grass roof

By Enviromat: 27th March 2013

How much does a green roof weigh?

This is something that our customer service team is asked almost every day and it’s probably the most important green roofing question there could ever be….after all, it’s the strength of your building that determines what sort of green roof (if any) you should be installing.

A grass roof like this needs a mighty
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 and the heavier it is.  So, for example, if you were aiming to put a wild flower meadow on your roof, you would need AT LEAST 10-15cm of growing medium to support the plants that have deeper root systems.  Expect the loading to be upwards of 250Kg per square metre…which is quite a lot, especially if your building is an average garden shed.  You would probably need to strengthen the walls and the roof deck before installing the green roof build up.

An Enviromat green roof is lighter than a wild flower roof because we use specially engineered blankets for water management and because the plant species used in the matting are very shallow rooted….so they don’t need deep soils or growing media.

A flat roof, built using the Enviromat green roof system will weigh

  • 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 summer time, 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