Cost estimating methods in construction project is mostly used estimating purposes. Here we discuss about preliminary estimating, cost estimating methods, approximate quantities method and elemental estimating methods.
Cost estimating methods in construction project is very important role of the quantity surveyor, because of the cost of construction project is everything and it's affected to client financial stability; therefore, the quantity surveyor should have to clearly identify what are the work item of whole construction project. In this article we will discuss about cost estimating method in building construction.
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Estimate means,
An estimate is predicting the Cost of the Building with a minimum information such as sketch or very brief information.Read more: Type of Form of Contract in Construction | FIDIC Books
Purpose of estimates
> For government works proper sanction has to be obtained for allocating the required amount . Works are often let out on a lump sum basis , in which case the estimator must be in a position to know exactly how much expenditure he is going to incur on them
> From the estimate of a work it is possible to determine what materials and in what quantities will be required for the work so that the arrangements to procure them can be made.
> The number and kind of workers of different categories who will have to be employed to complete the work in the specified time can be found out from the estimate .
> An estimate will help in determining amount and kind of equipment needed to complete the work.
> An estimate will help in determining amount and kind of equipment needed to complete the work.
> The estimate of a work and the past experience enable one to estimate quite closely the length of time required to complete an item of work or the work as a whole.
> To give the owner a reasonably accurate idea of cost to help to decide whether the work can be undertaken as proposed or needs to be curtailed or abandoned, depending upon the availability of funds and prospective direct and indirect benefits.
Read more: What is Taking off Principles in Taking off Quantities...
Methods of Estimating
Estimating methods can basically be divided into as follows,
- Methods of approximate estimating
&
- Methods of accurate estimating
Read more: Estimating and Tendering | Cost of Project
At the initial stage the quantity surveyor has only little information such as sketches and brief specifications of the proposed project and his approximate estimate is prepared based on that little information.
The quantity surveyor can make use of the following methods to prepare an approximate estimate of the proposed construction. Basically, approximate estimating can be dividing into two groups.
Read more: Basic Concepts of Economics in Construction Industry...
Function; units are defined according to the function to be performed the proposed building as shown below,
Example:-
Let us assume that a 150 bed hospital has to be constructed and the client has requested to calculate the approximate cost of this project. The quantity surveyor finds there is a 200 bed hospital situated at same area which has been constructed two years ago and the sum of money that had been spent was Rs.2,000,000.
Cost per bed of the previously constructed Project = 2,000,000 / 200
= 10,000/-
It means that the floor area has to be measured from the inner surface of the outer wall. But internal wall thickness areas stair well etc. Shall be calculated to the area without deduction, Then the calculated area is multiplied by the appropriate rate taken from a previously constructed building within that particular area.
This is mostly use for multi-storey building. In practice this method of estimating is probably the most popular of the preliminary estimating methods. Its major advance is simplicity of the method of the calculation and the availability of data in up to data from. Anyway this method also fails to taken in to account any variation in design, shape of plans story height and type of material used.
Assume the present cost pre squire meter of a same type of building situated in the same area is Rs.5,000/-
Therefore the cost of the proposed building = Rs. PQ x 5,000
Read more: Cost Planning Process in Construction Contract...
1.) Firstly the data have to be collected
> Area of each floor separately
> Area of roofs
> External wall areas
> Adjusted storey enclose unit rate
2.) The storey enclose unit is calculated by multiplying by a specified number.
3.) Finally the total of the storey enclose unit is multiplied by the storey enclose unit rate. So then the approximate project estimate could be obtained.
Example:- Assume the present value of one unit is Rs. 400. Calculate the estimated cost of the project.
Answer:-
* = Girth of the Building
* = Floor to Floor Height
* = Constant Value
The quantity surveyor has to choose the suitable method very carefully that could be employed at a particular stage during the designing of the project.
Contraction profit, overhead expenses and preliminary expenses also should be included with the relevant elements. Otherwise necessary adjustment should be made for them in percentage basis.
Methods of approximate estimating
The client must first make sure that his funds are sufficient to meet all requirements of the entire project, including all indirect costs. Since he is the person who spends money for the whole project and if allocated amount of money is not sufficient he can cut down the cost by reducing the size of the building or using some other technique. Therefore preparation of an approximate estimate is essential to plan his project within available financial resources.At the initial stage the quantity surveyor has only little information such as sketches and brief specifications of the proposed project and his approximate estimate is prepared based on that little information.
The quantity surveyor can make use of the following methods to prepare an approximate estimate of the proposed construction. Basically, approximate estimating can be dividing into two groups.
Read more: Basic Concepts of Economics in Construction Industry...
1.) Preliminary Estimates
There are four methods coming under this heading. They are,- The functional unit method
- The floor area method
- The cubic method
- The storey enclosure method.
The functional unit method
Before using this method the estimator has to collect information from previous similar contracts which were completed in the same area or in neighboring areas. This method is used mainly for large buildings and must be regarded as a very tough guide suitable only for preliminary investigations only.Function; units are defined according to the function to be performed the proposed building as shown below,
Example:-
Let us assume that a 150 bed hospital has to be constructed and the client has requested to calculate the approximate cost of this project. The quantity surveyor finds there is a 200 bed hospital situated at same area which has been constructed two years ago and the sum of money that had been spent was Rs.2,000,000.
Cost per bed of the previously constructed Project = 2,000,000 / 200
= 10,000/-
The floor area methods (Square method)
The square area method is an improvement upon the functional unit method and it gives more accurate figures. After basic design work has been done the total floor area is taken from the plans excluding the outer wall thickness area.It means that the floor area has to be measured from the inner surface of the outer wall. But internal wall thickness areas stair well etc. Shall be calculated to the area without deduction, Then the calculated area is multiplied by the appropriate rate taken from a previously constructed building within that particular area.
This is mostly use for multi-storey building. In practice this method of estimating is probably the most popular of the preliminary estimating methods. Its major advance is simplicity of the method of the calculation and the availability of data in up to data from. Anyway this method also fails to taken in to account any variation in design, shape of plans story height and type of material used.
Assume the present cost pre squire meter of a same type of building situated in the same area is Rs.5,000/-
Therefore the cost of the proposed building = Rs. PQ x 5,000
The cubical method
This method is more accurate than above two method. The volume of the building is taken in cubic meters for the purpose of calculation. The total floor area is work out by taking measurement from outer surface of the outer walls. Height dimension lines vary according to the design of the roof. One of advantage is that it takes relatively less time to calculate and easy to calculate the total cost of the project more accurately. One of the disadvantage is that it doesn’t indicate the chargers in cubic meter cost that occurs.Read more: Cost Planning Process in Construction Contract...
The storey enclose method
This is the best method based on the single price rate method system of calculation is as follows.1.) Firstly the data have to be collected
> Area of each floor separately
> Area of roofs
> External wall areas
> Adjusted storey enclose unit rate
2.) The storey enclose unit is calculated by multiplying by a specified number.
3.) Finally the total of the storey enclose unit is multiplied by the storey enclose unit rate. So then the approximate project estimate could be obtained.
Example:- Assume the present value of one unit is Rs. 400. Calculate the estimated cost of the project.
Answer:-
* = Girth of the Building
* = Floor to Floor Height
* = Constant Value
2.) Later Stage Estimates
These are used to make out a figure comparable with the average tender figure. The quantity surveyor uses the following methods at this stage.- The approximate quantities method
- The elemental estimating methods
The quantity surveyor has to choose the suitable method very carefully that could be employed at a particular stage during the designing of the project.
Approximate quantities method
This method can be regarded as the most accurate of all approximate estimating methods and techniques. Before applying this method for the whole project is allocated main elements to be priced may be classified as,- Foundation
- Ground floor
- Doors and windows
- First floor
- Walls
- Roofs
Elemental estimating
Under this method the hale project divided in two major elements. The elemental rate should be adjusted to accommodate any necessary quality alternation. The list of element are,- Sub structure
- Super structure
- Services
- Finishes
- External works
Contraction profit, overhead expenses and preliminary expenses also should be included with the relevant elements. Otherwise necessary adjustment should be made for them in percentage basis.
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