What is Bill of Quantities (BOQ)
Bill of Quantities also referred to as BOQ, is a document formulated in the construction industry to specify materials, labors, and their cost. It serves as a communication tool between client, consultant & the contractor. It is usually prepared by a cost consultant or a surveyor. Primarily there are two types of BOQs
- Bill of Materials
- Bill of Labour
Basic Format for preparing BOQ
The main sections included in the bill of quantities are Form of Tender, Information, Requirements, Pricing schedule, Provisional sums, and Day works. For the preparation of BOQ, 5 main components are to be considered which are as follows:
- Item Description
- Rate per unit
- Total Amount
Process of preparation of BOQ for RCC
Taking off Quantities:
Taking off is the process of analysing the drawing and its specifications to identify the elements required for the preparation of BOQ.
In this step, the appropriate narrative of a particular work is provided to explain and justify the work being done.
This step includes recording every measurement required into a sheet called the TDS Sheet. The times column (multiplier column) is for filling up the number of repetitions of the same work. It depicts the factor of multiplication. Dimension column is the one where all the dimensions like length, width & depth are recorded. Whereas in the Sums column we simply multiply the previous elements (Multiplication factor x Dimension) to get the total quantity of the work.
Calculation of materials for Reinforced Concrete Construction
Materials requires for reinforced concrete are cement, sand, coarse aggregate and steel. Let us assume a standard quantity of 1m3 Cement mortar and a mix proportion of 1:1.5:3 (1 part Cement, 1.5 parts Sand & 3 parts CA). The quantity can preferable calculated by two methods, which are weight & volume method.
Let us consider the volume method for reinforced concrete construction. Dry volume of total materials is equivalent to 1.54 times the volume of wet concrete. Hence let us take the quantity of cement mortar as 1.54 m3.
Quantity of cement
The formula to calculate the volume of cement is as follows:
Since the cement is available in bags, volume of 1 cement bag is 0.0347 m3.
0.28/0.0347=8.07 bags of cement
Quantity of sand
Formula to calculate volume of sand is as follows:
(1.5×1.54)/(1+1.5+3)=0.42 m^(3 ) of sand
Quantity of Coarse aggregates
To calculate volume of CA is as follows:
(3×1.54)/(1+1.5+3)=0.84 m^(3 ) of CA
BOQ of Steel reinforcement
Percentage of steel reinforcement usually depends on the type of components used. The values of percentage of steel differ from structure to structure. Some of which are mentioned below:
- Slabs = 1.0% of concrete volume
- Beam = 2 % concrete volume
- Column = 2.5% of concrete volume
- RCC roads = 0.6% concrete volume
Assuming 2.5% as the steel reinforcement required, the formula to calculate steel is:
Estimation of labour for reinforced concrete
The requirement for labour as per the specified quantity of work is as follows:
- Mason – 0.37 day
- Unskilled labour – 3.5 days
- Water carrier – 1.39 days
- Bar bender, per 100 kg of steel – 1 day
- Mixer operator – 0.0714 day
- Vibrator Operator – 0.0714 day
An additional contractor’s profit and sundries may be included. It generally differs according to place, organization and work. It ranges from 10 – 20%. In this case, assume 10% of total cost of materials, labour and equipment for contractor’s profit and 7% for sundries.
Advantages of Billing of Quantities
Anticipation of Difficulties & Challenges
As we write down the brief description of each work to be completed in a particular project, we can simultaneously assess the issues and obstacles tagging along with it. These obstacles can be tackled beforehand and thus saving time, energy and resources. Companies often outsource estimating companies to prepare BOQ for massive project as second layer of review to validate in-house estimates.
Comprehensive Planning of the Project
Once the initial project budget is laid down after taking into consideration the drawing & specifications, the planning of the project becomes much simpler. It will furnish a complete & comprehensive picture of the equipment and material necessary and helps the engineers involved in the project to quote for the work suitably.
BOQ Eliminates Guesswork
BOQ simply eliminates any scope of guesswork in the entire process of project construction. In the paucity of BOQ, the quotes of each work needs be worked out separately and independently only on the basis of guesswork. It withholds everything transparent, hence there is zero chance for corrupt practices by the tenderers or the contractors.
Saves Time & Cost of Construction
If the materials are available on time according to the specifications mentioned in the BOQ, the time of construction can be minimized effectively. It also gives fair amount of time to compare the prices of all the materials and choose the best rate. Thus saving the cost of construction.
Limitations of Bill of Quantities
Bill of Quantities should be prepared according to a standard methodology. Otherwise, chances of errors substantially increases. The errors that could possibly occur during the BOQ process are incorrect measurement of the quantities, arithmetic errors, errors due to various changes made during the project, incorrect assumptions, counting the same item twice or omitting an item, and ignoring the change in currencies or units.