An active radon sump, fitted with a fan, is the best way to reduce indoor radon levels. Sumps work effectively under solid floors, and under suspended floors if the ground is covered with concrete or a membrane. Occasionally, passive sumps without a fan may reduce radon levels.

  • Active sumps: these are the most effective and are powered by an electric fan. They will reduce even the highest radon levels.
  • Passive sumps: these do not have a fan and are less effective. They work best with a pipe ending above the eaves of the roof and may be an option for homes with lower radon levels - for example around 300 Bq m-3

Sumps can be constructed from outside. A small hole, big enough for a 110 mm pipe, is made in an exterior wall just below ground level and a bucketful of material is removed to create a space just below the floor slab. A pipe goes from the space through the wall then usually up the side of the house to roof level. The system is powered continuously by an electric fan. The end of the exhaust pipe should not be near any doors or windows.


  • Consider using a 110mm core drill to create the hole.
  • Typically, a single sump will be adequate for an average sized home

Important point: Seal the pipe well in the wall.

Fittings for the pipes are available from DIY stores and builders merchants.

The typical cost of a system is £800, but can be around £2000; installation normally takes a day or two. The continuous running cost of a fan (less than 100 watt) will normally be less than £2 per week.





How to reduce radon levels overview


Disclaimer. It should be noted that the measures described on this sheet are not guaranteed to reduce the radon level in your home, however similar measures have been proven successful in many UK homes.