estimation,its types and methods
- 1. Estimation ,Costing And Valuation Engineering Prepared by:- P.GAYATHRI A.P, Civil Engg. AEC
- 2. An estimate is an anticipated or probable cost of a work and is usually prepared before the construction is taken up. Before undertaking any work or project it is necessary to know the probable cost which is obtained by estimating. The estimate is prepared by computing the quantities required and then calculating the cost at suitable rates, to get the expenditure likely to be incurred in the construction of the work or structure. Prepared by:- P.GAYATHRI A.P, Civil Engg. AEC
- 3. Drawings( Plans, section, etc) Specifications a) General Specifications: This gives the nature, quality, class of work and materials in general terms to be used in various parts of work. It helps to from a general idea of building. b) Detailed Specifications: These gives the detailed description of the various items of work laying down the Quantities and qualities of materials, their proportions, the method of preparation workmanship and execution of work.
- 4. Rates : For preparing the estimate the unit rates of each item of work are required. For arriving at the unit rates of each item. The rates of various materials to be used in the construction. The cost of transport materials. The wages of labor, skilled or unskilled of masons, carpenters, Mazdoor etc
- 5. Prepared by:- P.GAYATHRI A.P, Civil Engg. AEC
- 6. Preliminary/Appx./Abstract/Rough Cost Estimate Plinth Area Estimate Cube Rate or Cubical Content Estimate Appx. Quantity Method Estimate Detailed Estimate or Item Rate Estimate Revised Estimate Supplementary Estimate Supplementary and Revised Estimate Annual Repair or Maintenance Estimate (A.R or A.M Estimate)
- 7. Preliminary Estimate is prepared by various ways for different structures as mentioned below : Buildings Per Unit Basis – Per student for schools and hostels, per class room for schools, per bed for hospitals, per seat for cinema and theatre halls, per tenement for residential buildings. Plinth area basis Cubic content basis Appx. Quantity method Roads and Highways – Per km basis depending upon nature of road, width and thickness of metalling. Irrigation Channels Per km basis Per hectare basis (Area of land commanded)
- 8. Bridges and Culverts – Per running meter of span depending upon type of structure, type and depth of foundation. Sewerage and Water Supply Project Per head of population served Per hectare basis (Area covered) Over Head water Tank – Per liter or per gallon of tank depending upon type of structure and height of tank.
- 9. Plinth area is approximate estimate Plinth area should be calculated for covered area by taking external dimensions of the building at the floor level Courtyard and other open area should not be included For multi storeyed building Plinth Area for each storey is determined separately. Plinth area rate is known from cost of similar building in the locality. Estimate is prepared by Plinth area × Plinth area rate
- 10. Cube rate estimate is again approximate estimate Cubical content of the building is determined by multiplying length, breadth and height of the building. External length and breadth at the floor level are calculated for the purpose Height should be taken from the floor level to the top of roof. For multi storeyed building height is taken from floor level of one storey to top of next higher floor. Cube rate estimate is more accurate as compared to the plinth area estimate. Cubical content= plinth area × height
- 11. Structure divided into two parts – (i) Foundation including plinth (ii) Superstructure Total length of walls is found out. Tofind running meter rate of foundation, appx. quantities of various items are calculated per running meter Similarly for superstructure appx. Quantities of brickwork, roof, flooring etc is calculated per running meter.
- 12. It is the accurate estimate prepared by working out quantities of each items of work. It is prepared in two stages – Details of measurements and calculation of quantities. Abstract of estimated cost – 3% to 5% of estimated cost is added to cover miscellaneous expenditure Detailed estimate is prepared work-wise. Detailed estimate consists of – Report General Specifications Detailed specifications Drawings Calculation and designs Analysis of rates Detailed estimate is prepared for technical sanction, for arranging contract and for execution of project.
- 13. Revised estimate is prepared when original sanctioned estimate is likely to exceed more than 5%. When expenditure on work is likely to exceed amount of administrative sanction by more than 10% When there are material deviation from original proposal even though cost may be met from sanctioned cost. It is accompanied by comparative statement showing variations in each item of works and reason for the same.
- 14. It is the fresh detailed estimate of the additional works in addition to the original estimate. It is required when further development is required during the progress of work. Abstract should show the amount of original estimate and total amount including supplementary amount.
- 15. When a work is partially abandoned and estimated cost of remaining work is less than 95% of original sanctioned estimate. When there are material deviations and changes in the design If at any time before or during the execution of work, it is found that original estimate is excessive then divisional officer may sanction a revised estimate of reduced amount.
- 16. It is prepared to maintain structure or work in proper order and safe condition For buildings like white washing, painting, minor repairs etc. For road works A.R. estimate provides for patch repairing, repairs of bridges and culverts etc.
- 17. Long wall - short wall method Centre line method. Partly centre line and short wall method
- 18. In this method, the wall along the length of room is considered to be long wall while the wall perpendicular to long wall is said to be short wall. To get the length of long wall or short wall, calculate first the centre line lengths of individual walls. Then the length of long wall, (out to out) may be calculated after adding half breadth at each end to its centre line length. Thus the length of short wall measured into in and may be found by deducting half breadth from its centre line length at each end. The length of long wall usually decreases from earth work to brick work in super structure while the short wall increases. These lengths are multiplied by breadth and depth to get quantities.
- 20. Long wall length (out to out)= centre to centre length + half breadth on one side+ half a breadth on other side (Or)=centre to centre length + one breadth Short wall length=centre to centre length – one breadth
- 21. This method is suitable for walls of similar cross sections. Here the total centre line length is multiplied by breadth and depth of respective item to get the total quantity at a time. When cross walls or partitions or verandah walls join with main all, the centre line length gets reduced by half of breadth for each junction. such junction or joints are studied carefully while calculating total centre line length. The estimates prepared by this method are most accurate and quick.
- 23. This method is adopted when external (i.e., alround the building) wall is of one thickness and the internal walls having different thicknesses. In such cases, centre line method is applied to external walls and long wall short wall method is used to internal walls. This method suits for different thicknesses walls and different level of foundations. Because of this reason, all Engineering departments are practicing this method.
- 24. Contingencies – Indicates incidental expenses of miscellaneous character which cannot be classified under any distinct item. (3% to 5% of the estimated cost is provided to allow for contingencies) Work-charged Establishment – Work-charged employees are temporary staff whose services are terminated at the expiry of sanctioned period but usually one month notice is given. (1 .5% to 2% of the estimated cost is added) Tools and Plants – Normally contractor has to arrange tools and plants. (1% to 1 .5% of estimated cost is provided) Centage charges or Departmental charges – Also known as Supervision charges for works. Tomeet the expenses of establishment, designing, planning, supervision etc. (10% to 15% of the estimated cost). When engineering department takes up work of other department.
- 25. Expenditure Sanction – It represents allotment of money to meet the expenditure. It is usually accorded by Finance Department. Technical Sanction – It is the sanction of the detailed estimate, design calculation, quantities of work etc. Technical sanction is accorded by engineering department and execution of work is carried out thereafter. Quantity Survey – It means estimating of quantities of different items of works.
- 26. Sub-Head items of work – Works like earthwork, concrete work, brick work etc. Under each sub head there are different items of work. Sub- Work – Large project may consist of several buildings. Detailed estimate of each sub-work is prepared separately. Schedule of Rates – It is a list of rate of various items of works maintained by engineering department under the name “Schedule of Rates Book”. “Road Metal Rate Book” is also maintained by PWD. Administrative Sanction/ Approval – It is the formal acceptance by the department concerned of the proposal. After the approval, design, estimates etc. are prepared and thereafter execution of work.