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Wednesday, May 4, 2022

Construction Costs and Material Estimation for your House - homeslibro

Estimating Costs and Material Requirements for Your Home | Guide of Home Construction Material and Cost Estimation | How do you estimate the materials needed to build a house?


It is always worthwhile to estimate the cost of the proposed construction so that it does not exceed the available finances. We have already seen in the article “Classification of Buildings how a building can be classified as class I, II or III. If the approximate cost to build a building of a particular class in a given locality is known the total cost of the building, can be estimated on an area basis. In this article, we will examine the various components of the cost of the building so that we can control the cost during the execution stage itself. Charges for supervision and the supply of labour and materials which are paid for by the owner are usually taken as 7 to 10% of the overall cost of the building. In lump sum and item-wise contracts, because of the new tax laws, contractors expect a profit of 15 to 20% of the cost of the work.

 

BREAK UP OF COST OF CONSTRUCTION

The table below gives the approximate average percentage cost of civil works for a residential building. It also indicates the possible savings that can be made. The actual values will depend on many factors like foundation condition and architectural features.


Table: Percentage cost of civil works

S.No.

Works

Cost

(% of the total cost)

Possible savings

(% of the total cost)

1.

Foundation and plinth

10 to 15

1 to 3

2.

Superstructure

 

 

 

(wall + roof, including plastering)

30 to 40

4 to 13

3.

Painting

5 to 20

1 to 8

4.

Doors and windows

12 to 20

1 to 8

5.

Flooring

10 to 20

2 to 7


In addition, the cost of services is usually estimated as a percentage of civil works and is taken as follows:

 

Water supply and sanitation

10 to 12.5 per cent

Electrical works

8 to 12.5 per cent

External works

2 to 5 per cent

Total

20 to 30.0 per cent (max)

 

RATIO OF COST OF MATERIALS TO LABOUR

It has been found that the total cost can be divided into the following percentages for an ordinary building built in India in the traditional way:

1. Material cost - 60 per cent of the total cost

2. Labour cost - 30 per cent of the total cost

3. Other costs - 10 per cent of the total cost

 

The break up of the cost of materials can be approximated as given in the Tables below

 

Cost of principal materials

S.no

Item

Approximate cost as % cost of the civil work

1.

Bricks

15 to 18

2.

Cement

12 to 18

3.

Steel

5 to 15

4.

Timber

10 to 15

5.

Sand

7 to 10

6.

Aggregate

8 to 10

7.

Paint

5 to 10

 

Cost of labour

S.no

Worker

Approximate cost as %

of civil works

1.

Mason

12

2.

Unskilled labour

12

3.

Carpenter

6

 

CONSUMPTION OF MATERIALS FOR BUILDINGS

The data given in the Table below can be taken as very approximate quantities of materials required for construction of an ordinary building.

Table: Very approximate quantities of materials required for a 1 m2 plinth area

S.No.

Materials

Quantity per m2 of plinth area

1.

Bricks (9" ordinary)

250-300 nos.

2.

Sand

0.5 to 0.7 m3

3.

40 mm aggregates

0.2 m3

4.

20 mm aggregates

0.2 m3

5.

Steel for buildings with load bearing walls

10 to 20 kg

6.

Steel for framed flats and hostels

30 to 50 kg

7.

Steel for framed offices

40 to 70 kg

8.

Cement for load bearing walls

3 bags

9.

Cement for framed buildings

4 bags

10.

Lime for brick jelly

40 litres

 

 

ANALYSIS OF ITEMS OF WORKS

The quantities of important items of work for buildings can be worked out to control cost as shown in the Table below which is for a middle-class building on load bearing walls. The values shown are not exact but only indicative.

 

Table: Items of works for residential buildings on load-bearing walls (Quantitative are only indicative. Actuals will depend on the design.)

 

 

s.no

Materials

Approximate quantity per m2 of the plinth area

G.F ONLY

G.F + F.F

1

Earthwork

0.52 m3

0.30 m3

2

Mass concrete in foundation and under floor

0.22 m3

0.15 m3

3

RCC in foundation

0.11 m3

0.06 m3

4

Brickwork in foundation (varies)

0.16 m3

0.09 m3

5

Brickwork in superstructure

0.40 m3

0.40 m3

6

RCC in superstructure:

 

 

Plinth/lintel/beam

0.05 m3

0.05 m3

Slab and stairs

0.01 m3

0.18 m3

Sunshade/shelves

0.18 m3

0.01 m3

7

Doors and windows

0.45 m3

0.45 m3

8

Plaster

2.60 m3

2.60 m3

9

Painting of walls and ceiling

3.5 m3

3.5 m3

10

Waterproofing

0.98 m3

0.60 m3

11

Flooring

0.75 m3

0.75 m3

 

 

CEMENT REQUIREMENTS IN CEMENT WORKS

Cement is an important material and its consumption must be controlled. Some of the data used for the calculation of cement requirements in concrete, mortar and plaster are given in the Tables below

 

Table: Cement consumption for concrete

Mix

W/c ratio

Strength

Cement per (m3 of concrete (kg)

With control

Without control

1 :1.5: 3

0.42

20

30

405

1 : 2 : 4

0.55

15

25

310

1 : 3 : 6

0.75

10

15

215

1 : 4 : 8

Used only for base concrete, etc.

160

1 : 5 : 10

Used only for base concrete, etc.

130

 

Note: 1 cubic metre = 35.315 cubic feet; Approximate yield = 2/3 x Volume of mix. Hence, volume of cement required per m3 of concrete is taken as (1.52/ Volume of mix) (approx).

 

Table: Requirements for 1 m3 of cement mortar

Mix of mortar

Cement (bags)

Sand (m3)

1:3

2.6

0.267

1:4

1.9

0.275

1:6

1.4

0.299

1:8

1.1

0.308

 

Note: For brick masonry, we need 500 metric bricks (and 520 ordinary bricks) per cubic metre of brickwork and 25 to 30% of the volume of brickwork will be taken up by a mortar. Hence, we need about 0.25 to 0.30 cft of mortar. One bag of cement is considered as 50 kg in weight and 35 litres in volume.

 

Table: Requirements for 100 m2 of 12 mm thick cement plaster

Mix

Cement (bags)

Sand (m3)

1 : 2

21

1.4

1 : 3

15

1.5

1 : 4

12

1.6

1 : 6

9

1.8

Note: 1 square metre = 10.764 square feet

 

ESTIMATION OF STEEL IN RC WORKS

For preliminary estimation, it is usual to assume the steel requirement on a percentage basis (or kg/m3) of the easily calculable volume of concrete based on the data given in Table below. The actual requirement by proper design will be much less.

(Note: Steel rods usually come in lengths of 11 m. Hence we can check the weight of a consignment by counting the rods. For example, the weight of a consignment consisting of 8 rods each of length 11 m = 11 x 0.395 = 4.4 kg, approximately.)

 

Table: Estimation of steel in buildings components (Fe 415 steel)

Item

Coefficients for estimation of steel

As % of steel

As Kg/m3

Footings

0.25 to 0.65

20 to 50

Cast In-situ Piles

0.40 to 0.75

30 to 60

Rafts

0.75 to 1.50

60 to 120

Columns

1.00 to 4.0

80 to 320

Beams

0.5 to 1.5

30 to 100

Slabs and lintels

0.3 to 0.6

25 to 50

Sunshades

0.3 to 0.5

25 to 30

 

Note: 1% steel = 78.5 (say 80 kg) of steel per cubic metre of concrete.

Example: Find the steel required for a slab 15 x 10 m and 120 mm thick.

Volume of concrete = 15 x 10 x 0.12 = 18 m3

Assume % of steel is 0.4 % = (or 0.4 x 78.5 = 31 kg/m3)

Wt of steel = 18 x 31 = 565 kg

(Note: This works out to 565 ÷ 150 = 3.76 kg/m2 for slab only. In addition we have foundation beams, columns etc. so that the total quantity will workout to 10 to 20 kg/m2)

 

TYPICAL MINIMUM CONSUMPTION

The minimum consumption of steel in kg/m2 by proper design and detailing for a typical four storey building on good soil using to Fe 415 steel can be a total of 20 kg/m2 as follows

Minimum steel for a four-storey flat

ITEM

STEEL CONSUMPTION

Foundation

2.0 kg/m2

Plinth beam

2.0 kg/m2

Columns

4.0 kg/m2

Beams

5.0 kg/m2

Slabs and stairs

5.5 kg/m2

Lintels, sunshade etc.

1.5 kg/m2

 

ANALYSIS OF RATES

One of the topics studied in "estimating" is the analysis of the rates of various items of works. The data for the cost of materials, labour and other items such as scaffolding required per unit of work for each item of work in each region of the country is available. From these data, the cost per unit of work can be estimated. As it is a subject to be studied underestimating, we will not go into a detailed study of the subject in this article.

 

ESTIMATION OF PAINT REQUIRED FOR PAINTING AN AVERAGE RESIDENTIAL BUILDING

(a) Rough estimate of areas to be painted in terms of plinth area: Area of ceiling = Floor area (say plinth area)

Area of internal walls = 3 x plinth area

Area of external walls = 2 x plinth area

Area of windows = 30% plinth area on each side

Area of doors = 30% plinth area each side

 

(b) Approximate coverage of different types of paints per coat (Second and third coats will have 25% more coverage).

1. Fat lime for lime-washing 10 m2/kg

(For colour wash add 1 to 2 kg colour per 100 m2)

2. Dry distemper 10 m2/kg

3. Cement paint 5 m2/kg

4. Cement wall primer 8 m2/L (litre)

5. Oil bound distemper 8 m2/kg

6. Plastic emulsion paint 10 m2/L

7. Acrylic exterior paint 12 m2/L

8. Metal primer 10 m2/L

9. Synthetic caramel paint 10 m2/L

10. Copal varnish for wood 10 m2/L


MUST READ: Cost Percentage Of Building Materials For 1000 Sqft of House Construction


MUST READ: Material and labour Cost of One Room Construction | Room Estimation

 

FAQ

How Much Paint do I Need?

Example: Find the approximate quantity of paint required for painting 200 m2 of wall with plastic emulsion paint in two coats.

Paint required for first coat = (200/10) = 20.0 litres

Paint required for second coat = 16.0 litres (10% less)

Total = 36.0 litres (approx)

 

Note: Generally one painter can be assumed to paint 15-20 m2 of wall surface per day, depending on the type of paint and finish.

 

How much paint do I need for one coat?

Approximate coverage of different types of paints per coat (Second and third coats will have 25% more coverage).

1. Fat lime for lime-washing 10 m2/kg

(For colour wash add 1 to 2 kg colour per 100 m2)

2. Dry distemper 10 m2/kg

3. Cement paint 5 m2/kg

4. Cement wall primer 8 m2/L (litre)

5. Oil bound distemper 8 m2/kg

6. Plastic emulsion paint 10 m2/L

7. Acrylic exterior paint 12 m2/L

8. Metal primer 10 m2/L

9. Synthetic cramel paint 10 m2/L

10. Copal varnish for wood 10 m2/L

 

What is rate analysis?

One of the topics studied in "estimating" is the analysis of the rates of various items of works. The data for the cost of materials, labour and other items such as scaffolding required per unit of work for each item of work in each region of the country is available. From these data, the cost per unit of work can be estimated.

 

How many cement bags are used for plastering?

Requirements for 100 m2 of 12 mm thick cement plaster

Mix

Cement (bags)

Sand (m3)

1 : 2

21

1.4

1 : 3

15

1.5

1 : 4

12

1.6

1 : 6

9

1.8

Note: 1 square metre = 10.764 square feet

 

What is the percentage of cost of materials and Labour?

1. Material cost - 60 per cent of the total cost

2. Labour cost - 30 per cent of the total cost

3. Other costs - 10 per cent of the total cost

 

How much steel is in a building?

Estimation of steel in buildings components (Fe 415 steel)

Item

Coefficients for estimation of steel

As % of steel

As Kg/m3

Footings

0.25 to 0.65

20 to 50

Cast In-situ Piles

0.40 to 0.75

30 to 60

Rafts

0.75 to 1.50

60 to 120

Columns

1.00 to 4.0

80 to 320

Beams

0.5 to 1.5

30 to 100

Slabs and lintels

0.3 to 0.6

25 to 50

Sunshades

0.3 to 0.5

25 to 30

 

How to Calculate Construction Cost per Square Feet?

Costs and Material Estimation for your House

Estimating-Costs-and-Material-Requirements

How to Calculate Construction Cost per Square Feet

Estimating-Costs-and-Material-Requirements



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