The Bombay High Court held that the expression “built-up area” in section 80-IB(14)(a) refers to the inner measurements of the residential unit at floor level, including only such projections and balconies as are habitable or capable of effective use by the flat purchaser, together with wall thickness, but excluding common areas. The flower bed area, admittedly outside the residential unit, below floor level, open to the sky and merely ornamental, could not be treated as part of built-up area. Likewise, cupboard projections already formed part of the wall area, the service area was a common duct space for pipes and not usable by flat owners, and window projections at sill level were unsafe and only elevational features. Accordingly, these areas were rightly excluded while computing the 1000 sq. ft. limit, and the assessee was entitled to deduction under section 80-IB(10). (AY. 2010-11)