| There are a number
of ways we can make our roofs more environmentally sound: improving energy
efficiency through optimum insulation and better air tightness for example.
But what about the option of literally greening up a roof? A green roof
enhances thermal performance, helps to retain storm water (thereby aiding
flood management), cleans the air, reduces dust and smog levels and lessens
the urban heat island effect in cities. In a country setting it enables
buildings to blend in with their surroundings; in a city it breathes green
life into the glass and concrete jungle. The benefits are multiple and
significant. |
| Of course the idea
is far from new, with evidence of turf roofs on buildings going back as far
as 2500 BC in the Orkney Isles of Scotland, providing excellent thermal
protection from the often harsh weather, and weather protection could once
again be a crucial factor in the rising popularity of this highly
environmentally friendly construction genre. |
| For example, the
issue of flood management is particularly important in light of the severe
flooding experienced across the country last year. Green roofs will not
solve the problem of persistent rain, but they can certainly reduce the
impact and should be a consideration in any future developments,
particularly in vulnerable areas. |
| If all of the
above benefits are not enough for you, a green roof creates a protective
layer which increases the life expectancy of the roof and provides a heat
shield in the summer. It visually enhances quality of life for the occupants
of the building and those surrounding it, and increases the available
natural habitat for animals and plants. It also provides a very effective
barrier to noise, greatly enhancing acoustic performance. Last but not
least, it utilises what could otherwise be dead space, offering immense
recreational and educational possibilities. |
| So, what is
involved in building a green roof? Well, in the first place it is important
to understand the various types available, as they all have different
attributes, advantages and requirements. |
| There are several
types of modern green roof: Intensive, Semi-Intensive, Extensive, and
Biodiverse. The latter carries the least commercial or aesthetic benefit,
comprising of rubble strewn across the roof to allow the local wildlife to
continue to thrive in a city setting – a movement symbolised by the Black
Redstart bird that began to thrive in bombed London during the Second World
War. |
| Extensive green
roofs are constructed using low maintenance planting such as succulents,
grasses and herbs. This type of roof performs the various vital functions of
improving the aesthetics of or masking the building, controlling rainwater
run off, and improving thermal performance by helping to keep the building
warm in the winter and cool in the summer. It is not suitable for
recreational purposes, but requires very little maintenance, and can provide
a pleasing carpet of colour as well as an ideal environment to encourage
biodiversity. This is generally the most practical and popular choice,
offering multiple benefits over time following the initial investment. |
| Intensive green
roofs, on the other hand, can be far more flexible, whether they are
designed as simple gardens or fully landscaped recreational areas with all
the features of a green space at ground level. Added to the many
environmental, ecological and economical benefits then is the advantage of a
useable outdoor living space, providing people with the beneficial effects
associated with being in contact with a green environment. Naturally, this
also carries the commitment of high maintenance with it, as any cultivated
garden or green space does. |
| One potential
downside of all of these projects is that a green roof can dramatically
increase the loading on a building, so a primary factor is to determine
whether a building structure can take the additional weight that the green
roof imposes, particularly where an existing structure is being
retro-fitted. |
| Clearly this is
less of an issue where the green roof is part of a new design, as the
loading will be taken into account when specifying the supporting structure.
The challenge then is to identify materials and products that are capable of
sustaining the high loading without intruding excessively on the internal
space or substantially increasing the capital costs. |
| The additional
loading of a green roof varies depending on the type. Although they all
consist of the same basic series of layers, the depth of the growing medium
and type of vegetation and features will produce significant differences. |
| Typically these
layers would include a waterproof layer, which must be root proof as well as
waterproof. A drainage layer, which could comprise lightweight aggregates or
preformed plastic cellular layers, performs the task of removing excess
water and preventing the plants from sitting in waterlogged soil. |
| A filter mat will
normally be used between the growing medium and the drainage layer to
prevent the latter getting clogged. The growing medium itself would usually
be a lightweight ‘soil’ artificially manufactured using material such as
vermiculite mixed with organic compost, which may then need an erosion mat
to prevent wind erosion in exposed areas whilst the vegetation establishes
itself. |
| Perhaps the
hardest aspect to assess is the vegetation itself, certainly for an
intensive green roof which may incorporate trees or larger shrubs that will
grow to maturity, necessitating a long term projection of weight. Any
calculations should of course also be based on the growing medium and
substrate being saturated. |
| So what are the
likely impacts of this additional loading on a building? Naturally the
primary structure must be designed to withstand the weight, but there would
also be an expectation of increased secondary steelwork, which would have
cost and possibly space implications. An innovative way round this is to use
a structural insulated panel that has the strength to reduce or even
eliminate secondary steelwork. |
| Market leaders
Kingspan Insulated Panels have recently launched Kingspan Envirodek™,
designed to provide a durable, high performance base for a green roof. The
system can provide spans of up to 6 metres and a load bearing capacity of up
to 500kg/m2 at 3 metre double spans. Kingspan Envirodek™ is
suitable for both flat and curved roof applications and can be installed in
an efficient single fix application. Its versatility and strength makes it
an excellent choice for green roof constructions. |
| The potential for
such a system to revolutionise the market for green roofs is great, as it
simplifies the design process, speeds up construction, lends excellent and
instant weather tightness, as well as added quality assurance for projects.
The elimination of secondary steelwork also helps to keep costs down whilst
maximising space. Even more importantly it reduces the overall loading on
the primary structure. |
| Greening up
rooftops is already well underway in other parts of the world: In Germany,
for example, it is estimated that 7 percent of all newly constructed flat
roofs are green, and over 108 million square feet of green roofs have been
planted in recent years. With so much at stake in terms of climate change,
flood management and thermal performance, not to mention the aesthetic
benefits, it would be good to see a similar step change in our approach to
roofing in the UK. |
| A full, free
technical advisory and compliance service is available through Kingspan
envirocare Technical Services. |
| FREEPHONE: 0800
587 0090 Fax: 01352 716111
Envirocare@kingspanpanels.com |
