The paradox in green roofs are as follow:
1- The roofs of the buildings in humid area with annual precipitation more than about 400mm/year, are mostly sloped roofs, so cannot be suitable for vegetated rooftops.
2- The vegetated rooftops can be used in flat roofs but these types of house are mostly has been built in dry climate with low precipitation and therefore, the storm water management and minimizing the development impact on hydrology cannot be reached, when there are no precipitation and even in summer all of the plants can be easily dry and will need irrigation. In other words, in a dry climate with annual precipitation less than about 400mm/year, there is no water to be managed with vegetated rooftops methods and even for irrigation of vegetated rooftops in summer, excess water is required (this will increase evapotranspiration as well). If the vegetated rooftops not being irrigated in dry periods and become dried it can be a source of dust in windy condition itself.
3- In the best conditions, if we find a house with a flat roof in a humid area that be suitable for vegetated rooftops, we must check the construction feasibility. Because the design of the roofs are according to many factors like live and dead loads (earthquake, snow weights and etc.). Therefore at the constructed buildings the weights of vegetated rooftops (the plants, sands and the materials for green roofs) has not been calculated and placing more weight on the roof structure than designed cannot be done.
Technical Report Conflicts in green roofs as a LID method
Dear Prof. Bachir ACHOUR
Thank you for your information. It seems that, If we choose a native plant in a case study in arid area from the list of the drought tolerant plants that you mentioned some of them, the problem of the irrigation of the green roofs in the summer will be solved. Thus, if the structural problem that I mentions as the 3rd paradox also become solved it can be useful in arid area.
But, I think the LID (low impact development) means that we must use the methods to turn the conditions of the urban area like the past and before urbanization and also for stormwater management.
In arid area with low precipitation the sustainable condition of the area that was exist before the urbanization was low dense vegetation pattern (not dense vegetation like green roofs). Moreover, usually there is no need for stormwater management with this method.
Of course in arid area use of green roofs with the plants you mentioned can be very beneficial for decreasing the roofs temperature and energy usage, but maybe we must choose another name for it, not "LID method".
Finally, what about the area with high precipitation, since of the main benefits of green roofs as a LID method must be stormwater management and the main problems for deforestation because of urbanization belongs to these area. If green roofs is easily feasible for the houses with sloped roofs?
I must repeat that, I really appreciate your answer and it is very useful and I am also trying to improve the feasibility of green roofs like you.
Best Regards
Pirouz
Dear Behrouz,
Just for information. For green roofs, the following plants that require little maintenance and are drought tolerant are used: Aster, sedum, astragalus (milk vetch), campanula, boreal galium, petalostemum (purple prairie clover), solidago (goldenrod), baptisia australis (false indigo), asclepias tuberosa (butterfly weed), evening primrose, cinquefoil, black-eyed Susan, silphium perfoliatum (cup plant), to name a few.
With my best regards
Prof. Bachir ACHOUR
Dear Prof. Bachir ACHOUR
Thank you for your information. It seems that, If we choose a native plant in a case study in arid area from the list of the drought tolerant plants that you mentioned some of them, the problem of the irrigation of the green roofs in the summer will be solved. Thus, if the structural problem that I mentions as the 3rd paradox also become solved it can be useful in arid area.
But, I think the LID (low impact development) means that we must use the methods to turn the conditions of the urban area like the past and before urbanization and also for stormwater management.
In arid area with low precipitation the sustainable condition of the area that was exist before the urbanization was low dense vegetation pattern (not dense vegetation like green roofs). Moreover, usually there is no need for stormwater management with this method.
Of course in arid area use of green roofs with the plants you mentioned can be very beneficial for decreasing the roofs temperature and energy usage, but maybe we must choose another name for it, not "LID method".
Finally, what about the area with high precipitation, since of the main benefits of green roofs as a LID method must be stormwater management and the main problems for deforestation because of urbanization belongs to these area. If green roofs is easily feasible for the houses with sloped roofs?
I must repeat that, I really appreciate your answer and it is very useful and I am also trying to improve the feasibility of green roofs like you.
Best Regards
Pirouz
- Badges
- Science topic
- Similar topics
- Geoscience
- Hydrology