Estimating or Estimate
Estimating refers to the process of predicting or calculating the quantities of materials, labor, equipment,
And other resources required to complete a construction project. It involves assessing the costs
Associated with these resources to arrive at a budget for the project. Estimating provides an essential foundation for project planning, scheduling, and decision-making.in other word
An estimate is the anticipated or probable cost of work and is usually prepared before the construction Is taken up. It is indeed calculations or computations of various items of an engineering work.
NEED / REQUIREMENTS FOR ESTIMATION AND COSTING
Estimate give an idea of the cost of the work and hence its feasibility can be determined i.e. Whether the project could be taken up with in the funds available or not.
Ø Estimate gives an idea of time required for the completion of the work.
Ø Estimate is required to invite the tenders and Quotations and to arrange contract.
Ø Estimate is also required to control the expenditure during the execution of work.
Ø Estimate decides whether the proposed plan matches the funds available or not.
Ø Estimate is required to invite the tender sand Quotations and to arrange contract. Estimate is also required to control the expenditure during the execution of work. Estimate decides whether the proposed plan matches the funds avail or not.
Ø To know the quantities of various items of work, a material and labour and their source of identification.
Ø To decide whether the proposal can match the available funds to complete the structure.
Ø To obtain the administrative and technical sanction of estimate from the competent authorities to release the funds for construction.
Ø To invite tenders or quotations based on the estimate quantities for entrust of works to the execution.
NECESSITY OF ESTIMATES
Ø To know about the approximate cost of the building construction.
Ø To calculate the tax of the building
Ø To fix the rent of building and valuation of projects.
Ø To know about the various items of works involved in the building construction and arrange the
Ø Available materials of the construction.
Ø To arrange the labors of the construction works.
Ø Take the approval for the government projects.
Ø To having the loan from the bank
PROCEDURE OF ESTIMATING OR METHOD OF ESTIMATING.
Estimating involves the following operations
Ø Preparing detailed Estimate.
Ø Calculating the rate of each unit of work
Ø Preparing abstract of estimate
DATA REQUIRED TO PREPARE AN ESTIMATE
ü Drawings i.e. Plans, elevations, sections etc.
ü Specifications.
ü Rates.
DIFFERENT TYPE OF ESTIMATES
Ø Preliminary/Approx./Abstract/Rough Cost Estimate
Ø Plinth Area Estimate
Ø Cube Rate or Cubical Content Estimate
Ø Appx. Quantity Method Estimate
Ø Detailed Estimate or Item Rate Estimate
Ø Supplementary Estimate
Ø Revised Estimate
Ø Sub-Estimate
Ø Annual Repair or Maintenance Estimate (A.R or A.M Estimate)
Ø Complete Estimate
Preliminary or Approximate estimate:
Ø This estimate is prepared to decide financial aspect, policy and to give idea of the cost of the proposal
To the competent sanctioning authority.
Ø It should clearly show the necessity of the proposal and how the cost has been arrived at.
The calculations for approximate estimate can be done with the following data.
Ø The data can be had from a similar construction already complete in the nearby area, executed by the
Department.
Ø The following documents should be attached with it.
ü Detailed report
ü Site plan of the proposal
ü It should also clearly mention about the acquisition of land, Provision of electric and water
Supply etc.
Types of Approximate Estimate:
Ø Plinth area method
Ø Cubical content method
Ø Unit cost (or) service unit method
Ø Typical bay method
Ø Carpet area method
Ø Rough quantity method
Plinth area Estimate:
Ø P.A. is approximate estimate
Ø Plinth area should be calculated for covered area by taking external dimensions of the building at the
floor level.
Ø Courtyard and other open area should not be included.
Ø For multi storied building Plinth Area for each storey is determined separately.
Ø Plinth area rate is known from cost of similar building in the locality.
Ø Approx. Cost of the building = Plinth area Rate/ m2 x Plinth Area
Cubic Contents Estimate:
Ø Cube rate estimate is again approximate estimate.
Ø Cubical content of the building is determined by multiplying length, breadth and height of the building.
Ø External length and breadth at the floor level are calculated for the purpose.
Ø Height should be taken from the floor level to the top of roof.
Ø For multi storied building height is taken from floor level of one story to top of next higher floor.
Ø Cube rate estimate is more accurate as compared to the plinth area estimate.
Unit cost (or) service unit method:
Ø The unit method of estimating is the simplest and quickest method.
Ø In this method, the quantity surveyor counts the number of units which are going to be accommodated in a building, for example the number of occupants or main furniture objects used by an individual.
Ø The number is then multiplied by the cost per unit to get the total estimated cost of the project.
Typical bay method:
Ø This method is useful and is generally followed in case of building having several bays.
Ø The cost of the one class room is worked out and then multiplied by the number of bays in that building.
Ø The extra cost of the end walls and difference in framing. If there is any, should be made, so as to arrive at the correct cost.
Carpet area method:
Ø Carpet area the covered area of the usable spaces of rooms at any floor.
Ø It is measured between walls to walls within the building and is the sum of the actual areas of the rooms where you can carpet.
Ø Floor area = Plinth Area –Area of Walls.
Ø This includes the floor areas of all rooms, verandahs, passages, staircase rooms, bathroom etc.
Ø In residential building, the carpet area will be about 55% to 65% of the plinth area.
TYPES OF ESTIMATE
There are several types of estimates used in construction projects, each serving a specific purpose and
Stage of project development. The main types of estimates are:
1. **Preliminary Estimate: ** also known as a rough or initial estimate, this is an early-stage
Approximation of the project's cost. It's used to provide a quick cost assessment before detailed
planning. The accuracy of a preliminary estimate is relatively low, typically within a range of ±20% to ±30%.
2. **Approximate Estimate: ** this is a more refined version of the preliminary estimate, prepared with
more detailed information. It's used for budgetary planning and to assess the feasibility of a project.
The accuracy of an approximate estimate is around ±15% to ±25%.
3. **Detailed Estimate: ** this is a comprehensive and accurate estimate, prepared with detailed
quantities of materials, labor, and equipment required for each project activity. It forms the basis for contract pricing, bid preparation, and project execution. The accuracy of a detailed estimate is
typically within ±5% to ±10%.
4. **Supplementary Estimate:** Also known as a revised estimate, this type is prepared when there are significant changes in the project scope, design, or specifications after the initial estimate has been made.
It reflects the adjustments needed due to these changes.
5. **Quantity Survey Estimate: ** Quantity survey estimates involve detailed measurement of quantities
Of materials and labor required for each component of the project. This estimate is often used in
Conjunction with detailed cost data to determine accurate project costs.
6. **Parametric Estimate: ** Parametric estimating involves using historical data and statistical
Relationships to estimate costs based on specific project parameters, such as size, area, or volume.
It's useful for quickly estimating costs when detailed information is not available.
7. **Unit Rate Estimate: ** this estimate is based on unit rates for different components of the project,
Such as cost per square meter or cost per unit length. It's especially useful for repetitive tasks or items
With standard specifications.
8. **Engineer's Estimate: ** Prepared by professional engineers, this estimate is often used in public
sector projects and involves a detailed analysis of quantities, labor, and material costs. It serves as a benchmark for evaluating contractor bids.
9. **Detailed Design Estimate: ** this estimate is prepared after the detailed design phase of a project,
using accurate quantities and specifications. It provides a refined cost assessment before the project
goes into construction.
Each type of estimate serves a specific purpose in the project lifecycle, helping stakeholders make
informed decisions, allocate resources, and manage costs effectively. The level of accuracy varies
among these estimates, with more detailed estimates typically being more accurate but requiring
more time and effort to prepare.
FACTORS AFFECTING
These factors influence the accuracy of estimates and should be carefully evaluated. Some key factors affecting estimation include:
Ø **Project Scope and Complexity: ** the complexity of the project's design, layout, and engineering requirements can significantly impact costs. More intricate designs may require specialized
materials, labor, and construction techniques, leading to higher costs.
Ø **Project Size and Scale: ** the size of the project in terms of square footage, height, or length can
affect the quantities of materials, labor, and equipment needed, thereby influencing costs.
Ø **Type of Construction:** Different types of construction, such as residential, commercial, industrial,
or infrastructure, have unique cost considerations due to variations in materials, equipment, and
labor requirements.
Ø **Location: ** Construction costs can vary based on the geographic location of the project. Factors
such as local labor rates, availability of materials, transportation costs, and regulatory requirements play a role.
Ø **Site Conditions: ** Soil quality, terrain, accessibility, and environmental conditions can impact construction methodologies, material transportation, and foundation requirements, affecting
overall costs.
Ø **Labor Costs: ** Labor rates vary based on location, availability of skilled workers, and union agreements. Complex projects or those in regions with high labor demand may have higher labor
costs.
Ø **Material Costs: ** Fluctuations in the prices of construction materials, such as steel, concrete,
Plumber, and specialized components, can significantly affect overall project costs.
Ø **Equipment Costs: ** The type and quantity of equipment required for construction activities,
including rentals and operating costs, contribute to the project's budget.
Ø **Regulatory and Permit Costs: ** Obtaining permits, adhering to building codes, and complying
with environmental regulations can lead to additional costs that must be factored into estimates.
Ø **Inflation: ** The impact of inflation on labor, materials, and equipment costs should be considered, especially for projects with long timelines.
Ø **Market Conditions: ** Supply and demand dynamics within the construction industry can
influence costs. During periods of high demand, costs may rise due to increased competition for resources
Ø **Design Changes: ** Changes made during the design phase can affect estimated costs. Frequent changes can lead to cost overruns if not carefully managed
Ø **Contingency:** A buffer for unforeseen events or changes in project requirements is usually
included in estimates as a contingency allowance
Ø **Economic Conditions:** Economic fluctuations can impact interest rates, financing costs, and
investor confidence, which in turn affect overall project costs
METHODS OF TAKING OUT QUANTITIES
The calculations of quantities of materials can be done using various methods of estimates. The application
of individual methods is as upon the design and shape of the building. The different methods are as follows:
ü Centreline method: This method is used mostly if the offsets are symmetrical and the building is
more or less rectangular in shape. This centerline acts as length for the complete calculations of the estimate. If the deductions not cared for the results of estimates may be wrong. All the walls should
have the same section.
ü Crossing Method: The lengths and breadths of the masonry walls at the plinth level are taken ( internal dimension of the room + thickness of the walls ) for calculating quantities.
The symmetrical offset as much as in the case of the centerline method. The centerline length is
obtained by calculating the overall perimeter of the building and subtracting the four times the
thickness of the wall on it.
ü Out to Out and Into In ( Long wall and Short wall ) Method: In this method, the wall along the
length of the room is considered to be a long wall while the wall right-angled to longwall is said to
be the short wall. To determine the length of the longwall or short wall, calculate first the centerline lengths of individual walls. Then the length of longwall ( out to Out )may be determined, after adding
half breadth at each end to its centerline length. Thus the length of the short wall is measured by deducting half breadth from its centerline length at each end.
ü Bay Method: This method is generally followed in the case of the building having several bays.
The cost of the one classroom is worked out and then multiplied by the number of bays in that
building which gives the total cost of the building. The extra cost is required for the end walls and differences in framing.
