Design Variables that affect building construction

DESIGN VARIABLES THAT AFFECT BUILDING COST.

OFOSU-ENNIN KOFI 3243509 DESIGN ECONOMICS. 4/9/2012

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Introduction

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Conclusion

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Referencing

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Bibliography

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 IN TR OD UC TI ON 

“Design variable: the parameter or unit of a building design that can be kept constant in one case, but which may be varied in another case”. (Al Zahrani, 2005). They can be freely varied by the designer to define a design object. The variables that influence building cost include: 

Plan shape

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Building size

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Circulation space

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Number of storeys

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Storey height

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Grouping of buildings

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Build ability

These factors depending on how they are used by the architect can increase or reduce building cost, as is explained below. Plan shape

The simpler the building shape, the lower the unit cost of the building. Complicated and irregular shapes increase the walls. Additional cost will be incurred from setting out, drainage and site works. Ventilation and lighting requirements as well as shape of  the site may call for a complicated plan. Building size

A larger building size leads to a decrease in the per unit cost of the building. Costs like transportation remain constant. Discounts on bulk purchase of materials also reduce cost. High rise buildings have lifts serving a large floor area making it cheaper. Circulation space

This describes areas such as corridors, entrance halls and lif t wells. They increase cost per unit of usable floor area. These areas are expensive to maintain as they have to be cooled, heated and cleaned. They serve as accesses between different parts of the building, performing no economical function. They are mostly found in buildings like hotels which require large entrance halls and corridors for prestige.

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Number of storeys

Construction cost usually rise with the number of storeys, but this can be offset by the efficient use of highly priced land. The effect of the number of storeys varies with the type, form and construction of the building. The higher the building, the more complex the construction becomes. Specialist may have to be brought in, increasing costs. Increased maintenance cost will also have to be reckoned with. Storey height

Though floor area remains the same, when storey height rises additional cost may be incurred. 

Increased wall and partition area and associated finishes.

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Longer service and waste pipes to and from sanitary installations.

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Higher costs in applying finishes to soffits of ceilings.

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Higher costs of staircases and lifts.

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May require enhanced and more costly foundations.

Grouping of buildings

Grouping buildings maximises the use of confined sites. “Interlinking buildings saves cost in finishes, foundations and external walls”, (Abuza, 2010). Buildability

This is the extent to which the design of a building facilitates construction. The structural form of the building should encourage simple sequences of operations. This helps to keep cost of project within budget and on schedule, avoiding any extra cost.

CONCLUSION 

The relationship between design variables and building cost can’t be ignored. Plan shape, storey height, circulation space and the like directly impact on the design. Ignoring design variables can make building cost spiral out of control. Detailed attention given to it helps projects fall within budget.

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REFERENCES 1. Abuza A.A., 2010.  Building Economics.

2. Al Zahrani Ahmed S., 2005. Cost Implications of Architectural Design Variables.

3. Devsar T, 2009.  Design variable concepts.

BIBLIOGRAPHY 

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Building Economics for Architects.