Marley Sustainable Drainage Rainwater Harvesting Kits ... - BHL.co.uk

RAINWATER HARVESTING KITS - INSTALLATION MANUAL
Site preparation and excavation
The fitment of the Marley Rainwater Harvesting system
requires the excavation of a pit in order to contain the
Waterloc cells and tank liner. Excavation requires a range
of safety measures to be undertaken.
You are advised to refer to your local authority
environmental dept and/or the Health and Safety Executives
web site: http://www.hse.gov.uk for the most current
guidance (or your own company health and safety adviser)
In accordance with Building Regulations Approved Document H,
excavations for soakaway systems must be located a minimum
distance of 5m from any building boundary.
Therefore, before starting work:
Waterloc cell and tank liner
installation
a) The coarse sand base of the excavation should be tamped
and levelled.
b) The bottom and sides of the excavation are lined with the
geotextile material supplied, one strip being laid lengthways and
the other widthways. Lay the excess material on the ground on
each side of the excavation, allowing an equal overlap all round.
c) The tank liner is laid out in the excavation, over the geotextile
material, and the first layer of Waterloc HD cells (black) installed,
leaving the centre position vacant for the bottom housing and
riser sections.
d) The edges should abut and corners align with each other.
e) Lock them together at the intersecting corners of the upper
face with the Waterloc cell connectors.
Waterloc connectors
a) Plan the location of the excavation to suit both the proximity
of the building boundary and the elevation of the ground
relative to the available water collection point.
b) Establish the location of any other underground services to
the site by contacting the various service providers or
conducting a CAT scan.
Note: the system is designed for installation in areas subject to
pedestrian loading only. Light vehicle traffic requires a minimum
cover depth of 900mm which would limit filter access.
Figure 4
The rainwater harvesting system is constructed from three layers of
Marley Waterloc cells and requires an excavation plan area of 2.4m
x 1.8m, with an additional allowance of approximately 150-200mm
around the perimeter for backfilling with coarse granular material.
The minimum overall depth of the excavation needs to be 2.15m,
which allows 100mm for levelling the base with coarse sand.
If additional soakaway capacity is required in the top layer, the
upper volume of the excavation can be increased, typically by
adding blocks of three cells to the length or width of the
construction.
In order to accommodate any rise in ground level from the water
collection point, the inspection cover height can also be adjusted
to provide up to 850mm soil depth over the surface of the upper
cells. (2.5m overall excavation depth, including 100mm allowance
for levelling)
It is strongly recommended that the system is only fed with
rainwater from roof drainage outlets to avoid the risk of
contamination. Rainwater downpipe connections should be
routed through the 250mm silt trap, UG60 provided to prevent
debris entering the inlet chamber and to reduce the build up of
silt. When setting out the rainwater supply pipe from the silt trap
to the inlet chamber, ensure that there is a minimum fall of 1:80.
To assist with the installation of control cables and pipework it is
advisable to fit a long radius bend, UBL488 to the service pipe
from ground level. General setting out details are shown on
figure 6.
Figure 5
The connectors are designed to be fitted ‘back to back’ and
can be configured for use either on an upper face or
between layers of cells. (See figures 4 & 5)
NB: connectors must not be fitted to the underside of the
first cell layer.
f) Assemble the second layer of Waterloc (blue) cells and pull the
tank liner and geotextile taut over the vertical faces, backfilling
around the edges of the excavation with granular material to
within approximately 150mm of the upper cell surface.
g) The backfill should be lightly compacted at each stage.
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