Green Roofs – Is it time?

Background to Greening
The electric car and use of lithium batteries and the like will transform the way in which we use the car and don’t think for a moment that this will take 25 years or more – it won’t; within a decade the use of the combustion engine as the primary choice of powering a car will be well on the way towards the history books. Other green initiatives and technologies that affect the built environment will also start to become the norm. There is no doubt there is a developing wider appetite for “green technologies” including green roofs, in part because of a shift in cultural attitudes but it is also due to a maturing of the “green” market and it being seen as more mainstream. There are of course the health benefits or rather the health disadvantages of not changing.
Here are a couple of facts to get you thinking in the context of air pollution.
1. Levels of nitrogen dioxide have been above legal limits in almost 90% of urban areas in the UK since 2010.
2. Toxic fumes are estimated to cause 23,500 early deaths a year in the UK (4,000 per year in London alone.
Any initiatives that help tackle these problems will be a good thing. With the demise of diesel (and petrol eventually) powered methods of transportation the source of significant pollution will be removed but this does not present a total solution to how best we can make our built environment greener. The creation of green roofs is one way in which could form part of a wider solution to creating and transforming public and private spaces.
Green Roof Benefits
When we refer to green roofs [certainly for the purposes of this article] we are thinking really in the context of flat roofs on existing buildings. The types of buildings that have large expanses of flats roofs vary from schools and educational buildings to office buildings, industrial and factory buildings to hotels and of course residential blocks. For landlords and freeholders to consider green roofs as a viable option as part of an integrated planned maintenance, they must first understand the advantages of doing so.
The creation of green roofs, particularly in built up towns and cities can have a number of advantages as summarised below:
1. Improved air quality
2. Improved temperature regulation
3. Reduced rainwater run-off
4. Creates wildlife habitats & promotes biodiversity
5. Extends life span of roof
6. Roof membrane protection
7. Improves efficiency of solar panels
8. Improved aesthetics
9. Reduced energy costs
10. Positive effect on well-being
Green Roof Options
There are a number of different types of garden roof, defined by the way they are used. The basic types of green roof fit into either extensive or intensive categories. There are of course hybrid versions (i.e. semi- extensive or semi-intensive).
Extensive Green Roofs
Extensive green roof systems are generally intended to be viewed from another location as a decorative / ecological feature. They are not normally used as a recreational space to be walked through or sat in and often have limited access, used for maintenance purposes only. Due to the shallower substrate depths of extensive systems, the plant choices are more restricted to drought tolerant species such as sedums, grasses, wildflowers and mosses.
Extensive systems would be more ideally suited to flat roof areas where there is no access available other than for maintenance staff. Extensive systems can also be adopted for pitched roof applications.
Intensive Green Roofs
These systems are designed to be used as recreational spaces and often involve many features similar to traditional ground level gardens which can include paving, water features, lawns, shrubs and trees. These intensive 'roof gardens' are soil based multi layered systems and are so called because they are labour-intensive; requiring higher levels of irrigation, feeding, and other forms of maintenance compared to their extensive counterparts.
Intensive systems are more suited where an area of flat roof is able to be used by the buildings users
which in the case of residential blocks would be the lessees and tenants. By the nature of these types of
systems they are less suited for pitched roofs.
Green Roof Considerations & Costs
The option of choosing a green roof is undoubtedly a more complex undertaking than choosing a more traditional roofing solution. There are some very real and positive social and environmental reasons for choosing a green roof which have been outlined in this article. There are also some more practical considerations including:

  • What will the green roof be used for (extensive or intensive)?
  • What are the maintenance requirements?
  • Can the flat roof take the additional structural load of a green roof?
  • Is there sufficient drainage provision?
  • What is the buildings position, height, roof orientation? Is it shaded or too exposed?
  • Are there any ancillary works required? i.e. raising of parapets.
  • Is the type of waterproofing membrane / system adequately designed?
  • What are the irrigation requirements?
  • Are there any temporary water supply requirements?
  • How quickly will the green roof mature / blossom?
  • Is a green roof tantamount to betterment – if so, is this a problem?

In terms of cost, this is a difficult one to get right as every roof and every building and situation will be different. As a general guide, the initial capital outlay cost of a green roof can be as much as 200% more expensive than a more traditional flat roof waterproofing solution. This figure does not take into consideration the fact that the overall lifespan of a green roof can be twice that of a traditional roof. Over a 25 to 50-year period the green roof would win out (despite the high initial capital cost).

To Green or Not To Green
The benefits of creating a green roof are indisputable. The current levels of capital expenditure are however a perceived barrier to more green roof solutions being adopted. What is clear is that a careful, detailed and fully costed scheme appraisal should be carried out before a decision is made as to whether to take the plunge and go green.


It is likely that with regulatory changes and social and cultural changes, the take up of green roofs will increase over the coming years and the capital costs of green roofs will reduce accordingly. This will make the option of creating a green roof a very attractive proposition indeed and so like the rise of electric cars we see the rise of green roofs to follow a similar upward curve. You heard it here first!

For more info contact: Shaun Harris  |  0203 195 0857

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