Techniques Estimating Cost

Techniques of Estimating During the Design Stages

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Techniques of Estimating During the Design Stages Functional unit method Superficial method Cube method Functional area method Storey enclosure method Approximate quantities method Elemental method 2

Functional Unit Method 1 Examples of cost per functional unit: (Used at Stage A - Brief)

Schools, universities, colleges - per student Hotels, hospitals - per bed Restaurants, cinemas - per seat Car parks - per car

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Functional Unit Method 2 Example: Hospital of 640 beds Cost per bed = $16,000 Total estimated cost = 640 x $16,000 = $10,240,000

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Superficial Method - 1 Cost per square metre of floor area: (Used at Stage A - Brief and Stage B Outline Proposal)

Example: Project of 852 m2 Cost per m2 = $1,106 Total estimated cost = 852 x $1,106 = $942,312

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Superficial Method - 2 Advantages: Unit is meaningful to all parties Most cost data is published in $/m2 Estimates are quickly and easily prepared

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Superficial Method - 3 Disadvantages: Difficult to allow for effects of design decisions such as plan shape, storey height, quality, etc Separate allowance must be made for site works and external services (Note: These also apply to functional unit and functional area methods) 7

Cube Method Cost per cubic metre of building volume: (Could be used at Stage A - Brief and Stage B - Outline Proposal, but obsolete!)

Example: Project of 16,000 m3 Cost per m3 = $325 Total estimated cost = 16,000 x $325 = $5,200,000 8

Functional Area Method 1 Examples of cost per square metre of functional area: (Used at Stage A - Brief and Stage B Outline Proposal)

Primary schools and secondary colleges TAFE colleges and universities Hospitals and medical/community centres 9

Functional Area Method 2 More accurate than simple superficial method No published cost data Not useful for “one-off” projects Useful only for client body involved in continuous and consistent program of similar projects 10

Storey Enclosure Method Cost per square metre of building envelope: (Could be used at Stage A - Brief and Stage B Outline Proposal, but obsolete!)

Uses single price rate similarly to functional unit and superficial methods Incorporates cost effect of design features such as height and shape 11

Approximate Quantities Method - 1 Cost per square metre of building structure: (Used at Stage C - Sketch Design and Stage D - Tender Document)

Not single price rate method Most accurate method Uses actual construction rates for each group of related items 12

Approximate Quantities Method - 2 Figure 5.1 Ground Slab and Foundation Detail

Trowelled surface for Carpet Galvanised Iron Flashing

Ground Level 400 x 500 Reinforced Concrete F42 Fabric Polythene Sheet 150 Concrete Slab 150 Crushed rock 50 Sand Bed under Polythene Sheet 13

Approximate Quantities Method - 3 Example per m2:

$

100mm hardcore 9.50 50mm sand 2.50 Polythene 2.80 150mm concrete @ $125/m3 18.75 F42 steel fabric 4.25 50mm screed 4.00 Total cost per square metre $41.80

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Approximate Quantities Method - 4 Simple, reliable and accurate method Can clearly reflect adjustments of quantity and/or quality Cost data readily available Time-consuming Applicable only to building work Applicable only in later stages of cost planning

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Elemental Method - 1 Cost per m2 of NPWC elements: Element groups used in Stage B Outline Proposal Individual elements used in Stage C Sketch Design and Stage D - Tender Document (Note: For format of element codes and makeup of element groups, refer to Topic 3) 16

Elemental Method - 2 Element costs are expressed in: Percentage of total building cost Cost per m2 of gross floor area Unit rate per m2 of element Total element cost

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Elemental Method - 3 Advantages: Flexible, adaptable method, suited to Stages B, C and D Easily understood by all parties Facilitates comparison between projects Facilitates analysis of cost implications of design decisions

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Elemental Method - 4 Disadvantages: Time-consuming High level of expertise required

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Sources of Cost Data Rawlinsons Australian Construction Handbook (published annually, index updated quarterly) Cordell’s Building Cost Guide (published quarterly) The Building Economist (published quarterly)

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Selection of Estimating Technique Recognise that design does not proceed uniformly across all elements Use both rough and sophisticated techniques in the one estimate if necessary Use an appropriate technique for each element Technique must reflect amount and quality of information available 21