Winchester Flood Proofing


This historic commercial property had flooded due to an extremely high water level in the river directly next to the building. The walls and footings of the property formed the side of the river, because of this the water got to the bottom of the windows but entered through the wall floor junction and defects in the concrete slab.

  • Winchester Flood 4
  • Winchester Flood 1
  • Winchester Flood 3
  • Winchester Flood 2


MacLennan surveyors attended during the flooding and installed emergency automatic pumps to keep the water down, the basement area had flooded in previous years and had been tanked with a cement based tanking system. MacLennan deemed the installation to be defective and the system not suitable due to the friable historic brickwork laid in lime mortar. MacLennan’s proposal was as follows:

  • Replace the existing defective and poor quality concrete slab with a new engineer designed slab attached to the walls to prevent flotation. To achieve this constant de-watering was required.
  • Detail the joints and the base of the wall to further reduce ingress. Manage any water that did come in with a pumping system in a cavity drain membrane system, MacLennan carried out surveys and calculated the flow rate of water into the property and the required flow rate out to give a 100% failsafe.
  • Install suitable back up systems which would keep water pumping during power cuts.
  • To reduce the amount of water coming in through the masonry, all masonry was repaired and then received a polymer modified cementitious tanking system. The aim of this was to reduce the amount of water coming in.
  • To manage any water that does come into the property a cavity drain system was installed. The pumps where designed around the amount of water that had flooded into the property over a given time. Once the litres per minute had been calculated, MacLennan’s designed a pumping system which could pump the water out. The specification included enough pumping power so that the pumps would only be required to work half as hard as they could. Further to this full redundancy was built in, meaning if half the pumps failed the system could still cope.
  • Battery back ups and alarms were installed so as the pumps would continue to work during a power cut.


The property is completely protected against water ingress and at no risk of further damage from flooding. The installed system is capable of pumping out a vast amount of water during the event of further rising water levels, to almost double the possible predicted needed capacity. The flood proofing was successful and leaves the residents of the building sheltered from any further distress. All work was completed extremely quickly and within budget.


Solid Wall Detail

Get in touch!

Ready to start a project or require more information about us?
Call us about your project or problem and we will be happy to help.

Call us today on:

0845 658 7777
Or email us here