Quantity Survey professionals in Kenya rely heavily on precise and systematic measurement of building works to prepare accurate bills of quantities and tender documents. The process of abstracting measured quantities is fundamental in translating raw measurements into organized, tabulated data that supports cost estimation and project control. Mastery of abstracting sheets and running through dimensions ensures measurement accuracy and consistency, critical in managing construction costs and contractual obligations.

4.1 Abstracting sheet

Abstracting sheets are essential tools used by Quantity Surveyors to organize and tabulate measurements taken from drawings or site surveys. They provide a structured format to compile quantities before transferring them to bills of quantities. Understanding how to prepare and use these sheets correctly is vital for accuracy and efficiency in quantity surveying tasks.

4.1.1 Preparation of abstracting sheet

Abstracting sheets are prepared to systematically record and organize measurements from building works. The preparation process ensures that all relevant data is captured clearly to facilitate accurate quantity calculations.

The preparation of an abstracting sheet follows these steps:

1. Identify the work section
   Begin by clearly stating the work section or trade (e.g., concrete works, masonry, finishes) at the top of the sheet to maintain organization.

2. List the item descriptions
   Write detailed descriptions of each measured item or element, referencing the drawings or specifications precisely.

3. Set out measurement columns
   Create columns for dimensions such as length, width, height, depth, or quantity counts, depending on the nature of the work.

4. Include units of measurement
   Clearly indicate the units for each column (e.g., m, m², m³, number) to avoid confusion during calculations.

5. Provide space for calculations
   Allocate columns or areas to perform intermediate calculations such as area or volume derived from linear measurements.

6. Number the sheet and date it
   Assign a unique sheet number and record the date to track revisions and updates systematically.

Worked Example

Example: Prepare an abstracting sheet for a masonry wall at Kenyatta National Hospital measuring 10 m long, 3 m high, and 0.2 m thick. Show columns for length, height, thickness, and volume.

Calculation:

$$ \text{Volume} = \text{Length} \times \text{Height} \times \text{Thickness} $$$$ = 10 \times 3 \times 0.2 $$$$ = 6 \text{ m}^3 $$

Answer: The volume column is filled with 6 m³.

This abstracting sheet is now ready for transfer to the bill of quantities.

4.1.2 Transfer of booked quantities

Once measurements are recorded and calculated in the abstracting sheet, the next step is to transfer these booked quantities accurately to the bills of quantities or summary sheets. This transfer is critical to ensure that quantities used for costing and tendering are consistent with measured data.

The process for transferring booked quantities involves:

1. Verify calculations on abstracting sheet
   Check all intermediate and final calculations for accuracy before transferring.

2. Match items with bill descriptions
   Ensure that the descriptions on the abstracting sheet correspond exactly with the bill of quantities items.

3. Record quantities in the bill of quantities
   Enter the calculated quantities into the appropriate bill item rows, maintaining the same units.

4. Cross-reference sheet numbers
   Note the abstracting sheet number against each bill item for audit trail and verification.

5. Check for omissions or duplications
   Review the bill to confirm all measured items are included and none are duplicated.

6. Update quantity summaries
   Adjust summary totals and cost estimates to reflect the newly transferred quantities accurately.

Worked Example

Example: Transfer the booked quantity for a concrete slab at Moi University measuring 8 m by 6 m with a thickness of 0.15 m to a bill item.

Step 1: Calculate volume

$$ \text{Volume} = \text{Length} \times \text{Width} \times \text{Thickness} $$$$ = 8 \times 6 \times 0.15 $$$$ = 7.2 \text{ m}^3 $$

Step 2: Transfer to bill item

Answer: The quantity 7.2 m³ is entered into the bill item row, referencing Sheet No. 1 for audit trail.

Chapter Summary

This chapter focused on the process of abstracting measured quantities in building works, beginning with the preparation of the abstracting sheet, which organizes and records all necessary data systematically. It explained how quantities already booked are transferred accurately onto the abstracting sheet to maintain consistency and clarity. The chapter then covered the technique of running through dimensions, including the use of specific symbols that facilitate the clear representation and interpretation of measurements. Following this, the casting up of dimensions was discussed, highlighting the importance of correct notation through designated symbols to ensure precise calculations. Finally, the chapter detailed the calculation of net quantities, emphasizing the need to derive accurate final measurements for effective project costing and resource allocation. Each stage was presented to build a comprehensive understanding of quantifying building works efficiently and accurately.