We're having our kitchen extended and the architect has noted (on our
building plans) that we need an air extraction rate of 60 l/min. Question:
Can this all be catered for just using a cooker hood (extraction to the
outside), or does it need a 'higher up' fan?

Be careful if you are using any length of ducting. Any significant length
will annihilate the extraction rate, especially if it is an axial fan,
rather than centrifugal. If it is straight through an external wall, then
there is no problem.

Christian.