What is the Cost Implications of Design variables ?

Costs of buildings are influenced by changes in shape , size storey , heights , user's needs , planning and local authorities requirements , site conditions , form of contract , period for completions and etc .

Changes in shape

• General rule is the simpler the shape of the building the lower will be the unit cost
• When the building becomes more complicated and irregular , the perimeter / floor area ratio will increase and acco,mpanied by a higher unit cost .
• Rectangular shaped building would be more expensive than a square one with the same floor area because of smaller perimeter / floor area ratio .

Size of Building

• General rule is increases in the size of buildings will produce reductions in unit costs i.e. cost / m2 of gross floor area (GFA) .
• Costs do not rise proportionately with increases in the plan size of a building because :

- Fixed costs i.e. transportation , erection and dismantling of site building , storage of materials , temporary water supply arrangements , provision of temporary roads do not vary with an extension of the size of the building .

- Larger projects is often less costly to build as the wall / floor ratio reduces 
- Cost advantage of highrise building may accrue due to lifts serving a larger floor area