The current and future requirements of Part L of the Building Regulations along with other standards and regulations have led to an increase in the depth of thermal insulation in suspended floors along with an increase in cavity widths to accommodate greater amounts of cavity wall insulation. This has meant that clear access to an underfloor void has been increased. Litecast offer the Dual Vent as a solution to this problem. Traditional telescopic underfloor ventilators would not be able to achieve this without the use of additional vertical and horizontal extension sleeves.

The ventilator can be used in conjunction with a traditional clay airbrick, although this would reduce the overall airflow through the system.

Litecast offer airbricks in 4 colours (terracotta, buff, blue/black, brown) with grilles to prevent the entry of vermin with water deflectors and 2 different ventilators:

Vent Airflow Courses Covered Maximum distance Minimum distance
      bottom of bottom to top of top bottom of bottom to top of top
Standard 6600mm² 3-5 364mm 215mm
Dual 7600mm² 5-8 575mm 318mm



Voids should be ventilated by openings providing not less than 1500mm² per metre run of external wall or 500mm²/m² of floor area, whichever gives the greater opening area.

Ventilation openings should be provided on at least two opposite sides. Where this is not possible, effective cross ventilation from opposite sides should be provided by a combination of openings and air ducts.

Where the finished level below the floor is lower than the finished adjoining ground level, appropriate drainage should be provided.

A minimum void of not less than 150mm should be provided below the underside of floor slabs and beams.

On shrinkable soil where heave could take place, allowance should be made for the void to accommodate the following movements according to the shrinkage potential of the soil:

  • high potential - 150mm
  • medium potential - 100mm
  • low potential - 50mm

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