Plot Envelope, FAR and the Sixth-Floor Request
A developer owns a rectangular plot 40 m wide (frontage) and 60 m deep. The local bye-laws require a 6 m front setback, 4 m rear setback and 3 m side setback on each side. The maximum ground coverage is 40% of the plot area and the FAR is 2.0. The height limit is 18 m, and the structural consultant's floor-to-floor height is 3.2 m for the proposed mixed-use building (retail on the ground floor, offices above). The client wants the maximum permissible built-up area and asks whether a sixth floor can be added by reducing floor-to-floor to 3.0 m. The architect's first sketch places a 960 m² rectangular footprint and claims five floors 'because 5 × 3.2 = 16 m is under 18 m'. A neighbour's plot has a 2 m side setback, and the client argues that this sets a precedent. The parking requirement is one ECS per 100 m² of built-up area, with surface parking at 25 m² per ECS.
1. Calculate the plot area, buildable envelope, maximum footprint, maximum built-up area and permissible number of floors. Identify which constraint actually governs.
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Plot area = 40 × 60 = 2400 m². Side setbacks reduce the width to 40 − 3 − 3 = 34 m; front and rear setbacks reduce the depth to 60 − 6 − 4 = 50 m. The buildable envelope is 34 × 50 = 1700 m². Ground coverage caps the footprint at 0.40 × 2400 = 960 m². FAR caps the total built-up area at 2.0 × 2400 = 4800 m². Height permits 18/3.2 = 5.625, so only 5 whole floors. With a 960 m² footprint, 5 floors give exactly 4800 m². The FAR, coverage and height limits therefore all bind at the same solution; none is redundant. The architect's sketch is numerically correct but the stated reason is incomplete: 16 m is under 18 m, yet FAR and coverage also have to be satisfied.
2. Can a sixth floor be added by reducing floor-to-floor to 3.0 m? Show the trade-off and state the conditions under which it is permissible.
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Six floors at 3.0 m use 18.0 m, so the height limit is met only if no parapet, rooftop equipment or lift overrun is counted; otherwise it fails. FAR still caps total area at 4800 m², so six floors force the average footprint down to 4800/6 = 800 m². That is 33.3% coverage, below the 40% cap, and 800 m² fits inside the 1700 m² envelope. So a sixth floor is possible only with a smaller floor plate, not by keeping 960 m². The reduced plate may disrupt the structural grid, parking and core efficiency. A 3.0 m floor-to-floor also lowers ceiling height and service space. The correct answer is conditional: feasible on paper, but subject to height measurement rules and a redesigned 800 m² plate.
3. The client cites the neighbour's 2 m side setback as precedent. Is that argument valid? Also check the parking implication of the maximum scheme.
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No. Setbacks are statutory minimums applying to the plot; a neighbour's smaller setback is either a non-conforming existing condition or a violation, and it does not create a right for this site. The applicant must comply with the 3 m requirement unless a formal variance is granted. For parking, 4800 m² of built-up area requires 4800/100 = 48 ECS. At 25 m² per surface space, that is 1200 m², half the plot. Combined with a 960 m² footprint, 2160 m² of the 2400 m² plot is occupied before circulation and landscaping, which is unrealistic. The scheme therefore needs a basement or a reduced built-up area; the parking requirement can become the practical binding constraint even though it is not in the FAR calculation.