On Feb 11, 8:25*pm, fred wrote:
In article , David Hearn
writesOn 11/02/2011 15:42, wrote:

There's a formula for the vent minimum area based, based on floor area
of the room, but can't recall the % right now.

Is that the case for window replacement (if the existing windows do not
have any permanent background ventilation), or just for new
builds/extensions/conversions etc?

I'm afraid the need for background ventilation is re-assessed on window
replacement and it makes no difference if the old ones had it or not.

....but AFAIK a BCO won't be involved when windows are replaced without
other building work, and DG companies will provide whatever you ask
for.

Cheers,
David.