What does a green roof weigh? Something that our customer service team is asked on a daily basis. Perhaps one of the most important green roofing questions there is. This is an excellent question and one that everyone should consider when starting any green roof project.
The simple answer is that the weight of a green roof is determined by the strength of your build or structure, so there are a few things to consider when creating your own green roof.
What is a Green Roof?
A green roof or living roof is a roof of a building that is covered with plants (often wildflowers or grass) and a growing medium, planted over a waterproofing membrane. Green roofs may also include additional layers, like a root barrier or drainage and irrigation systems.
Green roofs are a stunning addition to any garden or outdoor space. They provide many benefits to a garden as they are environmentally friendly and provide insulation, saving you money on heating costs.
How much does a green roof weigh?
A grass roof like this needs a mighty strong building to support it
A grass roof requires a strong building to support it. As a rule of thumb, the more biodiversity you want on a roof, the deeper the layer of growing medium needs to be. Thus, the heavier it will be.
If you are aiming to put a wildflower meadow on your roof, you would need at least 15cm of growing medium to support the plants that have deeper root systems. You can expect the loading to be upwards of 250Kg per square metre. This is quite a lot, especially if your building is an average garden shed. As such, you may want to consider strengthening the walls of your structure and the roof deck before installing the green roof.
A Lighter Option
If you’re looking for a lighter option to green roof, Enviromat green roof is lighter in weight than a wildflower roof. This is because we use specially engineered blankets for water management and the plant species used in the matting are very shallow-rooted. So they don’t require such deep soils or growing media.
A flat roof, built using the Enviromat green roof system will weigh the following:
- Drainage mat: Weight is negligible
- Water retention mat; holds up to 9 litres of water per square metre, so saturated weight is 9KG/m2
- Enviromat; when saturated with water in the summertime, when the plants are at their biggest and heaviest, the mats weigh 40-45Kg/m2
- Live Loading: Always allow a bit of extra strength in your structure to support extra weight such as snow or the maintenance man
- Total weight of an Enviromat roof* including live loading is 120Kg per square metre
*installed as per our recommendations and using Enviromat components
If you’d like to learn more about installing a green roof or the different options available to you, we have a selection of useful guides via our blog page.