Contents
Cost estimation methods and types of cost estimation methods used in building construction
Cost estimation methods are defined as the process of determining the probable or approximate cost of the project in order to finish the project in given time at given cost. The estimated cost is not accurate value it will give only an idea regarding the cost of the project before construction. There are several factors which are affected on the cost of the project in which the following are the some of the important aspects.
- Quality of materials
- Time of construction
- Availability of materials
- Workmanship cost
Quality of materials
Quality of materials is an important and first most factor we have to consider before estimation. Some projects requires high quality first class materials in such cases the cost of the project will be high other hand some projects required low quality materials related to the second class or third class materials in that case the cost of the project is less.
Time of construction
Time of construction is the second most factor we have to consider before estimation. If the duration of the project increases then the cost of the construction will be increases. So we have to finish the project with nominal duration only.
Availability of materials
Before cost estimation we have to check the availability of materials like cement, sand, coarse aggregates, steel and other major material from suppliers. If the materials are not available near to construction site there will be change of increase in the transportation cost this will leads to increases the project cost.
Workmanship cost
The workmanship is the temporary staff and labour which are provided in the construction site. For the workmanship approximately 1.5 percentage to 2 percentage total cost of the project is provided. If the duration of the project increases then this percentage may increase that results in increase in the total cost of the project.
Types of cost estimation methods used in construction
The following are the various types of methods estimates used in construction
- Approximate (or) Preliminary (or) Rough estimate
- Detailed estimation
- Revised estimation
- Supplementary estimate
- Supplementary and revised estimation
- Annual repair and (or) annual maintenance estimate
Approximate (or) preliminary cost estimation methods
This estimate is used when the time available is less and it will take less cost. The rough estimate of the project is calculated and the value is less than true cost.
Depending upon the accuracy of cost estimation. The following are the various types of the preliminary estimates used in the construction
- Service rate (or) unit rate method
- Plinth area method
- Cube rate method
- Elemental bill method
- Bay method
- Cost comparison method
Note : From the above specified method the cost comparison method is most accurate method.
Service rate (or) unit rate method
This method is used when these is n similar units exists in the project ( Example: cost per table, cost per bed, cost per student etc).
The below specified expression is used to determine the cost of the new project
Total cost = (Cost/Number of service units of existing project) X Number of service units of new project
Plinth area method
Plinth area is the built up covered area of building measured at the floor level. For the calculation of the plinth area we will consider the external dimensions only. In the plinth area some excluding and some including are considered.
Excluding are court yard area, area of lofts, cornice, open stair cases, lift area, plinth offsets, tower projections, lift machine area, etc.
Including are mezzanine floor, wall covered area, covered stair cases, galleries etc.
After excluding and including the things we will calculate the cost of the project by using below expression
New cost = (Cost/Plinth area of existing project) X Plinth area of new project
Cube rate method
This method is used to calculate the cost of the project by considering the volume of the structure (LXBXH). Total cost is determined by using below expression
New cost = (Cost/Volume of existing project) X Volume of new project
Elemental bill method
In this method the cost calculation is carried out by considering cost of each individual elements like foundation, plinth, walls, plastering, flooring, painting, finishing etc. the cost of the element is determined by using below formulae
Cost of an element = (Cost/group of existing project) X group of new project
Bay method of estimation
This method of estimation is used when the similar bays are exist in the structure. The cost of new project is calculated by using below formulae
Cost of proposed project = Cost per bay of existing project X Number of bays of proposed project
Cost comparison method
This method is used to calculate the approximate cost of project when the project has similar kind of things repeatedly. Example of this kind of buildings is low income group houses and MIG housing boards etc.
Detailed estimation
This method used to determine the detailed cost of the project and it is done by 3 stages which are given below
Stage 1: Calculation of quantities
Stage 2: Calculation of cost
Stage 3: Preparing abstract of estimate
The detailed estimation of G+2 building concepts are explained in my earlier blog please read with the blow specified link
Complete cost estimation of G+2 building
Revised cost estimation method
This method of estimation is used when the original sanctioned amount is likely to extend more than 5%. After revised estimation cost of the project will be increases.
Supplementary cost estimation method
When the project required to add additional work this type of estimation is used.
Supplementary and revised cost estimation method
Supplementary and revised estimation is prepared when contractor left the project or any material deviation in the project and this estimate is prepared when the remaining work is left with less than 95 percentage.
Annual repair and (or) annual maintenance cost estimation method
This estimation is used to maintain structure in regular intervals generally road patch works or painting works etc comes under this estimation.
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Conclusions on cost estimation and types of cost estimation methods
Well now the above explained concepts are related to the factors effecting the cost estimation and various methods used. The basic factors considered as quality of materials, time of construction, availability of materials and workmanship cost. And the methods related to Approximate (or) Preliminary (or) Rough estimate, Detailed estimation, Revised estimation, Supplementary estimate, Supplementary and revised estimation and Annual repair and (or) annual maintenance estimate are used.
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