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Monday, March 21, 2011

Secondary Spaces

Secondary Spaces: Roof Gardens in Denver

Husein Krvavac & Karla Dakin

Recently my colleague Husein Krvavac, a graduate of the master’s program in Urban Planning at CU Denver, told me about some interesting roof gardens and green roofs that he had seen while working in the new Excel building in downtown Denver. Because of our backgrounds, we decided to check out these places which we call secondary spaces. Here follows some background and our journey.

Husein: I have always had an interest in roof gardens, they give a building much more than heating and cooling efficiency. They provide buildings with these special places were nature can thrive in the middle of a dense urban area. While working on Museum of Contemporary Art Roof Garden, I was introduced to all aspects of a roof garden from loads and weight issues on the roof structure to height of plants that can be planted and not be blown by a wind the next day. It is difficult to build a roof garden so when I saw all of the roof gardens around new Excel building in northeast corner of downtown Denver it made me question when these roof gardens were built and why so many of them were built in this area.

Karla: When Husein and I collaborated, along with an incredible team, on the roof garden at MCA, the curiosity about roof gardens and green roofs stuck. My interest comes from a landscape perspective rather than urban planning background. I am curious about habitat matrixes and green oases above ground in the urban core of downtown Denver.

As a part of our adventure, we came up with eight questions: four from an urban planning perspective and four from a landscape architecture perspective. Here follows the questions and our responses.

1. 1. Private vs. Public or semi public. What defines this? (Control, Maintenance, Access)

From the sites visited we can conclude that there is no public vs. private, it is private vs. private. Historically, cities encourage developers to provide open space for public use and gatherings in exchange for additional floor space. Municipal, state and federally owned public places are usually less controlled then privately owned places. Our taxes maintain our public places, and private landscapes are usually privately maintained. Then there is this third category of which we write about here: privately owned public places. They have a different and strict set of rules for the public accessing these spaces. The owner has a right to limit or restrict access to the area (2009 Nemeth, Schmidt. The Privatization of Public space: Modeling and Measuring of Publicness). Historically privately owned exterior spaces provided for “the public”, (defined here perhaps as visitors not owners/taxpayers) gathering were built in exchange for additional floor space.

But wait, it gets more confusing. The first site, 1125 Seventeenth Street, had a sign that read, “Private Property: Facilities are for Tenant Use Only. Violators Subject to Arrest.” At the same time, the roof garden has huge, wide stairs with planters, providing clear connection to Skyline Park area without any physical barriers to the street level.


The second site, which we will call the sibling site as it is across the street and connected by an elevated walkway, is open to the public from four sides without any restriction. You can enter at several points along 17th Street passing through a gesture of an urban forest with grass and planters filled with mature plant material. There are no deterring signs that we could find but you definitely have to do some wandering to explore. Lest you think you are in a public park and want to take pictures of the beautiful space, security guards emerge from the building to inform you that photography is prohibited.


The third site is on the second level, adjacent to an apartment complex and is only available to those living there. There is no access, except for locked gates, from the street level and the only way to get in is via the central elevators inside the building. This place is definitely private.

2. 2. 2. Why were these green spaces above ground built in the first place? They all seem to come from a similar time period in Denver’s construction, around the seventies? Was there a city requirement? Privilege of being able to construct more floors? Credit of some kind or trade off?

As previously noted, we assume that these green spaces were usually built by developers so city governments would allow more floor space to be added to the development. As part of the agreement perhaps, these spaces would be accessible to all people, but the developer would have a right to limit access to the roof garden in certain hours along with a set of rules that would be different from typical public places, such as parks (2009 Nemeth, Schmidt. The privatization of public space: modeling and measuring of publicness. The usage at site number is restricted to tenants. The question is if an agreement was reached between the developer and the city, the manifestation being an exterior “public” space, is the developer a breaking their part of the bargain by limiting or eliminating access?

The next question is why the sites were built on the second and third levels, usually on top of garage structures. This might seem like an obvious place to put them as ground level real estate is a premium. However, by the look of the buildings and the plant material in these secondary spaces, it can be concluded that the sites were built 25-30 years ago before any LEED requirement. So why would developers go for roof gardens that require special structural plans that cost much more then traditional roof membranes? Was the tradeoff worth the cost?3. Who uses these spaces & how? More than one person or a single family (as in a private garden) uses these spaces. There is probably a lot more passive use with people smoking cigarettes on a bench or having lunch vs. active use of site like running around or playing basketball though there is a curious amount of programmed athletic space up in these areas.

Of the three sites, only one is “open” or readily accessible to the public. The other two are limited to tenants; one is an office building and the other is an apartment complex. Based on multiple site visits, one might conclude that all three sites are underused. Two of the sites have recreational playgrounds in the forms of a basketball court, tennis court and putting greens but the day we visited, the wind was howling and nobody was around. The only users we can surmise would be office workers on lunch break who stay to eat a sandwich or salad around noon, going back to work after an hour or so. Based on conversation with the management of the apartment complex, we found that the roof garden there is used mostly for barbecue parties.The real users or inhabitants of these secondary spaces might be the insects, birds and other flora, who make these brief respites from the harsh urban core their home or way station.

4. How does time affect these spaces? What are the maintenance issues? Who does what and why?

As all of the spaces are privately owned, the maintenance varies from very well maintained, (one place is planted every year with annuals) to barely maintained where the floor tiles are deteriorating and landscape fabric shows through mulch in the raised beds. What we are unable to ascertain is whether the maintenance or lack there of is affecting the structure, i.e. leaks.


5. How do these roof gardens affect or impact urban habitat? What is the size and scope of the landscape installed? What shape is the plant material in?

These secondary landscapes are at least twenty years, and it is interesting to note that not only is the plant material still alive, it is thriving and mature. In three to four inches of soil, Ponderosa pines reach upwards of twenty feet. Deciduous trees, especially Crabapples have calipers ranging from four to six inches or more. In terms of trees, there are mostly ornamentals as well as large shrubs, ornamental grasses, and perennials and groundcovers. Only where annuals are planted, one does not get a sense of being in an established garden. It feels more like an amusement park entrance.

The plant material exists for the most part in raised beds above roof decks except for the turf areas. Plantings range from dense arrangements to solitary trees and scattered shrubs. There is an exception at 1225 Seventeenth Street. This building has a large, west facing, civic plaza, flush to the street on the north with a large kinetic sculpture, and one level above the street on the south. On the roof level on the south, there is patch of trees in turf, simulating a forest of sorts with stair access to the street. On the east side of the building there is another roof garden with an eating & gathering area surrounded by swirls of turf, annual beds, and a putting green.



Due to the extent and maturity of the plant material present, we can only assume these secondary spaces are urban oases for insect, bird and to some extent, animal life. When we return during the growing season, we will spend some time gauging other living creatures besides humans.

6. 6. How does the design fit into today’s design framework? Are these places for gathering, oases, parks?

These private parks can be categorized as roof gardens with some sort of decking and seating areas. Some have grills, basketball courts, putting green, garbage cans. Plant material occupies raised beds with the exception of the roof garden described in question five. Some of the spaces could be considered green roofs because of the percentage of “green” coverage on the roof. The design intention is perhaps to create exterior amenities or pseudo parks in exchange for more built space. But wouldn’t it be interesting if they were also thinking about sustainable, stormwater, heat island mitigation issues.Another interesting point is that we have this design idea being implemented 20-25 years ago that form these park like urban areas, far different from the rest of downtown Denver, whereas now we have new, design trends (encouraged by LEED standards) where new buildings have roof gardens, hence Excel building and Four-Seasons hotel.

The existence of these roof gardens in this relative small area makes us think of a new theory in urban planning; “Landscape Urbanism. The most outspoken person behind this theory is Charles Waldheim, currently a professor at Harvard. The idea is that urbanism is not about arrangement of buildings, street grids, and parks, rather it is about living processes, flows and the importance of respecting ecological infrastructure”… (2010, Neyfakh. “Landscape Urbanists’ Challenging OldSchool ‘New Urbanism’ for future of…”)to create holistic systems or matrixes made of several landscape components like roof gardens or pervious paving…” We think these secondary spaces are such a system comprised of several landscape components, i.e. roof gardens, pervious paving andstorm water drainage systems that affect a larger area of the city beyond the immediate site.

7 7 7. Do the roof gardens address any of our current sustainable directives like storm water filtration or heat island mitigation?

The spaces with larger beds and more extensive coverage must play a role however indeterminate on storm water filtration. The trading out of hardscape for soft along with mature trees definitely help reduce heat island mitigation.

8. . 8. Do the roof gardens begin to form a matrix or patchwork within the urban fabric, intentionally or not?

Without further research, intentionally or not, because of the proximate locations of the all the secondary spaces we discovered, there is without a doubt a matrix of urban landscape ecology within a dense built environment. This is readily apparent from the google earth image. When we walked onto one roof, we could see across the street to another one. It was this process of discovery, like being on the high seas of tall buildings where we found the next island to explore.

Pedestrian connections are available but limited; two neighboring roof gardens are connected by a bridge above the street, but one roof garden is for tenant use only and the second one is open for anybody. There are visible rules to access the first site posted by sign and physical rules manifested by a chain baring entry to the second site.

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