Over 50% of flood damages comes from back flow. Backflow arises when drains become overwhelmed by storm water during in flood events. A drain non return valve has a single flap to prevent water backing up the drain pipe and flooding your property.

There are two types of anti-flood non return valves: Retro-fit and In-Line.

  • Retro-fit – the easiest way to protect from backflow is a retro-fit non return valve, which are simply pushed into the pipe leading into the inspection chamber or into the end of drain pipe. These valves are DIY, require no expertise or tools to fit. Example retro-fit drain non return valves are:
  • In-line – if you cannot find the inspection chamber outside your house, you will need to install an in-line non return valve. These require a lot more work, as a hole will need to be dug before the cutting of the pipe is required. We would recommend you call a specialist to advise on the best location and works required.
    • WaStop InLine Non Return Valve

Where in the drain to install an anti-flood non return valve?

Inspection Chamber – every property needs to be connected to the drainage system, and therefore an inspection chamber is outside your property. This allows the council to inspect the drains without requiring access to your home. The inspection chamber will be approximate 350mm wide, but can be 450mm wide at the bottom. The inspection chamber can be up to 3m but the majority of inspection chambers are easily accessible and within an arms length (12-18 inches below ground level). A manhole cover will be in place which you will need to remove to access the drain pipe.

  • Buffalo 110mm Non Return Valve
  • Buffalo 150mm Non Return Valve

End of Pipe – if you have a drainage pipe leading to a pond, stream or river, you may want a non return valve to go over the top of the pipe. In this situation, you can install a end of pipe non return valve. Example includes:

New chamber outside your property – if you cannot find an inspection chamber or the end of the drain pipe, you will need to find plans to understand where your drains are connecting into the drainage system. Once you have found the pipe call a drainage expert to discuss installing a new chamber for a non return valve.

How does anti-flood non return valve work?

Retro fit non return valves can be inserted into the foul pipe inside the inspection chamber. The valve has a single flap, which is in the closed position most of the time. When water leaves the property, the flap opens and will close again once the pressure has rescinded. The valve is designed open with just the pressure from the flush of a toilet. In a flood event, or a back up of water due to blocked drains, the valve is closed shut to prevent back flow. In addition, a stainless steel flap stops rats in the drains.

Size of Anti-flood Non Return Valves

The size of the drain pipe will depend on the type of property leading to the drainage system. In the UK, the standard drain pipe sizes are:

  • Residential properties – 110mm
  • Commercial properties – 150mm

Where to buy?

You can buy non return valves from: