LANDSCAPING SERVICES
existing, paving if it is not SuDS
compliant. With national and
increasing local planning policies
encouraging or requiring SuDS, such
applications may well be rejected.
The measures have applied in
England since 2008 and in Wales
since September 2013. They
apply to paving that is: over 5m2
(replacement paving only in Wales)
and in the front garden only. In
Scotland, similar measures apply
to work initiated after February
2012 and to paving of any size and
between the house and any street,
therefore not just front gardens.
All three sets of measures refer to
a government guide on permeable
paving and this, in turn, refers to
important guidance documents on
the Interpave website
www.paving.org.uk
Commercial and Domestic
Properties
For industrial, warehouse, office and
shop premises, similar changes take
away permitted development rights
from new or replacement paving on
a property, unless it is permeable
paving or drains water onto a
permeable area within the curtilage
of the property. Otherwise planning
permission will be needed. In
England, these measures took effect
in April 2010. In Scotland, similar
measures were applied in 2014.
But the growing awareness of the
importance of SuDS and permeable
paving in the fight against flooding
means increasingly robust
enforcement by local authorities,
which landscape designers and
contractors need to consider.
On-site Water Attenuation
The aim of the Permitted
Development requirements is to
hold back (i.e. attenuate) water on
the property during heavy storms
to avoid downstream flooding and
treat it to remove or trap pollution.
What happens after that depends
on the ability of the ground to
absorb water (i.e. permeability) and
whether it is intended to make use
of it through rainwater harvesting.
With good ground permeability,
such as sandy soil, the water can
simply soak away into the ground.
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This is the cheapest option and helps
replenish the water table, as well as
sustain plants and trees. With poor
ground permeability, such as heavy
clay, some of the stored water is
collected and gradually soaks away,
or eventually discharges into sewers
or streams after storms have passed
– but with far less impact than piped
drains.
Alternative techniques can be taken
to satisfy the requirements. It is
for the local planning authority
to decide whether a particular
proposal will meet the aims of the
Permitted Development Order.
Concrete Block Permeable
Paving
There is a growing choice of concrete
blocks and paving slabs available
from Interpave manufacturers,
designed specifically for permeable
paving. Essentially, they have the
same impressive performance as
conventional precast concrete
paving products, being slip resistant,
durable, strong and sustainable. And
today there are more shapes, styles,
finishes and colours than ever to
give real freedom of choice.
The difference with permeable
paving is the enlarged joints,
filled with a permeable aggregate
specifically chosen for each product
– but never sand (which is
used with conventional block
paving). This ensures that water will
continue to pass through the joints
over many years. The materials used
below the blocks are also specifically
selected to accommodate water,
unlike conventional drive and road
construction.
Permeable paving is specifically
designed for a dual role, acting
as the drainage system as well as
supporting people and vehicles. At
the same time, many pollutants are
substantially removed and treated
within the paving layers before
the water leaves it. Concrete block
permeable paving can be laid level
and still avoids puddles without the
need for drainage gulleys and pipes.
It also provides a safe, firm surface
for everyone, including wheelchair
users and people pushing prams,
unlike gravel and other loose
materials that may also satisfy the
permeability rules. But the
accessibility Building Regulations
don’t allow these loose materials for
access paths and drives.
Spotting the Difference
Conventional block paving is not
designed to be permeable. Its sand
filled joints soon clog up to provide
a sealed-up surface and the material
below is not intended
to handle water. Although looking
similar to conventional block
paving, permeable paving should
have permeable aggregate (looking
like coarse, sharp or crushed stone)
filling the joints and under the
blocks, not sand. In addition, a
recent planning appeal decision
highlighted that a permeable sub-
base must also be used below
to comply, not standard ‘Type 1’
aggregate which has sand and silt
filling voids.
For more information, download
the brand new edition of
Interpave’s ‘Permitted Paving’
and other guidelines from the
Permeable Paving & SuDS section of
www.paving.org.uk
www.landud.co.uk
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