I live in a block of flats that was built in the 1950s. In my living room there is a hole in the wall which is covered by wire mesh and is 'framed' (presumably to keep the mesh in place) but suggests to me that the hole is meant to be there. The hole in the wall is the space left when at some point the chimney wall and fire place were filled in. The chimney wall is the wall shared between the two flats. My first question is why did the people who filled in the wall and fireplace leave a hole that is connected to the now non-used chimney (no one in the block of flats uses it and there is no fireplace in my flat), and my second question is how can I fill in the hole to stop the enromous drafts? And finally I have a third question which is is it ok to fill in the ventilation hole in the wall in the bedroom and what is the best way to do this?