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The Influence of Design on Building Cost - Size of Building
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Increases in the size of a building usually produces reductions in unit cost such as the square meter rate. The prime reason for this is that on costs do not rise proportionally with increases in the plan size of a building. Expressed in another way we can say that the Preliminary and General items expressed as a percentage of total cost tends to decline with an increase in size and cost. A practical illustration would be the construction of two shops for R500,000.00 and R1,500,000.00 respectively:


Cost : R500,000.00
Foreman’s salary : R10,000.00/month
Construction time : 3 months

Percentage of on-costs = R10,000 x 3 ÷ (R500,000 – (R10,000 x 3))
=R 30,000.00 ÷ 470,000


Cost : R1,500,000.00
Foreman’s salary : R 10,000.00/month
Construction time : 5 months

Percentage of on costs = R10,000 x 5 ÷ (R1,500,000 - (R10,000 x5))


In larger buildings other reductions in unit costs may arise due to savings in:

  1. Prices paid for materials by the builder
  2. Vertical transportation costs in high rise buildings
  3. Larger room sizes etc.


  Shape on Plan                     Fullness on Plan