--- title: "Procedure of preliminary estimate (office building)" subject: "Estimating and Costing" chapter: 3 key: "semester_7/estimating_and_costing:prelim-estimate-procedure-office" source: https://www.bctengineer.com/q/semester_7/estimating_and_costing/prelim-estimate-procedure-office site: BCT Engineering --- # Procedure of preliminary estimate (office building) Estimating and Costing · Chapter 3: Types of Estimate - Asked in: 2071 Chaitra, 5 marks; 2067 Poush (old course), 5 marks (asked 2 times) - Video: [Preliminary Estimate of a Building|Plinth Area|Building Cost|Overall cost|#contingencies#estimating](https://www.youtube.com/watch?v=BVs7PPEkQXI) — Shree Krishna - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/estimating_and_costing/prelim-estimate-procedure-office - Whole chapter: https://www.bctengineer.com/md/semester_7/estimating_and_costing/chapter-3 ## Question Explain with example the process of preparation of a preliminary estimate of an office building. (Describe how you will prepare a preliminary estimate of a government office building for administrative approval, including external services.) ## Short answer Determine carpet area from staff norms, compute plinth area = carpet area / (1 – (circulation% + wall%)), with 20–30% circulation and 8–10% walls. Multiply by plinth area rate, add services (electrical, sanitary, etc.), external works, and then contingency (3–5%) and supervision charges (3–8%). ## Answer A preliminary estimate is prepared by the **plinth area method**, as follows. It is for the administrative approval, so the drawings are not yet detailed. #### Steps 1. **Establish the requirement:** the number of staff and rooms, and from these the total **carpet area** (usable floor area) from the norms for office space per person. 2. **Find the plinth (built-up) area:** $$ \text{Plinth area} = \frac{\text{Carpet area}}{1 - (\text{circulation \%} + \text{wall \%})} $$ The circulation area (corridors, verandah, stairs, toilets) is taken as 20 to 30% and walls as 8 to 10% of the plinth area. 3. **Select the plinth area rate** prevailing in the locality (or the DUDBC / department rate) for the type of building. 4. **Building cost** = plinth area x plinth area rate. 5. **Add the extras** as percentages of the building cost: special architectural treatment, water supply and sanitary works, electrical installation (and lift), deep foundation, and other services. 6. **Add external services:** compound wall, approach road, drainage, septic tank and landscaping. 7. **Add contingency** (3 to 5%) and **supervision/departmental charge** (3 to 8%). 8. **Total** is the estimate for approval. #### Example (assumed) Carpet area 1,000 m²; circulation 30% and walls 10%, so plinth area = 1000 / 0.6 = 1,666.67 m². Plinth area rate Rs 20,000 per m² gives a building cost of Rs 33.33 million. Electrical at 8% and other services at 5% add Rs 4.33 million. Contingency 5% and supervision 5% are then added on the total. The result, about Rs 41.4 million, is submitted for approval. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the first step of the plinth area method? A. Add contingency B. Establish requirement and find carpet area from staff and room norms C. Apply plinth area rate D. Prepare working drawings Answer: B. Plinth area is derived from carpet area. (Key point: First step) 2. How is plinth area found from carpet area? A. Carpet area x (1 + circulation % + wall %) B. Carpet area - circulation area C. Carpet area / (1 - (circulation % + wall %)) D. Carpet area / (circulation % + wall %) Answer: C. Carpet area is what is left after circulation and walls are removed. (Key point: Plinth formula) 3. Carpet 1,000 m2, circulation 30%, walls 10%. Plinth area is: A. 1,400 m2 B. 1,111.11 m2 C. 600 m2 D. 1,666.67 m2 Answer: D. 1000/0.6 = 1,666.67 m2. (Key point: Example plinth) 4. How are extras (electrical, water supply, etc.) added? A. As percentages of the building cost B. As fixed arbitrary amounts without basis C. As percentage of carpet area D. They are ignored Answer: A. Contingency and supervision are added afterwards. 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