Flood resistance measures

Flood resistance measures designed to keep the water out of the property by sealing off points of entry (windows, doors, pipe entry points, air bricks).  If the flood water is very deep (over 600 mm) planning guidance from the government warns that it can be dangerous to use flood resistance measures to keep the water out, as this produces stresses on the building which may lead to collapse or permanent structural damage. Flood resilience measures may work if the expected flood depth will be in excess of this 600 mm threshold.

Flood resistance measures work well against river and surface water flooding.  They may give limited protection against coastal flooding and cannot be used against groundwater flooding.  Many flood resistance measures will not work for one property in a terrace, as the water will find its way in through adjacent properties in the terrace if these do not have effective PLP fitted.  Also, PLP measures must be fitted correctly in order to work properly.  Some require regular maintenance as well (eg lubrication of watertight seals). This government guide gives an idea of the possible cost of these measures

There are recognised standards for effective PLP – click here for further detailsManufacturers often offer a guarantee against defects in the design or manufacture of the product (should this allow flood water to get into the property) but this guarantee is likely to be conditional upon the property owner using and maintaining the PLP measure properly.


Not all flood resistance measures will be suitable for every property, a full on-site flood risk assessment will determine which of these measures are most suitable.

Here is a list of possible flood resistance measures:

Flood barriers

Barriers (sometimes called baffles) create a watertight seal around the opening to which they are fixed, to prevent floodwater getting in.  For example, they can be mounted across doors, windows and air bricks which fall below the predicted flood water level.  They may be passive (closing automatically in response to a sensor which triggers when it comes into contact with water) or manual (the barrier has to be fitted by the homeowner or business employees when a flood is imminent.   This runs the risk that no one is at the property when this needs to be done, or the homeowner is too frail to mount the barrier).

Flood doors are specially adapted doors which have an inbuilt flood seal.  They look almost the same as standard UPVC doors so are more attractive and practical. However, they are more expensive.  Flood windows (which work in a similar way) can also be fitted.

2 - Sands Morpeth 2012


Sealing weep holes and pipe entry points

Weep holes are small openings in walls which allow air into the wall cavity for ventilation.  They can be blocked up using either rubber seals or plastic covers. Both passive and manual versions of these seals exist to prevent water ingress which will damage the insulation’s properties.

Pipe entry points and drainage exit points provide another access point for floodwater to enter a property.  They can be sealed (fairly cheaply) by using expanding silicone sealant or service entry bungs. Using this resistant sealant to ensure a watertight seal around these service entry points may also save significant investment on cavity wall insulation. If the current seals around these entries are looking old or worn, it is always a good idea to replace them with new seals. This is a very low cost measure but may save you on the loss of a significant investment.



Air Bricks
In cavity-walled, masonry constructions – especially in homes with a suspended floor – it is common for builders to include airbricks in order to sufficiently ventilate the property. These airbricks can provide direct access inside the property for flood water. However, affordable solutions to this are available. There are both passive and manual options are available for air bricks. The cheaper manual measures screw on over the front of the airbricks, while the passive airbricks close automatically as soon as the water level reaches the height of the air brick. The number of airbricks on the property may decide which of the two options is most applicable for the property. Below we can see an example of a passive airbrick.

FGS Smart airbrick



Floor Membrane

This is a waterproof membrane that sits below the floor screed.  It prevents water rising up into the floor, and is essential to help prevent groundwater flooding.  It is important that it is not torn or punctured as this will impair its integrity.  [If your property has a suspended floor (timber, concrete or any other material) then you should already have this membrane. For solid concrete floors, this layer is optional however it is always a good idea to consider if this is financially viable for you.

If you are unsure whether there is a floor membrane already installed, you may be able to see what looks like a sheet coming out through a gap between the first few levels of brickwork externally. Alternatively you may be able to see it by lifting up your main floor surface.



Injected damp proof course

Damp proof course can be injected into walls in order to create an impermeable moisture barrier within a masonry construction to prevent rising damp. This involves the drilling of holes along mortar joints in the brickwork. This should be carried out at a height of no less than 150mm from the finished floor level.

These holes are then used to insert a pipe down into the brickwork, through which a liquid course can be transmitted. These will form the dispersion points for the impermeable layer within the wall. These dispersion points within the wall will join together into a single planar layer of impermeable protection as the course spreads laterally. This should prevent rising damp from progressing up the wall past this point. The dispersion tubes in the walls can either be left in or sealed up and the ends of all holes should be sealed with a waterproof mortar.

Please click here for explaining how injected damp proof course can prevent rising damp in a property. The Centre for Resilience does not endorse this company in any way.


Non-return Valves

A non-return valve is a one-way flow regulator that can be placed on any sewage, drainage or waste effluent piping. It should prevent mains sewage flooding the property.  This is a great advantage, as flood waters contaminated with sewage require more extensive repair works and can leave lingering odours in the property.

In normal use, the valve allows waste water and effluent to flow out of the property into the mains drainage system.  However, when flooding causes the pressure in that mains drainage to rise and effluent to push back towards the property, the valve will close, preventing contaminated water flooding the property through the toilet, sink or shower.  Commercial premises or larger effluent pipes will need a larger, more robust non-return valve.

An alternative to a non-return valve would be the use of a toilet bung or pan seal. A bung is a small inflatable ball that is inflated to block up the water water flow pipe when inflated down the pipe. A pan seal is a large watertight disk that fits inside the toilet bowl to prevent water from raising any higher.

See the video below for technical guidance from Mary Dhonau OBE on the types of flood resilience measures that are available to you.