Ventilation and loft conversions
As part of your loft conversion build process there is a building regulation requirement for proper ventilation to your altered roof and the loft conversion itself.
There is a requirement for ridge or high level ventilation, and around the roof.
The ventilation is required because temperature changes in the roof cause condensation and this will lead to damp if there is not adequate ventilation.
Your current roof-space will be converted to a loft conversion and this space will therefore require adequate ventilation.
There must be ventilation between the roof covering and the insulation so there must be a cavity of at least 50mm for the flow of air from the eaves. This is known as cross ventilation. The eaves ventilation must ne a continuous 25mm opening.
The ventilation can be via the eaves by way of a aperture or a vented soffit with a continuous gap of 5mm.
The ventilation can also be at the ridge level by way of ridge vents or roof vents that are placed at various locations on the slope of the roof.
In adequate ventilation leads to many problems including damp which leads to mould and an unhealthy environment, not to mention a big building repair bill.
Vapour control layer is always fitted to prevent moisture reaching the insulation.
Ventilation of rooms
All habitable rooms require ventilation. A window opening equivalent to 1/20th of the floor area of the room and background ventilation, or trickle vents of 8000mm2, the can be closed.
Bathrooms and shower rooms
Bathrooms and shower rooms (with W.C. or not) require a mechanical extraction of 15 litres per second capacity and either background ventilation of 4000mm2 and an opening window or an extract fan that overruns by 15 minutes controlled by humidistat.
A window with an opening equivalent to 1/20th of the floor area and background ventilation of 4000mm2 or mechanical extract of 6 litres per second with a 15 minute overrun controlled by light switch or a humidistat.