Strolling through the territory of ARCH Moscow, it was hard not to notice one of their key exhibits in the form of a terraced roof. There we met the author of this project. Ilya (IM) has been involved in landscape architecture for many years. Considering the stable trend in the development of exploitable roofs in development projects (judging exclusively by the requests for such renders in the specifications), it was extremely interesting to talk to a professional in this field and dispel or confirm several myths that have long roamed in my mind)
I propose a theses recap of our dialogue. But first - let's establish one important definition.
Substrate is an artificial mix (not soil!) on a green roof with a minimal amount of organics, containing an optimal amount of essential nutrients necessary for the growth and development of plants.
Now, to the interview)
GJ - Ilya, you developed a GOST for exploitable and green roofs. What were the difficulties and how do our standards differ from foreign ones?
IM - Let's start with dispelling myths.
Myth #1 - the harsh climatic conditions of the central belt of Russia. In fact, the climate of Russia is if not ideal, then very favorable for landscaping in general and for the development of roof gardens, in particular. As an example of unfavorable conditions, one can take Calgary, Canada. The weather is very similar to ours, except for one "but". Very often the temperature during the day jumps over the 0 degrees mark. That is, there can be -20, and then a warm wind rolls over the mountains, and the temperature becomes +15-20 degrees. Such freeze-thaw cycles are most detrimental to plants. We don't have such a sharp delta, and plants simply hibernate in winter. By the way, in Siberia, precisely because of the rare thaws, conditions are even better than in Moscow.
Myth #2 - for plants, supposedly, the problem is the complete freezing of the roof substrate in the winter period. It can be reasonably objected that the depth of soil freezing at the 0 mark is 1.8 m. Therefore, there is absolutely no difference whether the plants are on the roof or on the ground in winter, both are completely frozen, and this does not harm the plants.
Myth #3 - plants on the roof need to be heated in winter. This is harmful, moreover, for the substrate on the roof, it is necessary to make thermal and vapor insulation so that the roof gives off less heat. Firstly, this is necessary according to the concept of energy efficiency. Secondly, so that the roof does not heat the plants on the exploitable roof with its heat. If this is not observed, the plants will not be able to properly enter winter hibernation and will die.
For example, I can cite an egregious case: in 97 we made the Alexandrovsky Garden and along the Kremlin wall we planted decorative firs at the request of Luzhkov under the control of the Kremlin commandant. According to the concept of Mosproekt-2, firs were supposed to stand along the entire wall, including behind the Tomb of the Unknown Soldier, where the eternal flame and the heat line pass. To my arguments that this should not be done under any circumstances, I was ordered to plant. As a result, all the firs there predictably died. You can walk around yourself and see: all the other firs have been growing successfully for 25 years, except for this place.
Myth #4 - it's difficult to come up with a list of plants that will survive in these conditions. Nothing needs to be invented, and I recommend everyone to learn from nature. She herself gives us a great variety of types of grasses, shrubs, and trees that grow without any watering and care.
GJ - Right now, a garden is being created outside our office. When they dug it up, they found an old entrance to the Tretyakov Gallery and decided to concrete it over. This resulted in a concrete pool about a meter deep. Am I correct in thinking that such a configuration has no effect on plant growth?
IM - There are nuances. Since concrete is a very heat-conductive material, the contact of roots with it adversely affects the plants. That's why thermal insulation is made not to preserve the concrete and heat within the structure, but to isolate and protect the roots of the plants. This is relevant for the now popular mobile urban containers with trees.
GJ - Is it possible to create a garden in the form of Amazon's headquarters, which would exist under the open sky in summer and be covered by a dome in winter, existing in greenhouse conditions?
IM - From a technical point of view, there is no limit to perfection. Technologically, this is possible. Regarding the assortment of plants, it's necessary to select according to the climate you will create inside the greenhouse. It's important to note that there are ecological groupings of plants. Roughly speaking, these are plants:
of the tropics (constant temperature of +25-30 degrees Celsius, high humidity, and high light) suitable for interiors and constant human presence.
of the subtropics (require a hot summer and a fairly cool winter (+9 +10 degrees Celsius)). It's uncomfortable for a person in such conditions.
of the middle zone of Russia (extremely cold winter and extremely warm summer).
Therefore, the difference in designing greenery in, say, Singapore (tropics), Chicago (prairies), or Moscow (middle zone of Russia) lies precisely in the selection of the plant assortment.
GJ - A layman's question that haunts me. What is the maximum height of a tree that can be placed on a roof?
IM - In terms of imagination, it's not limited at all :) In my practice, I've seen fifteen-meter lindens growing on a roof with only 50 cm of substrate. In this case, the roots spread in its thickness, limited by a special certified root protection film. The only limit to the height of plants on the roof is its load-bearing capacity, considered during the design. It's also important to note that the distributed load reaches optimal values after the plant grows. In the early stages, questions of wind resistance and how the plant will be held in place until it finally takes root must be included in the project as a separate block.
Conclusion
For me personally, the dialogue with Ilya turned into a quite interesting lecture. I can confidently summarize that developers are not deceiving when creating open terraces in their residential complexes. And what we draw on the renders is indeed implemented. As an example, we walked to the roof of their office, where a beautiful meadow has been independently living on a 10 cm substrate for 13 years, the center of which is occupied by a seven-year-old elm) Just like in the village, beautiful!