We have a great tits' nest.
I've heard the noise of babies above our front door, near roof level, for a couple of days, but couldn't see how they could have got into the roof space, or why we couldn't hear them from inside the house.
It's because they've nested in the sewerage venting pipe, presumably where it bends out to go round the guttering. That means that, when the babies fledge, they are going to have to scale about 2' 6" of vertical pipe before they escape. I think that's going to be difficult for them, but I would imagine that the parents wouldn't build a nest where the babies are doomed.