Fidler Associates Ltd
STRUCTURAL ENGINEERS, SURVEYORS & PROJECT MANAGERS
61A ELSHAM ROAD, LONDON.
FLOOD RISK ASSESSMENT:IN RESPECT OF A NEW EXTENSION UNDER RAISED FRONT GARDEN.
1 General:
The following Assessment has been prepared in accordance with The Environments
Agency’s Important Guidance on the Submission of Flood Risk Assessment for Minor
Extensions (extensions with a footprint of less than 250m²).
2 Environs:
The property is a lower ground floor flat located within a 5 storey 19th century terraced
property of brick construction. The upper floors comprise of additional dwelling flats.
The property is situated on the South side of Elsham Road. The area is predominantly
residential.
3 The Site:
61a Elsham Road is a lower ground floor flat to a terraced property arranged over 5
storey’s with the upper floors comprise of additional dwelling flats. The foot print of the
existing lower ground floor flat is 112m². The site also comprises adjacent areas of hard
and soft landscape used as amenity space. The rear garden is surrounded by adjoining
structures and timber fences. The front gardens has flower bed to the front then a section
of raised hard standing with a light well comprising further hard standing.
The existing class unit is C3 residential.
The building is constructed of load bearing brick walls. The walls are punctuated by
windows at the front and rear.
The property falls within the furthest edge flood risk areas 2 defended (this means there is
a medium risk of flooding). The property is located 1.5km north of the Thames and in an
area that benefits from the Thames defences including the Thames Barrier. The site is
protected to the 1 in 1000 year floor event.
In the unlikely event of a breach/ overtopping of the floor defence, due to the distance of
the site from the tidal floor source, there would be suitable warning to evacuate / seek
refuge.
Given the tidal / residual risk flood setting, the level, extent and depth of flooding on the
site can be managed in terms of resilient measures, the EA flood warning and easy
evacuation to areas in Flood Zone 1 for the lifetime of the building. Based on the likely
flooding risk and small scale of the proposed development. It is considered that the
proposed development can be constructed and operated safely in flood risk terms, without
increasing flood risk elsewhere. It is therefore considered appropriate development in
accordance with the NPPF.
4 Proposals:
It is proposed to extend the existing front vaults under the raised front garden area a
section of garden area for a planter will be retained along the front boundary 600mm
wide. The proposal would extend the property from the existing footprint of 112m² to
123m². The extension will have a retained section of hard standing and new window
MICHAEL FIDLER M.A.P.M
31 HILLSIDE ROAD, NORTHWOOD, MIDDLESEX, HA6 1PY.
Company No 6271455
Tel No 01923.840482, Fax 01923.840483, Mobile 07956.895384, email: mikefidler@blueyonder.co.uk
Consultants: Terence Fidler C Eng.,MIStructE - Tel 01923.291554 / 07973.450278, Richard Doling BSc, MAPM
Fidler Associates Ltd
STRUCTURAL ENGINEERS, SURVEYORS & PROJECT MANAGERS
which will remain in style with the original windows of the main house. The proposed
use would still remain as C3 residential.
5 Flood Precautions:
The proposed development will use of the following flood resilient construction
techniques as part of the design process as recommended in the NPPF technical guidance
where appropriate:
 Basement to be fully waterproofed (tanked) and waterproofing to be tied in to the
existing basement and ground floor slab as appropriate, details to be provided at
detailed design to building regulations requirements.
 Waterproofing to be installed to 600m above ground level as appropriate.
 Plasterboards will be installed in horizontal sheets rather than conventional
vertical installation methods to minimise the amount of plasterboard that could be
damaged in a flood event.
 Floor finishes would use high quality durable material likely to withstand
exposure to flood water without significant damage.
 The extension would use good quality bricks or blocks for the external face with a
concrete render cavity walls with concrete blocks used for the internal face.
Internal wall linings would be with lime plaster, rendered or compromise
horizontally laid plasterboard.
 Air bricks will be raised to as high as is feasible practicable.
 The damp proof membrane and basement waterproofing will be installed above
the main floor slab and tied into the walls where appropriate, to reduce the
turnaround time for returning the property to full operation after a flood event.
 All service pipes entering the building via the new extension will be sealed with
waterproof materials closed cell insulation.
 The concrete sub floor will likely be laid to fall to drains or gullies which will
remove any build-up of ground water to a sump pump where it will be pumped
into the mains sewer. This pump will be fitted with a non-return valve to prevent
water backing up into the property should the mains sewer become full.
 All new sockets will be located at 450mm above ground floor level in accordance
with Part M of the Building Regulations, thereby further reducing risks in the
event of flooding and allowing more rapid re-occupation.
6 Evacuation:
Given the proximity to an area of flood Zone 1 less than 20m to the Northeast and given
the tidal residual risk along with the site being located outside of the rapid inundation
zone. There should be sufficient time to undertake evacuation which is the preferred
response and as noted above is feasible at this site with observations of flooding to the
south.
If evacuation is necessary the route should be North on Elsham Road to reach Lower
Addison Gardens (unrestricted Flood zone 1) which is less than 20m.
MICHAEL FIDLER M.A.P.M
31 HILLSIDE ROAD, NORTHWOOD, MIDDLESEX, HA6 1PY.
Company No 6271455
Tel No 01923.840482, Fax 01923.840483, Mobile 07956.895384, email: mikefidler@blueyonder.co.uk
Consultants: Terence Fidler C Eng.,MIStructE - Tel 01923.291554 / 07973.450278, Richard Doling BSc, MAPM
Fidler Associates Ltd
STRUCTURAL ENGINEERS, SURVEYORS & PROJECT MANAGERS
7 Surface Water Run Off – Flood Risk from the development:
In accordance with the NPPF, this flood risk assessment also considers the risks posed
from the development to surrounding areas.
The proposal is to maintain existing planters built in to the main structure to the front
garden area this will maintain the vegetation screening to the property but will also
maintain the existing drainage the SUDS report attached shows that the increase in
impermeable areas of 4m² this is combated by the 2m² area of green roof.
Given the small scale of the proposed development it is considered likely that the
development will have a negligible effect on the surrounding infrastructure. There will
not be any significant increase in overland flow from the site.
MICHAEL FIDLER M.A.P.M
31 HILLSIDE ROAD, NORTHWOOD, MIDDLESEX, HA6 1PY.
Company No 6271455
Tel No 01923.840482, Fax 01923.840483, Mobile 07956.895384, email: mikefidler@blueyonder.co.uk
Consultants: Terence Fidler C Eng.,MIStructE - Tel 01923.291554 / 07973.450278, Richard Doling BSc, MAPM