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CC301 QUANTITY MEASUREMENT
Chapter 1: Preliminary Estimation Methods
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1.1. Preliminary Estimation Method • Definition & importance of Preliminary Estimation Method What?
Why?
The Preliminary Estimation Methods is a technique used to estimate the project cost for budgetary purposes. The function of preliminary estimate is prepared is to forecast the likely cost of any future project before details design is prepared. This preliminary estimate will inform the client about their commitments (as the project owner) before the design works is undertaken (Ibrahim, 2006)
Kaedah Anggaran awal adalah teknik yang digunakan untuk membuat anggaran kos projek untuk tujuan belanjawan. Fungsi anggaran awal disediakan adalah untuk meramal kos yang mungkin apa-apa projek masa depan sebelum reka bentuk butirbutir disediakan.
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1.1. Preliminary Estimation Methods Three(3) methods used known as :
Unit valuation method. Floor area method. Cubic content method.
• Unit kaedah penilaian. • Kaedah keluasan lantai. • Kaedah kandungan padu.
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1.1. Preliminary Estimation Methods • Unit Valuation Method @ Unit Kaedah Penilaian $The simplest method to get rough project cost. $ The project cost is derived from the functional design capacity of sample projects. $ To get estimated cost for the proposed project, unit cost is multiplied with the design capacity of the proposed project.
Kaedah yang paling mudah untuk mendapatkan kos projek kasar. Kos projek yang berasal dari kapasiti reka bentuk fungsian bagi projek sampel. Untuk mendapatkan anggaran kos bagi projek yang dicadangkan, kos unit didarabkan dengan kapasiti reka bentuk projek yang dicadangkan.
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1.1. Preliminary Estimation Methods • Unit Valuation Method Example of Unit Design Capacity or Accommodation Unit
Project
Function
Unit for design capacity
Hospital
To provide bed for patients
Bed
Polytechnic
To provide semi-professional training in Technical and Vocational Education sector
Student
School
To provide education for students
Student
Hostel
To provide temporary accommodation for student
Bed
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Exercise 1 Let say, polytechnic A was built in 2006 with cost of RM 350,000,000.00 with design capacity of 4200. Find : a) Unit Cost of Polytechnic A b) Total estimated cost for polytechnic B.
Project
Design Capacity (Students)
Project Cost (RM)
Unit Cost (RM)
Polytechnic A
4,200
350 mil
?
Polytechnic B
6,000
?
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1.1. Preliminary Estimation Methods • Unit Valuation Method Example of Calculation Project
Design Capacity (Students)
Project Cost (RM)
Unit Cost (RM)
Polytechnic A
2,500
250 mil
100,000.00
Polytechnic B
3,000
360 mil
120,000.00
Polytechnic C
4,200
630 mil
150,000.00
Hence, it can be said that the unit cost of a polytechnic is about RM 123,333.33 per student ROUND UP TO RM124,000.00 If new polytechnic to be built with the capacity of 5,000 student, roughly the estimated cost will be RM620mil. Calculation: 5,000 students x RM124,000.00 = RM620,000,000
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1.1. Preliminary Estimation Methods • Unit Valuation Method… further explanation This method is normally applied when a client requires a preliminary estimate for a building project based on the number of persons or units of accommodation in the proposed project. The unit method of approximate estimate seeks to allocate a cost to each accommodation unit of the particular building, based on persons, seats, beds, car spaces or etc. The total estimated cost of the proposed building is then determine by multiplying the total number of units in the building by the unit rate. Thus the mathematical process in very simple but the cost computation of a single unit is extremely difficult. The unit rate is normally obtained by a careful analysis of a unit costs of recently completed buildings of the same type; allowance for cost differences are made in respect of the variations in site conditions, design, form of construction and materials used. Variation in rates stemming from differences in design and constructional methods are difficult to assess as there are normally insufficient information available to make a realistic assessment. Hence although the method has the great merit of speed of application, it suffers from the major disadvantage of lack of precision and at best can only be a rather blunt tool for establishing general guidelines, more particularly for budgetary estimating on a rolling programme covering a three to five-year period ahead. Ostwald (2001) has stated that the main weakness of the method lies in its lack of precision, the difficulty of making allowance for a whole range of factors, from shape and size of building to constructional methods, materials, finishing, and fittings and it is not sufficiently accurate for the majority of purposes. This method may serve a limited number of uses such as establishing an overall target for a cost plan or calculating a sum for investment purposes, in cases where the project owner or his professional advisers have considerable experience of the construction and cost of similar buildings, such as hospitals and schools. Source: Ibrahim (2006)
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1.1. Preliminary Estimation Methods • Floor Area Method $
The construction cost base is derived from the cost per square meter of sample projects.
$
To get estimated cost for the proposed project, unit rate (in RM/m2) should be multiplied with the total gross floor area (GFA) of the proposed project.
$
To get more accurate estimation, project components should be detailed out into blocks and estimated cost calculation should be based on cost per square meter of the construction for the similar block. Using this approach, cost derived is only the building construction cost and other costs (preliminary, piling, mechanical & electrical works, external works and contribution to Local Authority) should be added separately to get more accurate estimates.
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1.1. Preliminary Estimation Methods • Floor Area Method Measuring From Drawing 5100
Gross Floor Area = 20.15m2
3950
5100 and 3950 is measured using external dimension (outside of enclosing walls)
Enclosing wall
Enclosing wall Internal Dimension Centre Dimension External Dimension
Floor
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1.1. Preliminary Estimation Methods • Floor Area Method Variations in GFA definition The gross floor area of all floors(GFA) measured to the outside of containing walls. (Pratt 2004) • …total floor area of the building on all floors is measured between the internal faces of the enclosing external walls, and it includes internal walls, partitions, columns, stairs, chimney breasts, lift shafts, corridors and the like. (Ibrahim, 2006) • The floor Area shall mean the Gross Floor Area of all enclosed spaces fulfilling the functional requirements of the building measured flat on plan to the internal face of the enclosing walls (PWD notes for ATDA format)
Conclusion: Both approaches can be applied. However, consideration must be given if PWD ATDA is used to get the unit rate, then GFA of the proposed project must be defined as area of all enclosed spaces fulfilling the functional requirements of the building measured flat on plan to the internal face of the enclosing walls
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1.1. Preliminary Estimation Methods • Floor Area Method There are TWO(2) ways of getting gross floor area (GFA) of a building: 1. Measuring the gross floor area from the concept drawing (if applicable); 2. From Schedule of Accommodation (SOA) of the proposed project. The common way of getting accurate cost per square meter basis is from As Tendered Detailed Abstract (ATDA) of previous projects.
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1.1. Preliminary Estimation Methods • Floor Area Method How to get GFA from drawing?
To get gross floor area from the concept drawing: The area of all floors measured to the outside of enclosing walls. (Length x width) and must be in meter unit 5100
Gross Floor Area = 20.15m2
3950
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1.1. Preliminary Estimation Methods • Floor Area Method GFA for area without wall or half wall For area with no wall or half wall, only half of its Gross Floor Area (GFA) should be considered for cost calculation if the unit rate is based on a lump sum rate of a building. In this example, GFA to be considered for cost calculation purpose is only 2 m2 (half from its actual GFA = 4m2).
2000
GFA = 4m2 2000
However, if unit rate of similar area (gazebo for instant) is available, then the actual GFA should be used.
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1.1. Preliminary Estimation Methods • Floor Area Method Schedule of Accommodation (SOA) Size (ft)
Gross Floor Area (ft2)
Living Room
22' x 20'
440
40.88
Master Bedroom (inc toilet)
20' x 16'
320
29.73
Room 1 (inc toilet)
16' x 16'
256
23.78
Room 2 (inc toilet)
16' x 16'
256
23.78
Room 3 (inc toilet)
16' x 16'
256
23.78
Room 4 (inc toilet)
16' x 16'
256
23.78
Maid's Room
12' x 12'
144
13.38
8' x 8'
64
5.95
Kitchen
12' x 12'
144
13.38
Dining Area
12' x 12'
144
13.38
Family Area
12' x 12'
144
13.38
8' x 8'
64
5.95
22' x 22'
484
44.96
2,972.00
276.10
Area
Common Toilet
Store Covered Parking Area
Total Gross Floor Area
Gross Floor Area (m2)
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1.1. Preliminary Estimation Methods • Floor Area Method Example 1 Project
GFA (m2)
Project Cost (RM)
Unit Rate (RM/m2)
Polytechnic A
90,000
300 mil
3,333.33
Polytechnic B
75,000
250 mil
3,333.33
Polytechnic C
60,000
200 mil
3,333.33
Hence, it can be said that the unit rate of a polytechnic is about RM3,400 per m2. If new polytechnic to be built with the GFA of 100,000m2, roughly the estimated cost will be RM340mil. Calculation: 100,000m2 x RM3,400 = RM340,000,000.00
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1.1. Preliminary Estimation Methods • Floor Area Method Example 2 Area
GFA (m2)
Unit Rate (RM/m2)
Area with full wall
231.14
1,000
231,140.00
Area without wall
44.96
1,000
22,480.00
Total Estimated Cost
Total Cost (RM)
253,620.00 44.96/2 x 1,000
Example of 3 Area
GFA (m2)
Unit Rate (RM/m2)
Area with full wall
231.14
1,000
231,140.00
Area without wall
44.96
500
22,480.00
Total Estimated Cost
44.96 x 500
Total Cost (RM)
253,620.00
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1.1. Preliminary Estimation Methods • Floor Area Method … further explanation In this method the total floor area of the building on all floors is measured between the internal faces of the enclosing external walls, and it includes internal walls, partitions, columns, stairs, chimney breasts, lift shafts, corridors and the like. Also included are lift plant, tank rooms and the like above the main roof slab. Sloping surfaces such as staircases, galleries, tiered terrace, and the like are measured flat on plan. A unit rate is then calculated per square metre of floor area and the probable total cost of the building is obtained by multiplying the total floor area by the calculated unit rate. Where the building varies substantially in constructional methods or in quality or finish in different parts of the building, it will probably be advisable to separate the floor areas to enable different unit rates to be applied to the separate parts. Consideration must also be given to varying storey heights in assessing unit rate and when extracting rates from cost analyses. As with the cube method, special items such as piling, heating, and lift installations are normally covered by lump sums which are added to the overall cost calculated on a floor area basis. The specialist lump sums may be derived from quotations obtained from specialist or be based on information arising from previous contracts. The estimating cost of external works is usually based on priced approximately quantities. This is popular method of approximate estimating, as it is comparatively easy to calculate the floor area of a building and the costs are expressed in a way which is fairly readily understood by a building client. Furthermore, most published cost data is expressed in this form. It has advantages over the cube method as the majority of items with a cost impact are related more to floor area than to volume and it is therefore easier to adjust for varying storey heights. Nevertheless, it has a number of inherent weaknesses and, in particular, it cannot directly take account of changes in plan shape or total height of the building. Similarly, difficulties are experienced in building up unit rates from known rates for existing buildings because of the need to make allowance for a number of variable including site conditions, constructional methods, materials, quality of finishing and number and quality of fittings (Pratt, 2004). Source: Ibrahim (2006)
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1.1. Preliminary Estimation Methods • Cubic Content Method $ The construction cost base is derived from the cost per cubic meter of sample projects. $ To get estimated cost for the proposed project, unit rate (in m3) is multiplied with the total volume of the proposed project. $ As described before, floor area method does not consider the height of a particular building. For building with height more than standard building height (2.5 m – 3.0 m), the volume of the building should be considered, hence building height must be calculated. Examples of building that should use this method are hall, garage, factory, warehouse, workshop, store, canteen, lecture theatre and cinema.
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1.1. Preliminary Estimation Methods • Cubic Content Method How to get Volume of a building? Volume = GFA x Building Height To get GFA for this method, the same technique of getting GFA for Floor Area Method should be applied. However, Building Height is determined according to the types of roof Pitch (Full pitch, half pitch and butterfly)
Roof
Flat with parapet wall Flat Flat with without parapet wall
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1.1. Preliminary Estimation Methods • Cubic Content Method How to get Building Height? Pitch Roof (Full & Half) r
b
Full Pitch Building Height = b + ½ r
r
b
Half Pitch Credit: http://www.tpub.com/
Building Height = b + ½ r
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1.1. Preliminary Estimation Methods • Cubic Content Method How to get Building Height? Pitch Roof (Butterfly)
r
b
Butterfly Building Height = b + ½ r
Credit: agreenliving.org
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1.1. Preliminary Estimation Methods • Cubic Content Method How to get Building Height? Flat roof with parapet wall
p
b
With parapet wall Building Height = b + p
Credit: Chief Architect Software
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1.1. Preliminary Estimation Methods • Cubic Content Method How to get Building Height? Flat roof without parapet wall
b
Without parapet wall Building Height = b + 0.6 m Credit: Chief Architect Software
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1.1. Preliminary Estimation Methods • Cubic Content Method Example 1 Project
Volume (m3)
Project Cost (RM)
Unit Rate (RM/m3)
Warehouse A
4,500
170,000
37.78
Warehouse B
6,000
215,000
35.83
Warehouse C
8,400
300,000
35.71
Hence, it can be said that the unit rate (RM/m3) of a polytechnic is about RM37. If new warehouse to be built with the GFA of 1,000m2, and height of 7m, roughly the estimated cost will be RM259,000. Calculation: 1,000m2 x 7m x RM37 = RM259,000.
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1.1. Preliminary Estimation Methods • Comparison of the methods Advantages & Disadvantages of Unit Valuation Estimation Method
Advantages
Disadvantages
1.The most easiest method so that less time consuming for the estimator 2.The method only required two(2) information to be used namely as design capacity of the proposed building and total project costs for the similar projects (previous projects). 3.The cost estimated come out in one lump sum figure and simpler for client for budgetary purposes 4.The cost reflects capital expenditure required to serve a unit of its function. eg: To train one student in polytechnic, it needs RM105,000 capital cost.
1.The estimation is so rough and less accurate. 2.The accuracy of the estimate is highly dependent on the similarity of the project nature between proposed project and sample projects. If this estimated cost to be maintained, it will limited the creativity of the design team. 3.Project will be executed in its traditional way, so it will limit the innovation and improvement.
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1.1. Preliminary Estimation Methods • Comparison of the methods Advantages & Disadvantages of Floor Area Estimation Method Disadvantages Advantages 1.The calculation only needs total gross floor area of the proposed building and previous data of the price/m2 for the similar nature of projects. The calculation is straight forward and less time consuming. 2.Using PDA format, the cost derived is detailed into various item such as preliminary, piling, building works, mechanical & electrical works, external works and contribution to Local Authority. Hence, the estimation seems to be more accurate compared to Unit Valuation Method. 3.Client can visualize the impact of gross floor area to the building cost, so client can revisit the needs of floor area according to functional requirements.
1.The method does not consider the height of the building. For building that does not designed according to the standard height, the accuracy of estimated cost can be questionable. 2.The accuracy of the estimated cost is highly dependent on the sample projects (previous projects). The more similarity of the sample projects to the proposed project, the more accurate the estimating will be. Besides that, the sample’s location and year of construction will also effects the accuracy of cost estimation.
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1.1. Preliminary Estimation Methods • Comparison of the methods Advantages & Disadvantages of Cubic Content Method
Disadvantages Advantages 1.The estimation is more accurate compared to the Unit Valuation Method and Floor Area Method 2.The calculation is straight forward and less time consuming if the gross floor area and height of proposed buildings are given 3.Can be used at any building at any floor height. It is very useful in estimating buildings cost for building where height is not according to the standard provision by Building by Law (e.g. Single story house with 4.25 m floor to ceiling height)
1.Cannot be done if the designer cannot specific the building height at the time of estimation. 2.Client difficult to visualize the size of a building if the costing is given in cubic unit 3.Difficult to get cost data for cubic unit. Most of the cost data come in area unit.
