Learn : Types of estimates | Approximate Estimate | Detailed Estimate |Preliminary or Approximate or Rough Cost Estimate Plinth Area Estimate.Cubic Contents MethodApproximate Quantity MethodDetailed Estimate (or Item Rate Estimate Revised EstimateSupplementary EstimateSupplementary and Revised EstimateAnnual Repair (A.R) or Annual Maintenance (A.M.)
TYPES OF ESTIMATES
The estimates are broadly classified as
(i) Approximate Estimates, and
(ii) Detailed Estimates
- Before a detailed estimate of the proposed work is to be taken up, it is necessary to prepare its approximate estimate.
- An approximate estimate gives the approximate cost of the work and is prepared on the basis of cost of the similar works carried out in the past.
- Such an estimate is required to obtain administrative approval in case of Government works.
- Once the work is administratively approved by the Government, a detailed estimate is worked out.
- A detailed estimate is prepared after its complete set of drawings are ready.
- The quantities of various items of work are worked out from such drawings and are multiplied by the present rates of items of works to arrive at the estimated cost of the work.
Thus the various types of estimates prepared according to their requirements may be classified as follows:
- Preliminary or Approximate or Rough Cost Estimate
- Plinth Area Estimate.
- Cubic Contents Method
- Approximate Quantity Method
- Detailed Estimate (or Item Rate Estimate)
- Revised Estimate
- Supplementary Estimate
- Supplementary and Revised Estimate
- Annual Repair (A.R) or Annual Maintenance (A.M.)
Estimate Of the above estimates, the first four belong to approximate estimates and the remaining five are detailed estimates.
(i) Preliminary or Approximate or Rough cost estimate:
- This approximate estimate is prepared for preliminary studies of the various aspects of the work and also to decide the financial position and policy for administrative approval by competent sanctioning authority.
- In case of commercial projects such as residential buildings, irrigation and power projects that earn revenue, the probable income is also mentioned and the investment in the project is justified.
- If the project is non-commercial, having no direct return, its necessity, utility, prospects in future and availability of finance etc. are considered before final decision is taken.
- This estimate is prepared on the basis of practical experience of carrying out similar works in the past and their rates.
- In this estimate, the approximate cost of all important works such as cost of land, roads, buildings, water supply, sanitary works, electrification etc. are mentioned separately.
- A brief report of the project indicating its necessity, utility and method of arriving at the cost of each item and the site or layout plan is also enclosed with the estimate.
(ii) Plinth Area Estimate:
- As the name implies, this estimate is prepared by multiplying the plinth area of the proposed building by the plinth area rate of similar building having same specifications and height that is constructed very recently in the same locality.
- The plinth area of the proposed building is calculated for the covered i.e. roofed portion by measuring the outer dimensions at the plinth level.
- The area of courtyards, and other open areas are not to be included while calculating the plinth area.
- The plinth-area method of preparing estimate gives the approximate cost of the building to be constructed.
- Even if the plan of the proposed building is not ready, the floor areas of different units (i.e. rooms) are worked out from the users requirements and about 35% of it is added for thickness of walls, circulation and waste to obtain the approximate total plinth area.
- This plinth area is then multiplied by the current plinth area rate in the locality to obtain the approximate cost of the proposed building.
- The method is simple and is usually adopted in practice.
(iii) Cubic Content Method:
- The cubic content method is an approximate method of preparing an estimate of a proposed building and differs from the method (ii) described above in that, in addition to the total plinth area of the proposed building, it also takes into consideration its height.
- The total cubic contents of the building are obtained by multiplying its total plinth area by the height.
- Knowing the cubic content rate of recently constructed building having similar specifications in the locality, the approximate cost of the proposed building is worked out by multiplying the total cubic contents by its cubic content rate.
- In order to calculate the cubic contents of the building, the length and breadth are measured as the external dimensions at the floor level and the height of the building is measured from the floor level to the top of the flat roof or upto half way of the sloped roof.
- For multistoreyed building, the height is measured between floor level of one storey to the top of next floor above it.
- As per I.S. 3861, the foundation and plinth and the parapet above the roof are not taken into consideration in calculating the cubic contents.
- The cubic content method is more accurate as compared to plinth area method as it accounts for the height of the building.
- In practice, however, this method is not used.
(iv) Approximate Quantity Method:
In this method the structure is divided into:
(a) Foundation Inclusive of Plinth
(b) The Super Structure.
- The cost per running meter of foundation inclusive of plinth is worked out and is multiplied by the total length of foundation to determine the total cost of foundation inclusive of plinth.
- Similarly the cost per running meter of the superstructure is found out and is multiplied by the total length of all the walls of superstructure to get the total cost of superstructure.
- The total cost of the structure is then obtained by the addition of total cost of foundation inclusive of plinth to the total cost of the superstructure.
- A line plan of the proposed structure is required for the above computations.
(v) Detailed Estimate (Or Item Rate Estimate):
- This is the accurate method of estimating in which the entire building work is subdivided into individual items of work
- The quantities of each item of works are calculated from the complete set of drawings (i.e. plan, elevation, sections etc.)
- The abstract of the estimated cost is prepared by multiplying the quantities of each of the above items by the rate of the completion of that item.
- The rates of various items of work can be obtained from the ‘schedule of rate’ prepared by the Government organisation or from analysed rates of item.
- In order to make provision for unforeseen expenditure for miscellaneous petty items (for which no provision is made in the estimate) and contingencies a 3 to 5% of the estimated cost is added to it.
- An additional 1 to 2% is also provided for the work-charged establishment i.e. for the salaries to be paid to the chawkidars, technical assistants, supervisors etc. appointed by the Government (or owner) to look after the work.
- The grand total of all the above cost is known as the total estimated cost of the proposed work.
- After the administrative approval for the work is obtained, its detailed estimate is prepared and sent for obtaining technical sanction from the appropriate competent Government authorities.
- The actual execution of the work commences only after obtaining technical sanction (from the Government) and necessary allocation of funds are made available in the budget grants for that year.
- The detailed estimate is accompanied by the following documents:
- A comprehensive report of the proposed work.
- General specifications of the work.
- Detailed specifications of various items of work.
- Detailed working drawings consisting of plan, elevations, sections, details of foundations etc. with site or layout plan.
- Calculation and design of component parts of the work.
- Analysis of rates for the items of work not included in the schedule of rate.
Detailed estimate is generally prepared in the following two steps:
(a) Taking out dimensions
and squaring them i.e. the dimensions of the various items of work are taken from the relevant drawings and are multiplied (i.e. squared) to obtain its quantities and are entered in the ‘Measurement Sheet Form’.
i.e. the quantities of the various items of work calculated as above are multiplied by the rates of those items obtained either from the schedule of rate or worked out by rate analysis and are entered in the ‘Abstract Sheet Form’. If ‘rate’ and ‘amount’ columns in the abstract sheet form are left blank (to be entered by the contractor) then it is termed as the ‘Bill of Quantity’.
(vi) Revised Estimate:
It is also a detailed estimate and is to be prepared when:
- The original sanctioned amount of estimate exceeds by more than 5%.
- Amount spent on the work exceeds administratively sanctioned amount more than 10%.
- When there are drastic changes in original proposal i.e. the original load bearing structure is now proposed to be converted into a framed structure, even if the cost of the work does not exceed the sanctioned amount.
- The revised estimate is accompanied by a comparative statement in the prescribed format indicating the changes in each item of works, its rate and amount as per original and revised with full justification for such variations and excess etc.
(vii) Supplementary Estimate:
- It is a fresh detailed estimate which is to be prepared when additional works are required to supplement the original proposed work or when further development or extension of the work is required to be carried during progress of the work.
- The abstract must indicate the original amount of the estimate and the total amount including supplementary amount for which fresh sanction is to be obtained.
(viii) Supplementary and Revised Estimate:
- This estimate is prepared when a particular work is abandoned and the cost of the work remaining is less than 95% of the original sanctioned amount of the work
- or where there are material deviations from the original proposed work which may result in substantial saving in the estimate.
- In such cases a fresh supplementary and Revised Estimate is to be prepared and sent for revised technical sanction.
(ix) Annual Repairs (A.R.) or Annual Maintenance (A.M.) Estimate:
- Annual Repair (A.R.) or Annual Maintenance (A.M.) is a detailed estimate prepared to keep or maintain the building or roads in proper working and safe condition.
- In case of buildings, this includes items such as white washing, painting of doors and windows, inside and outside plastering and minor repairs etc.
- The amount of such estimate should be within 1.5 to 2% of the original cost of the building.
- In case of roads, it includes items such as filling patches, minor repairs to bridges and culverts, repairs to berms etc.
- In case of damages caused to the works during monsoon, which cannot be repaired within the annual repair grants a ‘Special Repair Estimate’ is to be prepared.