February 2022

Blue/Green Roofs
OVERCOMING THE INSTALLATION
DILEMMAS OF BLUE / GREEN ROOFS
Following the Mayor of London’s pledge to increase the number of blue / green roofs
in the city, and various ongoing legislative changes in the pipeline, ACO Building
Drainage says installation of these roofing systems is set to increase over the next few
years. This raises the stakes for those involved in the delivery of blue / green roof
solutions, and as Neill Robinson-Welsh, of ACO Building Drainage explains, requires
a detailed understanding of how best to specify and install these systems.
As is well known across the construction
industry, green roofs provide several
benefits when compared to traditional
roofs. They are a way of incorporating greenery
and vegetation onto the top of buildings, which in
turn provides improved insulation to the
structure, helping to combat the urban heat
island effect, whereby city and suburban
developments absorb and trap heat.
They can also play a significant role in the
sustainable mitigation of heavy rainfall, when
combined with a blue roof attenuation system.
Blue / green roofs deliver on the four pillars of
SuDS, as they can achieve the objectives of water
quantity, water quality, amenity, and biodiversity,
whilst also performing the primary function of a
roof – to keep the building dry and warm.
The green roof rising
It is fair to suggest that blue / green roofs will
become increasingly prevalent in the years ahead
owing to their many advantages. According to
recent market research, the global green roof
market size accounted for $1.45 billion in 2019,
and is expected to reach $4.19 billion by 2027,
registering a CAGR of 15.6% from 2020 to 2027.
This trend is underpinned by urban greening
projects that seek to deliver more green areas
into cities without impacting existing
infrastructure.
In the UK, London is arguably the best example of
where blue / green roofs are starting to take hold
“It is fair to suggest
that blue / green roofs
will become
increasingly prevalent
in the years ahead
owing to their many
advantages”
in popularity. The London Plan – the spatial
development strategy for the city that
governs much of the planning of
new and existing developments
– specifically addresses blue
and green roofs. In the plan, it
suggests that blue / green roofs,
wherever possible, should be
included in major development
proposals.
Blue / green roofs are also backed
significantly by public figures. The
Mayor of London, Sadiq Khan,
recently pledged to increase the
number of blue / green roofs in
the Capital as part of his reelection
manifesto. As such,
roofing professionals must know the
key installation considerations ahead of
this trend taking hold.
The dilemma of the flat roof
When it comes to blue roof design, managing
Above: Uptake of blue/green roofs is expected to increase
further. Below: Installing RoofBloxx.
Bottom: ACO’s blue roof calculation software.
rainfall is simultaneously the
most important, yet also the
most challenging aspect.
This is because they are
technically flat roofs, which
means they must be designed
and installed according to the
British Standard for gravity drainage
on flat roofs, BS EN 12056-3:2000,
and meet the requirements of
BS 6229:2018
However, the primary
drainage function of a flat
roof and a blue roof are not
the same. The former
requires the roof to drain very
quickly in an extreme event, while
the latter is designed to retain water for up to 24
hours or longer.
Continued on page 38
36 TC FEBRUARY 2022