Spring and summer holiday time is ideal for travelling. If you stop in Austria, don't miss the attractive, greened Kunst Haus in Vienna. Magnificent building, eye-catching with breeze of the fresh air coming from the plants, successfully incorporated into building envelope. It feels good, to be in touch of the nature in the cities. Vienna city planners are obviously aware of that – more green means better life quality for urban dwellers.
Picture 1: Green Kunst haus in Vienna (source)
Lightweight extensive versus semi- intensive and intensive green roof system
But very often, buildings are not suitable for such a load bearing due to the construction limits. Do you know how much does a bulk bag (one cubic meter) of a rooftop substrate weight? It can easily reach 800 kg per bag, or even more. And imagine, how many of these bulk bags must be delivered on a building rooftop to create a roof garden with lushy green bushes, trees, perennials and flowers.
Picture 2: Intensive green roof installation: substrate delivery (source)
Beside limited infrastructure possibilities in cities (e.g., dense roads full of traffic, limited traffic regime…), availability of suitable equipment, municipality traffic permits, you must also engage bunch of professionals, dedicate significant amount of time and money, and to wait for the right season in the year for the installation. On the other hand, lightweight green roof system installation is far more flexible in terms of logistics and also regarding the season of installation. See lightweight Urbanscape installation process here.
Possibilities to create rich vegetation on a rooftop can be limited. But this does not mean that you need to live in a grey concrete jungle. There are numerous options to select a lighter version of a green roof system and enjoy it throughout the years on new or retrofitted building.
Load dilemma
As well explained in a book of Lucket (2009), in case that rooftop garden will be publicly accessible, the place where people can gather, you must ensure that the rooftop structure has the structural capacity for such activity on the roof. It is important to determine the building codes and local requirement for live loads and dead loads. The green roof assembly, with plants and water required to saturate the growing media is dead load of the structure, while excess water, snow and people visiting the green roof are the live load of the structure. One must therefore formulate on time the green roof as accessible or not, with desired plants and subsequently appropriate growing media depth (and weight) to support them.
Picture 3: Scheme and general characteristics of different green roof systems (Ujma, 2023).
With no doubt, evaluating loading requirements and uploading the structure in case of publicly accessible and intensive green roof is the most viable and economical in the design phase of the buildings’ construction. When retrofitting, evaluation of the structural capacity and upgrading already existing structure is significantly more difficult and expensive. That is why it is often that in case of retrofit, many intensive green roof planning drops out due to inadequate structural capacity and significant costs of upgrades. Nevertheless, dead loading could be reduced by employing the irrigation system and decreasing substrate depth, while live load decrease can lead to abandon public accessibility of the rooftop garden and design simpler, extensive roof.
When the green roof is not publicly accessible, the live load structural requirement is less complicated. First the local building code with load requirements is determined and then the saturated weight of the green roof system is calculated or obtained via green roof system provider (check dry and saturated weight of the Urbanscape green roof system in Table 1). The entire green roof has usually uniform dead load based on saturated weight of green roof assembly, but keep in mind that in case of positioning large planters, or deeper growing media for larger showcase plants, you must take their weight into account, which can lead to trade-offs between green roof assembly and structural costs.
Study case – industrial facility in Spain
Lightweight green roof systems are more adaptable and easier to implement across various building types, making them more practical solution for widespread urban applications. Their ability to reduce stormwater runoff, improve air quality and promote building’s energy efficiency without requiring significant structural modification makes them sustainable and environmentally friendly option for many rural areas.
Picture 4: Urbanscape Premium High system on the metal roof in Spain
This production facility has been facing a challenge of weight restrains which is common on the metal roofs with long spans between the ribs. The traditional green roofs with sufficient storm-water handling capacity (soil based heavy weight system) could not be implemented. The lightweight Urbanscape green roof system is focusing on good storm-water handling capacity which can capture up to 45 litres of water /m2 but still limiting weight to only 70 kg/m2 which is half of traditional green roofs with similar capacity. The provided system can capture up to 60% of yearly rain water.
Turn grey into green
Urbanscape green roof system features unique rock mineral wool substrate alternative that is highly efficient in water retention, while being significantly lighter than traditional green roof substrates. It provides immediate green coverage by pre-grown vegetation blankets above the light-weight, high water retention multipurpose growing media, commercially known as Urbanscape Green roll. Urbanscape technical figures (including weight), together with the environmental footprint are disclosed in Urbanscape Green Roof System Environmental Product Declaration (see table below).
| Parameter | Value | Unit |
| Water storage capacity | 37 | Vol. % |
| System sound absorption (EN ISO 10140-1 / EN ISO 10140-2) | 57 | dB |
| System height | 100 | mm |
| System weight (saturated) | 57,55 | kg/m² |
| System weight (unsaturated / dry) | 20,55 | kg/m² |
| Maximum water retention capacity | 37 | l/m² |
| pH value of growing media (CaCl₂) | 7,5 | - |
| Fire resistance class of growing media (EN 13501-1) | A1 | - |
| Salt content of growing media (KCl) | 0,03 | g/l |
Table 1: technical characteristics of Urbanscape green roof system (EPD, 2022).
Main Urbanscape benefits:
- Lightweight: suitable for a wide range of buildings, including those with limited load-bearing capacity.
- High water retention: efficiently manages stormwater, reducing runoff
- Thermal insulation: improves energy efficiency of the building (decreasing energy demand for heating and cooling)
- Biodiversity: supports plant species, enhancing urban biodiversity and offering shelter to pollinators
Comparison to other green roof systems:
While other green roof systems may offer similar benefits, Urbanscape lightweight nature and high water retention capacity make it particularly advantageous for urban environments where structural load and water management are critical concerns. Its ease of installation and immediate green coverage also set it apart from traditional, heavier systems.
Would you like more details on how to implement this system in your project? Check our tools and documents:
Literature:
Luckett, K., 2009. Green roof construction and maintenance. McGraw - Hills GreenSource Books.
Ujma, A., 2023. Prospect for creating surfaces with vegetations on buildings in Pola. Environmental safety and natural resources. 2023.