So my old chimney stack has been taken down and sealed in at roof level. Understanding from research and comments from previous thread I made that the chimney breast (which sits within the cavity) needs venting at the top in order to allow condensation and moisture to get out. What is the best way of accomplishing this? An airbrick at the top going outside (so effectively drilling through the outer wall) or a vent at the top of the wall in the upstairs rooms (so effectively drilling through the internal wall)? There's a possibility that the chimney hasn't been capped entirely and that air can freely flow into the loft; would this be sufficient and avoid me needing to have a vent fitted. The chimney stack was formerly on a hip roof so I cannot actually check/see within the loft where it goes.