Many homes have a suspended ground floor with a space underneath. Good ventilation of this space can reduce indoor radon concentrations.

There are two types of suspended floors:

  • Timber: floorboards or chipboard supported on wooden joists
  • Concrete: blocks supported on concrete beams is more common in modern homes

TIPS

  • To identify a suspended timber floor, look outside for ventilation grilles just above ground level.
  • If there are not any vents outside it may be a solid floor. See our fact sheet: Radon sumps
  • Sometimes the vent leads only to the wall cavity and not to the under-floor space.

Under-floor vents can become blocked and will no longer ventilate the under-floor space. The blockage may be dirt, foliage, improperly installed cavity insulation or raised paving. Vents are sometimes deliberately blocked to reduce draughts or are covered by extensions or garages.

Solution: Clear obstructions to improve the ventilation.

Older style air-bricks, made of terracotta or cast-iron, have smaller openings.

Solution: Replace using modern plastic vents with bigger openings. Vents in cavity walls should be sleeved through the cavity to the under-floor space.

You should have vents in at least two opposite walls.

Solution: Fit plastic vents to all outside walls every 1.5 to 2.0m. Install these vents above ground level, connected to the under-floor space.

TIPS

  • Consider using a 110mm core drill to break through the wall.
  • In some cases you may need periscopic ventilators.

The typical cost is £200, but might be up to £600. The materials needed are widely available in DIY stores.


Download

Quick Guide 1 Improving natural under-floor ventilation

PDF format, 530 KB

BRE Good Repair Guide on Improving underfloor ventilation

PDF format, 638 KB

 

 

 

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.