Why Ventilate?

Each ventilation requirement has its own specific purpose but in general ventilation is provided for the health of the building structure and the health of the occupants.  With new builds getting ‘tighter’ and therefore less adventitious air entering through cracks and gaps in the building fabric it is essential that the correct amount of ventilation is installed in each area.  For help and advice calculating ventilation requirements in domestic buildings please call our technical team on 01536 511874 (00441536 511874 International).

Below are the main areas of a house which require ventilation and a brief summary of each purpose.

Habitable Rooms (Building Regulations Part F)

Background ventilation via through-wall ventilators and/or window trickle ventilators allows fresh outside air to circulate around a habitable room to dilute and remove airborne pollutants (including odours).  It can also control the amount of moisture in the air to reduce the risk of mould growths which can be a health hazard to the occupants of the building.

Note: A habitable room is classed as a room used for dwelling purposes but which is not solely a kitchen, utility room, bathroom, cellar or sanitary accommodation.

Boilers, Stoves & Fires – Gas and Solid Fuel (Building Regulations Part J)

Ventilation is of paramount importance for combustion (i.e. the burning of carbon, such as gas, coal, wood or oil).  It is also vital for the efficient operation of flues, for compartment cooling and the prevention of over-heating.  Combustion appliances (i.e. boilers, water heaters, fires, stoves and cookers) have different ventilation criteria dependent upon the type, size and placement of the appliance and it’s important to accurately calculate specific venting requirements for each situation.  Inadequate ventilation can cause the build-up of carbon monoxide (CO) gas.  This poisonous gas has no smell or taste and can seriously affect the health of the building’s occupants, or even prove fatal.

Cavity Walls (NHBC Standards, British Standard BS 5250)

Perpend cavity ventilators assist in the drying out of walls and are essential in timber frame cavities.  Efficient cavity ventilation prevents the build-up of excessive moisture which could cause damage to the fabric of the building.


Weep Hole Ducts (NHBC Standards, British Standard BS 5250, Building Regulations Part C)

Weep hole ducts are required in external cavity walls as an outlet for moisture which penetrates through the external leaf.  They should also be installed above windows and openings where lintels are provided.

Suspended Timber Frame & Block and Beam Floors (Building Regulations Part C)

Underfloor ventilation combined with a suitable dpc prevents moisture from the ground reaching the upper surface which could lead to damp.  In areas with high levels of radon or soil gases, i.e. methane, underfloor ventilation alleviates the build-up of such gases which if allowed to reach high levels can become harmful to the building’s occupants.

Roof Space (British Standard BS 5250, Building Regulations Part C)

Eaves and soffit ventilation creates a stable atmosphere within the roof void, which prevents the moist warm air generated from within the building becoming condensation when it reaches the cold surfaces of the roof.  Harmful condensation can cause damage to the building fabric, degrade its thermal performance and support mould growth.