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Prepare your property for flooding

By on February 14, 2014
Weekley Round Up Content2

It’s impossible to completely flood-proof a property but there are lots of things you can do to reduce flood damage.

Source: Environment Agency

If you’re imminently at risk of flooding, read What to do when it floods.

Keep flood water out

If you know your property is in an area that could flood, buy protection equipment and prepare your property well in advance to reduce the risk of flood water getting inside. Remove flood protection equipment once the water has gone to help dry out your property.

  • Sandbags: contact local builders’ merchants for stocks of bags and sand. Alternatively, you can find suppliers of modern non-sand bags designed for flooding on the National Flood Forum Blue Pages Directory. Note that sandbags are ineffective for groundwater flooding. Please refer to the ‘keep groundwater out’ section for advice on this.
  • Doors and windows: buy automatic flood-proof doors and windows, or purpose-built flood boards that can be fitted when flooding is expected. Raise door thresholds to help keep shallow water out.
  • Exterior walls: check the pointing, and apply water-proofing sealant to exterior walls.
  • Floors: raise damp-proof brick courses. Seal floors or replace wooden floodboards with concrete with a damp-proof membrane. Be aware that water can enter where the floor and walls join.
  • Air bricks: buy automatic flood-proof air bricks or specially designed covers that are easy to fit over air bricks when flooding is expected.
  • Drains and pipes: fit non-return valves to drains and water inlet and outlet pipes. This will prevent wastewater from flowing back into the property through sewerage pipes for ground floor toilets and sinks.
  • Barriers: you could arrange free-standing temporary flood barriers, but remember that water could still get in through the drainage system. Talk to your neighbours about building a single barrier around several houses to help spread the cost and the benefits. You may need Environment Agency permission to install a barrier so call 0370 850 6506 and ask to speak to someone in the Development Control team in your local office.
  • Landscaping: landscape garden areas and driveways to help divert water away from your property.

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Keep groundwater out

If your property could flood through the ground, a pump will be the best way to keep water out. Other methods such as sandbags will be ineffective because water comes up through the ground. You are likely to have to pump water for days, weeks or months. Pumps work best when the inlet is installed in a low point where water can drain (a sump).

Pumps can be electric or petrol/diesel. Electric pumps may be the most convenient, but you will need to take care using an electric pump near floodwater. You may need a back up generator in case of power cuts during a flood. Contact a qualified electrician for further advice. Petrol or diesel pumps can be noisier and will require refueling. Position the generator outside as generators produce carbon monoxide fumes which can kill.

Only pump out water when flood levels outside your property are lower than inside to reduce the risk of structural damage. Contact a structural engineer before pumping very deep water from basements.

A good quality pump should last around 10 years. However, this depends on how often it is used and the acidity and dirtiness of the water. Regularly check and test your pump. Remove and thoroughly clean the pump at least once a year. Disconnect the pump from the power source before you handle or clean it.

Pumping from one place to another may cause flooding elsewhere. You must not pump water into the public foul sewer. When deciding where to pump water, you should contact:

  • your local Environment Agency office if you are thinking about pumping water into main rivers or boreholes
  • your local authority if you are thinking about pumping water into ditches, watercourses or piped watercourses
  • the water company if you are thinking about pumping water into public surface water sewers or foul sewers
  • the Highways Authority if you are thinking about pumping water into a highway drain

Reduce flood water damage

Prepare your property in advance to reduce the damage floodwater might cause inside, making drying out and cleaning up quicker and easier.

  • Shelving: keep irreplaceable or valuable items on high mounted shelves.
  • Home entertainment: fix your audio-visual equipment such as your TV and hi-fi to the wall, about 1.5 metres above floor level.
  • Skirting: fit water-resistant skirting boards or varnish wooden ones.
  • Walls: use horizontal plasterboard or lime-based plaster to dry-line, instead of gypsum. Get a special draining system for cavity walls.
  • Floors: lay tiles with rugs rather than fitted carpets.
  • Internal doors: fit synthetic or waxed doors, or make sure wooden doors are easy to remove before a flood.
  • External doors and windows: install synthetic or waxed windows and doors, or varnish wooden ones.
  • Kitchen and bathroom: use water-resistant materials such as stainless steel, plastic or solid wood rather than chipboard. Where possible raise fridges and other appliances on plinths.
  • Electricals: raise electrical sockets, fuse boxes, controls and wiring to at least 1.5 metres above floor level. If re-wiring, bring cables down the wall to the raised sockets so cabling isn’t affected by flood water.
  • Large items: buy extra large, sealable bags that you can use to protect items that are difficult to move such as electrical goods and sofas.

Reduce groundwater damage

If your property could flood from groundwater, there are things you can do in advance to reduce damage.

Pump

Fit a pump in a basement or under-floor void so you have a way to extract flood water. This will also help to dry out the property .

Floors

A reinforced concrete floor with a continuous damp proof membrane can be effective where groundwater pressures are low. Take particular care where the floor and the walls join as water can penetrate through this point.

If there’s enough headroom, you could raise the floor level either by laying a reinforced concrete floor directly onto the existing floor or by creating a suspended floor. Remember that water exerts considerable pressure: a 300mm depth (1 foot) of water pressure will lift a 125mm thick (5 inch) concrete slab. It’s this pressure that makes groundwater flooding difficult to prevent.

Suspended floors create a void beneath the floor which will flood before water rises to enter the house. They may be built from timber or concrete, but flooding beneath wooden floors will often cause the timber to rot so get specialist advice before carrying out this work.

Basements

Basements are prone to flooding and it’s difficult to prevent. ‘Tanking’ materials are available, but these are best applied on the outside walls. This is often impractical and you may have to construct an inner wall. Specialist advice is strongly recommended. Sealing the walls can lead to an increase in water pressure which may cause structural damage.

Foul drainage

Foul sewage is the waste from sinks, baths and toilets, which often backs up and causes problems during groundwater flooding. What you can do to prevent sewage flooding depends on your system.

Main drainage systems: Report any flooding problems with main drainage systems to the water company or housing association that operates them. For further advice you can also contact Ofwat, the economic regulator of the water and sewerage industry. If you have a continuing problem with sewage flooding which the authorities are unable to solve, you can try fitting non-return valves. Get guidance on these from the Construction Industry Research Information Association (CIRIA).

Septic tanks: These frequently have problems when groundwater levels rise. You may need to hire portable facilities, or arrange to have your tank emptied and the contents tankered away by an appropriate contractor. Adding a pump to the outlet side of the tank may help keep your system working and pump the sewage to high ground above the groundwater table. You must contact the Environment Agency if you want to do this as you may need a permit to discharge, which will be dependent upon local circumstances. You should take steps which are reasonable and practical in the circumstances to minimise pollution and advise us as soon as practical. The design of pumped sewerage systems is complex and you should always seek specialist advice.

Cesspits: If these are well built, they should not be a problem. Rising groundwater will test the integrity of the structure and small leaks may occur which will quickly fill the tank. Be aware that if you call a tanker to empty a septic tank or cesspit when the toilet will not flush, but the tank has not been installed with a sufficient concrete surround, there is a risk it could float the tank or it will quickly fill with groundwater.

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