How Much Weight Does a Planted Roof Add?
Weight does not only concern the substrate and the plants.
It concerns the saturated system, that is, the weight when the substrate is fully wetted.
Indicatively:
Extensive system 120 – 150 kg/m² saturated
Semi-intensive 180 – 300 kg/m²
Intensive (roof garden) 300 – 600+ kg/m²
In special cases (trees, large plantings) it can exceed 800 kg/m²
These numbers are not theoretical. These are real loads that must be taken into account in the static study.
What Does a Civil Engineer Check?
The static check examines:
- The load-bearing structure (slabs, beams, columns)
- The permanent and mobile loads
- The additional load from the planted system
- The water loads in case of heavy rainfall
- Local reinforcements for zones with greater planting depth
In many apartment buildings from the 70s–90s, there is the possibility of an extensive system without reinforcement. In intensive systems, however, the check is necessary.
Myth: “The Roof Can’t Hold Up”
In most cases, the problem is not that the roof can’t hold up.
The problem is that the load distribution has not been done correctly.
A properly designed green roof:
- Distributes loads evenly
- Avoids overloads at specific points
- Takes into account the position of the pillars
Technical detail makes the difference.
Which Factors Increase Weight?
- Deep substrate depth
- Trees with heavy roots
- Poor drainage (standing water = additional weight)
- Incorrect substrate (e.g. common soil instead of a light mix)
The use of a specialized substrate, such as ERSM – Ecoverti Roof Substrate Mix, significantly reduces the load compared to conventional soil.
Why Stratigraphy Is Crucial
Weight is not just a matter of substrate.
Certified systems, such as those of Optigreen, are designed to:
- have controlled water retention
- drain properly
- avoid supersaturation
Poor drainage can increase the weight much more than calculated.
What Happens If a Static Check Is Not Done?
The risks include:
- Cracks
- Settlements
- Overloading of beams
- Waterproofing problems
A static study is not a standard procedure. It is a safety issue.
Can I Do a Green Roof on an Old Apartment Building?
Yes — in most cases an extensive system can be applied.
However, the final decision is made after:
- Checking the plans
- Inspection
- Calculation of loads
Each building is different.
Conclusion
The question is not “can it withstand?”
The correct question is:
“Which system can withstand?”
With proper design, proper load distribution and technical precision, most buildings can support some type of green roof.
Success lies in:
- working with a civil engineer
- using certified systems
- applying the right technology
Want to Know If Your Building Can Withstand?
ECOVERTI works with engineers and provides technical guidance for the proper design of green roofs, with high-end systems.
A green roof can be done safely. It just has to be done right!