Maintenance will depend on the type of green roof:

Intensive - as these are park like they will need regular maintenance; weeding, irrigating and other general garden activities

Semi intensive – will need periodic maintenance depending on the character of the planting. There are interesting developments in the UK to create semi intensive green roofs that need very little maintenance especially in terms of irrigation

Extensive green roofs – generally these are low maintenance. However low maintenance doesn't mean no maintenance. Depending on the type of green roof there may need to a degree of post installation maintenance in terms of watering/fertilizing. This is particularly true of sedum plugged or hydro seeded roofs. Mat type systems may need more maintenance as time goes on as they develop to grass quickly.

In Germany there is a rule of thumb that states '...one year sedums, two years sedums some grass, three years grass some sedums, four years grass...'

It is quite common to encounter extensive green roofs on the continent that have changed to dry grass roofs. This is because building managers cancel maintenance packages offered by the suppliers and allow the roof to do it's own thing.

The important point is that as long as all drainage elements and shingle perimeters are kept free of vegetation a roof left to its own devices will not harm the integrity of the building.

Another perceived barrier is the cost of maintaining a green roof. This cost though is relative to what kind of green roof is installed and how the owner wishes it to be used. Intensive green roofs can generally be considered as elevated parks and therefore require similar maintenance. Extensive green roofs require less maintenance and in general this can add only about £1/m2 per year more than the cost of maintaining a standard roof.

However, it is worth noting that in Germany most companies stop green roof manufacturers' recommended maintenance regimes after a number of years as they have fulfilled the planning criteria and have let the roofs go 'wild'. They merely visit the roof once a year to ensure that problematical shrubs and trees that could impact on the membranes have not colonised. This is generally a safety precaution, as green roofs are installed with root membranes and as they have shallow growing mediums, such plants would wither in time.

In general therefore extensive green roofs should be reasonably self-maintaining unless the client requires the roofs to look 'manicured'.