ABM Lofts Brochure Page 12

Part F - Ventilation

New habitable rooms

Windows to newly formed habitable rooms must include an opening proportional to the floor area of the
room (the new windows must achieve a minimum of 1/20th of the floor area of the room). There must also be
background ventilation provided by window trickle vents minimum 8000 mm2.

Bathrooms

A new bathroom must either have an openable window plus background ventilation minimum 4000mm2 and
extract ventilation of 15 litres/second. If no windows are present mechanical extract must be provided with a
minimum 15 minute overrun.

WC's

If a window is not present mechanical extract of 6 litres/second with a 15 minute overrun must be provided. If
a window is present it must have an opening of 1/20th of the floor area.

Roof (cold roof)

The introduction of a room into a previously open roof space will restrict the existing cross ventilation and
could cause condensation to form on the underside of the roof. To prevent this the existing eaves ventilation (if
any) will need to be increased to at least a continuous strip 25mm wide. An air gap of at least 50mm is
needed between the pitched roof and any insulation fitted to ensure cross ventilation. Roof vents must also be
added at the ridge equivalent to a continuous strip 5mm wide.

Breathable felt

An Alternative approach to roof ventilation is where a breathable sarking felt is used. The sarking felt should
have an appropriate BBA Certificate and be installed in accordance with the manufacturers specification. If
this already exists to the roof system additional ventilation will not be necessary.

at least equal to continuous strip
5mm wide

at least 50mm

at least equal to
continuous strip 25mm
wide

at least equal to continuous strip
5mm wide

at least 50mm

at least equal to continuous

Think of the space and leave the rest to us

a: Ceiling not following pitch of roof

b: Ceiling following pitch of roof