Methods of Estimation in Construction

1.1 Introduction and Importance of Estimation

• Estimation is the process of predetermining of cost and size of any works. Also, in other words it is the process of calculating the quantity and cost of various item required in proposed work.

Importance of Estimation:

• To fix budget for the proposed project.
• To calculate required quantities of materials and number of labors for proposed projects.
• To draw up a work schedule for proposed project.
• To prepare tender document for the project.
• To prepare valuation of land and building.
• To fix up a completion period of the proposed project.

1.2 System of Unit

• In general, the units of different item of work are based on following principle.
• Mass, voluminous and thick work: L*B*H = m³
• Shallow, thin and surface work (thickness < 75 mm): L*B = m²
• Linear work/ long and thin works: L = Running meter
• Pierce works/ job works: Number

1.3 Units of Measurement and Payment for items of work and Materials

S/N	Description of work	Units of measurement	Units of payment
1	Earthwork
a	E/W in excavation	m^3	per m^3
b	E/W in filling	m^3	per m^3
c	Surface dressing	m^2	per m^2
d	Quarrying of stone or boulder	m^3	per m^3
e	Blasting of rock	m^3	per m^3
f	Rock excavation	m^3	per m^3
2	Brickwork
a	Flat brick soiling	m^2	per m^2
b	Brickwork in foundation	m^3	per m^3
c	Brickwork in cornice, capping, drip course	m	per m
d	Half brick thin wall	m^2	per m^2
3	Stonework
a	Stone masonry, Random rubble masonry in walls	m^3	per m^3
b	Stone slab in roofing, shelve etc	m^2	per m^2
c	Stone work in wall facing or lining	m^2	per m^2
4	Concret work
a	PCC in foundation	m^3	per m^3
b	Lime concrete in foundation	m^3	per m^3
c	75 mm thick pcc	m^2	per m^2
d	DPC (thickness specified)	m^2	per m^2
e	RCC work	m^3	per m^3
f	Formwork	m^2	per m^3
g	Precast PCC and RCC	m^3	per m^3
5	Woodwork
a	Woodwork indoor and window frame	m^3	per  m^3
b	Woodwork in rafters, beam, roof trusses	m^3	per  m^3
c	Timbering of trenches, boarding etc.	m^2	per  m^2
d	Plywood, window and door shutters	m^2	per  m^2
e	Woodwork in partition	m^2	per  m^2
f	Bellies	m	per  m
6	Flooring work
a	Sand filling	m^3	per  m^3
b	Mosaic flooring	m^2	per  m^2
c	Marble flooring	m^2	per  m^2
d	Screed	m^2	per  m^2
e	Cement sand punning	m^2	per  m^2
7	Finishing work
a	Plaster work	m^2	per  m^2
b	Painting work	m^2	per  m^2
c	Skirting	m^2	per  m^2
d	White washing, color washing, cement washing	m^2	per  m^2
e	Distempering	m^2	per  m^2
f	Enamel painting on door and window	m^2	per  m^2
g	Painting letters and figures	No.	per  No.
8	Roofing work
a	Tiled roofing	m^2	per  m^2
b	Tile on ridge of roof	m	per  m
c	CGI roof	m^2	per  m^2
d	Asbestos Cement (AC) sheet roof	m^2	per  m^2
e	Stable roofing, timber roofing	m^2	per  m^2
9	Steel work
a	Steel reinforcement	quintal	per  quintal
b	Channels, Angles, I-section, Beam etc.	quintal	per  quintal
c	Bending, binding of steel reinforcement	quintal	per  quintal
d	Iron work in truss	quintal	per  quintal
e	Iron gate	m^2	per  m^2
f	Iron grill, collapsible gate	m^2	per  m^2
g	Rolling Shutter	m^2	per  m^2
h	Steel door and window	m^2	per  m^2
i	Threading in iron	cm	per  cm
j	Boring holes in iron	no.	per  no.
10	Miscellaneous items
a	Cutting trees	no.	per  no.
b	Railing	m	per  m
c	Pile driving	m	per  m
d	Pipe laying	m	per  m
e	Site clearance work	m^2	per  m^2
f	Furniture	no.	per  no.
g	Fixing door and window	no.	per  no.
h	Bituminous road surfacing	m^2	per  m^2
i	Water closet (W.C), Wash Basin	no.	per  no.
j	Electric wiring	point	per  point
k	Grouting work in crack	m	per  m
l	Grouting work in road	m^2	per  m^2
11	Material
a	Brick	no.	per  no.
b	Cement	bag of 50 kg	per  bag of 50 kg
c	Sand	m^3	per  m^3
d	Aggregate	m^3	per  m^3
e	Brick, ballast, stone ballast	m^3	per  m^3
f	Steel	quintal	per  quintal
g	Bitumen	ton	per  ton
h	Ac sheet	m^2	per  m^2
i	Switches, plugs, bulbs etc.	no.	per  no.
j	Pipe	m	per  m
k	Explosive for blasting	kg	per  kg
l	Varnish oil	liter	per  liter
m	Paint	liter	per  liter

1.4 Requirement of Estimating

1. Drawings:

• Drawings are required for the calculation of the quantities of the materials.
• It shows plans, elevation, different section and other relevant detail with clear and complete dimensions.

2. Specification:

• Specification describes the nature and class of the work, material to be used, workmanship and is very important for execution of work.

Types of specification:

a. General specification:

• This gives a general idea about the nature, quality, class and material in general terms to be used invarious types of work.

b. Detailed specification:

• This gives the detailed description of the various items of work laying down the quantities and qualities of material, their proportions, method of preparation, workmanship and execution of work.

3. Rates:

• Rates are essential for the computation of estimate by multiplying quantities of materials with unit rates.
• Rates include of various material to be used in the construction, cost of transport materials, wages of labor.

4. Method of measurement:

• Updated mode of measurement for standard deduction or additions are also necessary to determine the correct quantities of work.

1.5 Methods of measurement of building and civil engineering works

1. Earthwork

• Measurement in m³.
• Includes throwing of excavated earth at least one meter clear of the edge of excavation.
• Dressing or trimming, levelling or grading, ramming and consolidation thickness of each layer can be describe and include in the item of earthwork.
• No separate measurement is taken for setting out works or site clearance.

2. Concrete work

• Measurement in m³.
• No deduction is done for opening upto 0.1 m² (1 sq.ft).
• No deduction shall be made for volume occupied by reinforcement.

3. Brickwork

• Measurement in m³.
• Deduction for doors, windows and other opening including lintel.
• Different kinds and classes of brickwork shall be taken under separate item.

4. Plastering work

• Measurement in m².
• Plastering of all roofs ceiling, walls etc shall be measured under separate item.
• No deduction is done for joints, beam upto 0.5 sq.m or 5 sq.ft.

5. Painting work

• Measurement in m².
• Different types of surfaces such as steel, wood, concrete etc shall be taken under separate item.

1.6 Subheads of various item of work

• Earthwork
• Concrete work (a. PCC work b. RCC work)
• Masonry work (a. Brick work b. Stone work)
• Wood work
• Flooring work
• Finishing work (a. Cement plaster work b. Painting work c. Roofing work)

1.7 Various Methods of Taking Out Quantities

1. Centre Line Method:

• This method is suitable offsets are symmetrical and the building is more of less rectangular in shape.
• According to this method, total length of centerline of wall is calculated and this length is multiply by corresponding breadth and height of item of work to find its quantity.

2. Long Wall and Short Wall Method:

• According to this method, the long wall is consider first and the wall perpendicular to this wall is consider as short wall.
• The long wall is measured from out to out and the short wall is measured from in to in. After, finding the length of wall, this length is multiplied by corresponding breadth and height of item of work to find quantity of that item.
• Used for building having unsymmetrical layouts, wall for varying thickness, height etc.
• Upto plinth level from footing we can use this method to estimate the quantity.

3. Crossing Method:

• In this method, length and breadth of the masonry walls at plinth level are taken (internal dimension of room + thickness of wall) for calculating quantities.
• The center line length is obtain by calculating the overall perimeter of building and subtracting four times thickness of wall on it.

1.8 Abstracting Bills of Quantities

• A bill of quantities is a document used in tendering process which includes the materials, parts and labor with respect to their cost.
• It is also a detail term and condition of the construction or repair contract and itemizes all work to enable a contractor to price the work for which he/she is bidding.

References:

• Dutta, B.N. – Estimating and Costing in Civil Engineering, UBS Publishers, New Delhi.
• CPWD (Central Public Works Department), India – Standard Schedule of Rates and Analysis of Rates.
• IS 1200 – Indian Standard for Method of Measurement of Building and Civil Engineering Works, Bureau of Indian Standards (BIS).
• Punmia, B.C. – Estimating and Costing, Laxmi Publications.
• Building Estimation and Costing Notes – Department of Civil Engineering, Pokhara University.
• MoUD Nepal – Standard Norms and Guidelines for Public Infrastructure Development Projects.