have a very strong sense of natural comfort, so you’ll see a lot of these kinds of missions and adobes that have these internal courtyards that are shaded, you’ll have covered walkways, paseos, and even today you’ll see a lot of this in Spanish revival architecture or outdoor malls that have goofy Spanish-ish names.
Sam Bloch:
Los Angeles was also in a way a dusty old west town. So you think about these covered boardwalks, you think about large canvas awnings that are cooling people who are living outside and also cooling indoors, which at the time didn’t have air conditioning. And another way that Los Angeles tried to stay cool was through rich, beautiful, flamboyant, not just tree canopy, but a syncretic overwhelming variety of exotic flora and fauna.
Roman Mars:
So during this period, there was a recognition of the environment and how to be comfortable inside of it. And when did that go wrong?
Sam Bloch:
Funny that you put it that way. Things started to go wrong after cheap electricity came down to Los Angeles with the completion of what’s now called the Hoover Dam. So you start to see the city rebuild itself and the new development becomes like we see today. You have controlled air conditioning, you have the automobile which comes to dominate the city in the 30s in the 40s, and with the automobile, you just have a whole new way of seeing the city.
Archival Clip:
“The names of the streets are household words translated into magic. Fabulous stacks of freeways, tremendous tone-wise.”
Sam Bloch:
The city started to think about how to market itself and how to make itself seem more attractive to outsiders. And this is where you get palm trees. Palm trees one essayist said ‘were about as useful for shade as a telephone pole’. She hated them, but the city was enamored of them. And interestingly, you have different philanthropists and celebrities starting to think about trees as being a public good, but the palm tree, in particular, being one that doesn’t just message LA as a semi-tropical paradise, but also as Mary Pickford said, it’s very good for window shopping from the seat of your car because the tree trunks aren’t that robust. So if you’re driving down some Boulevard, you can see all the great stuff because the palm tree is so narrow.
Sam Bloch:
So Los Angeles was also rezoned in the 1930s to become a single-family city. Los Angeles in order to – not pacify, not suck up – but to remake itself in the image of the FHA, decided that all new single-family homes had to come with a front and a side yard. So you start to create a lot of space around them. Los Angeles really starts to hate the idea of density.
Roman Mars:
And so when you have this type of sprawling, not very dense city, how was the shade distributed?
Sam Bloch:
Unevenly. Shade is distributed to people who can afford it. If you go into these neighborhoods that were laid out to be wealthy residential enclaves, you have very wide sidewalks, and the strip of grass where you can tree plant, which is called the parkway becomes four or five, maybe even 10 feet wide. And when you have these wider parkways, you have a greater space to plant a bigger, thicker leafier tree.
Roman Mars:
So the Parkway is the area between the sidewalk and the road, and those can be pretty wide and, therefore, have trees with them?
Sam Bloch:
Correct. In other neighborhoods that have been redlined, that were designed as worker housing that were meant to jam people in together, you don’t have these kinds of wide residential sidewalks, instead of what you have are very narrow sidewalks because these neighborhoods are designed to facilitate automobile passage. So if you have a narrow sidewalk, you don’t really have the space to plant a thick leafy tree. Furthermore, it’s been incumbent upon property owners and renters to maintain this semi-public space of the parkway. You would think that in a city, whatever is on the sidewalk, whatever is outside of the property line would be managed by the city. That is not historically been the case in Los Angeles. It’s been incumbent upon property owners to water trees to maturity and to maintain them. If there’s a tree there, it’s because someone has taken it upon themselves to water it to maturity and to care for it.
Roman Mars:
So each part of that process, the design of where the sidewalk is relative to the street, the fact that a person of wealth could plant and maintain a tree, all of these things cause more uneven distribution of shade trees.
Sam Bloch:
That’s right. And I would also add that in some neighborhoods, I’m thinking about a neighborhood called Hancock Park, which is a flat neighborhood, landlocked in the center of the city. There is nothing about it that naturally lends itself to being a lush verdant tree festooned paradise. But the neighborhood was developed as an exclusive wealthy residential enclave and when that happened, the power lines were undergrounded. There is nothing in the way. It is designed specifically to allow for tree growth. This is not the case in most of Los Angeles.
Roman Mars:
So because of this lack of shade trees, there’ve been efforts to build in shade, especially around bus shelters. But it’s been incredibly hard according to your reporting. So like in your article you talk about one bus shelter at Glassell Park. Could you tell me about that and why it was so hard to put shade there?
Sam Bloch:
It was hard because shade is a tripwire. In the instance of the Glassell Park Transit Island, you had a concerned neighborhood resident and a neighborhood activist or maybe you’ll call them a homeowner who wanted to throw just a simple bus shelter over a space where she saw people naturally congregating. She ended up talking to an architect who said, let’s not do a regular bus shelter. Let’s throw some big shade sails in here. And when that happens, you have to start thinking about how are we going to fix these shade sails to the ground. And when that happens, you have to start thinking about what’s underneath the ground. And you have water mains, you have underground utilities. In order to upgrade a sidewalk or a Transit Island, you then have to start honoring newer regulations like the Americans with disabilities act. So then you have to start making curb cuts to make it wheelchair accessible. So you have to take care of all these other things before you can decide to do this very lightweight, sort of low-res fix.
Roman Mars:
The enemies of shade are not always bad guys. In this case, ADA compliance is not a bad guy.
Sam Bloch:
No.
Roman Mars:
Like curb cuts, not a bad guy. All these things are not bad. It’s not just sort of around sidewalks. LA doesn’t have a lot of shading in city parks either. So why is that? Why was this never considered valuable?
Sam Bloch:
I wouldn’t go as so far as to say it was never considered valuable because I’m thinking about a park downtown called Pershing Square that up until the 1950s was a tropical paradise. It was incredibly shady. It was meant for people to kind of hang out and shoot the breeze and after awhile the business elite in the neighborhood decided first of all to install underground parking, which gets rid of the whole root system so you can no longer plant thicker, denser tree canopy and part of the reason why Pershing Square was redeveloped in short of its tree canopy is because Los Angeles is a city where residents are worried about crime, a city where residents are worried about homelessness. As I was working on this story, I came across multiple instances where LAPD had installed pole cameras in parks or in public housing projects. And I had been told about something called crime prevention through environmental design, which is this idea that we need to have increased visibility in public spaces. And you can go on Google Street View and go back five, six, seven years and you can see over time when a pole camera goes up, a mature street tree goes down.
Roman Mars:
So there’s all these selective pressures where other things are just more important like whether it’s, I would call it somewhat the illusion of crime prevention-
Sam Bloch:
Correct. No one told me that it actually prevents crime. What this detective told me was that it helps the police catch and prosecute criminals. Not that it stops them.
Roman Mars:
Right. And then this preference for this underground parking, which makes a shallow ground, which therefore you can only have trees that have ball root systems like palm trees. It just seems like everything is working against it, especially in this city. And so how do you think about how to balance these different factors and their value in an urban setting?
Sam Bloch:
Great question. There are a few ways to think about this. I mentioned that in Los Angeles, it’s homeowners and residents who are responsible for the maintenance and cultivation of street trees. Why does it have to be that way? Why doesn’t the city decide that a public urban forest, why isn’t that a value? You might also think about the question of density. I spoke to an architect and what he told me is that maximizing floor space is the name of the game, which means if you only have so much space to work with, which developer is going to say, “Let’s actually carve out some of our floor space to make an arcade or a Portico.” That’s a tough sell. So why doesn’t the city properly incentivize developers to create these sort of semi-public shaded environments behind the property line that are contiguous with the sidewalk?
Roman Mars:
And what about just placing trees? I mean, what is LA doing about just adding to the canopy in general?
Sam Bloch:
The city is trying to plant more trees. The city has a goal of planting 90,000 trees in the next few years. I am not sufficiently convinced that the city recognizes the infrastructural challenge to planting 90,000 trees because as we’ve been talking about, the space in which you can plant a tree is limited when you have things like a narrow sidewalk or overhead power lines or even regulations that limit or prohibit the planting of a street tree within 45 feet of a driveway, which let’s be real, that’s practically all of Los Angeles. That makes me think that the city is not understanding the complete wholesale re-imagining of the street that’s needed in order to plant 90,000 trees.
Roman Mars:
So we’ve talked a lot about informal urbanism in this show and sort of interventions. People could install umbrellas and canopies without permission to fix this kind of problem just in their own neighborhood. Did you find evidence of people doing this and what is the reaction when this happens?
Sam Bloch:
People do it all the time. Particularly I will add in Latino neighborhoods. There’s an urbanist named James Rojas who writes about Latino Urbanism. And he has a pretty compelling theory that Latino residents of Los Angeles know how to use the shade and he leads these wonderful walking tours where he’ll point out shade sails that have been connected between two garages and an alleyway for kids to play in because it’s more comfortable under the shade. Or he’ll point out these elaborate front yards where you have blue poly tarps just strung across a space. Or maybe I’m exotic trees that are sort of overflowing into the street.
Roman Mars:
Well, that sounds great to me, but I get the impression that the city doesn’t always see things the same way.
Sam Bloch:
What I did find is that in the private realm, those things are tolerated when they step into the public and when they step onto the sidewalk, things become more complicated. I write about a grassroots shade shelter on Figueroa and Avenue 26 in the Cypress Park neighborhood near the LA River. And a barber named Tony Cornado would not admit that it was he who made this really great, fantastic shade shelter made out of like an I-beam and a great tarp and a couple of bus benches. But he told me that he recognized the need for people when they’re waiting for the bus just to have some protection. Tony or someone had to take down this grassroots bus shelter because it was an obstruction in the public right of way. The city processes 16,000 obstructions in the public right of way every year. If property owners, if residents, did not fear that the city would come after them, threatening them with fines, perhaps we would see more grassroots urbanism.
Roman Mars:
I think it’s pretty surprising to think of shade as a political inequity issue. I think it surprises a lot of people. Tell me about your awakening of this and convincing people of it and just make your best case for what it is that you want people to think about when they think about shade in a city.
Sam Bloch:
Shade in a city is to me respect for people who can’t afford to duck into an air-conditioned cafe or a lift when it gets too hot. Shade is to me, an understanding that the world is changing and we want to protect citizens, the most vulnerable citizens who can’t protect themselves, and it’s also just nicer to be in the shade. It’s cooler in the shade. I always walk on the shady side of the street. It’s easier to see in the shade. You know, I spoke to a scientist who said that direct sunlight is the kind of light that you have when you perform oral surgery.
Roman Mars:
That’s not pleasant.
Sam Bloch:
No. Dappled light is more like reading a book. So I want my city to help me read a book. I don’t want to perform oral surgery.
Roman Mars:
Yeah. Thanks for coming in. I appreciate that.
Sam Bloch:
Yeah. Thanks for having me, Roman.
Roman Mars:
Sam Bloch’s article called ‘Shade’ appeared in Places Journal.
Comments (20)
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Fascinating as always, but surprising you don’t look around the world to see how other cities address the problem. MITs treepedia project shows just how bad LA scores for trees. I live in Singapore, which is more humid than LA and the government here is very aware of the heat island effect ( which I don’t think you mentioned). We have trees everywhere and also a lot of covered walkways to shade people from sun and equatorial rain. We also have underground parking everywhere – surely LA can figure it out, if it wants to.
I wish there were more pictures in these posts. I tap on the link in the podcast show notes every time I listen to a 99PI episode and often wonder why there aren’t 5 times as many pictures to show me visually what I’m listening to an audio description of during the episode.
If you’re referring to the discussion at the end, please see the link at the end of the companion for images and analysis of “treescrapers” in urban environments!
The removal of trees in order to increase surveillance visibility for policing completely goes against research that indicates increasing green spaces in poor urban neighborhoods reduces crime in the area by 9%. I learned this listening to an interview with social scientist Frances E. (Ming) Kuo a couple of years ago on another program, “Hidden Brain”. The research, “Environment and Crime in the Inner City:
Does Vegetation Reduce Crime? is co-authored with William C Sullivan (both from U. Ill. Urbana-Champaign) and linked to the HB episode “Our Better Nature” from Sept. 2018. Maybe no one has told the LAPD and all the other stakeholders in LA that greening is a better way to reduce crime in the first place, and cool the city at the same time?
Great episode, as always, but I disagree with most of the second half of it.
If you would live in Europe, or understand European, or especially Italian cities better then you would know that Italian streets are normally quite narrow, in fact they can be very narrow, which makes them shadier, but also means that there is simply less room for trees.
Its true that the Bosco Verticale building in Milan is hardly an architectural masterpiece, but it takes a very simple idea, and makes it happen in a very effective way.
The argument that the carbon footprint of making the building stronger to hold the trees is greater than the offset the trees themselves give is short term thinking and it only makes sense if looked at from an american perspective where old is measured in decades, not in centuries. Think about how this building will look ten, 30 or 50 years from now. Think about the developement of the building’s facades over time, I expect it will be beautiful.
Finally, what about Hundertwasser? He was doing this 40 years ago, and the unfortunate result was not that anybody of consequence. ie. austrian city planners, listened to him, but that what he built became a tourist trap. His vision was about radically changing the way people live. He called the trees on his house tenants, and he made sure that the adjoining street couldn’t be driven on with cars….. His Hundertwasserhaus is the perfect example of how a house like that looks after several decades.
Kurt here. As I mentioned in the episode, I have not done load or carbon calculations for this building, but part of the point is not just that there are initial inputs to be offset (lifting trees) but also ongoing inputs (watering and maintaining trees, as well as keeping up the infrastructure to do these things over time). In short: keeping trees healthy and alive in the sky is more challenging than doing so on the ground, and if we think of this as an experiment, time will tell if the gains outweigh the monetary or carbon costs. It may well be that in some cases the net payoff over time is greater than the inputs required to sustain a project, but I personally have not seen that case being made in a mathematically rigorous way.
It’s unfortunate that the landscape architect you interviewed in this episode was so inaccurate in his discussion of architects performing structural analysis for vertical forests. Architects don’t do structural design, structural engineers do.
Kurt here – that conversation at the end was somewhat casual, unscripted and meant to be a short introduction, not an in-depth overview – nonetheless: I do apologize for not mentioning engineers. It is absolutely true that in these projects, at least the ones that are meant to become real and not just be renderings, a dedicated engineering team is going to be crucial to the execution. In the course of the conversation, I was trying to keep things simple and streamlined, focusing on the challenges, and did not mean to sell short the role of engineers in making these buildings possible, whether or not they are well-designed. But while architects may not do the actual calculations, they can and should be aware of the engineering challenges their (real or conceptual) designs will face in reality. I can’t speak for all architects, but when in architecture school, multiple Structures courses were a core part of the M Arch curriculum and we were taught to keep engineering in mind when designing buildings.
Just a note that the interviewee was definitely NOT a landscape architect, but a buildings architect
You guys should definitely look into Soviet city planning. There are great lessons to learn from Khrushchev-era cities, especially when it comes to public space, shaded and green areas. Look at Almaty, Khazakhstan, for instance. In the parts where they have preserved the original neighborhood structures, the inner courtyards (which are, by the way, huge in comparison with most European cities and are open to public), the trees that were planted are now creating urban jungles. Almaty is not an exception, anywhere you look, whenever they saved the original Soviet city planning, those cities (which used to be much-ridiculed in the West precisely in terms of urban planning) turned into green heavens with enormous public spaces which people actually use!
Roman, Shade was a good episode .
I take exception with the Vertical Forest in Milan comments. Directly adjacent to the Vertical Forest is the tree museum.
Over 100 trees of various species has been planted and is open to the general public.
Keep up the good work.
Best regards,
Tony
Some interesting discussion about plantings in this podcast but I didn’t hear too much about other ways of generating shade in cities—apologies if it was in there and I just got distracted and missed something. A hundred and fifty years ago—after the elevator but before air conditioning—many of the tall buildings in cities had operable windows and retractable awnings to shade the sides of the buildings exposed to sunshine. At street level, large retractable canvas awnings covered half the side walk—shading window shoppers and providing a space for retail advertising as a bonus. Advances in glazing have made it possible to filter out undesirable UV light and heat.
Many modern buildings incorporate a “brise-soleil”, a projecting awning made of metal louvers, screens, or tinted glass, to shade the windows and vertical surfaces of the building. Arcades at sidewalk level do make financial sense on retail buildings because they can attract window shoppers, keep them comfortable, and provide more advertising and lighting opportunities
In California, due to our ever-drying climate, the solution of adding more trees carries a risk of wildfire. So far, only suburban areas have been affected but if there were too many trees in downtown Oakland, would it bring the wild fire threat into the inner city? When trees are planted in California cities it’s important to consider the species for high drought tolerance and lowest risk of fuel contribution (dry leaves, brittle bark, high oil content) in case there is a fire.
Love your podcast it’s always informative and thought-provoking.
Loved the beginning of this podcast, but felt the second half was quite unfair to architects, Any architect who intends to put greenery will have put thought into the process. The weight of the tree + soil, the tree’s suitability to a higher altitude + higher winds, the process to get the tree there. As has been mentioned already in the comments, engineers are of course involved – trees are not simply added to a design as an afterthought as was implied by the discussion.
As for placing more trees at the base of the building, this is of course the most logical, but many buildings will be using the entire base footprint to gain the most sqm – to make the development viable. Also the plazas in front of these buildings are subject to the same urban planning laws that can make significant planting difficult – which you mentioned in this podcast.
Really enjoy this podcast so please be more careful with the misinformation next time!
As others above have noted, planting on top of buildings is often not done by architects at all (though they may be involved/have a say in the process), but by landscape architects and structural engineers. Additionally, many high rises with plantings on top of them fall somewhere between the two types you mention (greenroof and the vertical forest). It is very common and totally feasible to have planting with trees on a roof top deck or amenity space. And a greenroof often is just as difficult to figure out as any other planting, though with fewer benefits. These intermediate planting types can also be put on ground level OVER underground parking. Both of these methods are done ALL THE TIME, so it feels like a misrepresentation to say that there are a lot of cRAZy proposals for buildings completely covered in enormous amounts of tree cover. There MAY be some of these but there are so so many examples of practical and achievable on structure plantings.
An example of a public park on top of a building. The trees and spaces are for everyone.
https://www.capitalonecenter.com/the-perch
It would be great to hear the perspectives from a landscape architect who is actually the one designing these spaces. Architects are integral, but it’s misleading to always hear urban landscape commentary from someone is only a piece of the puzzle.
I would just like to mention that trees need water and LA had a big drought recently. It was mentioned that Los Angeles was a prairie and that implies the climate cannot naturally sustain large numbers of trees.
Great piece, Roman. Like a few others have noted, there are good examples of urban tree planting and green infrastructure in other cities. LA has only to look beyond itself to see how things can be done. I live in Atlanta (of course, a much wetter environment) where I volunteer with an organization called Trees Atlanta (treesatlanta.org). It was founded in 1985 by city leaders who saw that downtown Atlanta had become denuded of trees and worked to replant the parks and plazas. About 10 years later, the program moved into residential neighborhoods, where every weekend from October to March, volunteers turn out to plant 6-10 foot tall trees along streets and sometimes in homeowners front yards. TA surpassed 130,000 trees planted last year and we are going strong!
We are not winning, however. Rampant development is the same everywhere in the US, and tree canopy loss to new buildings and subdivisions is greater than our little army of volunteers can make up for. But the City of Atlanta is revising its tree ordinance to try to provide greater protection for existing trees, and it also supports tree planting by providing trees free of charge to homeowners. It’s hard work, and never-ending, but there is no alternative if we want to avoid broiling to death on the sidewalk.
Great episode! I was wondering if you are familiar with the ficus tree elimination controversy along 24th Street in San Francisco. Claims have been made that the trees are diseased, buckle the sidewalk, and encourage crime because of their dense shade. Some have already been cut down. It would be more than a shame to lose this shade, as well as the gorgeous green tunnel effect made by their canopy. For a glimpse of 24th Street before them, watch old episodes of Streets of San Francisco, or the Louis Malle film “Crackers” (featuring an embryonic Sean Penn and Christine Baranski), which show the stark sleaze of the 70s and early 80s perfectly. I hope they are replaced quickly if we do lose them, with perhaps the Chinese elms that line Folsom Street. I love ginkgo trees but they are very slow growing.
An example of wrong headed preservation can be seen along 18th Street between Bryant and Florida, where a six story apartment building is nearing completion. A great effort has been made to keep the messy, soot-prone strawberry madrone trees, which are perfectly nice in parks or yards, but make terrible street trees. All around the area the only new plantings are purple leafed plums, which are a rant subject for another time.
Anyway, thanks for your podcast!
I wish this episode had included discussions with licensed and practicing landscape architects (*spoiler, I am one). A landscape architect could have provided some perspective that was missing from the entire episode. I had a really hard time listing to an architect talk about the in-feasibility of over structure designs. I work primarily in urban settings and I deal with street tree planting and over-structure or rooftop installations on a daily basis and there was a lot of basic information missing in this story. Both at-grade planting and over-structure planting are tightly interconnected with other disciplines (structural, architectural, civil, plumbing, waterproofing, architectural, etc.) and we all have to jump through the hoops the municipalities have in place for us (fire access, vision triangles, utilities clearances). Lastly, the San Francisco Bay Area is lacking in space as well as housing and often the only viable option to get some green gathering space is to built roof terraces or over structure courtyards.
Please, please, please interview some urban planners or architects or landscape architects from Europe or Asia. These are themes we are dealing with on a daily basis! Daily! And yes, landscape architects should know how to calculate the wind impact on vegetation in high altitudes!