8 types of construction estimations and Methods of building estimates

What is an estimate for construction?

An estimate is the anticipated or probable cost of work and is typically prepared before the start of construction. Before beginning the construction of a project, it is necessary to determine its likely cost, which is determined by estimating.

A computation or calculation of the quantities required and expenditure likely to be incurred in the construction of work is referred to as an estimate. The actual cost becomes known only after the completed work is accounted for.

If the estimate is carefully and correctly prepared, there will be little difference between the estimated and actual costs.

What is the Actual cost in Estimate?

Actual cost – The actual cost of a work is known when it is completed. The account section keeps track of all expenditures daily during the execution of work, and the actual cost is known at the end of the work when the account is closed.

Types of Estimates in construction

• Preliminary estimate
• Plinth area estimate
• Cube rate estimate
• Approximate estimate
• Detailed estimate
• Revised estimate
• Supplementary estimate
• Annual repair estimate.

Types of Estimates in construction

Preliminary estimate –

The preliminary estimate is required for preliminary studies of various aspects of a work or project and to determine the financial crisis position and policy for administrative sanction by the competent administrative authority.

In the case of commercial projects such as irrigation projects, residential building projects, and similar projects that generate revenue income, the probable income can be calculated, and the approximate cost can be determined from the preliminary estimate. It can then be determined whether the investment in the project is justified. A percentage of approximately 5% is added as a contingency. (Construction Estimation Types)

Plinth area estimate –

This estimate is an approximation; it consists of calculating the plinth area of a building and multiplying it by the plinth area rate to obtain an estimate for that building. The covered area's plinth should be calculated by taking the external dimensions of the building at the floor level. The courtyard and other open spaces should not be considered plinth areas.

Cube rate estimate –

This estimate is also an approximation; it is the workout of the proposed building's basis cubical content, which is then applied at the rate per cubic content. The length and width should be measured from the floor to the roof's peak.

Approximate estimate –

The approximate total length of walls is found in the running meter in this method, and this total length multiplied by the rate per running meter of the wall yields a fairly accurate cost.

The approximate quantities of items such as excavation, foundation brickwork up to plinth, and dampproof course are calculated per running meter to determine the running meter rate for the foundation.

Detailed estimate –

A detailed estimate is an accurate estimate that includes calculating the quantities of each item of work and the height of each item. The detailed estimate is prepared in two estimates. (Types of estimates in construction)

1. Quantity measurement and calculation in great detail.
2. Estimated cost summary

Revised estimate –

A revised estimate is a detailed estimate that must be prepared in the following circumstances:

• The original sanctioned estimate is greater than or likely greater than 5%.
• When the work expenditure exceeds or is likely to exceed the administrative sanction by more than 10%.
• A material deviation from the original proposal occurs, even if the cost can be met from the sanctioned amount. Types of estimates in construction

Annual repair maintenance estimate –

An annual repair or maintenance estimate is a detailed estimate prepared to keep the structure or work in good working order and in a safe condition. This includes whitewashing, color washing, painting, minor repairs, and so on. There may also be a special repair estimate, a monsoon damage repair estimate, and so on.

Supplementary estimate –

The supplementary estimate is a detailed estimate that is prepared when additional work is needed to supplement the original works or when further development is needed during the work process. In addition to the original estimate, this is a detailed estimate of the additional work. (Construction Estimation Types)

Method of building estimates

Dimensions such as length, width, and height or depth must be extracted from the drawing – plan, elevation, and section. The building must be imagined and pictured in mind as a result of the drawing study, and the dimensions must be correctly taken out. Following are two estimation methods –

Separate or individual wall method –

Measure or find out the external lengths of walls running in the longitudinal direction, generally the long walls, out to out, and the internal lengths of walls running in the transverse direction to in, i.e., of the cross or short walls in to in, and calculate quantities by multiplying the length by the breadth and the height of the wall. The same rule applies to foundation excavation, concrete in the foundation, and masonry.

It is important to note the difference in dimensions at different heights caused by offset footings. It is easier to visualize plans at various heights, such as foundation trench plans, foundation concrete plans for each footing, etc. The simplest method is to take the plan's long and short walls. (Types of estimates in construction)

For long walls, add one breadth of the wall to the center length, which gives the length of the wall out to out. Multiply this length by the breadth and the height to get the quantities. Thus, to find the quantities of earthworks in excavation for the length of the trench out to out, add one breadth of foundation to the center length.

( Longwall out to out = center to center length+ half breadth on one side+ half breadth on another side = center to center length + one breadth)

For short walls, subtract one breadth from the center length of the wall, which gives the length in, and repeat the process as for long walls, subtract one breadth instead of adding.

( Short wall length in to in = center to center length – one breadth)

Centreline method –

The total length of the center lines of walls, long and short, must be found using this method, known as the center line method. Calculate the total length of center lines of walls of the same type, long and short, with the same type of foundation and footing, and then multiply the total length by the respective breadth and height.

The length will be the same in this method for excavation in the foundation, concrete in the foundation, all footings, and the superstructure. This method is simple for rectangular, circular, or polygonal buildings with no inter or cross walls.