Open Fireplace Recesses ~ these must have a constructional
hearth and can be constructed of bricks or blocks of concrete or
burnt clay or they can be of cast in-situ concrete. All fireplace
recesses must have jambs on both sides of the opening and a
backing wall of a minimum thickness in accordance with its position
and such jambs and backing walls must extend to the full height of
the fireplace recess.Open Fireplace and Flues