Detail Quantity Estimate of Building Works

4.1 Two room load bearing single-storey building with verandah

The procedure, once, for every building

1. Read the drawings and list the items of work under sub-heads (§3.6).
2. Find the wall length by the centre line or long wall – short wall method (Chapter 2). This one length drives most of the estimate.
3. Take out the quantities item by item into the measurement sheet, working from the bottom of the foundation upward.
4. Apply the deduction rules of §1.4 for openings.
5. Analyse the rates (Chapter 6) and abstract the cost (§3.7).

Work bottom-upward and the items come out in a natural order that is hard to forget: excavation → PCC bed → footings → DPC → plinth filling → superstructure masonry → lintels and slab → floor → plaster → doors and windows → finishing.

Items for a two-room building with verandah

The three quantities that are always asked

Verandah. A verandah is measured with the building but its walls are usually thinner and it is often open on one or more sides, so its length must be taken separately from the main block. Its plinth area is included in full if it is covered; a projected balcony or open terrace is normally taken at 50%.

Doing it fast — the method that saves the most time

A detail estimate is long but it is not hard. Almost all the time is lost re-deriving lengths that never needed re-deriving. Work in this order and the whole question becomes one table.

1. Get the two centre-line lengths first, and never touch them again.

Half a wall at each end, plus every internal room and every internal wall in between. Write these two numbers in a box at the top of your answer book.

2. Use the ±b rule instead of re-measuring. For an item of breadth b, the long wall is 8.10 + b and the short wall is 4.30 − b. Write the b column down the page first, then fill the two length columns mechanically — no thinking, no drawing:

Six items, and you did one subtraction and one addition each. Every length in the sheet below comes out of this table.

3. Check each row with the centre-line method before you multiply. This is the one check worth its time in an examination, because it catches a wrong length before it is multiplied through three columns. The total centre-line length of this building is fixed:

The two methods must agree exactly, for every value of b. If they do not, you have either miscounted the short walls or used the wrong sign in the ±b rule — and you have found out in ten seconds instead of losing the whole item.

4. Take the deductions in one block at the end, not opening by opening as you go. The volume deducted from brickwork for any opening is simply L × wall thickness × H, and the same L and H serve the plastering deduction (twice, for two faces). One row per opening type, multiplied by the number of them.

5. Fixed order of items. Never hunt for what comes next — it is always this, from the ground upwards:

6. Sanity checks that take five seconds each.

The mistakes that cost marks in this question

Worked estimate — a two-roomed load bearing building

Step 1 — the centre-line lengths. Everything below follows from these two numbers, so they are worked out once and once only:

There are three short walls, not two — the two external end walls and the partition between the rooms. Forgetting the partition is the commonest single mistake in this question.

Length of a lintel. l = clear span + 2 × bearing. Where the bearing is not given, take it as equal to the thickness of the lintel, with a minimum of 12 cm. Here the lintel is 150 mm thick, so the bearing is 150 mm and a 1.20 m door gets a lintel 1.20 + 2(0.15) = 1.50 m long — which is the figure used throughout the sheet below.

Step 2 — the measurement sheet.

Item 1 — Earthwork in excavation in foundation

Item 2 — PCC 1:3:6 bed in foundation

Item 3 — First class brickwork in foundation and plinth

Notice how the length changes for every footing because the breadth changes: the long wall grows and the short wall shrinks by exactly the same amount, so the total length stays 2(8.10) + 3(4.30) throughout. That identity is the arithmetical check on the whole sheet.

Item 4 — 50 mm damp proof course

Item 5 — First class brickwork in superstructure

Item 6 — RCC 1:2:4 in slab and lintels

Item 7 — Steel reinforcement

Where no bar bending schedule is given, reinforcement is taken as a percentage of the volume of concrete — about 1% for a slab, 1.5% for a lintel or beam, 2% for a column and 5% for a footing — converted to weight at the density of steel, 7850 kg/m³. A full bar bending schedule is worked out in §4.2.

Item 8 — Formwork to the slab and lintels

Item 9 — Sal wood in door and window frames

Item 10 — 12 mm cement plaster 1:6

Openings over 3 m² are deducted on both faces, which is why each opening appears with twice its number in the deduction rows. A window of 1.5 × 1.5 = 2.25 m² would strictly be deducted on one face only (§1.4); it is deducted on both here because both faces of these walls are plastered and the reveals are then measured separately — state whichever convention you adopt.

Step 3 — abstract of cost. The quantities are carried forward and priced. The rates below are illustrative; in the examination take them from the district rate or from your own rate analysis, and say so.

Abstract of cost

Estimated cost of the building ≈ Rs 934,973, to which must still be added the flooring, painting, door and window shutters, and the provisions for water supply and sanitary work (8–10%) and electrification (8–10%).

Deductions for openings in brickwork. Deduct the full volume of each door and window opening (area of opening × thickness of wall) and the volume of the lintel over it, since the lintel is measured separately as RCC. Do not deduct for lintel bearings up to 0.1 m³, or for openings up to 0.1 m² (§1.4).

Geometry and item sequence after Er. N. P. Dawadi's worked example; every quantity recomputed here from the dimensions.

4.2 Four room frame structured building with reinforcement calculations

A framed building differs from a load-bearing one in what carries the load, and therefore in what is measured:

Order of taking out a framed building

1. Excavation for each isolated footing — number × length × breadth × depth.
2. PCC bed, footing pad, and the column pedestal below plinth.
3. Columns from footing top to slab soffit, then plinth beams, then floor beams.
4. Slab — area × thickness, deducting large voids only.
5. Infill brickwork panel by panel, deducting openings.
6. Reinforcement, from the bar bending schedule.

Reinforcement calculation

This is the part that carries the marks. Steel is measured as the length of each bar in place, converted to weight:

Cutting length is the clear length plus hooks and bends, less the cover:

Two rules save marks: always add 1 when counting stirrups or bars from a spacing, and remember that binding wire and rolling margin are not measured separately — they are inside the rate.

Worked estimate — a four-roomed framed building

Item 1 — Earthwork and bedding

Item 2 — RCC in the frame

The beam depth is measured below the slab, 500 − 125 = 375 mm. Measuring the full 500 mm would count the flange twice, since the slab has already been measured right across the beams. This is the single commonest error in a framed-building estimate.

Item 3 — Formwork

Item 4 — Bar bending schedules

Bar bending schedule — one column C1, 400 × 400 mm, 3.00 m high

Bar bending schedule — one beam B1, 250 × 500 mm, 5.00 m clear span

Steel in a framed building normally works out to 80–120 kg per m³ of concrete overall, or roughly 4–6 kg per m² of built-up area. The figure above is lower because the slab and footing reinforcement has not yet been added. A result far outside that band means an error in the cutting length or the bar count — check before writing it down.

Bar bending rules after IS 2502; frame arrangement after Dawadi, Beam, slab and pillar.

4.3 Septic tank with soak pit

A septic tank is a watertight settling chamber that treats sewage from a building where no public sewer exists; the effluent then percolates into the ground through a soak pit (soakaway).

Sizing

The tank is deliberately made long and narrow. The sewage has to travel the length of the tank while it settles, so a squat tank short-circuits and settles badly. That is also why a baffle wall is set about 0.80 m from the inlet — it stops the incoming flow from disturbing the scum.

Worked estimate — septic tank for 25 users, with soak pit

Step 1 — capacity and internal size

Step 2 — measurement sheet for the tank

The internal plaster of a septic tank is specified 20 mm thick in 1:2 cement sand mortar with a waterproofing compound — richer and thicker than ordinary 12 mm plaster, because the tank must stay watertight. No plaster is measured on the scum board.

Step 3 — inspection chamber

An inspection chamber is built between the septic tank and the soak pit so that the effluent line can be opened, inspected and cleared. It is a small covered masonry box with a benched and channelled floor, and it is measured as a separate item:

Where the cover slab carries a manhole opening, remember the IS 1200 rule: an opening larger than 0.1 m² is deducted, a smaller one is not. A 0.45 × 0.45 m cover is 0.2025 m² and therefore is deducted.

Step 4 — soak pit

The soak pit lining is honeycomb brickwork precisely so that effluent can escape through it — and honeycomb brickwork is measured in m², not m³ (§1.2). That is a favourite one-mark question.

Items to be measured

Dawadi, RCC T-beam, well, septic, caisson, pier; sizing per the standard septic tank design practice.

4.4 Underground water tank

An underground water tank (reservoir) is estimated exactly like a septic tank but is designed to hold clean water, so the whole shell is watertight RCC and the internal finish matters.

Sizing

Remember 1 m³ = 1000 litres. A tank for 20 people at 135 l/head/day for one day needs 2700 litres = 2.7 m³, plus free board.

Worked estimate — RCC underground water tank

Step 1 — check the capacity

Step 2 — the measurement sheet

Item 1 — Earthwork and bedding

Item 2 — RCC 1:2:4, excluding reinforcement

Item 3 — Steel reinforcement

Item 4 — Formwork and finishing

Item 5 — Fittings

Pipes, valves and fixtures of different sizes are counted or measured in running metre from the drawing, each size as a separate item — they are never lumped together.

Items to be measured

1. Earthwork in excavation — outside dimensions plus working space, to the full depth; classed by soil, and separately below the water table.
2. PCC levelling course under the base slab.
3. RCC base slab, walls and top slab, with the manhole deducted.
4. Reinforcement from the bar schedule, or as a percentage of the concrete.
5. Formwork to both faces of the walls and to the soffit of the top slab.
6. Waterproof cement plaster inside, and plaster outside.
7. Manhole cover, rungs, vent, inlet, outlet, overflow and washout pipes.
8. Backfilling in layers around the tank, and disposal of surplus earth.

Note the difference from a building: for a tank the internal dimensions are fixed by the capacity, so the centre-line perimeter is found by adding one wall thickness to each internal dimension — the mirror image of the crossing method in §2.3.

Geometry after Dawadi, 1 km highway, RCC water tank and building §6.12; every quantity recomputed here from the dimensions.

Sources consulted for this chapter

• Er. Narayan Prasad Dawadi, Estimating and Costing lecture notes (IOE, Pashchimanchal Campus) — the two-roomed load bearing building and the RCC underground water tank — geometry and item sequence of the worked sheets
• M. Chakraborti, Estimating, Costing and Specification in Civil Engineering — ch. III estimate of buildings, ch. IV RCC works, ch. VI water supply and sanitary works (septic tank and reservoir)
• B. N. Dutta, Estimating and Costing in Civil Engineering — ch. 1 — length of a lintel (clear span + 2 bearings, bearing = thickness of lintel, minimum 12 cm) and the mean-length rule for arch masonry
• IS 1200 — Method of Measurement of Building and Civil Engineering Works — mode of measurement and the deduction rules used in the sheets
• Pandey & Katwal, Complete Manual of Estimating and Costing (T.U., B.E. Civil) — the septic tank – inspection chamber – soak pit sequence, the 20 mm waterproofed 1:2 plaster inside a tank, and the rule that a manhole cover over 0.1 m² is deducted
• Notes by RK Sir (course handwritten notes) — reinforcement taken as a percentage of the volume of concrete

End of Chapter 4 — Detail Quantity Estimate of Building Works