Chapter (Estimating)

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hapter Six

ESTIMATING

6.1 ESTIMATING

An estimating is trial to judge the value size, cost etc or to forecast of what a job or

service is expected to cost. Normally it is generally based on similar works or projects

taken up in the past, making necessary amendments especially for the cost materials

and wages. The total cost of a work is made up of the cost of various individual

elements. The estimating of the total cost consists of

!i" #stimating the cost of the $ndividual #lements of the %ost.

!ii" &uilding up the total cost, taking into consideration each individual

element of the cost concerned.

The cost of various individual elements may be under the work section of

!i" 'reliminaries ( which shall include insurance, progress photographs

report, warning sign, lamps, signboard, watchman, and etc.

!ii" )ain work ( which shall include building, roads, water tanks, bridge, tower,

and etc.

!iii" $nternal services ( which shall include air conditioning, fire extinguisher,

electrical installation, sprinkler

!iv" #xternal works ( which shall include electrical mains comprise of

capital*service charge, sewerage, water supply, special foundations, site

work, surface drainage, road and paths, fencing and gates.

!v" Advertisement

!vi" +upervision

!vii" )iscellaneous!viii" 'rofessional fees ( which shall include surveyor, designer.

!ix" %ontingencies ( it is a sum entered to allow for possible additional work or

dayworks assume it was -/ of the total cost estimated.

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6.2 OBJECTIVES OF ESTIMATING

The main objectives of estimating are as follows

gives prior indication of the economic viability of a particular project

to make a decision whether to proceed the project or not due to its cost

an estimate helps establish data for the purpose of comparing

estimating may help a new design to reduce the cost of the project, when the original

design is found uneconomical.

6.3 STAGES OF ESTIMATING

Traditional civil engineering projects can be divided into six stages

i" $dentification,

ii" Appraisal,

iii" 2efinition,

iv" Approval,

v" $mplementation and

vi" 3peration.

Figure 6.3 : Variati! I! T"pe O# E$ti%ate &ith Cha!ge$ I! 'r(e)t Stage$

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Preliminaryestimate

Appraisal

estimates

Proposal

estimate

Approvedestimate

Post-contract

estimate

Achieved

estimate

Pre-tender

estimate

Time

Operation

Implementation

Approval

Definition

Appraisal

Identification

ProjectStage


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5igure 0.- shows the se6uence of these project stages and indicates the types of

estimate used in each stage.

Preliminary estimate ( an initial estimate at the earliest possible stages.&ased on crude indication of the project size or

capacity, to be used in planning stage.

Appraisal estimate ( should include all costs which be charged against the

project in order to provide best estimate off anticipated

total cost.

Proposal estimate ( based on a conceptual design and design study

specifications.

Approved estimates ( proposal estimate was modified due to client7s view

Pre-tender estimate ( a refinement of the approved estimate based on the

definitive design work using the information provided in

the tender documents. At this stage the estimate

should reflect the total capital cost of the project and all

the charges and fees and allowances or contingency

for the client7s risk.

Post-contract estimate ( a further refinement of the pre(tender estimate

Achieved cost ( actual costs of the job in order to review performance

and provide data for future projects.

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6.* T+'ES OF ESTIMATING TEC,NI-E

The five common estimating techni6ues are summarised as follows (

G/0a/ ( a simple estimating techni6ue which based on existence of data

from similar projects.

Fa)tria/ ( a techni6ue used widely on process plants where the key

components can be easily identified and priced and all other works

are calculated as factors of these components.

Ma!hur ( works is estimated in total man(hours and cost in conjunction with

plant and material costs.

!it rate ( based on bill of 6uantities, where the 6uantities if work are defined

and measured in accordance with standard method of

measurement.

Operati!a/ ( based on all the constituents operations necessary to construct

the works and estimating the labour, plant and materials costs

together with the overheads.

Table 0.8 shows the five estimating techni6ues in terms of their project data

re6uirements and estimating data re6uirements.

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Ta0/e 6.* : Mai! E$ti%ati!g Te)h!iue$ A! Their 4ata 5euire%e!t$

4ATA5E-I5EMENTS

ESTIMATING TEC,NI-E

G/0a/ Fa)tria/ Ma!hur$ !it rate Operati!a/

'roject data %ompletiondate

9ocation

+ize*capacity

%ompletiondate

9ocation

9ist of maininstalledplant items

%ompletiondate

9ocation

:uantities

+implemethod

statement

;ey dates

%ompletiondate

9ocation

&: !at leastmain items"

%ompletiondate

)aterials

:uantities

)ethodstatement

'rogram

&asic #stimating

2ata

'otential

'roblems,

eneralinflationforecasts

)arkettrends

$nflationindices

Achievedoverallcosts ofsimilarprojects!ade6uatelydefined"

>eneralinflationforecasts

)arkettrends

$nflationindices !forhistoricalprices"

#stablishedfactorialestimatingsystem

eneralinflationforecasts

)arkettrends

$nflationindices

?istoricalunit rates forsimilar workitems

'reliminaries

)aterialscosts

9abour ratesandproductivity7s

'lant costsandproductivities

3verheadcosts

)aterialscostsforecasts

9abour rateforecasts

'lant capitalandoperatingcostsforecasts

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6. CONSTITENTS OF ESTIMATE

The price of an item of work is made up of the following components (

%ost of materials ( calculate the materials re6uired for the item of work and

allow for waste and delivery to site.

%ost of labour ( this is very uncertain factor, the output of labour varies

considerably accordingly to place of works, weather

condition, heights etc.

%ost of tools and plants ( the cost should include

initial cost of machine

interest on capital cost

the economic life span of machine

maintenance

cost of transporting machine to site

number of hours machine is operated in one year

consumption of machines fuel cost

driver*foreman unskilled workers ( wages

output of machine

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6.6 &O57E4 E8AM'9ES

Exa%p/e 6.6.1 E$ti%ati!g O# Ex)aati! &r;$ 3 hr

The labour time costs 3 hr

9abour cost of excavating 1 m-of rock including 1@/ profit

F


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Exa%p/e 6.6.1.a E$ti%ati!g O# Ex)aati! &r;$


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Exa%p/e 6.6.2 E$ti%ati!g O# Fr%r;

=sing 9a0ur a! Materia/ C!$ta!t$, prepare estimation cost for fixing one !1" piece

-mm x -mm heavy duty car porch tile with 4mm thick of cement and total cost ofthe proposed car porch tiles project abiding on data below. The project duration is

expected to be two !4" days and re6uires two !4" skilled workers and two !4" unskilled

workers.

2ata

1. Dhite horse heavy duty tile !-mmx-mm" F


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4. Ce%e!t

a" vol. of cement F .- x .- x .4

F .1Bm-

Total vol. of cement F @ x .1BF 1.-C@m-

%ost of cement F !1.-C@ x 4Bbag" x rm1@.

F

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Chapter (Estimating)