Hello everyone,
Our local development plan requires a green roof if building with a flat roof. Since we are building with a flat roof, it seems we have no choice but to install a green roof.
The specifications from the prefab home manufacturer state the following: an increase in roof load of 1.8 kN/m² (37.5 psf) for the green roof. The green roof is to be installed by the client. [Provider] will construct the flat roof system with a rainproof rubber membrane, which is not root-resistant. Further in the text, it states that the roof structure is designed for a standard snow load of 0.85 kN/m² (17.8 psf).
Can I therefore correctly assume that the roof's load-bearing capacity is 2.65 kN/m² (55.3 psf)? Which corresponds roughly to 265 kg (584 lbs).
How should I properly install the green roof? According to the house seller, it was roughly explained that you only need to put some soil and seeds on it, and the rest happens on its own. The cost for the green roof was also mentioned as “around 1,000 euros.” Apparently, this statement isn’t entirely accurate, as I have found various contradictory information online.
Additionally, I have received a quote where an excavation contractor offers to deliver, spread, and level lava rock for the flat roof with a thickness of 10 cm (4 inches) – without green roofing. Doesn’t there need to be an additional protective layer on the roof beforehand? Or is the rubber membrane from the home manufacturer sufficient?
What other costs should I expect?
Our local development plan requires a green roof if building with a flat roof. Since we are building with a flat roof, it seems we have no choice but to install a green roof.
The specifications from the prefab home manufacturer state the following: an increase in roof load of 1.8 kN/m² (37.5 psf) for the green roof. The green roof is to be installed by the client. [Provider] will construct the flat roof system with a rainproof rubber membrane, which is not root-resistant. Further in the text, it states that the roof structure is designed for a standard snow load of 0.85 kN/m² (17.8 psf).
Can I therefore correctly assume that the roof's load-bearing capacity is 2.65 kN/m² (55.3 psf)? Which corresponds roughly to 265 kg (584 lbs).
How should I properly install the green roof? According to the house seller, it was roughly explained that you only need to put some soil and seeds on it, and the rest happens on its own. The cost for the green roof was also mentioned as “around 1,000 euros.” Apparently, this statement isn’t entirely accurate, as I have found various contradictory information online.
Additionally, I have received a quote where an excavation contractor offers to deliver, spread, and level lava rock for the flat roof with a thickness of 10 cm (4 inches) – without green roofing. Doesn’t there need to be an additional protective layer on the roof beforehand? Or is the rubber membrane from the home manufacturer sufficient?
What other costs should I expect?
So, it’s done now. Yesterday at 6:00 PM the delivery arrived, and by 12:00 PM today the green roof was finished: 34 m² (365 sq ft), 6 hours of work, 2 people. The result is impressive.
Before:
Delivery:
Root barrier membrane, drainage layers, substrate trays, gravel strips:
Finished:
Before:
Delivery:
Root barrier membrane, drainage layers, substrate trays, gravel strips:
Finished:
M
Marcel_ST29 Jan 2023 12:14Thank you for the great experience report.
I am currently building as well and need to green about 75% of the roof, approximately 100 m² (1,076 sq ft).
Do I need to consider a specific load-bearing capacity? Does the roof need to be specially prepared for this, or can I simply install it on our flat roof like you did? Thanks for your response.
I am currently building as well and need to green about 75% of the roof, approximately 100 m² (1,076 sq ft).
Do I need to consider a specific load-bearing capacity? Does the roof need to be specially prepared for this, or can I simply install it on our flat roof like you did? Thanks for your response.
Marcel_ST schrieb:
Thanks for the detailed report.
I am currently building as well and need to green about 75% of the roof, roughly 100 m² (1,076 sq ft).
Do I need to consider any specific load capacity? Does the roof need to be prepared for this, or can I just install it directly on our flat roof, like you did? Thanks for any advice. Whether you can install directly on the existing roof depends on the waterproofing. It works with a membrane roof. For roofing felt, an additional membrane layer is needed.
Regarding the load capacity, it’s helpful to check the structural calculations or consult a structural engineer. The manufacturer will specify the weight of the green roof per square meter. You also need to add the weight of retained rainwater, which can significantly increase the total load. For my green roof, I assumed a maximum of 150 kg/m² (31 lbs/sq ft). Since my roof has a concrete slab beneath the membrane and insulation, this was not an issue.
W
WilderSueden29 Jan 2023 15:44You should calculate a roof load of 10 kg/m² (2.05 lbs/ft²) per centimeter (0.39 inches) of substrate thickness.
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