I am closing up a disused fireplace opening with studwork and plasterboard. It is a brick chimney stack but above the roofline the chimney has been removed and there is just a metal flue. Ideally, I'd rather not fit a vent due to draughts and I think they are quite unsightly. I am aware it is good practise to keep the stack ventilated but my question is this: If I remove the flue and tile over the roof again leaving the chimney open in the loft space, protected from the elements, does that mean it will be acceptable to not have a vent downstairs in the room? If the top is protected from the elements by the roof I struggle to see how it makes plasterboarding over the fireplace any different to my single brick layer bay windows with studwork and plasterboard? I am considering having it swept first to remove as much hygroscopic material as possible. Thanks.