For building rough cost or simple quantities estimates we mainly use thumb rules. The thumb rule doesn’t give us a exact quantity but provide us a approx quantity which is nearly equal or less to the exact quantity.
Thumb rule is define as we develop a constant number with our past experience and our field daily work experience. For example 0.2, 0.5 etc.. by multiplying our desire covered area by thumb rule which we develop for specific quantities we git approx quantities of the material.
For your better understanding lets take this example.
EXAMPLE:
Suppose we done a 3 different house construction having a covered Area 1050 square feet each. In each house construction work different amount of Cement bags, Sand and Aggregates are consumed. So construct a thumb rule for cement, sand and aggregates quantity estimations.
IN 1ST HOUSE CONSTRUCTION:
Cement = 600 Bags (just for example).
Sand = 2,000 cubic feet.
Aggregates = 1700 cubic feet.
IN 2ND HOUSE CONSTRUCTION:
Cement = 590 Bags (just for example).
Sand = 1900 cubic feet.
Aggregates = 1600 cubic feet.
IN 3RD HOUSE CONSTRUCTION:
Cement = 570 Bags (just for example).
Sand = 1800 cubic feet.
Aggregates = 1500 cubic feet.
THUMB RULE DEVELOPING:
To develop Thumb rule for each construction material. We must take average of the consumption of each specific material.
CEMENT:
Average Consumption = (600 + 590 +570)/3
= 586.66 bags.
Averagely consumption of cement was 586.66 bags. Now it is important to know how much cement was consumed in 1 square feet area.
Covered area = Material consumption.
1050 sft = 586.66 bags..
1sft = (586.66/1050) bags.
1sft = 0.55 bags
The o.55 is basically our cement thumb rule. Now if we need to calculate the quantity of cement for 5,000 square feet area (if the conditions are the same) we just multiply the 0.55 with our covered area we get the cement quantity.
SAND:
Average Consumption = (2,000 + 1900 +1800)/3
= 1900 cubic feet.
Averagely consumption of the sand was 1900 cubic feet. Now calculate sand was consumed in 1 square feet area.
Covered area = Material consumption.
1sft = (1900/1050) cubic feet.
1sft = 1.8 cubic feet.
The 1.8 is basically our sand thumb rule.
AGGREGATE:
Average Consumption = (1700 + 1600 +1500)/3
= 1600 cubic feet.
Averagely consumption of the Aggregate was 1600 cubic feet. Now calculate sand was consumed in 1 square feet area.
1050 sft = 1600 cubic feet..
1sft = (1600/1050) cubic feet.
1sft = 1.52 cubic feet.
The 1.52 is basically our Aggregate thumb rule
Continue Reading about the "HOW WE DEVELOP THUMB RULES FOR DIFFERENT ESTIMATION OF THE BUILDINGS" on the next page below
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