Cost and estimate l6 Y2 semester 2
CHAPTER ONE: DEFINITION OF ESTIMATE AND ITS DIFFERENT TYPES
For all engineering work, it is required to know beforehand the probable cost of construction known as “Estimated cost”. If the estimated cost is greater than the money available, then attempts are made to reduce the cost by reducing the work or by changing the specifications.
In preparing an estimate, the quantities of different items of work are calculated by simple measurement methods and from these quantities the cost is calculated.
Cost estimation is the iterative process of developing an approximation of the monetary resources needed to complete project activities.
Project teams should estimate costs for all resources that will be charged to the project.
Project managers should be knowledgeable of and consider the various industry techniques and tools in the definition and execution of project cost estimation.
Project underestimation of resources and costs is one of the most common contributors to project failure.
1.1DEFINITION OF ESTIMATE
Estimating is the technique of calculating or computing the various quantities and the expected expenditure to be incurred on a particular work or project.
Estimation is the scientific way of working out the approximate cost of an engineering project before execution of the work. It is totally different from calculation of the exact cost (Actual cost) after completion of the project.
Estimation requires a thorough Knowledge of the construction procedures and cost of materials & labor in addition to the skill, experience, foresight and good judgment.
An estimate of the cost of a construction job is the probable cost of that job as computed from plans and specifications.
Actual cost of work is known at the completion of work. Account of all expenditure is maintained day to day during the execution of work in the account section and at the end of the completion of the work when the account is completed, the actual cost is known.
For a good estimate the, actual cost of the proposed work after completion should not differ by more than 5 to 10 % from its approximate cost estimate, provided there are no unusual, unforeseen circumstances.
1.2NEED FOR ESTIMATION AND COSTING
Estimate is required to control the expenditure during the execution of work.
Estimate decides whether the proposed plan matches the funds available or not.
It help to work out the approximate cost of the project in order to decide its feasibility with respect to the cost and to ensure the financial resources, it the proposal is approved.
Requirements of controlled materials, such as cement and steel can be estimated for making applications to the controlling authorities.
It is used for framing the tenders for the works and to check contractor’s work during and after the execution for the purpose of making payments to the contractor.
From quantities of different items of work calculated in detailed estimation, resources are allocated to different activities of the project and ultimately their durations and whole planning and scheduling of the project is carried out.
1.3STEPS AND DATA NEEDED FOR ESTIMATING
Estimating involves the following three steps:
Preparing detailed Estimate.
Calculating the rate of each unit of work
Preparing abstract of estimate Estimating requires the following data:
1.Drawings (plans, elevations, sections etc):
If the drawings are not clear and without complete dimensions the preparation of estimation become very difficult. So, it is very essential before preparing an estimate.
2.Specifications
General Specifications: This gives the nature, quality, class and work and materials in general terms to be used in various parts of wok. It helps no form a general idea of building.
Detailed Specifications: These gives the detailed description of the various items of work laying down the Quantities and qualities of materials, their proportions, the method of preparation workmanship and execution of work.
3.Rates:
For preparing the estimate, the unit rates of each item of work are required:
The rates of various materials to be used in the construction.
The cost of transport materials.
The wages of labour, skilled or unskilled of masons, carpenters, Mazdoor, etc
1.4SITE CONDITIONS AFFECTING THE OVERALL COST
Each type of work requires a different method of construction. Construction may be of an ordinary house or office and it may also be of a Dam, Tunnel, Multistory building, Airport, Bridge, or a Road, already in operation. Each of these works requires totally different construction techniques, type of machinery, and formwork.
Quality of labour and labour output varies in different localities.
Weather conditions greatly affect the output and, hence, the overall cost.
Ground conditions vary and change the method of construction. For example, excavation may be dry, wet, hard, soft, shallow or deep requiring different efforts.
The work may be in open ground such as fields or it may be in congested areas such as near or on the public roads, necessitating extensive watching, lightening, and controlling efforts, etc.
The source of availability of a sufficient supply of materials of good quality is also a factor.
The availability of construction machinery also affects the method of construction.
Access to the site must be reasonable. If the access is poor, temporary roads may be constructed.
1.5ESSENTIAL QUALITIES OF A GOOD ESTIMATOR
In preparing an estimate, the Estimator must have good knowledge regarding the important rules of quantity surveying.
He must thoroughly understand the drawings of the structure, for which he is going to prepare an estimate.
He must also be clearly informed about the specifications showing nature and classes of works and the materials to be used because the rates at which various types of works can be executed depend upon its specifications.
A good estimator of construction costs should possess the following capabilities, also: Knowledge of the details of construction work.
Experience in construction work.
Having information regarding the materials required, machinery needed overhead problems, and costs of all kinds.
Good judgment with regard to different localities, different jobs and different workmen.
Selection of a good method for preparing an estimate. Ability to be careful, thorough, hardworking and accurate.
Ability to collect, classify and evaluate data relating to estimation. Ability to visualize all the steps during the process of construction.
Before preparing the estimate, the estimator should visit the site and make a study of conditions, there.
For example, if the construction of a large building is planned, the estimator or his representative should visit the site and:
Note the location of the proposed building. Get all data available regarding soil
Make a sketch of the site showing all important details. Obtain information concerning light, power, and water. Secure information concerning banking facilities.
Note conditions of streets leading to railway yards and to material dealers, and Investigate general efficiency of local workman.
1.6COMPLETE ESTIMATE
Most of people think that the estimate of a structure includes cost of land; cost of materials and labour, but many other direct and indirect costs included.
The complete estimate of a project or building structure should include all items of expenditure from the beginning up to the end.
All items of complete estimate are shown below
P.S: Petty supervision
Lump Sum
While preparing an estimate, it is not possible to work out in detail in case of petty items. Items other than civil engineering such items are called lump sum items or simply L.S. Items.
The following are some of L.S. Items in the estimate.
Water supply and sanitary arrangements.
Electrical installations like meter, motor, etc.,
Architectural features.
Contingencies and unforeseen items.
In general, certain percentage on the cost of estimation is assigned for the above L.S. Items
Even if sub estimates prepared or at the end of execution of work, the actual cost should not exceed the L.S. amounts provided in the main estimate.
Contingencies indicates incidental expenses of miscellaneous character which cannot be classified under any distinct item sub-head, yet pertain to work as whole.
Provision for contingencies 3% to 5% of estimated cost, is made in the estimate to cover the miscellaneous petty expenditures which do not come under any item of work.
Work charged establishment
During the construction of a project considerable number of skilled supervisors, work assistance, watch men etc., are employed on temporary basis.
The salaries of these persons are drawn from the L.S. amount allotted towards the work charged establishment.
That is, establishment which is charged directly to work. An L.S. amount of 1½ to 2% of the estimated cost is provided towards the work charged establishment.
1.7TYPES OF ESTIMATE
Before undertaking the construction of a project it is necessary to know its probable cost which is work out by estimating. The primary object of the estimate is to enable one to know beforehand, the cost of the work.
The estimate is the probable cost of a work and is determined theoretically by mathematical calculations based on the plans and drawings and current rates.
Approximate estimate may be calculated by various methods but accurate estimate is prepared by detailed estimate method.
Detailed Estimate
Detailed estimates are prepared by carefully and separately calculating in detail the costs of various items of the work that constitute the whole project from the detailed working drawings after the design has been finalized. The mistakes, if any, in the rough cost estimate are eliminated in the detailed estimate.
Detailed estimates are submitted to the competent authorities for obtaining technical approval. The whole project is sub-divided into different items of work or activities.
The quantity for each item is then calculated separately from the drawings as accurately as possible. The procedure is known as "taking out of quantities".
The quantities for each item may be estimated and shown in the pattern which is called "Bill of quantities." The unit, in which each item of the wok is to be calculated, should be according to the prevailing practice as followed in various departments of the country.
a)Details of measurements and calculation of quantities: BILL OF QUANTITIES
Item No. Description of item. No Measurements Quantity Total Quantity Remarks
Length
(L) Breadth
(B) Height
(H)
b)Abstract of Estimated Cost: PRICED BILL OF QUANTITIES
The cost of each item of work is worked out from the quantities that already computed in the details measurement form at workable rate. But the total cost is worked out in the prescribed form known as abstract of estimated form. 4% of estimated Cost is allowed for Petty Supervision, contingencies and Unforeseen items.
Item No. Description of Item Unit Quantity Rate Cost Remarks
Each item of the work is then multiplied by its estimated current rate calculated by a fixed procedure to find out cost of the item. At the end, a total of all items of the work are made to get the total estimated cost.
The rates are usually as per Schedule of Rates for the locality plus a premium to allow for rise in labor and material rates over and above the schedule of rates.
A percentage, usually 5% is also provided on the total estimated cost for the work to allow for the possible contingencies due to unforeseen items or expenditure or other causes, besides 2% establishment charges.
Besides drawings and details of measurements and calculation of quantities (Bill of Quantities), the following documents are also usually submitted with the detailed estimate for obtaining Technical Approval:
A report explaining History, necessity, scope and main features of the project, its design, and estimate, etc.
Specifications lying down the nature and class of work and material to be used in various parts of the work.
The abstract of cost (priced Bill of Quantities) showing the total quantities under each sub-head, rate per unit of measurement, and cost.
Calculation sheets showing calculations for important parts of the structure. In fact, in estimating the art and skill lies only in the computation of details without any omissions, of all parts of the building or work.
Unforeseen items in detailed estimate
While preparing a detailed estimate, one hand to be very careful to see that all items of the work are incorporated.
It is likely that a few Items, though unimportant in nature, might have been overlooked and which may result in raising the estimate of the project.
There may be also certain unforeseen circumstances affecting the project.
Hence, a certain allowance usually 3 to 5% of the total cost, is made in the estimation which will take care of all these Items that are unforeseen or are overlooked and are known as "Contingencies".
Approximate estimate or Rough cost estimate
Estimation of cost before construction from plans or architectural drawings of the project scheme, when even detailed or structural design has not been carried out, is called Rough cost estimate.
These estimates are used for obtaining Administrative Approval from the concerning Authorities. Sometimes, on the basis of rough cost estimates, a proposal may be dropped altogether.
Unit cost is worked out for projects similar to the project under consideration carried out recently in nearly the same site conditions.
Unit cost means cost of execution of a unit quantity of the work.
To find rough cost of any project, this worked average unit cost is multiplied with total quantity of the present work in the same units.
For example, in case of a building, plinth area (m2) of the proposed building is worked out, which is then multiplied by the cost per unit area (Rwf/m2) of similar building actually constructed in the near past in nearly the same site conditions, to find out the rough cost estimate of the building.
This cost is sometimes adjusted by the average percentage rise in the cost of materials and wages.
The rough cost estimate may be prepared on the following basis for different types of projects:
Cost per square meter of covered area (plinth area) is the most commonly adopted criterion for preparing rough cost estimate for most of the residential buildings.
For public buildings, cost. Per person (cost per capita) is used. For example,
Students hostel—cost per student Hospitals—Cost per bed Hotel——Cost per Guest
Cost per cubic meter is particularly suitable for commercial offices, shopping centers, and factory buildings, etc.
For water tank/reservoir, cost may be worked out on the basis of capacity in gallons of water stored.
For roads and railways, cost may be found out per mile/kilometer of length.
For streets, cost may be per hundred meters of length.
In case of bridges, cost per meter of clear span may be calculated.
1.8FACTORS TO BE CONSIDERED DURING PREPARATION OF DETAILED ESTIMATE
Quantity and transportation of materials: For bigger project, the requirement of materials is more. Such bulk volume of materials will be purchased and transported definitely at cheaper rate. Location of site: The site of work is selected, such that it should reduce damage or in transit during loading, unloading, stocking of materials.
Local labour charges: The skill, suitability and wages of local labors are considered while preparing the detailed estimate.
1.9MEASUREMENT OF MATERIALS AND WORKS Units of measurements
The units of measurements are mainly categorized for their nature, shape and size and for making payments to the contractor.
The principle of units of measurements normally consists the following: Single units work like doors, windows, trusses etc., is expressed in numbers.
Works consists linear measurements involve length like cornice, fencing, hand rail, bands of specified width etc, are expressed in running meters (RM)
Works consists areal surface measurements involve area like plastering, white washing; partitions of specified thickness etc. are expressed in square meters.
Works consist of cubical contents which involve volume like earth work, cement concrete; Masonry etc. are expressed in Cubic meters.
(BASED ON IS 1200 REVISED)
S/NO Particulars of items Units of
Measurement Units of
Payment
I
II Earth work:
1.Earth work in Excavation
2.Earthwork in filling in foundation trenches
3.Earth work in filling in plinth
Concrete:
1.Lime concrete in foundation
2.Cement concrete in Lintels
3.R.C.C.in slab
4.C.C. or R.C.C., Sunshade
5.L.C. in roof terracing (thickness specified)
cum cum
cum
cum cum cum cum
sqm
Per % cum Per % cum
Per % cum
Per cum Per cum Per cum Per cum
Per sqm
III
IV
V VI
VII 6.Cement concrete bed
7.R.C. Sunshade (Specified Width & Height
Damp Proof Course (D.P.C) (Thickness should be mentioned) Brick work:
1.Brickwork in foundation
2.Brick work in plinth
3.Brick work in super structure
4.Thin partition walls
5.Brick work in arches
6.Reinforced brick work (R.B. Work)
Stone Work:
Stone masonry
Wood work:
1.Doors and windows frames or chowkhats, rafters
beams
2.Shutters of doors and windows (thickness specified)
3.Doors and windows fittings (like hinges, tower bolts, sliding bolts, handles)
Steel work
1. Steel reinforcement bars etc in R.C.C. and
R.B. work.
2.Bending, binding of steel Reinforcement
3.Rivets, bolts, & nuts, Anchor
bolts, Lewis bolts, cum cum
sqm
cum cum cum sqm cum cum
cum cum
sqm
Number
Number, RM
number number per cum 1 RM
Per sqm
Per cum Per cum Per cum Per cum Per cum Per cum
Per cum Per cum
Per sqm
per number
per number, RM
per number per number
VIII
IX
X Holding down bolts.
4.Iron hold fasts
5.Iron railing (height and types specified)
6.Iron grills
Roofing
1.R.C.C. and R.B. Slab roof (excluding steel)
2.L.C. roof over and inclusive of tiles or brick or stone slab etc (thickness specified)
3.Centering and shuttering form work
4.A.C. Sheet roofing
Plastering, points & finishing
1.Plastering-Cement or Lime Mortar (thickness and proportion specified)
2.Pointing
3.White washing, colour washing, cement wash (number of coats specified)
4.Distempering (number of coats specified)
5.Painting, varnishing (number of coats specified)
Flooring
1.25mm cement concrete over 75mm lime concrete Floor (including L.C.)
2.25mm or 40mm C.C. floor
3.Doors and window sills (C.C. or cement mortar plain)
number number
sqm
cum
sqm
sqm sqm
sqm sqm sqm
sqm sqm
sqm sqm sqm
per number per number
per sqm
per cum
per sqm
per sqm per sqm
per sqm per sqm per sqm
per sqm per sqm
per sqm per sqm per sqm
XI XII XIII XIV
Rain water pipe /Plain pipe Steel wooden trusses
Glass panels(supply) Fixing of glass panels or
cleaning
1 RM
1No sqm
No
per RM per 1No per sqm
per no.
Rules for measurement
The rules for measurement of each item are invariably described in IS1200. However some of the general rules are listed below.
1.Measurement shall be made for finished item of work and description of each item shall include materials, transport, labour, fabrication tools and plant and all types of overheads for finishing the work in required shape, size and specification.
2.In booking, the order shall be in sequence of length, breadth and height or thickness.
3.All works shall be measured subject to the following tolerances.
Linear measurement shall be measured to the nearest 0.01meter
Areas shall be measured to the nearest 0.01 square meter
Cubic contents shall be worked-out to the nearest 0.01 cubic meter
4.Same type of work under different conditions and nature shall be measured separately under separate items.
5.The bill of quantities shall fully describe the materials, proportions, workmanships and accurately represent the work to be executed.
6.In case of masonry (stone or brick) or structural concrete, the categories shall be measured separately and the heights shall be described:
From foundation to plinth level
From plinth level to first floor level
From Fist floor to second floor level and so on.
1.10DEGREE OF ACCURACY IN ESTIMATING
Accuracy in estimate is very important, if estimate is exceeded it becomes a very difficult problem for engineers to explain, to account for and arrange for additional money.
Inaccuracy in preparing estimate, omission of items, changes in designs, improper rates, etc, are the reasons for exceeding the estimate, though increase in the rates are the one of the main reasons.
In framing a correct estimate, care should be taken to find out the dimensions of all the items correctly, and to avoid omissions of any kind of work or part. The rate of each item should also be reasonable and workable.
The rates in the estimate provide for the complete work, which consist of the cost of materials, cost of transport, cost of scaffolding, cost of tools and plants, cost of water, taxes, establishment and supervision cost, reasonable profit of contractor, etc.
The accuracy, to be observed in preparing an estimate depends on the rates of the item and unit of payment.
The higher the rates the greater should be the accuracy with which the quantities are calculated. Where rates are high and paid per unit dimensions should be absolutely correct, though taking dimensions to the nearest 1 cm to 0.5 cm may be allowed for practical purposes.
The quantities in such cases should be worked out to at least two places of decimal. But where rates are low and paid for % to % unit such extreme accuracy is not required.
In the case of wall where masonry is paid in cubic meter a few centimeter added to or subtracted from or height would but little affect the total content.
But the width or thickness of the wall, where every half centimeter or quarter centimeter affects the results considerably should be taken out with great accuracy.
EXERCISES: SHORT ANSWER QUESTIONS
1.What are the rules to be followed while taking off the measurements?
2.Mention the units for the following items of work.
a.Flooring
b.Stone Masonry
c.Plastering for pointing
d.Damp proof course
e.R.C. sunshade (Specified width and thickness)
3.What can you do, if after estimation you find that the probable cost is greater than the available money?
4.Why do we need estimating in civil engineering projects?
5.List three main reasons that cause the actual cost to be greater than the estimated cost?
6.State the important data needed for estimating.
7.Give the difference between detailed estimate and rough cost estimate
8.What is the difference between “Estimated cost” and “Actual Cost”?
CHAPTER TWO: METHOD OF BUILDING ESTIMATES
The quantities like earth work, foundation concrete, brickwork in plinth and super structure etc., can be work out by any of following three methods:
Long wall - short wall method
Centre line method.
Partly Centre line and short wall method.
The dimensions, length, breadth and height or depth are to be taken out from the working drawings (plan, elevation and section).
Junctions of walls, corners and the meeting points of walls require special attention.
For symmetrical footings, which is the usual case, earthwork in excavation in foundations, foundation concrete, brickwork in foundation and plinth, and brickwork in superstructure may be estimated by either of the two methods:
Separate Or Individual Wall Method
Center Line Method
2.1SEPARATE OR INDIVIDUAL WALLS METHOD
The walls running in one direction are termed as "long walls” and the walls running in the transverse direction, as "Short walls", without keeping in mind which wall is lesser in length and which wall is greater in length.
Lengths of long walls are measured or found “Out-to out" and those of short walls as "In-to-in". Different quantities are calculated by multiplying the length by the breadth and the height of the wall. The same rule applies to the excavation in foundation, to concrete bed in foundation, D.P.C., masonry in foundation and super structure etc.
For symmetrical footing on either side, the center line remains same for super structure, foundation and plinth.
So, the simple method is to find out the centre-to-centre lengths of long walls and short walls from the plan.
Long wall length out-to-out
= Center to center length + half breadth on one Side + half breadth on other side.
= Center to center length + one breadth
Short wall length in-to-in = Center to Center length - one breadth.
This method can also be worked out in a quicker way, as follows:
For long walls
First of all, find the length of the foundation trench of the long wall “out-to-out” in the same manner as explained above.
The length of the foundation concrete is the same.
For the length of the first footing or first step of the brick wall, subtract two offsets (2x6"=12") in foundation concrete from the length of the trench or concrete.
For the second footing subtract from the length of the 1st footing two offsets (2x2.25"= 4.5"), for 3rd footing subtract from the length of the 2nd footing 2 offsets (4.5") and in this way deal with the long walls up to the super-structure.
For short walls
Follow the same method but instead of subtracting add two offsets to get the corresponding lengths in-to-in.
2.2CENTRE LINE METHOD
In this method, total length of centre lines of walls, long and short, has to be found out.
Find the total length of centre lines of walls of same type, having same type of foundations and footings and then find the quantities by multiplying the total centre length by the respective breadth and the height.
In this method, the length will remain the same for excavation in foundations, for concrete in foundations, for all footings, and for superstructure (with slight difference when there are cross walls or number of junctions).
This method is quicker but requires special attention and considerations at the junctions, meeting points of partition or cross walls.
For rectangular, circular polygonal (hexagonal, octagonal etc) buildings having no inter or cross walls, this method is quite simple.
For buildings having cross or partition walls, for every junction, half breadth of the respective item or footing is to be deducted from the total centre length.
Thus in the case of a building with one partition wall or cross wall having two junctions, deduct one breadth of the respective item of work from the total centre length.
For buildings having different types of walls, each set of walls shall have to be dealt separately. Find the total centre length of all walls of one type and proceed in the same manner as described above. Similarly find the total centre length of walls of second type and deal this separately, and so on.
Suppose the outer walls (main walls) are of A type and inner cross walls are of B type.
Then all A type walls shall be taken jointly first, and then all B type walls shall be taken together separately.
In such cases, no deduction of any kind need be made for A type walls, but when B type walls are taken, for each junction deduction of half breadth of A type walls (main Walls) shall have to be made from the total centre length of B type walls.
At corners of the building where two walls are meeting, no subtraction or addition is required.
In the figure, the double cross-hatched areas marked P,Q,R, & S come twice, while blank areas, A,B,C, & D do not come at all, but these portions being equal in magnitude, we get the correct quantity.
2.3PARTLY CENTER LINE AND PARTLY CROSS WALL METHOD
This method is adopted when external (i.e., all-round the building) wall is of one thickness and the internal walls having different thicknesses. In such cases, center 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.
2.4Examples on long wall and short wall method and centerline method Example 1
Given the plan of a residential building below,
Lintels over doors and windows are 20cm thick and internal wall are 90cm wide
Figure 2.1: Plan of superstructure of building 1
Figure 2.2: Section S-01 of figure 2.1
Estimate the quantities of the following items of building by longwall short wall method
1.Earthwork in excavation for foundation trenches of 60cm wide
2.Stonework in foundation
3.2cm damp proof course
4.Brick work in superstructure
Calculation of centerline length
Center to center long wall = 10m-2*0.2m= 9.8m
2
Centre to center short wall = 7m-2*0.2m= 6.8m
2
Details of measurement and calculation of quantities
Item no.
Description of items No. of items Dimensions
Quantity
Unity
Explanation
Length Breadth Height
1 Earthwork in excavation for foundation trenches
Long wall 3 10.4 0.6 0.6 11.232 m3 9.8+0.6
Short wall 3 6.2 0.6 0.6 6.696 m3 6.8-0.6
Total earthwork in excavation for foundation trenches 17.928 m3
2 Stonework in foundation
Long wall 3 10.2 0.4 0.6 7.344 m3 9.8+0.4
Short wall 3 6.4 0.4 0.6 4.608 m3 6.8-0.4
Total stonework in excavation 11.952 m3
3 2Cm Damp proof course
Long wall 3 10.2 0.4 12.24 m2 Same as above
Short wall 3 6.4 0.4 7.68 m2
Total DPC 19.92 m2
Total DPC 19.92 m2
4 Brickwork in superstructure
Long wall 3 10 0.2 3.5 21 m3 9.8+0.2
Short wall 3 6.6 0.2 3.5 13.86 m3 6.8-0.2
Total quantity of brickwork in superstructure 34.86 m3
Deduct windows 4 1 0.2 1.2 0.96 m3
Deduct simple door 3 0.9 0.2 2.1 1.134 m3
Deduct double door 1 1.5 0.2 2.1 0.63 m3
Deduct lintel over
windows
4
1.4
0.2
0.2
0.224 m3
1+2*0.2
Deduct lintel over
simple doors
3
1.3
0.2
0.2
0.156 m3
0.9+2*0.2
Deduct Lintel over
double door
1
1.9
0.2
0.2
0.076 m3
1.5+2*0.2
Total deduction 3.18 m3
Net Total brickwork in superstructure 31.68 m3
Example 2
Given the plan of a residential building below, Lintel over doors and windows are 15cm thick Estimate the quantities of the following items of building by centerline method
1.Earthwork in excavation in foundation if the width of excavation is 50cm
2.Stonework in foundation
3.2.5cm damp proof course
4.Brickwork in superstructure 1:6 cement mortar (Lintel over opening are 15cm thick)
Figure 2.3: Plan and section of building 2
Calculation of centerline length
Center to center long wall = 0.2m+ 2m+0.2m+2m+0.2m+ 1m+0.2m+ 2m +0.2m = 7.8m
2 2
Centre to center short wall = 6m-2*0.2m= 5.8m
2
Inter wall 1 = 0.2m+ 2.5m+0.2m = 2.7m
2 2
Inter wall 2 = 0.2m + 2m+0.2m +2m + 0.2m = 4.4m
2 2
Inter wall 3= 0.2m+ 2.5m + 0.2m+1.2m - 0.2m = 3.9m
2 2
Inter wall 4 = 0.2m+ 2m +0.2m = 2.2m
2 2
Inter wall 5 = 0.2m+ 1m +0.2m =1.2m
2 2
Total centerline length= 5.8*3+7.8m*2+2.7m+3.9m+1.2m+2.2m +4.4m= 47.4m with 10 junctions
Details of measurement and calculation of quantities
item no.
Description of items No. of items Dimensions
Quantity
Unity
Explanation
Length Breadth Height
1 Earthwork in excavation
for foundation trenches 1 44.9 0.5 0.6 13.47 m3 47.4-10*0.5/2
2 Stonework in
foundation
1
45.4
0.4
0.6 10.896
m3
47.4-10*0.4/2
3 2Cm Damp proof course 1 45.4 0.4 18.16 m3
Deduct simple door sills 7 0.9 0.2 1.26 m2
Net Total DPC 16.9 m2
4 Brickwork in
superstructure 1:6
cement mortar
1
46.4
0.2
3
27.84
m3
47.4-10*0.2/2
Deduct
Windows 5 0.6 0.2 0.5 0.3 m3
Doors 7 0.9 0.2 2.1 2.646 m3
Lintel over doors 7 1.2 0.2 0.15 0.252 m3 1+2*0.15
Lintel over windows 5 0.9 0.2 0.15 0.135 m3 0.9+2*0.15
Total deduction 3.333 m3
Net Total Brickwork in superstructure 24.507 m3
Note: For building with internal walls centerline method of building estimate is most accurate in calculation of quantity of different items and it is highly recommended.
Example3
Given the plan of superstructure and the section of residential building below
Figure 2.4: Plan of superstructure
Estimate the quantity of the following items
1.Earthwork in excavation in foundation if the width of excavation is 70cm
2.Stonework in foundation
3.Earthwork in backfilling
4.2.5cm damp proof course
5.Brickwork in superstructure 1:6 cement mortar ( Lintel over opening are 20cm thick)
6.Pavement finishing
7.Quantity of R.C.C Work in lintels above opening
8.Inside and outside plastering
Figure 2.5: Section S-01 of Figure 2.4
Calculation of total centerline length
Long wall centerline length = 12m-0.2m = 11.8m Short wall centerline length = 9m -0.2m = 8.8m Inter wall centerline length = 6.8m +0.2m = 7m
Total centerline length = 11.8m*3+8.8m*3+7m = 68.8m with 8 junctions
Details of measurement and calculation of quantities
Item no.
Description of items No. of items Dimensions
Quantity
Unity
Explanation
Length Breadth Height
1 Earthwork in excavation
in foundation
1
66
0.7
0.8
36.96 m3
68.8-8*0.7/2
2 Stonework in
foundation 1st footing
1
66.4
0.6
0.2
7.968 m3
68.8-8*0.6/2
Stonework in
foundation 2nd footing
1
67.2
0.4
0.6
16.128 m3
68.8-8*0.4/2
Total stonework in foundation 24.096 m3
3 Earthwork in backfilling 36.96-24.432 12.864 m3
4 2.5cm damp proof
course
1
67.2
0.4
26.88 m2
5 Brickwork in
superstructure 1:6
cement mortar
1
68
0.2
3
40.8
m3
68.8-8*0.2/2
Deduct windows 4 0.9 0.2 1 0.72 m3
Deduct doors 6 0.9 0.2 2.1 2.268 m3
Deduct Lintels over
windows
4
1.3
0.2
0.2
0.208 m3
0.9+2*0.2
Deduct Lintels over
doors
6
1.3
0.2
0.2
0.312 m3
0.9+2*0.2
Total deduction 3.508 m3
Total net brickwork in superstructure 37.292 m3
6 Pavement finishing
Room1 1 5.4 3.5 18.9 m2
Room2 1 6 3.5 21 m2
Room3 1 1.9 6.8 12.92 m2
Room4 1 2.8 6.8 19.04 m2
Room5 1 4.6 4.9 22.54 m2
Add doors sills 6 0.9 0.2 1.08 m2
Total pavement finishing 95.48 m2
7 Quantity of R.C.C Work in lintels
Deduct Lintels over
windows
4
1.3
0.2
0.2
0.208 m3
0.9+2*0.2
Deduct Lintels over
doors
6
1.3
0.2
0.2
0.312 m3
0.9+2*0.2
Total quantity of R.C.C work 0.52 m3
8 Inside and outside plastering
Room 1 Inside 1 17.8 3 53.4 m2 (5.4+3.5)*2
Room 2 Inside 1 19 3 57 m2 (6+3.5)*2
Room 3 Inside 1 17.4 3 52.2 m2 (1.9+6.8)*2
Room 4 Inside 1 9.6 3 28.8 m2 (2.8+6.8)*2
Room 5 Inside 1 19 3 57 m2 (4.6+4.9)*2
Outside plastering 1 42 3 126 m2 (12+9)*2
Total plastering inside and outside 374.4 m2
Deduct windows 8 0.9 1 7.2 m2 Inside+ outside
Deduct doors 12 0.9 2.1 22.68 m2 Inside+ outside
Total deduction 29.88 m2
Total inside and outside plastering 344.52 m2
CHAPTER THREE : CALCULATION OF QUANTITY DRY OF MATERIALS
6.1BRICK WORK
There two method of determining the number of bricks in a given wall:
1.Wall volume method
For this method you need to know the dimensions for brick used to build wall under estimation, and from these dimension determine the volume of each brick in wall.
Dimensions of wall should also been known and corresponding volume including volume of bricks and jointing mortar.
From the volume of wall deduct the volume of mortar and remain with the net volume of bricks Number of bricks in the wall will be calculated by taking the net volume of bricks divided by the volume of one bricks.
2.Area wall method
If we know how to obtain dimensions / sizes to calculate the area (m2) of a wall (rectangle) we need to be able to convert the ‘m and the m2’ into a quantity of bricks.
The size of a standard brick is shown below; as you can see the height of the brick is 65mm.
So, each brick has a height of 65mm. Then when you bed the brick onto mortar, the height of the brick is raised to 75mm.
Rmk: before starting the estimate we have to know the thickness of the wall as shown below.
EXAMPLE
How many bricks are needed for the following wall?
ANSWER
Step 1 Convert millimeters into meters
Length = 10000mm 1000 = 10m
Height = 2000mm 1000 = 2m
Step 2 Find the area of the wall.
USING THE FORMULA - Length x Height = Area So, 10.000m x 2.000m = 20m2
Step 3 Find the area occupied by the joints.
Rmk: let consider the given front section and the wall thickness of ½ brick thick, then at the end we multiply by two because we have a wall thickness of one brick thick.
For horizontal joints
The number of horizontal joints is equivalent to the number brick layers, so to find this number we divide the height of the wall by the height of brick with bed joint and the horizontal layer.
Joints = 2000 = 2000 = 27 joints
65+10 75
Area of one joint= 10m×0.01m= 0.1 m2
Area of all horizontal joints = 0.1 m2 ×27= 2.7 m2
For vertical joints
The number of vertical joints is equal to the number of bricks per layer minus one the number of vertical joints is equal to the length of the wall dividing by the length of one brick with one joint.
Number of bricks per layer = 10000
215+10
= 45
For this case take the number of joints equal to 45 bricks. The total number of vertical joints is 45×27=1215 joints.
The area of one vertical joint= 0.01×0.065= 0.00065 m2 Area of all vertical joints = 0.00065× 1215= 0.78975 m2 The total area occupied by all joints (horizontal and vertical)
=2.7+0.78975= 3.48975 m2
Step 4 Find the area occupied bricks.
To find the area occupied by bricks, take the total area of the wall minus the area of joints
= 20-3.48975= 16.51025m2
Step 5 Find the number of bricks
To find the number of bricks, take the area occupied by the bricks by the area of one brick =
16.51025
0.215×0.065
= 1181 ππiπππ .
To find the total number of bricks we multiply by two i.e 1181×2= 2362 bricks.
We can even add 2 to 5% for wastage. NB: the quantity of sand and cement will be discussed below.
6.2CONCRETE AND MORTAR WORKS
1.CONCRETE
Note: For 1m3 wet concrete = 1.54m3 dry concrete materials approximately Specific weight of concrete= 1440 kg/m3 (or) 1.44 t/m3
1 bag of cement = 50 Kg
Example 1:- Calculate the Quantity of material for the following items.
a)R.C.C. (1:2:4) for 20m3 of work
b)R.C.C. (1:3:6) for 15m3 of work Solution (a):
Quantity of cement required= 1*1.54*20*1440 = 127 bags
7*50
Quantity of sand required=2*1.54*20= 8.8 m3
7
Quantity of gravel = 4*1.54*20 = 17.6 π3
7
2.MORTAR
Note: For 1m3 wet mortar = 1.33m3 dry mortar materials approximately Specific weight of cement = 1440 kg/m3 (or) 1.44 t/m3
1 bag of cement = 50 Kg
Example 2:- Calculate the quantity of materials for the following items.
a)C.M. (1:4) for 1m3 of work
b)CM (1:6) for 1m3 of work
4
6.3ANALYSIS ON RATES
To analyze something is to break it down into its constituent parts and study each part in detail. Therefore analytical estimating involves the analysis and costing of construction resources to produce an estimate.
2.1Definition of analysis of rate
The production of an estimate normally involves the calculation of unit rates i.e. the cost of an individual measured item for example a square meter of wall plastering, a cubic meter of concrete or a meter of skirting as found in a Bill of Quantities.
Analytical estimating is therefore the most accurate form of estimating as each resource and unit rate is analyzed and costed individually. This form of estimating is used for pricing contracts with bills of quantities, specifications and drawings or where the contractor has measured and prepared their own quantities of work.
Build up unit rate involve:
The determination of rate per unit of a particular item of work, from the cost of quantities of materials, the cost of labour and other miscellaneous petty expenses required for its completion is known as the ANALYSIS OF RATE.
A reasonable profit, usually10% for contractor is also included in the analysis of rate. Rates of materials are usually taken as the rates delivered at the site of work and include the first cost (cost at origin), cost of transport, railway freight if any, taxes, etc. If the materials are to be carried from a distant place, more than 8km, then cost of transport is also added.
The rates of materials and labour vary from place to place and therefore, the rates of different items of work also vary from place to place.
For the purpose of analysis, the details about all the operations involved in carrying out the work should be available, the quantities of materials required and their costs should be known and the number of different categories of labourers required and the capacity of doing work per labourer and their wages per day should be known. These can be known only from experience of practical work.
2.2Purpose of the rate analysis
The costs of materials are taken as delivered at site inclusive of the transport, local taxes and other charges.
Purposes of Analysis of rates are:
To work out the actual cost of per unit of the items.
To work out the economical use of materials and processes in completing the particulars item.
To work out the cost of extra items which are not provided in the contract bond, but are to be done as per the directions of the department
To revise the schedule of rates due to increase in the cost of material and labour or due to change in technique.
2.3Factors affecting rate analysis
In order to determine the rate of a particular item, the factors affecting the rate of that item are studied carefully and then finally a rate is decided for that item. The rates of a particular item of work depend on the following:
Specifications of works and materials, quality of materials, proportion of mortar method of constructional operation, etc.
Quantities of materials and their rate, number of different types of labourer and their rates.
Location of the site of work and its distances from the sources of materials and the rate of transport, availability of water.
Profits and miscellaneous and overhead expenses of contractor.
Overhead costs: Overheads may be defined as the cost of maintaining (running) the contractors organization.
Overhead costs include general office expenses, rents, taxes, supervision and other costs which are indirect expenses and not productive expenses on the job.
The miscellaneous expenses on overheads may be under the following heads:
A.General overheads: Establishment(office staff),Stationary, printing, postages, etc., Travelling expenses, Telephone, Rent and taxes
B.Job overheads: Supervision(Salary of Engineers, Overseers, Supervision, etc), Handling of materials, Repairs, carriage and depreciation of T. and P., Amenities of labour, Workmen’s compensation, insurance, etc., Interest on investment, Losses on advances.
The contactor may be allowed a net profit of 6 to 8%, and the miscellaneous overhead expenses may come to about 5 to 10%. For overhead expenses and contractor’s profit 15% of the actual cost may be reasonable amount but it is usually practice to add 10% for all these under the head profit. For small works overhead cost may be very little. A provision for water charges@ 1.5 % of the total cost is made in the rate.
2.4Method of preparation of rate analysis of work
The analysis of rate is usually worked out for the unit of payment of the particular item of work under two head: Materials and Labour
Unit Rates may be calculated in one of two ways:
•Net Rate – (Excludes Overheads and Profit)
•Gross Rate – (Includes Overheads and Profit)
In our industry most estimators will calculate costs based on net rates. Gross rates are sometimes referred to as all in rates. The Resources which compromise a unit rate are labour, materials and plant.
In the construction industry labour is often employed in two main ways, these are:
1.Direct
Often referred to as ‘cards in’, the employer pays all the costs of employment including for example national insurance and sick pay amongst others.
2.Indirect
These workers are self-employed or referred to in industry as ‘on the lump’ these are often labour only sub-contractors without the normal costs of employment along with the other legal protections such as redundancy, sick pay and minimum notice periods.
Labour may be paid for on an hourly, daily, weekly or piecework basis. Directly employed operatives are usually paid in accordance with a working rule agreement which will specify the rates and allowances to be paid. However, some contractors are trying to move away from the national wage bargaining and introduce local wage rates. Ultimately the actual rates paid for labour will depend on market forces.
2.5Task or Out-Turn Work
Task- the capacity of doing work by an artisan or skilled labour in the form of quantity of work per day is known as the task-work or out- turn of the labour.
The out turn of work per artisan varies to some extent according to the nature, size, height, situation, location etc. In bigger cities where specialized and experienced labour is available the out turn is greater than small towns and country sides.
The following may be taken as the approximate quantity of work or out- turn or task for an average artisan per day (IS 1200)
S/N Particulars of items Quantity per day per mason
1 Brickwork in lime or cement mortar in foundation and plinth 1.25 cum
2 Brickwork in lime or cement mortar in superstructure 1.00 cum
3 Brickwork in mud mortar in foundation and plinth 1.5 cum
4 Brickwork in mud mortar in superstructure 1.25 cum
5 Brickwork in cement or lime mortar in aches 0.55 cum
6 Brickwork in cement or lime mortar in jack arches 0.55 cum
7 Half Brick wall in partition 5.00 sqm
8 Coursed rubble stone masonry in lime or cement mortar
including dressing 0.8 cum
9 Random rubble stone in lime or cement mortar 1.00 cum
10 Ashlar masonry in lime or cement mortar 0.4 cum
11 Stone arch work 0.4 cum
12 Lime concrete in foundation or floor 8.5 cum
13 Lime concrete in roof terracing 6.00 cum
14 Cement concrete 1:2:4 5.00 cum
15 R.B (Reinforced brick) work 1.00 cum
16 R.C.C (Reinforced cement concrete) work 3.00 cum
17 12 mm plastering with cement or lime mortar 8.00 sqm
18 Pointing with cement or lime mortar 10.00 sqm
19 White washing or color washing three coats 70.00 sqm
20 white washing or color washing one coat 200.00 sqm
21 Painting or varnishing doors or windows one coat 25.00 sqm
22 Painting large surface one coat 35.00 sqm
23 2.5 cm C.C floor 7.5 sqm
32 Earthwork in excavation in ordinary soil 3.00 cum
33 Earthwork in excavation in hard soil 2.00 cum
34 Excavation in rock 1.00 cum
35 Sand filling in plinth 4.00 cum
36 Number of bricks laid by a mason in brickwork up to a height of
3 m. 600 bricks
37 Amount of work done by a helper
i)Mix
ii)Deliver brick
iii)Deliver mortar
3 cum
4000 bricks (from 15 m)
5.5 cum
LABOURS AND HELPERS REQUIRED FOR DIFFERENT WORKS (IS 1200)
(A)Earthwork per 28.3 cum
(1)Excavation in foundations, trenches, etc. in ordinary soil including disposal up to 30 m and lift of 1.5 m – 5 excavators and 4 helpers can do 28.3 cum per day.
(2)Refilling excavated earth in foundations, plinth, etc…, including consolidation in 15 cm layers – 3 fillers and 2 helpers can do 28.3 cum per day.
(3)Disposal of surplus earth within a lead of 30 m – 1 helper can do 28.3 cum per day.
(B)Cement concrete work per 2.83 cum
Laying cement concrete – 2 layers, 3 helpers, ¾ water carriers and ¼ Mason can do 2.83 cum per day.
(C)R.C.C Work per 2.83 cum
(1)Laying reinforced concrete – 3 layers, 3 helpers, 1 1/3 water carriers and ½ Mason can do 2.83 cum per day.
(2)Centering and shuttering for flat surfaces – 4 carpenters and 4 helpers can do 9.6 sqm per day.
(3)Reinforcement work for R.C.C – 2 benders can do 1 quintal (100 kg) of steel per day.
(D)Stone work per 2.83 cum
Random rubble masonry – 3 masons, 5 helpers and ¼ water carriers can do 2.83 cum.
(E)Brickwork per 2.83 cum
Brickwork in 1:4 cement mortars in superstructure walls - 2 1/4 Masons, 4 1/2 helpers and ½ water carriers can do 2.83 cum per day.
(F)Wood work
(1)For the frames of doors and windows – 2 carpenters and 1 helper can work 0.18 cum of wood equivalent to 4 door frames 7.5 cm×10cm of 1.2m×2.1m size per day.
(2)For paneled, glazed, shutters – 15 carpenters and 4 helpers can make and fix 4 shutters 40mm thick of size 2m×1.15m per day.
(G)Flooring
4 cm thick cement concrete flooring of 40 sqm require – 5 masons, 7 helpers and 1 water carriers for mixing, laying and finishing.
(H)Finishing
(1)Plastering with any mortar 12mm thick – 3 masons, 3 helpers and 1 water carrier can plaster 40 sqm per day.
(2)White washing or color washing (3 coats) – 1 white washer and 1 helper can do 60 sqm per day.
(3)Painting two coats such as chocolate, red, grey, etc, on wood or steel – 3 painters and 2 helpers can point 10 sqm per day.
2.6Estimating Labour
The labour can be classified into
1)Skilled 1st class
2)Skilled 2nd Class
3)Unskilled
The labour charges can be obtained from the standard schedule of rates 30% of the skilled labour provided in the data may be taken as 1st class, remaining 70% as 2nd class. The rates of materials for Government works are fixed by ANALYSIS OF RATES.
Lead statement: The distance between the source of availability of material and construction site is known as "Lead” and is expressed in Km, the unit of lead is 50m.
The cost of conveyance of material depends on lead. This statement will give the total cost of materials per unit item. It includes first cost, conveyance loading, unloading stacking, charges etc.
Lift: It is the average height through which the earth has to be lifted from source to the place of spreading or heaping. The unit of lift is 2.00m for first lift and one extra lift for every 1.0m. For example when earth is to be lifted for 4.5m, four lifts are to be paid to the contractor.
Ex: If one lift is paid 2000 Rwf how much money to be paid to an excavator who dug 23 m deep?
It is know that the unit of lift is 2m for the first lift and one extra lift every 1 m, so
For 23 m, 23-2=21.This is equivalent to 1 lift corresponding with the first 2 m and 21 lifts corresponding with the last 21 m. The total number of lifts is 21+1= 22 lifts
Amount of money to be paid= 22* 2000= 44,000 Rwf
SOME EXAMPLES ON THE COST BREAK DOWN OF AN ITEM
a)EARTH WORK
Information:
2 people can excavate 1.5 cum per day for ordinary soil,
The soil will be disposed in 5 km from the soil, and the cost per one trip for a truck of 4.5 cum is 30,000
The cost per one excavator per day is 2,000
Analysis:
if 1.5 cum is excavated by 2 people, 1 cum will be done 2
1.5
= 1.34 πππππππ
if the transport cost is 30,000 per 4.5 cum, 1 cum is transported at 30,000 = 6666.7
4.5
The table below shows how the cost break down for one cum of excavation work is done:
S/N ITEMS QUANTITY UNIT RATE AMOUNT
1 Labour 1.34 Person 2,000Rwf 2,680 Rwf
2 Transport 1 Cum 6666.7 Rwf 6666.7 Rwf
TOTAL 9346.7 Rwf
Add 13% of TOTAL provided for profit and overheads 1215.071 Rwf
RATE PER CUM OF EXCAVATION WORK 10561.771Rwf
b)RCC FOR COLUMNS
Information:
Form working: 2 carpenters and 2 helpers can work on 4 columns
Concreting: 2 masons and 2 helpers are able of finishing 2 columns per day
Column dimension (20×20×300 cm)
Mix ratio (1:1.5:3)
Carpenter salary per day=5,000 Rwf
Mason salary per day= 4,000 Rwf
Helper salary per day= 1,800 Rwf
Cost of cement including transport =10,500 Rwf per bag
Cost of sand per truck including transport=45,000 Rwf per truck
Cost of gravel per truck including transport=80,000 Rwf per truck
Longitudinal bars of ΓΈ12 at 10,000 Rwf per piece of 12m and stirrups of ΓΈ8 at 6,000 Rwf per piece of 12 m
Spacing of stirrups= 20 cm
Hooks = 9 ΓΈ
Analysis:
4 columns are equivalent to 0.2*0.2*3*4= 0.48 cum
Form works: 4 columns (0.48 cum) 2 carpenters
1 cum 2 = 4.17 carpenters
0.48
1 cum 2
0.48
= 4.17 helpers
Concreting: 2 columns (0.24 cum) 2 masons
1 cum 2 = 8.34 masons
0.24
1 cum 2 =8.34 helpers
0.24
Quantity of cement per cum : 1*1.52*1*1440 = 7.96 ππππ
5.5*50
Quantity of sand per cum : 1*1.5*1.52 = 0.416 ππ’π
5.5
Quantity of gravel per cum : 1*3*1.52 = 0.83 ππ’π
5.5
Length of 1 longitudinal in column = 3m + 2 x 9 x 0.012 – 2 x 0.02.5 = 3.166
1 column (0.12 cum) 4 long bars of each 3.166 m= 12.664 m
Length of longitudinal bars per cum: 12.664 = 105.5 m
0.12
Number of bar pieces per cum: 12m 1 piece
105.5 105.5= 8.8 pieces
12
One long stirrup: (20cm-2*2.5cm)*4+ 9ΓΈ=(20-5)*4+9*0.8= 67.2 cm = 0.672 m
Number of stirrups pieces per column: 3 +1= 16
0.2
length of stirrups per column (0.12 cum): 16*0.672= 10.752 m
length of stirrups per cum: 10.752 = 89.6 π
0.12
number of stirrups pieces per cum: 89.6 = 7.47 πiππππ
12
one truck (4.5 cum) of sand 45,000 Rwf
1 cum 45,000= 10,000 Rwf
4.5
One truck (4.5 cum) of gravel 80,000 Rwf
1 cum 80,000= 17777.78 Rwf
4.5
The table below shows how the cost break down for one cum of excavation work is done:
S/N ITEMS QUANTITY UNIT RATE
(Rwf) AMOUNT(Rwf)
1 Form works: Carpenters
helpers
4.17
4.17
Person Person
5,000
1,800
20,850
7,506
2 Concreting Masons Helpers
8.34
8.34
Person Person
4,000
1,800
33,360
15,012
3 Cement 7.96 Bags 10,500 83,580
4 Sand 0.414 Cum 10,000 4,140
5 Gravel 0.83 Cum 17,777.78 14,555.5574
6 Reinforcement bars
Γ8 Γ12
7.47
8.8
Piece Piece
6,000
10,000
44820
88000
TOTAL1 308,095.5574
Add 13% of TOTAL 1 provided for profit and overheads 40052.682462
RATE PER CUM OF RCC FOR COLUMN 348148.24
Exercises
1.Calculate the quantity of dry materials (cement, sand and coarse aggregates) required for a
R.C.C roof slab 12mm thick for a room having internal dimension of 4.5m length to 3.5m width. The bearing of slab is 15cm and the materials are in ration 1:2:4
2.Calculate the cost per meter for laying 100mm flexible jointed PVC drain pipes in runs not exceeding 500m
Labour
0.14hrs/m for 100mm diameter flexible jointed PVC drainage. All in rate 8500Rwf per hour plus 2600 Rwf/ hrs enhancement for additional skill and responsibility
Materials
100mm diameter flexible jointed PVC costs 18,000 Rwf each and are 6m long.
Flexible joints cost 4,340 Rwf each assumes one joint for every 2m of pipes for PVC drainage
Waste allow 15% of overall cost for wastage on pipes and couplings
3.Calculate the cost of mixing 1m3 of grade 15 cement concrete on site using the following information. To produce 1m3 of grade 15 cement concrete requires:
Materials required
250kg of cement at cost of 84,000 Rwf per tone
600kg of sand at cost of 10,500 Rwf per tone
1200kg of aggregates at cost of 9450 Rwf per tine Add 5% of wastage of materials
Labour
Concrete mixer all in rate 5000 Rwf per hour with the output of 2m3 per hour
Labour rate of 7560 Rwf per hour with labour output of 0.5m3 per hour
CHAPTER 4 VALUATION IN ESTIMATING AND COSTING
•Valuation: is the technique of estimating and determining the fair price or value of a property such as a building, a factory or other engineering structures of various types, land, etc. By valuation, the present value of a property is determined. The value of a property depends on its structure, life, maintenance, location, bank interest, legal control, etc. Cost means original cost of construction of purchase, while value means the present value (saleable value) which may be higher or lower than the cost.
•Main purposes of valuation:
Buying or selling property
Taxation
Rent function
Security of loans or mortgage
Insurance
etc
•Depreciation: is the gradual exhaustion of the usefulness of a property. It is a decrease or loss in the value of a property due to structural deterioration use, life wear and tear, etc. A certain percentage of the total cost may be allowed as depreciation to determine its present value. Usually, the percentage rate of depreciation is less at the beginning and gradually increase during later years.
D=Depreciation value
P= the cost at present market rate
rd= the fixed percentage of depreciation (rate of depreciation)
n=number of years the building has been constructed
Annual depreciation (D)=
•Gross income: is the total income including all receipts from various sources. The outgoings, operational and other expenses are not deducted.
• Net income or net return: is the saving or the amounts left after deducting all outgoings, operational and other expenses from the gross income or total receipt.
Net income = Gross income – outgoings.
•Outgoings: outgoings include taxes, repair fees, sinking fund, loss of rent, miscellaneous (e.g. electrical charges), etc.
•Sinking fund: the fund which is gradually accumulated by way of periodic on annual deposit for the replacement of the building or structure at the end of its useful life.
S= total amount of sinking fund to be accumulated
n= number of years required to accumulate the sinking fund
i= rate of interest in decimal (e.g. 5%=0,05)
I=annual installment required
•Scrap value: is the value of dismantled materials. Example for a building when the life is over at the end of its utility period, the dismantled materials as steel, bricks, timber, etc. will fetch a certain amount which is the scrap value of the building. The scrap value of a building may be about 10% of its total cost of construction. The cost of dismantling and removal of the rubbish material is deducted from the total receipt from the sale of the useable materials to get the scrap value.
•Market value: the market value of a property is the amount that can be obtained at any particular time from the open market if the property is put for sale.
•Book value: is the amount shown in the account after allowing necessary depreciations. The book value of a property at a particular year is the original cost minus the amount of depreciation up to previous year.
Annuity: is the annual periodic payments of the capital amount invested by a party
These annual payments are either paid at the end of the year or at the beginning of the year, usually for a specified number of years.
•Obsolescence: is the fact that the value of property or structure becomes less as it is becoming out of date in style, in structure, in design, etc. an old dated building with massive walls, arrangements of rooms not suited in present days and for similar reasons, becomes obsolete even if it is maintained in a very good condition, and its value becomes less due to obsolescence.
•Capital cost: is the total cost of construction including land, or the original total amount required to possess a property.
•Capitalized value of a property: is the amount of money whose annual interest at the highest prevailing rate of interest will be equal to the net income.
•Rate of interest = income/sale price.
•Year’s purchase (Y.P): is the capital sum required to be invested in order to receive an annuity of Rwf 1 at a certain rate of interest. Y.P = 1/i
CHAPTER 5 : TENDER IN ESTIMATING AND COSTING
•Tendering is the administrative procedure of sending out drawing and bills of quantities or specifications to contractors for them to state their prices for all the items of one contract. Besides the contractors price, other considerations include his competence and financial standing.
•Types of tendering:
Open tendering: an advert is placed in the press to invite any firm that wishes to do so to submit a tender for a project, the advert will give a brief description of the works to be undertaken. Interested firms apply for the tender document, collect them, upon payment of money deposit which is usually non-refundable,
This deposit covers the cost of documents and discourages the non-serious bidders.
Selective tendering: the procedure consists of selecting a limited number of firms and invite them to submit tenders. A short list of between 5 - 8 competent contractors is usually drawn up with one or two reserve firms to replace any on the original list who fails to accept the invitation to tender.
Negotiation: the client has a satisfactory association with a particular firm and is prepared to give them the contract on the recommendation that they are competent and their price is reasonable.
Stages in tendering:
Preparation of tender documents;
Tender documents;
Invitation to tender;
Collection of tender documents;
Preparation of bid documents;
Submission of bid documents;
Opening of bids.
Factors affecting tender price:
Action of tendering;
Market condition;
Availability of materials;
Availability of labour;
Transportation (farther the site id from town, more expensive will be the construction cost);
location (standard of living);
Location of site (road access, water & electricity, security measures, etc);
Site condition (the nature of ground);
Time consideration;
Total height of building;
Class of contractors (The larger the firm, the higher their cost: permanents staffs, board of directors, level of profit,…);
Type of client (some clients have methods to be taken into consideration while estimating construction cost);
Type of consultants (some architect are very difficult to work with, many variations, delays are frequent);
Types of tendering (open tendering generally brings lower price
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