lec.2 binifits of estamations...types of estimation

Northern Technical University Engineering Technical College of Mosul Building & Construction Technology Engineering Dept.

Estimation, Specifications and Contracts

SECOND CLASS

Lecturer: Dr. Muthanna Adil Najm ABBU

2017-2018

Estimation, Specifications

& Contracts Factors Lecture .2

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Dr. Muthanna Adil Najm Northern Technical University

PROCEDURE OF ESTIMATING OR METHOD OF ESTIMATING.

Estimating involves the following operations

1. Preparing detailed Estimate.

2. Calculating the rate of each unit of work

3. Preparing abstract of estimate

DATA REQUIRED TO PREPARE AN ESTIMATE

1. Drawings i.e.plans, elevations, sections etc.

2. Specifications.

3. Rates.

DRAWINGS

If the drawings are not clear and without complete dimensions the preparation

of estimation become very difficult. So, It is very essential before preparing

an estimate.

SPECIFICATIONS

a) General Specifications:

This gives the nature, quality, class and work and materials in general terms to

be used in various parts of wok. It helps no form a general idea of building.

b) Detailed Specifications:

These gives the detailed description of the various items of work laying down

the Quantities and qualities of materials, their proportions, the method of

preparation workmanship and execution of work.

RATES:

For preparing the estimate the unit rates of each item of work are required.

1. For arriving at the unit rates of each item.

2. The rates of various materials to be used in the construction.

3. The cost of transport materials.

4. The wages of labour, skilled or unskilled of masons, carpenters, Mazdoor,

etc.,



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LUMPSUM:

While preparing an estimate, it is not possible to workout in detail in case of

petty items. Items other than civil engineering such items are called

lumpsum items or simply L.S.Items. The following are some of L.S. Items

in the estimate.

1. Water supply and sanitary arrangements.

2. Electrical installations like meter, motor, etc.,

3. Architectural features.

4. Contingencies and unforeseen items.

Ingeneral, certain percentage on the cost of estimation is alloted for the above

L.S.Items.

Even if subestimates prepared or at the end of execution of work, the actual

cost should not exceed the L.S.amounts provided in the main estimate.

Factors affecting cost estimation:

There are three further factors that have a significant influence on how an

estimator

goes about preparing a construction estimate:

1. The type of project to be built

2. The delivery system used to move from the developer’s project idea to

a finished structure

3. The nature of the contract(s) used in the delivery system



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Types of estimation:

A. Detailed Estimate

The most accurate and most reliable type of estimate. It consists of the quantities

and the cost of everything required in the project. This includes:-

(1) report, (2) technical specifications, (3) detailed drawings, (4) design data and

calculations, (5) basis of the rated prices adopted in estimation.

B. Approximate (Rough/Order of magnitude/Preliminary) Estimate

This method is based on comparative Cost of Structure. It is readily adaptable to

virtually every type of structure, including bridges, stadiums, schools, hospitals, and

offices. Very little information is required about the planned structure except that

the following general characteristics should be known:

1. Use — school, office, hospital, and so on



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2. Kind of construction — wood, steel, concrete, and so on

3. Quality of construction — cheap, moderate, top grade

4. Locality — labor and material supply market area

5. Time of construction — year

By identifying a similar completed structure with nearly the same characteristics,

an order-of-magnitude estimate can be determined by proportioning cost according

to the appropriate unit for the structure.

There are several techniques to prepare the approximate estimate:-

(1) Service Unit or cost per unit Method

These units might be as follows:

• Schools — pupils

• Stadium — seats

• Hospital — beds

• Warehouses — cubic feet

(2) Unit-Area or Floor-Area Or plinth area

In this technique the cost of unit area of an already constructed building is

adapted as the basis to estimate the cost of a new similar building.

In the case of multi-storey buildings either one of the methods below may be

used:

I- consider the cost of the construction unit of area equal to all floors.

II- taking into account the different construction cost of some floors in

comparison to others.

(3) Unit - Volume or Cubic Rate Method

This is more accurate than its predecessor as it takes into account the third

dimension (i.e., height of floors).

(4) Approximate Quantities



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In this method approximate quantities of each item of the work are calculated

and priced then the approximate cost of the project is calculated.

Using approximate techniques of estimation one must consider the following

points: -

(1). Specification level & finishing requirements.

(2). Time & duration of construction and inflation effect.

(3). Site & location of the project.

(4). General & special requirements of project.

(5). The structural nature of the building.

(6). Shape & height of building compared to the prototype.

C- Quantity Survey or Quantity Estimate

This involves the calculation of the quantities of materials required to complete

the work in question.

D- Revised Estimate

This type of estimate is prepared during construction when the difference

between reality and prepared estimation exceeds 5% regardless the reason behind

this difference (except major structural changes).

E- Supplementary Estimate

Used for the additional works that may seem necessary during the construction

phase.

F- Complete Estimate

It is the cost estimation of each item of works related to the job. It includes:

1 - the cost of land or property including:

• the cost of purchasing the land or its monetary value.



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• fees of surveyor and the delimitation of the property.

• the cost of testing and transfer of ownership of the property.

• real estate tax and making the required improvements, if any.

2 - necessary expenses for legal actions between the owner and the contractor.

3 - the basic amount of main contract ( materials, labor .... etc).

4 - Emergency and unexpected conditions: to be calculated as a percentage of

the work (≈ 5%) and added to the cost of the extra works and supervision.

5 - Engineering fees including:

• Preparation of plans, designs and estimation.

• supervising.

6 - water and electricity fees during the construction phase.

7 - others, if any.

G- Annual Maintenance or Repair Estimate

This type of estimate is pertinent to the repair works and maintenance works that

are necessary to keep the project usable.

Practical examples on approximate estimation:

Example 1: Assume that the current cost for a 120-pupil school constructed of wood

frame for a city is $1,800,000. We are asked to develop an order-of-magnitude

estimate for a 90-pupil school.

Solution:

The first step is to separate the per-pupil cost.

$1,800,000/ 120 = $15,000 pupil

Apply the unit cost to the new school.

$15,000 pupil x 90 pupils = $1,350,000



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Example 2: The total cost of construction of a hospital with capacity of (50) beds

is150 million dinars.

Cost per bed (patient) = 150 ÷ 50 = 3 million dinars

We can use this number to estimate the cost of similar hospital but with 20 beds, as

follows:

20 x 3 = 60 million dinars.

Example 3: a 24x15 m building consisting of 6 floors including the basement,

ground and terrace. Calculate the cost of 1 m2 using both above-mentioned methods,

if the total cost of the building is (648) million dinars.

solution:

(1) first method:

Total construction area = 6x (24x15) = 2160 m2

Cost of 1 m2 = 648000000 ÷ 2160 = 300,000 ID

(2) second method: suppose the cost basement floor = 60% of the cost of any of the

other floors

The cost of terrace = 40% of the cost of any of the other floors (except for the

basement).

The equivalent area of the basement = 24x15x60% = 216 m2

The equivalent area of the terrace = 24x15x40% = 144 m2

Area of rest floors = 4x (24x15) = 1440 m2

Total area of construction =1800 m2

the cost of 1 m2 of construction for the (typical) floors

= 648000000 ÷ 1800 = 360000 dinars

The cost of 1 m2 of basement = 360000x60% = 216000 dinars

Finally, the cost of 1 m2 of the surface = 360000x40% = 144000 dinars



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Example 4: A 60x40m building consists of basement (2.8 m high), three other

floors (each 3m high). The total cost of building 2250 million I. D.

Calculate the cost of unit volume of the building assuming: -

a- identical cost of 1m3 for all floors.

b- costs of basement & ground floor are 60% and 120% of the other floors

respectively.

Solution: a-

Vbasement = 40x60x2.8 = 6720 m3

Vothers = 40x60x3x3 = 21600 m3

__________

Total =28320 m3

Cost of 1 m3 = 2250000000 / 28320 = 79450 I. D.

b- equivalent Vbas . = 40x60x208x0.6 = 4032 m3

equivalent VG. F. = 40x60x3x1.2 = 8640 m3

V others = 40x60x3x2 = 14400 m3

__________

Total = 27072 m3

cost of 1m3 of typical floor = 2250000000 / 28320 = 83112 ID

cost of 1 m3 of basement = 83112x0.6 = 49867.2 I.D.

cost of 1 m3 ground floor = 83112x1.2 = 99734.4 I.D.