I have just opened up a fireplace in the bedroom, and overall it is in good condition. It measures just 18'' wide so I plan to get a HETAS person to come and fit a STOVAX STOCKTON 3, as the blurb says it is suitable for as small as 16'' openings. This will take place when I have sorted the cosmetics out. I have rebuilt the hearth, and want to tile the fireplace out. My question is, The fireplace side walls are 9'' thick, and I would like to build a plasterboard wall on wooden frame so that it will fit flush to the fireplace side wall, but never coming forward of the fireplace front at any stage, is this possible/allowed? It would mean that the wood batton holding the plasterboard is 9'' away from the inner face of the fireplace wall to which it will be screwed.