Chapter9a.pdf

7/25/2019 Chapter9a.pdf

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EstimatingProcess

Agenda

Definitionofestimating

Whatisestimatinginconstruction?

Costvariableinconstruction

Typesofestimates

Conceptualestimate

Detailedestimate

AvoidingErrorsinEstimates


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ESTIMATINGCONSTRUCTIONCOSTS

Thekeytoagoodjobandsuccessfulcostcontrol

isthedevelopmentofagoodestimateasthe

basisforbidsubmittal.

Estimatingistheprocessoflookingintothe

futureandtryingtopredictprojectcostsand

resourcerequirements.

Tominimizeerrors,aconsistentprocedureorset

ofstepsforpreparinganestimateisneededto

minimizeerrorsandachievereliableresults.

TYPESOF

ESTIMATES


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TYPESOFESTIMATESType When? How?

Conceptual Priortothecommencementof

design

Arepresentative

unit

is

multiplied

byapriceperunittoobtainagross

estimate(10%accuracy)ofthe

facilitycost.

Preliminary 40%completionofthetotal

design

Bythearchitector

architect/engineertoreflect

expectedcostsbasedonmore

definitivedata.

Engineer Detaildesignisaccomplished

Totaljobcostminusmarkup

Shouldachieveapproximately

3%accuracy.

Bid Biddingphase

Onthe

basis

of

the

bidding

documents,

Includeamarkupforprofit.

ConstructionManagement,3/EbyDanielW.Halpin

Copyright 2006byJohnWiley&Sons,Inc. Allrightsreserved.


4/16

ConstructionManagement,3/EbyDanielW.Halpin

Copyright 2006byJohnWiley&Sons,Inc. Allrightsreserved.

Example1:A5MGPDdesalinization plant wasconstructed in 1995 at a cost of20M.

What

would

be

the

cost

of

15M

GPD

in

2005,

if

the

cost

capacity

factor

is

0.37,andDesalinizationIndexDI2005=107,andDI1995=99.

CostCapacityformulaisoftheform: 1)(cos,2

1

2

1


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DETAILEDESTIMATEDEVELOPING

STEPS

1.Breakthe

project

into

cost

centers.

2.Estimatethequantitiesrequiredforcostcentersthat

representphysicalenditems(e.g.,cubicyardsofearth,

linealfeetofpipe,etc.).Forphysicalsystemsthis

procedureiscommonlycalledquantitytakeoff.Forthose

costcentersthatrelatetononphysicalitems,determine

anappropriateparameterforcostcalculation(e.g.,the

levelofbuilder'sriskinsurancerequiredbythecontract

orthe

amounts

of

the

required

bonds).

ESTIMATEDEVELOPING

STEPS

(Contd)

3. Priceoutthequantitiesdeterminedinstep2usinghistorical

data,vendorquotations,suppliercatalogs,andotherpricing

information.Pricedevelopmentforphysicalworkitemsmay

requireananalysisoftheproductionratestobeachieved

basedonresourceanalysis.Ifthisanalysisisused,the

estimatormust:

a. Assumeworkteamcompositiontoincludenumberof

workers(skilledandunskilled)andequipmentrequired.

b.Onthe

basis

of

team

composition,

estimate

an

hourly

productionratebasedonthetechnologybeingused.

c. Makeanestimateoftheefficiencytobeachievedonthis

job,consideringsiteconditionsandotherfactors.

d. Calculatetheeffectiveunitprice.

4. Calculatethetotalpriceforeachcostcenter.


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TypicalEstimate

SummarySheet

QUANTITYTAKEOFF

(SURVEYING) Thedevelopmentofthequantitiesofworktobeplacedin

appropriateunits(e.g.,squarefeet,cubicyards,etc.).

Theproceduresemployedbytheestimatortocalculatethesequantitiesshouldincorporatestepstominimizeerrors.

Fiveofthemostcommonerrorsexperiencedduringquantitytakeoffare:

1. Arithmetic:Errorsinaddition,subtraction,andmultiplication

2. Transposition:Mistakesincopyingortransferringfigures,dimensions,

or

quantities

3. Errorsofomission:Overlookingitemscalledfororrequiredtoaccomplishthework

4. Poorreference:Scalingdrawingsratherthanusingthedimensionsindicated

5. Unrealisticwasteorlossfactor.


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ProjectControl 13

Foundation

Excavation Concrete Steel

WorkBreakdownStructureWBS

Workpackages

Aworkpackageisawelldefinedscopeofworkthatusuallyterminatesinadeliverableproduct.

Eachpackagemayvaryinsizebutmustbeameasurableandcontrollableunitofworktobeperform.

Italsomustbeidentifiableinanumerical

accountingsystem

in

order

to

permit

capture

of

bothbudgetedandactualperformanceinformation.

Aworkpackageisacostcenter.


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CE321ConstructionManagement

CSI MasterFormat 95 Titles for Divisions 1-16

1. GENERAL REQUIREMENTS

2. SITE CONSTRUCTION

3. CONCRETE

4. MASONRY

5. METALS

6. WOOD AND PLASTICS

7. THERMAL AND MOISTURE PROTECTION

8. DOORS AND WINDOWS

9. FINISHES

10. SPECIALTIES

11. EQUIPMENT

12. FURNISHINGS

13. SPECIAL CONSTRUCTION

14. CONVEYING SYSTEMS

15. MECHANICAL

16. ELECTRICAL


Division3 Concrete

Plain Concrete

Reinforced Concrete: Substructure

Reinforced Concrete: Superstructure

1. Concrete:

2. Formwork

3. Reinforcing Steel

Foundations

Columns

Beams

Slabs


9/16


PlainConcrete

Concrete is classified by type, strength, and location

Concrete volume is measured from detailed drawings

in cubic meters, rounded to the nearest 0.5 meter

Concrete Mat

Foundation (Spread,

Continuous, Raft)

Pedestal

Grade Beams

Shear Walls

Slab on grade

Columns

Beams

Slabs

Retaining Structures

Stairs & Landings

Use 5-10% waste factor


FoundationDetails


10/16


ASTMStandardReinforcingBars

SoftMetric

Size

NomDiam

mm

Areamm2

WeightFactors

kg/m

10 9.5 71 .560

13 12.7 129 .994

16 15.9 199 1.552

19 19.1 284 2.235

22 22.2 387 3.042

25 25.4 510 3.973

29 28.7 645 5.060

32 32.3 819 6.404

36 35.8 1006 7.907

43 43.0 1452 11.384

57 57.3 2581 20.239


Bar Size (kg/m) Area (mm)

6 0.222 28.3

8 0.395 50.3

10 0.617 78.5

12 0.888 113

14 1.21 154

16 1.58 201

20 2.47 314

25 3.85 491

28 4.83 616

32 6.31 804

40 9.86 1257

50 15.4 1963


11/16

SmallWall

Construction

Activity

Material

List


12/16

UnitPrice

Iftheworkisfairlystandard,thecostcanbecalculatedbysimplytakingdollarperunitcostfromcompanyrecordsandapplyingthiscostwithaqualitativecorrectionfactortothequantityofworktobeperformed.

Unitpricingvaluesareavailableinmanystandardestimatingreferences:

R.S.MeansCompany,buildingConstructionCostData

F.R.Walker'sTheBuildingEstimator'sReferenceBook

TheRichardson

General

Construction

Estimating

Standards

LineItemCostDevelopment

UsingR.S.Means


13/16

Figure13.1 (p.206)Costsbasedonarepresentativeunit.(FromBuildingConstruction CostData.CopyrightReed

ConstructionData,KingstonMA7815857880allrights

reserved.)

AvoidingErrors

in

Estimates

Theaccuracyofanestimateisameasureof

howaccurateorcorrectthenumbersinthe

estimateare

Thecompletenessofanestimateisameasure

ofwhether

the

bid

has

all

the

items

needed

fortheprojectwithoutduplicatingitems


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ListCostCodes

SpendMoreTimeonLargeCosts

PrepareDetailedEstimates

MarkItemsCountedDuringtheQuantity

Takeoff

AvoidingErrors

in

Estimates

DoubleCheckAllTakeoffs

IncludeUnitsinCalculations

AutomatewithSpreadsheets

UseWell

Tested

and

Checked

Formulas

DoubleCheckAllCalculations


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PerformCalculationsinTwoWays

DropthePennies

HaveSomeoneReviewtheEstimate

ReviewEachCostCodeasaPercentageofthe

TotalCosts

AvoidingErrors

in

Estimates

CheckUnitCostsforEachCostCode

CompareCoststoanotherProject

AllowPlentyofTime


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Questions

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