Christian McArdle wrote:
Second, a cooker hood capable of extracting at least 30 litres/sec
will comply.

Why is this?

It's in the regs. I believe it is because a cooker hood extracts from
where the steam and fumes are generated, so is considered to have the
same effectiveness as an extractor twice the size that might situated
away from the cooker.

Thanks.
Sounds logical. I wonder why my architect didn't mention this.
I don't suppose you know where abouts in the regs?