Estimating and Costing Chapter One Note

CHAPTER – 1 INTRODUCTION

1.1 Definition

Estimating is the process of calculating the quantities and cost of various item required in connection with work. It is necessary to estimate the amount of fund required for the proposed work otherwise; it may so happen that the work has to be stopped before its completion due to shortage of funds or of materials.

1.2 Estimated cost and Actual cost

Estimated cost is the theoretical cost of the work/ probable cost of the work. Actual cost is the expenditure, after completion of the work from account register of the completed work.

Estimate is never the actual cost of the work. Justify

An estimate is the probable cost of construction work which is computed from the dimensions on the drawings and the standing rates at the time of preparation of the estimate. The accuracy of the estimate depends on the skill and experience of estimator. Actual cost of construction can be known from the physical measurements of the dimensions for various items of works at site and the actual rates of at such items of works during execution off work. All expenses for all probabilities can be known after completion of works as well as account. So, it can be justified that whatever method may be adopted, in general all estimates are approximate in nature and the difference between the estimated cost and actual cost is vital issue. Although estimated cost is never the actual cost of work, it should be close.

1.3 Purpose of estimating

The estimating is very important for the developing country as they have taken fund as debt from different agencies which charges high interest rate. The estimating gives general idea about time and fund required. The main purposes of the estimating are highlighted below:

·         Too give idea of the cost of the work

·         To estimate various materials required to completing a particular work

·         To estimate various categories of labours required to completing a particular work.

·         To estimate various tools and plants required to completing a particular work.

·         To justify the investment from benefit/cost ratio

·         To estimate time of completion of work

·         To invite the tenders and prepare bills for payment

·         To estimate the existing property for valuation.

·         To draw up the construction schedule etc.

1.4 Principle of units and measurement

The units of measurement mainly depend upon shape, size and nature of work.

1. Mass, voluminous and thick works shall be taken in m³. (E/W, B/W)

2. Shallow, thin and surface works shall be taken in m²  (DPC, Shutters)

3. Long and thin walls shall be taken in running unit (rm). (Skirting, Handrail)

4. Piece works, Job works shall be taken in number (Tube light, wash basin)

1.5 Units of Measurement and Payment for various items of work

Item No.	Description of work	Unit of Measurement	Unit of Payment
1.	Earthwork
1.1	E/W in excavation in foundation	m3	Per % m3
1.2	E/W in filing	m3	Per % m3
1.3	Surface dressing	m2	Per m2
1.4	Surface excavation	m2	Per m2
2.	Brickwork
2.1	Brick on flat soling	m2	Per m2
2.2	B/W in foundation	m3	Per m3
2.3	B/W in superstructure	m3	Per m3
2.4	B/W in arches	m3	Per m3
2.5	B/W in Cornice	m	Per m
2.6	Half brick thick wall	m2	Per m2
3.	Concrete works
3.1	PCC in foundation	m3	Per m3
3.2	Lime concrete in foundation	m3	Per m3
3.3	PP for RCC walls	m3	Per m3
3.4	50mm thick PCC in floor	m2	Per m2
3.5	Formwork for RCC work	m2	Per m2
3.6	Steel Reinforcement	Kg or MT	Per kg or MT
4.	Wood work
4.1	Wood works for doors and window frame	m3	Per m3
4.2	Doors and window shutters	m2	Per m2
4.3	Wood works for trusses	m3	Per m3
4.4	Wood works for rafters, wall plate etc.	m3	Per m3
4.5	Wood work for false ceiling	m2	Per m2
4.6	Wooden partition	m2	Per m2
5.	Iron works
5.1	M.S grill	m2	Per m2
5.2	Tubular trusses and purlins	Quintal or kg	Per kg
6	Flooring works
6.1	Sand filling	m3	Per m3
6.2	Cement sand screed	m2	Per m2
6.3	Marble flooring	m2	Per m2
6.4	Flagstone flooring	m2	Per m2
7.	Roofing Work
7.1	C.G.I sheet roofing	m2	Per m2
7.2	Tile roofing	m2	Per m2
7.3	C.G.I sheet on gutter ridge	m	Per m
7.4	Tile on ridge	m	Per m
8.	Plaster and Pointing works
8.1	Pointing works	m2	Per m2
8.2	Plastering works	m2	Per m2
9.	Painting and Polishing works
9.1	Enamel Painting	m2	Per m2
9.2	Washable distemper	m2	Per m2
9.3	French Polishing	m2	Per m2

1.6 Data required for estimating

The requirements for estimating are mentioned below:

1.       Drawings:

The drawing is the basis from which quantities of various items for a work are calculated, so fully dimensioned drawings must be prepared showing plans, different sections and other relevant details for the work.

2.       Specification

i. General Specification:

In general specifications the nature and class of work and the names of materials that could be used are described. This forms a general idea for the project.

ii. Detailed specification:

Detailed specifications describe every item of work in the estimate. This specifies the qualities, quantifies and proportions of materials, workmanships, method of preparation and execution for different items of works in a project. Thus, specification of a work serves as a guide to the supervising staff of the contractor as well as to the owner to execute the works to their satisfaction.

3.       Rates

Quantities of different items of works are estimated from the drawing and these are multiplied by the rates. So, rates for different item of works are vital factor to determine the estimated cost. Normally, the Engineering Departments provide with the current schedule of rates per unit of work, materials, wages of labour transport etc. In case when such rate is not found in the schedule, this is worked out by analysis.  

4.       Updated mode of measurement

Updated modes of measurement for standard deductions or additions are also necessary to determine the correct quantities of works.

5.       Standing circulars

Standard circulars for taxes and insurance etc. are required to fix up rates of those items which are not in the schedule of rate.

Reference

1. “Estimating, Costing, Specification and Valuation in Civil Engineering” by M Chakraborti

2. “Estimating and Costing” by B.N. Dutta

Read More