flood divert diagram for flood protection

Flood Protection  -  A guide to household portection options

Floodwaters do not only enter properties above ground, see diagram below - which shows water routes into a property.

What does ‘Flood Protection’ mean?

It is possible to defend properties up to 0.90m above threshold level by the use of resistance measures such as flood barriers, flood resistant doors etc... Defending a property above this level could affect the structural integrity of the house. No attempt to increase the level (height) of protection above this limit should be undertaken. Based upon the information collected about the property, flood protection measures would be recommended to help reduce flood risk to the property. These measures are the minimum that are required to help reduce flood risk. All measures would have to be carried out to help reduce flood risk to the property.

When recommending products we consider the type of construction, age of the property and local circumstances etc and other factors that would offer the best solutions for flood protection.

It is possible to defend most properties up 0.90m above threshold level by the use of resistance measures as outlined below.

What to do to prevent flooding

External Walls  Make good to all masonry, seal up all holes, and apply proprietary colourless water resistant coating to the walls to above potential flood level.  All service entry routes, passing through the walls should be sealed with proprietary sealant. The use of sealants either for the treatment of masonry or walls and/or for joints is important. Sealing masonry and walls to just above flood level prevents ingress of water into the fabric of the building, likewise joints, holes etc...Should Be Sealed Wherever Possible (Within Reason). Ideal candidates for sealing are cracks in floors and walls and other obvious points of potential ingress. There is no need for wholesale application of such products by removing skirting boards and other fixed or semi fixed fittings – that process would only be required if tanking of a property was being undertaken. Sealants should only be used to a maximum of 1m above exterior ground level.

Sealants  Some sealants will bond directly to different types of substrate without the need for a primer. However, the gap should be free from dust and loose material and be prepared as described by the sealant manufacturer. The sealant should be applied so that it makes a substantial and continuous bridge from one side of the gap to the other. If this is not possible, the sealant should make continuous contact with surfaces either side of the gap.

There are many different varieties of sealant available from builder’s merchants and DIY stores. You need to select a material that will fill the maximum and minimum size of gaps. Sealants can be gun applied and/or worked into narrow gaps using an appropriate tool, and can be used to fill gaps up to 50mm wide or less than 1mm wide. For narrow gaps of less than 2mm, it may be easier to use a liquid applied penetrating sealant or surface sealant to bridge the gap at the surface. Common types of sealant include:

           Silicone - for accommodation of high movement, good for frames

           Water based acrylic - for internal, low movement situations

           Oil-based mastic - for perimeter seals to timber frames

           Polysulphide - for heavy duty applications

           Epoxy - for areas with low movement

           Polyurethane - for general purpose sealing

           Butyl - strips for compression seals


Vents and other openings   All vents/ openings in walls etc...Should be protected by a removable seal or removable cover. If the opening / vent is no longer required then wide or deep gaps should first be filled or packed, for example with expanding foam or gun-applied sealant capable of filling the required cavity. The outer part of the gap should be sealed at the outside face (if accessible) and the inside faces with a sealant suitable for the size of gap, type of surfaces and expected movement. Always use BSI Kite-marked or equivalent standard products if available. The policy is to prevent water entry into the building and into the fabric of the structure.  Where there is a ventilation requirement, the recommendation is to retain the vent, but protect it against water penetration, self-sealing devices or lifting the vent height are options.  It is occasionally the case that, where suspended floors have been replaced with solid floors, the original air bricks have been retained and are now redundant, in such cases the recommendation is that they are blocked up/sealed.  Vents are often to be found venting cupboard spaces, larders, and wall cavities, where ventilation is still required; lifting the vent outlet is a recommendation.

Waste pipes  Low level drainage pipes such as dishwashers, sink outlets, washing machine pipes up to 50mm dia should be fitted with non-return valves or be lifted to pass through the wall at a higher level - greater than 1.0m above ground level.

Sewage Pipes  Foul sewage pipes 100mm/110mm dia non-return valves to eliminate flood risk from the sewerage system, whilst preventing backflow, surcharging, and the ingress of rodents and insects. To BS 13564. These need fitting immediately or adjacent to the property in a manhole or inspection/rodding chamber.  Toilet seal valves (often known as Toilet Bungs) can be fitted to downstairs toilets if alternative valves and fitting are not suitable.

Floors  It is assumed that solid floors are water resistant and further works are not recommended.  If not cracks and service entry points through the floor should be sealed with proprietary sealant.

Solid floors Many solid floors do not have an effective connection between the damp-proof membrane for the floor and the damp proof course in the wall. This means water can seep into your home through gaps at the floor/wall joint. If you are replacing an existing floor with a solid concrete floor, special attention should be given to this detail.

If the solid floor is pre 1960 there may not be a damp proof membrane, plus cracks in existing floors may allow water through the floor and replacement should be considered.

Flood Barriers to Doors   suggested protection.  Exterior products - Flood barrier External Fix (Kitemarked) to BS PAS 1188:2003 or BS PAS 1188:2003 The product must have been tested to a standard to PAS 1188. Independent test evidence must demonstrate the product has been tested in static water, waves, and currents and has been repeat tested. The product provider also needs to demonstrate that a quality management system similar to ISO9001 is in place. Test evidence will be required to demonstrate that the leakage rate during independent testing did not exceed 1 litre per hour per metre of aperture edge seal below the designed maximum water depth.

Flood Barriers to Windows  suggested protection    Protection is required to windows to BS PAS 1188:2003 or BS PAS 1188:2003  if window bottom cill is below peak flood level

Reducing Flood Risk Based upon the information collected about the property the following flood protection measures are recommended to help reduce flood risk to the property. These measures are the minimum that are required to help reduce flood risk; all measures would have to be carried out to help reduce flood risk to the property.

Pumps – Pumps are not an admission of failure, the need for pumps is based upon an expert knowledge of building construction.  Regardless of how well an external wall is protected unless this is fully tanked with the floor, or sub-floor, there is always the possibility of water coming up through the sub-floor, which in the case of many older properties is simply compacted earth/ash/hard-core and even when there is a concrete sub-floor water can come up around the perimeter junction with the external walls.  The pump is there to deal with water getting into the under-floor void. There is also the issue of leakage rates from flood defence products which even under the BSI Kitemarked scheme allow  up to 1 litre per hour per metre of aperture edge seal below the designed maximum water depth.

Having said that this isn’t an admission of failure, where there is reliance upon householder fitted defences, there is the possibility that a) they will not be put up in time or b), they will not be fitted correctly, in either case the pump may help lessen the problem.

The surveyor in this case speaks from experience in that, at my own property, even having door barriers installed and the property being tanked to 0.9m, water still found its way into the ground floor area. Our recommendation (classed as desirable) is to have to hand a surface mounted electric submersible pump or a self-powered model. Surface mounted pumps sit at floor level and pump down to a few millimetres.

A typical specification for this type of pump is   -    Pumps are for clean water designed to drain domestic applications, empty and dry flooded rooms, basements, draw water from wells, basins or cisterns. The pumps are ideal for limited spaces. Complete with integral float switch, which can be selected in automatic or manual mode. In automatic mode the pump switches on when the water level reaches approx. 140mm and switches off at approx. 30mm. In manual mode the level of water can be pumped down to approx. 3mm. Maximum size of impurities 5mm. Supplied with check valve and a 1 1/4" adjustable hose connector for hose sizes 3/4" 1" and 1 1/4" and 10 metres of power cable. (other similar products/pumps are available)

Temporary Disposable Flood Protection   Smart Sandbags   A recent development in flood protection are bags that absorb water (up to 30 x their volume) to act just like sandbags, but don't have to be filled with heavy sand and are designed so they mould into doorways to keep floodwater out. The bags are immersed in water at the scene (or left in place as a barrier) and their semi-porous inner liner has hundreds of absorbent crystals which inflate and soak up water to for a semi rigid gel. The bags can be folded and take up a tiny amount of storage space compared to sandbags which are heavy, unwieldy and deteriorate if stored for a long time. The flood bags weigh hardly anything which solves any health and safety issues in terms of handling dead weights such as traditional sandbags.

General information relating to flood resistance measures  Our experience has shown us that flood-water isn’t predictable, the fact that water entered a building through a particular point/door/opening, and from a particular side, once, is no guarantee that during the next flood event the same process will happen.  With this in mind, consideration often has to be given to an ‘all round’ approach.

Sealing /sealants – This covers a multitude of potential issues.  Water will track along any joint no matter how thin, or visible to the human eye, proprietary paint on coatings seals such joints.  These coatings also stop water being absorbed into the material themselves, once fully saturated, brickwork or similar will allow water through.  In some instances the sealing between different materials may be recommended, the open joint between an external render coat and the masonry backing is such an example.

Mortar pointing and making good to masonry – A general note is often included without being overly specific to a particular area/location, this is to ensure that no area is missed.

General Advice We advise that if the recommended measures in this report are put into place, the property will have a higher level of flood protection. It is expected that the flood protection products will be fit for purpose and are installed as per the manufacturers requirements or even fitted by them. Some of the products specified above are suitable for DIY installation although in certain circumstances professional help will be required.

Groundwater   For property owners, the precautions that can be taken against groundwater flooding specifically are limited. If you have a basement which is frequently flooded and you would like to use it for storage or as a living area, it may be possible to ‘tank’ it. This involves sealing the basement with a water-proof membrane. The use of pumps in properties with ‘suspended floors’ is a recognised procedure for preventing flooding. These pumps are usually submersible models activated by float switches and can be set to automatic mode. Pipes and other cables might need installing. Access to the sub floor such as a hatch will be needed for installation and maintenance purposes

Recommended Flood Protection Products   British Standard Institute PAS 1188 Kite-marked Companies BS PAS 1188:2003 or BS PAS 1188:2009  The flood protection companies that have successfully tested at HR Wallingford to achieve the BS PAS 1188:2003 or BS PAS 1188:2009accreditation for door and window protection can be found on the following website


Insurance companies often look favourably (in terms of premiums) on properties in flood risk areas who have installed ‘Kitemarked’ flood protection

flood divert diagram for flood protection