Good ventilation is crucial to maintain the air quality when converting the loft.
With loft conversions a lot of effort and time is spent fitting vapour barriers so that the moist air can't attack the new timber in the roof space or the wooden structure of any dormers that have been added.
But all this means that unless adequate ventilation is provided the new loft room will suffer from damp and condensation.
To prevent this the home owner has several ventilation choices which should be considered when the first fix electrics are installed.
An easy option. Basically background ventilation is performed by the small air vents in windows.
This is a continuous process that can lead to draughts. To prevent this the vents in the window frames should be around two meters from the floor.
Sometimes referred to as rapid purge ventilation this is no more complicated than opening a window! All windows in habitable rooms must be openable so that any foul air can be quickly expelled by opening the window.
There are a few specific requirements here though. The casement of the windows must be equivalent to at least 5% of the rooms floor area or, where skylight windows have restricted opening, 10%.
Extractor fans can be installed very easily into most rooms at the first fix electrics stage and are simple to operate.
The three loft ventilation methods outlined above apply to any habitable room such as a living room or bedroom but bathrooms are a special case.
Unsurprisingly ventilation is more important in the bathroom than anywhere else in the home.
Hot baths or showers cause a lot of condensation and this obviously has to be dealt with before the moisture soaks into the new walls and ceilings.
Understandably the building regulations are more stringent for bathrooms than for the rest of the property but they are still very easy to comply with.
In bathrooms extractor fans must be fitted. The minimum specification for a fan is 15 litres per second (of air) and must have an overrun of 15 minutes (i.e they must continue working for 15 minutes after they have cleared the air.
This overrun period can be ignored if there is a vented opening window in the bathroom.
One safety point that should be mentioned is that extractor fans are of course wired into the mains so ensure they are positioned well away from where they can be accidentally touched by a wet hand.
For more info see the related pages below
Structural calculations for loft conversions are of course hugely important to ensure safety and that the proposed plans meet building regulations
What is the difference between planning permission and building regulations approval for loft conversions ?
Using And Fitting Loose Fill Insulation In Your Loft