Factors including size, shape, appearance and anticipated
drainage requirements need to be taken into account in planning
effective drainage solutions. Design is usually the responsibility
of consulting engineers familiar with the floor construction, floor
finish, piping systems, operations and function intended for
particular building areas.
Building Regulations /
International regulations and local building codes must be
observed for all sanitary and other drainage installations so it is
recommended these are considered as the first step.
As a matter of good practice drains should be considered for any
location where water is supplied or where surface drainage must be
To prevent foul air from entering a building a trapped gully may
be used and various types are available Bell, Bottle, P and S.
In other cases a non-trapped gulley may be used with a trap
installed in the drain line.
Weight Bearing and Load
As an integral part of the floor it is vital gratings and
assemblies withstand all anticipated loads. This website shows the
load rating class for each grating, cover or gully assembly based
on BS EN 1253, as follows :
Loading K3 (Pedestrian Only)
Areas for foot traffic only, such as washrooms, shower areas,
hotels, schools, museums, retail centres, swimming baths, leisure
centres, balconies, terraces and roof gardens.
Loading L15 (Light Industrial)
Areas with light vehicular traffic such as cycle ways and domestic
Loading M125 (Heavy Industrial)
Areas with vehicular traffic, such as car parks, factories,
warehouses and workshops.
Flow rate is the maximum amount of water (litres/second) which a
gulley will drain and is influenced by several factors such as
grating free area (i.e. gaps in the grating), sump capacity, body
free area, design of the gulley, outlet size, and additional
features and accessories such as filter buckets and traps.
At low heads of water the flow rate of a gully is mainly
governed by the size of grating free area. At heads of water above
50mm flow rate is governed by the body free area, or the grating
free area, whichever is the smaller.
Selected top size (i.e. grate free area), gully outlet size and
piping system size all relate to each other and should be within
The type and size of pipework in an installation is fundamental
to the correct selection of gullies. Frost drainage gullies can be
connected to all pipework in general use.
Floor and Flooring
Floor construction type has a direct influence upon appropriate
drainage selection and so should be established at the outset.
The depth of the structural slab and available space will
influence the selection of gullies, while selection of an extension
may be necessary to bring the grating or cover to finished floor
Installations with a drainage membrane will normally require the
use of gullies with a membrane clamping collar.
Drains located in pedestrian surfaces or access routes must be
Different kinds of floor finishes, such as concrete, epoxy
resin, ceramic tiles or sheet vinyl will influence the type of
grating or cover to be selected.
Strength, corrosion resistance and appearance are important
considerations when making drainage selections
Finished floor areas
Gullies with attractive gratings or covers made of satin nickel
bronze, polished nickel bronze or stainless steel are for use in
areas where they contribute to the aesthetic appeal of an area.
Unfinished floor areas
Ductile iron gratings, whilst extremely durable and visually
acceptable are best suited in unfinished and/or industrial settings
such as service areas or for restoration projects to match period
Satin Nickel Bronze and Polished Nickel
Bronze to BS1400:
Stainless Steel to BS EN 10088-1:2005 Grade
1.4301 (304) or Grade 1.4401 (316) if specified
Ductile Iron to BS EN 1563 & 1564 Cast with
the ductility of steel and more than doubling the tensile strength
of cast iron.