Method of estimation of unit cost - Unit Cost Calculation

Unit Cost Method of Estimation starts with dividing a construction project into various components or elements for the purpose of cost estimation. Then cost of each of the project’s components or elements are assessed and their cost estimation is calculated. Sum of costs of each project elements gives the total construction cost of the project. The unit cost method of estimation can be used for project design estimates as well as for bid estimates.

Construction cost estimates are of three types mentioned below:

• Preliminary Cost Estimates
• Detailed Cost Estimates
• Engineer’s Cost Estimates

During the preliminary cost estimate, as cost details of every minute elements are not of much importance, the project is divided into major components and cost estimate of these major units are calculated based on the past project experiences. The cost of equipment if any is also included. For example, estimating the cost of entire floor based on its area.

During detailed Cost estimates, the project is divided into components of various major systems and cost of each components is estimated to calculate project cost. For example, cost of installation of any equipment, cost of beams, columns or walls etc.

During Engineer’s cost estimates, each of the components of the major systems of the project is divided into various components that contributes to the cost of the major systems. For example, for cost estimation of an RCC column, the components are concrete, which is also divided into cement, sand and aggregates, reinforcement steel, form-works etc. The unit cost of each of these materials are considered by calculating the cost of an RCC column.

Unit Cost Method of Estimation

For bid estimates, the unit cost method of estimation can also be used even though the contractor divides the project into different levels in a hierarchy as follows:

Subcontractor Quotations: The general contractor of the construction project may get quotations for various items from the subcontractors. The rates prescribed by the subcontractors for various items of the projects can be used for the total construction cost estimate for the project. However, the reliability of accuracy of the cost depends on the method of cost estimates selected by the subcontractor.

Quantity Takeoffs: The division of a construction project into various items of quantities that are measured from the engineer’s plan will result in a procedure similar to that adopted for a detailed estimate or an engineer’s estimate by the design professional. The levels of detail may vary according to the desire of the general contractor and the availability of cost data.

Construction Procedures: If the construction procedure of a proposed project is used as the basis of a cost estimate, the project may be decomposed into items such as labor, material and equipment needed to perform various tasks in the projects.

Formula for Unit Cost Method:

Suppose that a construction project is divided into “n” elements for cost estimation. Let “Qi” be the quantity of the ith element and ui be the corresponding unit cost. Then, the total cost of the project is given by:

where n is the number of units. The unit cost of element ui is estimated based on the method of construction, technology used, type of materials used etc.

Factored Unit Cost Estimate Formula

Sometimes during the cost estimate, there can be some of the minute components which may not have been considered or there can be some variations w.r.t time. In such cases, the cost of units are factored as an allowance for variations or the elements not considered in the estimates. The formula for factored unit cost estimation is as follows:

where Ci is the purchase cost of a major component i and fi be a factor accounting for the cost variation of the item, n is the number of components included in the construction project.

Formula Based on Labor, Material and Equipment

Suppose that a construction project is decomposed into n tasks. Let Qi be the quantity of work for task i, Mi be the unit material cost of task i, Ei be the unit equipment rate for task i, Li be the units of labor required per unit of Qi, and Wi be the wage rate associated with Li. In this case, the total cost y is:

Note that WiLi yields the labor cost per unit of Qi, or the labor unit cost of task i. Consequently, the units for all terms in Equation above are consistent.

Open Space Requirements For Buildings

Open Space Requirements For Buildings

Open air space for ventilation. Every room intended for human habitation should abut an interior or exterior opening air space of the width r dimensions specified below.

Where height of building above plinth adjoining the open air space does not exceed	Minimum width of open air space throughout
5 m	3.0 m
6 m	3.0 m
9 m	3.9 m
12 m	4.8 m
15 m	5.7 m
18 m	6.6 m
21 m	7.5 m

OPEN SPACE AROUND RESIDENTIAL BUILDINGS

Front open space: every building should have a front yard of minimum width of 3m and in case of two or more sides a width of an average of 3 m but in no case it shall be less than 1.8 m. Such a yard shall form an inseparable part of the site.

Rear open space: Every residential building shall have a yard of an average width of 4.5 m and at no place the yard measuring less than 3 m as an inseparable part of the building, except in the case of back to back sites where the width of the yard could be reduced to 3m provided no erection, re-erection or material alteration of the building shall be undertaken, if at common plot line straight lines drawn downwards and outwards from the line of intersection of the outer surface of any rear wall of the building with the roof perpendicular to that line form an angle of more than 63.5 degree to the horizontal.

Side open space: every residential building may have a permanently open air space not less than 1m in width on one of its sides other than its front and rear and such side open space shall form an inseparable part of the site. In case, side open air space is to be used for ventilation, it shall be in accordance with the requirements mentioned in the previous paragraph. In case, the side open space abuts a road, the width shall not be less than 3m.

OPEN SPACE FOR BUILDINGS OTHER THAN RESIDENTIAL

The front, rear and side yards, widths and the rules governing those shall be laid down by the authority in each case.

The rules applicable to residential buildings with regard to front open space, rear open space and the side open space and the angle 45 and 63.5 degree governing erection, re-erection or material alteration of a residential building sall also be applicable to business and industrial buildings, provided, however that the local authority may prescribe the front and rear open spaces as required.

Fire Protection Of High Rise Buildings - Building Bye Laws

Fire Protection Of High Rise Buildings - Building Bye Laws

High-rise buildings have unique challenges related to fire protection such as longer egress times and distance, evacuation strategies, fire department accessibility, smoke movement and fire control. The numbers of persons living on high-rise buildings are high compared to low-rise buildings, and only evacuation method in case of fire is the staircase. So, the fire protections of high rise buildings have gained significant attention worldwide.

Thus, in case of high rise buildings, the following provision should be made for safety of buildings from fire:

(i) National building code should be followed for fire-safety requirement of high rise structures and at least one lift should be designed as fire-lift as defined in the Code and be installed.

(ii) At least one stair-case shall be provided as a fire staircase as defined in the National Building Code. Provided that this shall not be applicable if any two sides of a staircase are kept totally open to external open air space.

(iii) Water Supply: Underground tank of the capacity of one lakh liters and two lakh liters for the buildings situated within the municipal limit and outside of the municipal limit respectively be invariably provided in all the high rise buildings. Water in the normal use tank should come only through the overflow of fire tank so provided.

(iv) In high rise buildings, the internal fire hydrants shall be installed as provided in the National Building Code or as prescribed in the Indian Standard Code of practice for installation of internal fire hydrants in high rise buildings. The detailed plan showing the arrangement of pipe lines, booster pumps and water-tanks at various levels shall be submitted for approval of the concerned authority along with the plans and sections of the buildings.

(v) In case of high rise buildings, an external fire hydrant shall be provided within the confines of the site of the building and shall be connected with Municipal Water mains not less than 4″ in diameter. In addition, fire hydrant shall be connected with Booster Pump from the static supply maintained on site.

(vi) In case of high rise buildings separate electric circuits for lift installation, lighting of passages, corridors and stairs and for internal fire hydrant system shall be provided.

(vii) All the requirements under the above regulations shall be clearly indicated on plans duly signed by the owner and the person who has prepared the plans. The Competent Authority may direct the owner to submit such further drawings as may be necessary to clarify the implementation of the provisions of the above regulations.

(viii) Every building having a height of more than 25 Mts. shall be provided with diesel generators which can be utilized in case of failure of the electricity.

(ix) The standard of National Building Code must be adopted fully in providing stair-case and alarm system.

(x) There should be Provision of dry-powder fire extinguisher to the extent of two on each floor with a capacity of 5 kgs, in all the high rise buildings.

Labour Requirement For Various Building Works

LABOUR REQUIREMENT FOR VARIOUS BUILDING WORKS:

The table below shows the recommended labour requirement for various civil engineering/building/construction works:  Bhisti Means Water Carrier

S.No.	Description of work	Unit	Labour	Recommended constant in days.	Remarks
1)	Excavation over areas (hard/dense soil),depth up to 1.5m and removal (up to one meter from edge)	M3	Mate	0.06	_
			Labour	0.62	_
2)	Excavation in trenches (soft/ loose soil),for foundations not exceeding 1.5m in width and for shafts, wells, cesspits and the like, not exceeding 10m3 and on plan, depth up to 1.5m and removal(up to one meter away from edge)	M3	Mate	0.05	_
			Labour	0.5	_
3)	Returning, filling and ramming of excavated earth in layers not exceeding 20 cm in depth, watering, well ramming and leveling, lead up to 50m	M3	Mate	0.02	_
			Labour	0.25	_
			Bhisti	0.02	_
4)	Concrete :	M3	Labour	0.5	_
	Mixing by machine (mixer) at banker, cement concrete(with 20mm graded coarse aggregate)		Bhisti	0.1	_
			Mixer operator	0.07	_
			Mixer	0.07	_
5)	Mixer mixed cement concrete	M3	mason	0.1	_
			Labour	1.63	_
			bhisti	0.7	_
			mixer operator	0.07	_
			mixer	0.07	_
			vibrator	0.07	_
6)	Reinforced cement concrete in situ in foundations, footings, bases for columns, etc excluding form work and reinforcement	M3	mason	0.17	The constants for items include mixing, pouring, consolidating and curing. This does not include fair finish.
			Labour	2
			bhisti	0.9
			mixer operator	0.07
			mixer	0.07
			vibrator	0.07
7)	Reinforced cement concrete in situ in suspended floors/roofs excluding form work, and reinforcement.	M3	mason	0.24	_
			Labour	2.5	_
			bhisti	0.9	_
			mixer operator	0.07	_
			mixer	0.07	_
			vibrator	0.07	_
8)	Mortars :	M3	Labour	0.75	Labour required will be approximately same for different mix proportions.
	Mixing by hand, cement mortar of any mix/proportions		Bhisti	0.07
9)	Brick work (straight walls) :	M3	mason	0.94	The constants include labour involved in scaffolding.
	Brick work in walls exceeding one brick thick, in cement / lime mortar		Labour	1.8
			bhisti	0.2
10)	Brick work in walls, one brick thick, in cement/lime mortar	M2	mason	0.25	The constants could be adopted for brick work with any mix or mortar.
			Labour	0.4
			bhisti	0.1
11)	Formwork :	M3	Carpenter	0.25	_
	a) fabrication and erection with all supports, struts, braces, etc, and dressing with oil as cleaning of formwork :	M2	Labour	0.2	_
	1) rectangular column and walls	M2	Carpenter	0.23	_
	2) suspended floors/roofs		Labour	0.2	_
	3) sides and soffits of beam		Carpenter	0.3	_
			Labour	0.2	_
12)	Reinforcement:	Quintal	Bar bender	1	_
	Bar reinforcement including cutting to length, hooked ends, cranking or bending, hoisting and placing in any position, binding wire and holding firmly so as not to be disturbed while placing and ramming of concrete		Labour	1	_
13)	Plastering and pointing :	M2	mason	0.08	_
	a) 15mm thick cement plaster to ceiling including mixing of mortar.	M2	Labour	0.1	_
	b) 15mm thick cement plaster on brick walls (exterior) including mixing of mortar	M2	bhisti	0.1	_
	c) Tuck pointing to random rubble masonry in cement mortar including mixing mortar.		mason	0.06	_
			Labour	0.1	_
			bhisti	0.1	_
			mason	0.1	_
			Labour	0.15	_
			bhisti	0.1	_
14)	Damping proof course :	M3	Mason	0.1	_
	a) Laying damp proof course 40mm thick cement concrete including form work and fair finishing to edges and mixing.		Labour	0.1	_
			bhisti	0.01	_

Methods of Estimation In Building Works

Methods of Estimation In Building Works

The estimation of building quantities like earth work, foundation concrete, brickwork in plinth and super structure etc., can be workout by any of following two methods:

a) Long wall – short wall method

b) Centre line method.

c) Partly centre line and short wall method.

A) LONG WALL-SHORT WALL METHOD:

In this method, the wall along the length of room is considered to be long wall while the wall perpendicular to long wall is said to be short wall. To get the length of long wall or short wall, calculate first the centre line lengths of individual walls. Then the length of long wall, (out to out) may be calculated after adding half breadth at each end to its centre line length. Thus the length of short wall measured into in and may be found by deducting half breadth from its centre line length at each end. The length of long wall usually decreases from earth work to brick work in super structure while the short wall increases. These lengths are multiplied by breadth and depth to get quantities.

B) CENTRE LINE METHOD:

This method is suitable for walls of similar cross sections. Here the total centre line length is multiplied by breadth and depth of respective item to get the total quantity at a time. When cross walls or partitions or verandah walls join with main wall, the centre line length gets reduced by half of breadth for each junction. Such junction or joints are studied carefully while calculating total centre line length. The estimates prepared by this method are most accurate and quick.

C) PARTLY CENTRE LINE AND PARTLY CROSS WALL METHOD:

This method is adopted when external (i.e., around the building) wall is of one thickness and the internal walls having different thicknesses. In such cases, centre line method is applied to external walls and long wall-short wall method is used to internal walls. This method suits for different thicknesses walls and different level of foundations. Because of this reason, all Engineering departments are practicing this method.

Size and Quantity of Reinforcement Required For Building Works

Size and Quantity of Reinforcement Rebar Required For Building and Other Commercial Works

Reinforcement is required for reinforced concrete members such as footings, beams, columns, slabs, lintels etc. Estimation of reinforcement quantity is required prior to tendering stage to calculate approximate cost of project or construction work.

Following table gives the estimated quantities of reinforcement and its size generally used for various building works:

Sl. No	RCC Member	Quantity in kg/m3	Size of reinforcement required
1	Column footings	75	10mm  or 12mm
2	Grade beams	100	12mm, 16mm – 85%
			Stirrups – 6mm or 8mm– 15%
3	Plinth beams	125	8mm diameter – 85%,
			Stirrups 6mm – 15%
4	Columns	225	16mm, 20mm and 25mm – 90%
			Ties – 6mm or 8mm – 10%
5	Lintel beam	125	12mm, 16mm dia – 85%
			Stirrups – 6 mm or 8mm – 15%
6	Sunshades	60	8mm dia – 75%
			Distributer – 6mm – 25%
7	Canopy slab upto 2.0 m span	125	10mm dia – 80%
			Distributor bars – 6mm or 8mm – 20%
8	Staircase waist slab	150	12 or 16mm dia – 80%
			Distributor 8mm dia – 15%
9	Roof slab
	(a)  One way slab	80	8mm dia – 70%
			Distributor – 6mm – 30%
	(b)  Two way slab	100	8mm dia – 100%
	(c)  Square slab – 4m to 6m size	150	10 – 12mm dia – 100%
10	Main beams above 6m	250	20mm, 16mm, 12mm – 80 – 85%
			Stirrups – 8mm – 15 – 20%

All above mentioned steel are round tapered steel. This data is just for estimation of quantity of steel for various RCC works. This does not provide actual steel required for all the members. Actual quantity of steel required can be calculated from the drawings prepared after structural design. 

Units Of Measurement and Payment for Various Items

Units of measurement and payment for various items

Sl. No.	Particulars of items	Units of measurement	Unit of payment
1	Earthwork: Excavation, filling, cutting, banking	m3	m3
2	Surface dressing	m2	m2
3	Cutting of trees	Number	Per number
4	Stones: quarrying, blasting	m3	m3
5	Concrete : PCC, RCC, Precast	m3	m3
6	Jail works	m2	m2
7	Damp proof course	m2	m2
8	Brick work of any description	m3	m3
9	Thin partition wall	m2	m2
10	String course, drip course, water course coping etc	m	m
11	Stone work of any description	m3	m3
12	Stone work in wall facing (thickness specified)	m2	m2
13	Wood work: truss, rafter, beam etc	m3	m3
14	Door, window shutters	m2	m2
15	Door, window fittings	Number	Per number
16	Timbering, boarding, sawing of timber, timbering of trenches, partition, etc	m2	m2
17	Steel work	Quintal	Per quintal
18	Expanded metal, fabric reinforcement, cutting angles, plates, tees	cm2	cm2
19	Threading; welding; solder of sheets	cm	Per cm
20	Iron gate, grill collapsible gate, rolling shutter	m2	m2
21	Iron railing	m	m
22	Roofing: tiled, corrugated iron, caves board (thickness specified)	m2	m2
23	Centering, shuttering	m2	m2
24	Ridges; valleys; gutters (girth given)	m	m
25	Expansion and contraction joints	m	m
26	Ceiling timber, A.C. sheet, board, etc	m2	m2
27	Plastering; pointing; white washing; distempering; painting; varnishing; polishing; coal tarring; removing of paints	m2	m2
28	Flooring of any kind	m2	m2
29	Pipes, laying of pipes	m	m
30	Dismantling of brick masonry	m3	m3
31	Grouting	m2	m2
32	Grouting of cracks, joints	m	m
33	Supply of sand; brick ballast; aggregates; timber	m3	m3
34	Supply of cement	Bag	Per bag
35	Supply of steel, G.I. sheet, bare electric line	Quintal	Per quintal
36	Supply of GI sheet	m2	m2
37	Supply of sanitary items	Number	Per number
38	Supply of paint, varnishes	Litre	Per litre
39	Supply of explosives, stiff paint	Kg	Per kg