To comply with Building Regs the windows should be FENSA approved. FENSA require trickle vents.
Incorrect. FENSA is ONE way of proving compliance, not the only way.
Damp in houses? Damp, from breathing? or washing? or showering? Who'd 'a thunk it?
I tell you what, let's pay a fortune for energy efficient glazing and frames and then open all the windows to reduce the condensation, or worse still be forced to punch holes in them (fancy name of 'trickle vents' applied to sell it to the mugs out there).
And that condensation? Main cause of asthma and excema in the UK...as well as all sorts of other conditions.
Until we build properly insulated, airtight and then ventilated houses, this will be a problem.
(We cope with it by wiping it off the walls and windows each day and then drying towel outside. Yes, we live in usual crappy UK new-build....)