We intend to build a lean-to conservatory at the rear of our semi-detached house. The neighbour's house has a small extension already so our conservatory will be alongside it. There will be a gap of about 600mm between the two structures. Now currently the flue from our gas combi boiler is about 200mm below the level of the (flat) roof neighbour's extension and about 300mm on our side, but when we build the conservatory this flue will effectively be sandwiched between the two structures. Is this a potential problem?