Transcript Cost Implications of Architectural Design Variables Ahmed S. Al

King Fahd University of Petroleum & Minerals
Department of Construction Engineering & Management
CEM 520
Construction Projects Contracting & Administration
Cost Implications of Architectural
Design Variables
Ahmed S. Al Zahrani
December 2005
OUTLINE
 INTRODUCTION
 LITERATURE REVIEW
 RESEARCH METHODOLOGY
 RESULTS
 CONCLUSION & RECOMMENDATIONS
INTRODUCTION
 Background
 Early cost estimates
 Different cost estimation techniques
 Many factors affecting the estimation
 Objectives
 Investigate cost estimation techniques used in Eastern
Province for residential buildings.
 Investigate procedure in accounting for design variables in
the estimation.
 Study the effect of design variables on the construction
cost.
INTRODUCTION (cont’d)
 Significance of Study
 Establish scope & methodology of cost estimation for the
benefit of entire construction industry.
 Indicate the accuracy level in order to improve the current
techniques.
 Assist the designers in understanding the cost implications
of design variable.
 Scope & Limitations
 Eastern Province
 Residential building business only
 Design variables that architectural in nature.
LITERATURE REVIEW
 Estimation Techniques
 Accuracy depends on skills of the estimators
 Each estimates contains: quality, quantity, & cost
 Main Techniques:
 Order-of-Magnitude Estimate: (min info needed)
 Functional Unit Method
 Floor Area Unit Method
 Building Volume Unit Estimates, etc.
 Budget Estimates
 Requires a large extent of information
 Accurate
 Better for project feasibility
LITERATURE REVIEW (cont’d)
 Design Variables
 Design variable: the parameter or unit of a building design
that can be kept constant in one case, but which may be varied
in different case.
 Major design variables:
• Building Plan Shape
• Size of Building
• Average Storey Height
• Number of Storeys
• Building Envelope
• Circulation Space
• Grouping of Buildings
• Mech./Elect. Services
• Column Spacing
• Floor Spans
• Floor Loadings
• Constructability
RESEARCH METHODOLOGY
 Phase I: Literature Review
 Find out the main cost estimation.
 Find out the main design variables.
 Phase II: Survey of A/E Firms
 Questionnaire distributed to 140 registered firms.
 Only 30 firms satisfy the scope of the study.
 19 firms responded to the questionnaire.
 Questionnaire includes (48 questions):
 Firm General Information (21)
 Estimating techniques, factors influencing the choice of
a technique, & procedures for accounting for the variables
(27)
RESEARCH METHODOLOGY (cont’d)
 Phase III: Simulation for Design Variables
Preparation of Cost Estimate
Changing of Design Variables
Analysis of Changes Observed
DISCUSSION OF RESULTS
 Early Cost Estimates & Design Variables:
 only 10 firms (53%) prepare early cost estimate.
 Summary of Estimating Techniques:
Technique
Frequency
Percent
Cumulative
Frequency
Cumulative
Percent
Prevailing Cost of
Square Meter
3
30
3
30
Approximate
Quantities Method
2
20
5
50
Database of
Similar Projects
3
30
8
80
Unit Rate
2
20
10
100
Factors that Impact Descision on Method Selection
100
90
80
70
60
50
40
30
20
10
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DISCUSSION OF RESULTS (cont’d)
 Empirical Analysis of Design Variables:
Introduction
Hypothesis Statement
Analysis
Conclusion
CONCLUSION & RECOMMENDATIONS
 Conclusion
 53% only do early cost estimates.
 Project size was the most important factor that impacts the
method selection followed by the information available.
 Most important factors which impact the decision on design
variables are:
 shape of plot plan
 land cost for total number of storeys
 intended average storey height
 circulation space
 percentage of glazed area of building services.
 The simpler the plan shape, the lower is the cost.
 The cost per square meter increases with the average storey
height of a building.
CONCLUSION & RECOMMENDATIONS (cont’d)
 Recommendations
 Specialized cost estimating packages to enhance accuracy.
 Increased demand for early cost estimating for the clients to
enhance good planning.
 Innovative practices to be encouraged by A/E firms in order
to avert the consequences of over-assessment & underassessment of cost estimates.
 A/E firms to adopt the relationships between the design
variables and cost.