oh dear what have i started The air brick is louvered and isnt on a weather wall (gable end near apex of roof) and I checked initially, to see if their was any rainwater ingress which thankfully there isnt. The house is a northern counties HA 10yr old semi. So, presumably it should be compliant. "but then again!" ( se my new post wolf combi boilers) Ive already decided to send it through the wall, stick birds nest cap on and mortar up the gaps as I wanna convert the loft into office space. Problem is if I put an aav on there may be a problem with the basin and bath traps as the waste goes underneath the floor and must be bossed into the stack below the wc "T".