No Such Thing as No Maintenance for Green Roofs

A green roof has been installed on the building you have bought or leased. Now you just leave it to do its’ own thing and it won’t need maintaining…right? Wrong! Unfortunately, too often this is the fate facing a green roof and as a consequence many are not performing or looking as they should. The reality, however, is that all that is actually required are regular and occasional maintenance visits.

We’re mainly talking here about extensive green roofs with sedum or wildflower vegetation. All of these roofs have a relatively shallow build-up with a typical growing medium depth of around 80-150mm and are often not regularly seen. Intensive roofs are likely to be highly visible being either on a podium deck or an accessible roof and it becomes fairly obvious if they haven’t been maintained. They will also require a much higher number of maintenance visits in any one year.

The path to a well-maintained green roof should start when the building is being designed. The provision of permanent safe access and fall protection is vital to ensure that the maintenance operative can carry out works safely and without, ideally, there being the need to spend a lot of time of time organising external facilities every time a visit is due with, consequently, considerable expense to the owner or occupier of the building.

Another key feature to factor in is a water supply close to the green roof area. Although permanent irrigation may not be a requirement of the specification, the roof will at least need a temporary facility whilst it is becoming established. There may also be a need to water the roof during dry spells or droughts particularly if temperatures during heatwaves rise in the future, even for sedum plants.

Once the project reaches contract stage it’s important to establish who is responsible for the care of the green roof between installation and practical completion and handover of the building. There may be a considerable amount of time that elapses between these events and it’s important for responsibilities to be clear earlier in the contract. Many a green roof has suffered badly during his phase.

How often does a green roof require maintenance? For an extensive roof, once established, twice annually should be sufficient. Be aware, however, that roofs with dry seeding or plug planting may need more weeding during the early years of their life until vegetation cover reaches an optimum level. For intensive roofs the frequency of visits will depend on the type of planting involved.

For extensive roofs the maintenance tasks are-:

• Removal of unwanted weed and grass growth, tree saplings and other woody plants  from the roof area.
• Make sure that pebble margins are kept clear of vegetation. This is important as these margins are a  fire safety feature.
• For roofs with wildflower vegetation, it’s important, once seed heads have dropped that spent foliage is cut back every Autumn and the arisings removed from the roof.
• Ensure that rainwater outlets, gutters, and inspection chambers are clear of debris and clean out as necessary.
• Apply a purpose made slow-release fertiliser once a year.

In addition to the above,  localised areas of sparse vegetation or even bare patches may appear every few years. This is quite common and can be rectified by supplementary planting. In the case of sedum roofs plants removed from the pebble areas during maintenance visits can be relocated to fill in gaps in the vegetation. Alternatively, additional plug plants can be installed, or dry seeding carried out depending on the requirements of the individual roof.

Who should carry out this work? Ideally it should be left to an experienced specialist contractor with a full understanding of green roofs and their requirements as well as the health and safety implications of working at height. The good news is that costs for maintenance visits are relatively modest.