Building estimation is the feasible cost of all activities and estimating in construction prepared by mathematical calculations based on the drawings, plans, item rates of work.
14 Main work items in Building estimation
The following are the main items of work in building estimation.
1.Earthwork
2.Concrete in foundation
3.Soling
4.Damp proof course
5.Masonry
6.Lintels over openings
7.RCC work
8.Flooring and roofing
9.Plastering
10.Doors and Windows
11.Woodwork
12.Ironwork
13.Whitewashing or color washing
14.Painting of doors and windows
RCC Column cast in the foundation footing cost estimation can be estimated from the provided plan, section drawings, local work rates.
RCC Column specification, plan and section details
- Footing size is 2 m length x 2 m wide x 0.45 m depth
- PCC 1:4:8 is utilised in foundation
- RCC 1:2:4 is utilised in footing
- 300 dia is the column size above plinth level,350 mm x 350 mm is the size from footing top-level to plinth level and the RCC 1:2:4 is utilised,
- Reinforcement 12 mm dia @150 mm c/c both sides is utilised in footing
- Main bars 6 numbers 16 mm dia and stirrups 10mm dia @ 150 mm c/c is utilised in the column.
Read more related topics:
1.Earthwork
Earthwork in the filling and Earthwork in excavation is normally taken out individually under separate items and quantities are estimated in cum.
In the foundation Earthwork in an excavation is determined by taking the dimensions of Breadth, length, Depth using the formula=Length x breadth x Depth.
In plinth filling and backfilling excavated earth is utilised.
For the dressing, extra earth is brought from outward if needed.
After plinth filling and backfilling if there is surplus earth, this may be used in dressing and levelling of the site or carted apart and separated.
2.Concrete in the foundation
The breadth and length of foundation concrete will be the same as for excavation, only the thickness or depth only varies.
The concrete in building estimation is determined by breadth x length x thickness in Cum.
The concrete thickness ranges from 20 cm to 45 cm, normally 30 cm.
The proportion of cement concrete in the foundation is 1:4:8 or 1:5:10
3.Soling
When the soil beneath the foundation is bad or soft, stone soling (40mm or 60mm aggregate) or one layer of dry brick is filled beneath the concrete foundation.
The soiling layer is determined in Sqm ( breadth x length ), defining the thickness.
4.Damp proof course
D.P.C normally of 1” thick or 2 cm thick cement mortar 1:2 or 2.5 cm cement concrete 1:1.5:3 combined with approved waterproofing material.
One kg of Impermo or Cem-Seal or other approved waterproofing compounds per bag of cement is utilised.
This DPC is provided at the plinth level to the full width of the plinth wall and
the quantities are calculated in Sqm. (length x width).
DPC is not provided at the sills of doors and veranda openings.
5.Masonry
Foundation and plinth masonry (substructure)is taken under one item.
Masonry in the superstructure is considered in another item.
Calculation of Masonry is done in Cum ( width x Length x thickness).
In masonry,Standard bricks of size 9” x 4.5” x 3” or 19mm x 9mm x 9mm bricks are utilised.
Can also use other types of bricks like concrete bricks, lightweight bricks….etc
In multi-storied building, each floor,i.e ground floor, first floor etc masonry was calculated separately.
For openings of windows, doors.. etc deductions are made in estimating masonry.
Deduction for openings, bearings ..etc in masonry.
No deductions are made for the following.
i. Up to 0.1 Sq.m openings deductions are not done.
ii. Up to 0.05 Sqm in the section of Purlins, end beams etc deduction not done.
iii.Bedplate,wall plate,bearing of lintels..etc up to 10cm (4” depth)
iv. Bearings of wall masonry and floor are not subtracted from the masonry of the wall.
6.Lintels over openings
Lintels are constructed in RCC & estimated in Cum.
Length of the lintel is equivalent to the two bearings width plus clear span.
It is considered as the thickness of lintel with a minimum of 12 cm If the dimension of bearing is not provided.
The length of lintel is given by L= s +2t, s=clear span,t= bearing width.
Quantity of lintel= L x thickness of the wall x t
7.RCC work
RCC activity may be in the beams, roof, lintels, foundation, floor slab, columns..etc and the quantities are determined in Cum.
Centring and shuttering quantities in building estimation are calculated in Sqm.
Including bending the reinforcement is measured in MT(metric tons).
In general, 0.6% to 1 % of RCC by volume are taken for steel calculation.
8.Flooring and roofing
a.Ground Floor
The base PCC (plain cement concrete) and floor finishing of CC (cement concrete) or marble or vitrified tiles etc are taken as one job and quantity are calculated in Sqm. (length x breadth)
b. 1st floor,2nd floor..etc
Supporting structure for 1stfloor and 2nd floor is cast in Rcc and quantity is measured in Cum.
Floor finishing is laid in marble CC or vitrified tiles ..etc and quantities in building estimation are measured in Sqm.
c.Roof
Supporting structure is cast in RCC and quantities is calculated separately in building estimation in Cum.
Terrace waterproofing and protection screed of 75mm to 120mm thick is calculated in Sqm under the separate item.
In case of galvanized iron sheet or tile or asbestos cement sheet roofing, the roof covering is determined including overlays with all fitting in Sqm.
Supporting trusses and members are taken as a separate item in kgs.
9.Plastering
12 mm thick Plastering is normally used in general for a brick wall and it is measured in building estimation in Sq.m.
Both sides of the walls are granted as solid and estimations are exercised for both sides.
Deductions are made in the following manner
I. For ends of rafters, beams, ..etc, no deduction is executed.
ii.No addition is made for jambs, soffit’s, no deduction is made and sills of these openings for small openings up to 0.5 Sq.m.
iii. For openings exceeding 0.5 Sqm bit not exceeding 3 Sqm, the deduction is made for one face only and another face is allowed for jambs, soffits and sills which are not taken into account separately.
iv. The deduction is performed for both faces of the jambs, the openings and, soffits, sills are taken into account and totalled, for openings above 3 Sqm.
Plastering of the ceiling of 12 mm thick is calculated in Sqm.
10.Doors and windows
I. Frames or Chowkhat
window and Door frame estimation is done in Cu m.
Length is obtained by adding all member’s of the frame, two verticals and top if no sill member is given.
ii.Doors and window shutters
They are calculated in Sq.m by multiplying the breadth by the height of the shutters.
If there is no sill member, a clearance of 6mm is permitted at the bottom of the sill.
11.Woodwork
wooden roof trusses, Wooden beams, frames, posts, Interior items like TV units, wardrobes, modular beds, kitchen, etc..are come under this woodwork and quantities are estimated in Cum.
12.Ironwork
Ironwork is measured in kgs or MT by multiplying the weights per running meter (Unit weight).
The density of steel is equivalent to 7850 kg/cum.
Iron holdfasts Weight may be considered as 1.5 kg. each.
For doors, 6 holdfasts and windows 4 holdfasts are considered.
The weight of nuts, bolts and rivets with heads is estimated by counting their sizes, numbers and using steel tables.
For steel roof truss 5% of the steelwork is provided for rivets, bolts and nuts.
13.Whitewashing or colour washing
Whitewashing or colour washing quantities are measured in building estimation in Sq.m and these quantities will be the same as the quantities of plastering.
If internal walls whitewash is done, then the whitewash quantity is equal to the internal wall plastering quantity.
If external walls are colour-washed, then colour wash quantity is equal to external walls plastering quantity.
Two coats of paint are considered for whitewashing or colour washing.
14.Doors and window painting
Painting or varnishing of doors and windows are calculated in building estimation in Sq.m.
The following multiplying factor is utilised for both faces of windows and doors.
i. For framed, battened, Panelled, braced, etc: one surface area is used (for both sides)x2.25.
ii.Fully glazed: one surface area (for both sides) x1
iii. partly glazed and Partly panelled: one surface area (for both sides)x2
iv. For Flush doors: one surface area ( for both sides) x 2
v.Venetian : 3 cone surface area (for both sides)
vi. For grills, Iron bars in windows: area of clear openings in-between frames x 1.
Apart from the above items, the following items are also considered in building estimation.
1.Lump-sum item
A lump sum rate is provided for small items for specific quantities which cannot be taken out easily.
2. Electrification, sanitary and water supply works
For sanitary and water supply works 8% of the estimated cost of the building estimation is considered.
For electrification,8% of the building estimation cost is considered.
Specifications of items:
The specifications of items are fully described so that each item is clear.
Type and quality of materials, the proportion of motor, method of construction,..etc are included in the description of items of building estimation.
Rates :
Rates of the different items of work in the estimate include supply materials, transport, labour, scaffolding, overheads, contractors profit, taxes, etc.
How do you estimate a building?
An estimate is the essential estimation of quantities or computation and investment likely to be acquired in the various works of construction.
An approximate estimate is prepared based by various methods but the accurate estimate is prepared by
detailed estimate method.
What is the detailed estimate method?
Detailed estimate method consists of calculating the cost of each item of work and determining the quantities of different items of work.
This building estimation is achieved in two stages
I. estimates of quantities and details of measurements.
ii.Abstract of estimated cost
i.Details of measurements and calculations of quantities
This includes different items of work like earthwork, concrete, brickwork..etc and the items are classified and grouped under different sub-headings and each item measurements details of work are taken out and quantities under each item are determined.
Details of the building estimation measurement sheet are given below.
Measurement sheet | |||||||
Item/ SNo | Description | No | Length | Breadth | Depth/height | Item Quantity | Total quantity |
1 | |||||||
2 | |||||||
3 | |||||||
ii.Abstract of the estimated cost
The cost under the item of work is calculated from the quantities computed at workable rates and the total cost is worked out in abstract of building estimation form.
Abstract of estimate | |||||
Item/ SNo | Description | Quantity | Rate | Amount | Remarks |
1 | |||||
2 | |||||
3 | |||||
3% to 5% is added for contingencies, to allow for unforeseen changes in design, expenditures, changes in rates… etc which occur during the execution of works.
2 % of the estimated cost is also added to match the work expenditure.
The total cost thus obtained is the estimated cost of the building.
Actual cost :
The actual cost of work or building is known after the completion of work.
An account of all expenditure is maintained day to day during the execution of work.
From the estimated cost, the actual cost should not deviate much.
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