I'm building a chimney breast and hearth with a view to install a log burner. How far out should the hearth come out into the room ? I plan to tile with 300mm tiles and had planned one row of tiles in front of the fire on a concrete base but have read varying posts about the hearth should be 250mm or 500mm from the front of the fire. Is there a legal requirement as I don't seem to be able to find it online?