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
1
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

3
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.

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