- Three methods of approximate estimating
Accurate estimation helps project managers and clients to efficiently plan on where and how to get and utilize the resources needed to complete the project within the planned time and budget (Ji, et al., 2019). Some of the methods used in approximate estimating of building or construction projects are discussed below
- Analytical, deterministic or bottom-up estimating
This method involves identifying each separate activity that is needed to complete the project, breaking down these activities into smaller ones (lowest level of detail possible) and approximating the resources (financial, materials, equipment and labour), time and cost needed to complete each of these sub-activities. The project’s detailed estimate is them determined by adding up the activity totals. This method of approximate estimating should be used when the fine details of the project components and/or programme are known and well defined. This method may consume more time to complete but it is more accurate than comparative or parametric estimating.
- Analogous, top-down or comparative estimating
This method involves comparing known measures of resources and time that were used or needed to complete similar past or completed activities or project with those of the current project and use expert judgement to estimate the cost of the project. The method relies more on past experience in lieu of opinion but for it to be useful, there has to be definite similarity between the past and current projects that are being compared. For this method to be used, adequate information of the past project should be available. This information is then scaled down or up so as to meet the needs or description of the current project that is being estimated (2020ProjectManagement, 2020). This technique should be used when the information available about the project is limited hence its estimation is less accurate and less reliable.
- Statistical modelling or parametric estimating
This method involves analysis of technical, statistical, cost and programmatic data so as to determine the drivers or factors that influence cost and use them to develop cost models. The method develops the correlation between manpower and cost information with factors or constraints that describe the activity or task to be costed. In the process, a series of formulae or equations, referred to as cost estimation relationships (CERS), are drawn up and used to create outputs of cost for various components of the estimate. This method usually uses linear or non-linear (regression) analysis to establish the best algorithms for each of the cost models (Varghese and Kanchana, 2015). Parametric estimating method uses defined parameters that can be used to measure the project, such as cost or time that is needed to complete a particular deliverable of the project. This process is repeated for the different types of project deliverables and multiplied by the quantity of all the parameters needed to achieve the requirements of the project. For this technique to be used, it requires a significant amount of data about the project and its cost drivers.
- Suitable form of tendering procedure
The form of tendering procedure plays a key role in successful completion of construction projects (Laryea, 2017). The project in this report involves construction of a two bedroom bungalow in Essex. The most suitable form of tendering procedure for this project is single-stage selective (competitive) tendering. This is a more radical tendering procedure than the other traditional methods. In this method, the client or employer identifies prospective competent contractors and issues them with an invitation to tender. The client can select the prospective contractors on advice from his/her professional team, including the consultant, quantity surveyor, architect or engineer, or from his/her own list of preferences based on referrals or having worked with them in the past. The preferred contractors must be suitable for a contract of that complexity, nature and size. The invitation to tender issued to prospective contractors contains full tender documents with all the necessary information of the project, such as relevant drawings, the scope of work, design of the project and bill of quantities. This information helps the contractors to understand the actual needs of the client and appreciate the levels of responsibilities of each party.
After preparing the tenders, the prospective contractors return them to the client. The client analyzes and compares the tenders together with his professional team and then selects the preferred tenderer. The commonly used criteria used to select the preferred contractor include: quoted contract price, past experience of similar projects, technical capacity (availability of equipment and technical staff), track record and reputation. The client then starts negotiating with the preferred contractor about the final price of the project before the contract is awarded. There must be a mutual agreement between the client and contractor before the contract is awarded and signed by the two parties. The method is applicable in contracts where all the necessary information is available to determine the realistic price of the project.
Some of the key advantages of single-stage selecting tendering procedure are: saves time, saves tendering costs, and bids are only received from capable contractors. Disadvantages of this tendering procedure include: there is less competition compared to open tendering, and it does not give a chance for new contractors who may be more capable of doing the job than the preferred contractors. With single-stage selecting tendering, clients feel more confidence that the successful contractor will be able to meet their needs.
Use of single-stage selective tendering procedure is becoming more common in the construction market due to greater certainty of the project’s final price and faster decision making, which are beneficial to both the client and the contractor. In single-stage selective tendering, the process is more simplified because a completed design is provided to the preferred contractors who are asked to bid for the project. Cost risk management is one of the main factors that are driving use of single-stage selective tendering. In this method, there is a minimal chance of contractors varying the price by a big margin or making claims since their bids are based on the detailed completed building design. Additionally, all the potential contractors prepare bids using a single source of tender documents.
In this scenario, the detailed design of the building has already been completed and tender documents prepared. The next step is for the client to identify the most suitable or competent contractor to actualize the project. It means that the client has already specified his needs and wants to involve the contractor in construction activities only. Single-stage selective tendering process will enable the client to select qualified contractors with the required experience, resources (financial, equipment and technical) and track record to complete the project. The procedure clearly allocates risk to each party and also speeds up the procurement process. This means that the project will start more quickly and be completed within shorter timeframes thus reducing timing and cost risks than when other tendering procedures were used, such as open tendering or two-stage tendering.
- Suitable procedure to vet a contractor
Selection of a contractor is a very crucial process in ensuring successful implementation of any construction project. Therefore it is important to vet the contractor before awarding the tender. The vetting process involves performing a background check of the prospective contractor. As the client’s architect, vetting the contractor would involve use of the criteria below
Past and current performance: this information gives an idea of the type of projects that the contractor has been involved with in the past. Some projects are best done by contractors who have experience in executing similar projects (Belek, 2017). Generally, it is recommended to select a contractor who has completed similar projects before because they are more experienced on how to manage issues, such as complexity, resource management or disputes.
Workload: it is important to check the current and future workload of the contractor. This is so as to ensure that the contractor will give adequate attention to the project. Failure to allocate adequate attention, employees, equipment and other resources to the project can compromise the quality and speed of the project. The current workload of the contractor should not hinder project implementation.
Personnel: the contractor should have qualified employees with relevant academic qualifications (knowledge) and experience to complete the work. It is important to know the number of full-time, part-time, contract and casual employees. Where necessary, some employees should be licensed professionals and the workers should have the right tools for the job. The workloads for the employees must also be reasonable.
Technical capacity: besides qualified personnel, the contractor selected should have the required equipment and machinery to complete the project. The equipment can either be owned or leased, with proof (legal documents) to show the same.
Financial capacity: the contractor should also have adequate financial resources to start and complete the work. The contractor should have the financial capacity to pay staffs, lease equipment and purchase some materials without a struggle. This can be known by requesting for the contractor’s financial statements for at least two years, total sales or revenue and annual volume. Indicators such as declining income, big debts and poor cash flow are red flags.
Accreditation and registration: the contractor selected should be accredited by the relevant government agencies and be in possessing of legal, valid and up-to-date documents, such as registration certificates and applicable practicing licenses.
Safety practices: this involves checking various measures that the contractor has put in place or systems they use to ensure safety of their employees and visitors on site. Some of the key items to look for include: training of employees on occupational safety and health practices, availability of personal protective equipment, insurance policies, first aid and emergency response practices.
Quality control process: the contractor should have a system or practices for guaranteeing quality work. This should include practices (such as tests) to ensure that only quality materials are used and close supervision by qualified professionals to ensure high quality workmanship.
Contact past clients or references: it is also important to hear from past clients of the contractor so as to know the experience they had and how the contractor handles issues should something happen not as expected.
Others: it is also important to find out on other issues such as lawsuits, bankruptcies, litigations, complaints and disputes that the contractor has been involved in and how they handled them. This helps to understand the level of professionalism of the contractor and how they handle issues when they arise.
The vetting process can also be done by creating a pre-qualification questionnaire or contractor vetting form and sending it to the prospective contractor for filling, or conducting an interview with the contractor’s representative.
Question 2
- Take off and bill of quantities
The unpriced bill of quantities for the building is as provided below
| ITEM | DESCRIPTION | UNIT | QUANTITY | RATE | AMOUNT |
| EARTHWORKS AND EXCAVATIONS | |||||
| Provide all materials and construct a machine cut dressed 2.5m high wall/fence around the boundary of the plot | M2 | 375 | |||
| Excavate top soil of the site average 200mm deep to remove top soil and cart and deposit 100m away and later spread and level on site as directed | M2 | 178 | |||
| Excavate to reduce levels starting from stripped level and column pits not exceeding 1.5m deep | M3 | 3.35 | |||
| Trim and prepare bottoms of excavations to receive blinding | M2 | 22.5 | |||
| Remove surplus excavated material and cart away | M3 | 18.2 | |||
| Return fill and compact selected excavated material around foundations | M3 | 12.6 | |||
| Fillings | |||||
| Supply and spread approved murram fillings to make up levels and compact well in 150mm thick layers | M3 | 27 | |||
| Supply 300mm thick approved hardcore filling, spread, level and compact well in 150mm thick layers to receive concrete surface bed | M2 | 178 | |||
| Level and blind surface of hardcore with 50mm quarry duct to receive concrete surface bed | M2 | 178 | |||
| Provide and apply approved anti-termite treatment to the surface of blinded hardcore and surrounding areas in accordance with the manufacturer’s instructions | M2 | 178 | |||
| Mass concrete | |||||
| Blinding: provide all materials, mix and place 50mm thick concrete grade C20/25 (1:3:6) for blinding under strip foundations | M2 | 22 | |||
| Footing: provide all materials, mix, place, vibrate and compact concrete grade C30 (1:1.5:3) | M3 | 3.35 | |||
| Ground floor slab: provide all materials, mix, place, vibrate and compact 125mm thick concrete grade C25 (1:1.5:3) for ground slab | M2 | 178 | |||
| Sawn formwork | |||||
| Provide and fix sawn formwork to sides of strip foundations | M2 | 99 | |||
| Provide and fix shuttering and formwork, including propping, strutting and striking, on sides of ground slab | M2 | 59 | |||
| Reinforcement | |||||
| Provide fabric mesh reinforcement no. A142 mesh size 150 x 150mm (BRC) weighing 2.22kg/m2 and all other materials needed, including bends, tying wires and spacer blocks on floor slab. | M2 | 178 | |||
| Provide deformed high yield steel Y12 bars | Kg | 88 | |||
| Damp-proof course | |||||
| Provide polythene damp-proof membrane, gauge 1000mm laid over hardcore with 300mm welted lap | M2 | 178 | |||
| Provide bituminous felt damp-proof course under 200mm wide walls | M2 | 22.5 | |||
| Foundation walling | |||||
| Rough dressed natural stones and approved bedded and jointed in cement sand mortar (1:4): 225mm thick walls | M2 | 72 | |||
| Plinths | |||||
| 12mm thick mortar cement and sand (1:4) rendered to plinths | M2 | 178 | |||
| Prepare and apply three coats of bituminous: ditto | M2 | 178 | |||
| SUPERSTRUCTURE | |||||
| WALLING | |||||
| Brick walls bedded and jointed in cement and sand mortar (1:4) in: | |||||
| 305mm thick bricks/blocks for external walls reinforced with 32x2mm hoop iron every alternate course | M2 | 158 | |||
| 100mm thick internal walls/partitions reinforced with 32x2mm hoop iron every alternate course | M2 | 110 | |||
| Provide 100mm pipe vents in beam above all doors with wire gauze and 25mmx400mm approximately above all windows as permanent ventilation | No | 7 | |||
| Ring beam | |||||
| Concrete class 20/20 for ring beam | M3 | 9.0 | |||
| Reinforcements | |||||
| High yield Y12 reinforcement bars | Kg | 52 | |||
| High yield Y8 reinforcement bars | Kg | 16 | |||
| Formwork | |||||
| Sawn formwork for lintels (ring beam) | M2 | 119 | |||
| ROOF CONSTRUCTION | |||||
| 150×50 rafters (top member) and tie beam | M | 90.5 | |||
| 100×50 struts | M | 25 | |||
| Purlins | |||||
| 75×50 purlins | M | 6 | |||
| Ridge board | |||||
| 225x25mm ridge board | M | 1 | |||
| Wall plate | |||||
| 100×50 wall plate | M | 2 | |||
| Fascia board | |||||
| 200x25mm fascia board | M | 55 | |||
| IT4 sheets | |||||
| 28 gauge roof covering sheets fixed onto timber purlins | M2 | 162 | |||
| Matching ridge capping | M | 140 | |||
| DOORS | |||||
| Wrot cypress | |||||
| 50mm thick single leaf panel door size 950x2100mm high | No | 7 | |||
| Door frame and finishings | |||||
| Wrot mahogany | |||||
| Ex. 200x50mm rebated frame | M | 25.4 | |||
| 50x25mm architrave | M | 13.2 | |||
| 15mm quadrant | M | 7.1 | |||
| Ironmongery | |||||
| Supply the following items with matching screw stall | |||||
| 100mm pressed steel butt hinges | Pcs | 14 | |||
| Three lever mortice lock complete with set of lever handles with brass finish | No | 7 | |||
| Rubber door stop | No | 7 | |||
| Painting | |||||
| Prepare and apply two undercoats and one finishing coat gloss oil paint to: | |||||
| General wood surfaces | M2 | 45 | |||
| Wood surfaces 100-200mm girth | M | 35 | |||
| Prepare and apply aluminium wood primer to backs of wood before fixing them | |||||
| Wood surfaces 100-200mm girth | M | 35 | |||
| WINDOWS | |||||
| Supply and fix steel casement windows consisting of Standard Angline section frames and square rodes primed with one coat red oxide complete with steel metal hood permanent vents | |||||
| Windows size 2200x1500mm high | NO | 1 | |||
| Ditto size 2100x1500mm high | NO | 1 | |||
| Ditto size 1800x1500mm high | NO | 1 | |||
| Ditto size 1700x1200mm high | NO | 1 | |||
| Ditto size 1200x1200mm high | NO | 1 | |||
| Ditto size 1000x500mm high | NO | 1 | |||
| Glazing | |||||
| 5mm thick clear sheet glass and glazing to steel metal casements with putty in panes 0.10-0.50 square meters | M2 | 13.13 | |||
| Window board | |||||
| 125x25mm windows board from Wrot cypress | M | 34.8 | |||
| Curtain rods | |||||
| 25mm diameter chrome curtain rods | M | 7.0 | |||
| 20mm diameter chrome curtain net rods | M | 4.8 | |||
| Painting | |||||
| Prepare and apply a layer of priming coat, two undercoats and one finishing coat gloss oil paint to glazed metal surface | M2 | 12.5 | |||
| FINISHES | |||||
| INTERNAL WALL FINISHES | |||||
| 40mm thick cement sand render (1:4) to wall | M2 | 158 | |||
| 10mm thick cement screed to wall | M2 | 109.6 | |||
| Painting | |||||
| Prepare and apply three coats of first quality plastic emulsion paint to internal walls | M2 | 267.6 | |||
| EXTERNAL WALL FINISHES | |||||
| 40mm thick cement sand render (1:4) to ring beam | M2 | 29.7 | |||
| Painting | |||||
| Prepare and apply three coats of first quality plastic emulsion paint to: | |||||
| Ring beam | M2 | 29.7 | |||
| FLOOR FINISHES | |||||
| 40mm thick cement sand render (1:4) to floor | M2 | 178 | |||
| 5mm thick cement screed to floor | M2 | 178 | |||
| Ditto, but 100mm high skirting | M | 99 | |||
| CEILING FINISHES | |||||
| Suspended ceilings | |||||
| 50x50mm brandering on trusses at 600mm c/c to receive ceiling board | M2 | 178 | |||
| 12.5mm soft plasterboard suspended at height 2700mm above the finished floor level | M2 | 178 | |||
| Cornice | M | 99 | |||
| Painting | |||||
| Prepare and apply three coats of first quality plastic emulsion paint to ceiling board | M2 | 178 | |||
| ELECTRICAL INSTALLATION WORKS | |||||
| Allow PC sum of $3000 for electrical installation works (cables, lighting points and switches, lighting fittings, meter board and earthing) | Item | LS | |||
| MECHANICAL WORKS | |||||
| Allow PC sum of $5000 for mechanical works (kitchen sink, shower fittings, instant shower heater, bathroom shelf, curtain rail with shower curtains, towel rail, flexible tubing, water closet, CVPC pipes, bends/elbows, tees, reducers, threaded fittings and water storage tank) | Item | LS | |||
- Schedule of rates for the substructure
The schedule of rate of the building up to the substructure level is provided below
| ITEM | DESCRIPTION | UNIT | QUANTITY | RATE ($) | AMOUNT ($) |
| EARTHWORKS AND EXCAVATIONS | |||||
| Provide all materials and construct a machine cut dressed 2.5m high wall/fence around the boundary of the plot | M2 | 375 | 20 | 7,500 | |
| Excavate top soil of the site average 200mm deep to remove top soil and cart and deposit 100m away and later spread and level on site as directed | M2 | 178 | 2 | 356 | |
| Excavate to reduce levels starting from stripped level and column pits not exceeding 1.5m deep | M3 | 3.35 | 5 | 16.75 | |
| Trim and prepare bottoms of excavations to receive blinding | M2 | 22.5 | 2 | 45 | |
| Remove surplus excavated material and cart away | M3 | 18.2 | 7 | 127.40 | |
| Return fill and compact selected excavated material around foundations | M3 | 12.6 | 5 | 63 | |
| Fillings | |||||
| Supply and spread approved murram fillings to make up levels and compact well in 150mm thick layers | M3 | 27 | 18 | 486 | |
| Supply 300mm thick approved hardcore fillings, spread, level and compact well in 150mm thick layers to receive concrete surface bed | M2 | 178 | 3.6 | 640.80 | |
| Level and blind surface of hardcore with 50mm quarry dust to receive concrete surface bed | M2 | 178 | 2 | 356 | |
| Provide and apply approved anti-termite treatment to the surface of blinded hardcore and surrounding areas in accordance with the manufacturer’s instructions | M2 | 178 | 3.5 | 623 | |
| Mass concrete | |||||
| Blinding: provide all materials, mix and place 50mm thick concrete grade C20/25 (1:3:6) for blinding under strip foundations | M2 | 22 | 10 | 220 | |
| Footing: provide all materials, mix, place, vibrate and compact concrete grade C30 (1:1.5:3) | M3 | 3.35 | 320 | 1,072 | |
| Ground floor slab: provide all materials, mix, place, vibrate and compact 125mm thick concrete grade C25 (1:1.5:3) for ground slab | M2 | 178 | 35 | 6,230 | |
| Sawn formwork | |||||
| Provide and fix sawn formwork to sides of strip foundations | M2 | 99 | 4 | 396 | |
| Provide and fix shuttering and formwork, including propping, strutting and striking, on sides of ground slab | M2 | 59 | 3.5 | 206.50 | |
| Reinforcement | |||||
| Provide fabric mesh reinforcement no. A142 mesh size 150 x 150mm (BRC) weighing 2.22kg/m2 and all other materials needed, including bends, tying wires and spacer blocks on floor slab. | M2 | 178 | 8 | 1,424 | |
| Provide deformed high yield steel Y12 bars | Kg | 88 | 5 | 440 | |
| Damp-proof course | |||||
| Provide polythene damp-proof membrane, gauge 1000mm laid over hardcore with 300mm welted lap | M2 | 178 | 5 | 890 | |
| Provide bituminous felt damp-proof course under 200mm wide walls | M2 | 22.5 | 2 | 45 | |
| Foundation walling | |||||
| Rough dressed natural stones and approved bedded and jointed in cement sand mortar (1:4): 225mm thick walls | M2 | 72 | 25 | 1,800 | |
| Plinths | |||||
| 12mm thick mortar cement and sand (1:4) rendered to plinths | M2 | 178 | 7.5 | 1,335 | |
| Prepare and apply three coats of bituminous: ditto | M2 | 178 | 7.5 | 1,335 | |
| Total carried to collection summary | 25,607.45 |
- Programme in form of Gantt chart
The Gantt chart for the building substructure is provided in the attached Excel file
References
2020ProjectManageent. Estimating your Project, 2020. 2020ProjectManagement,
https://2020projectmanagement.com/resources/cost-management/estimating-your-project (accessed November 24, 2020).
Belek, J. 8 Steps to vet construction subcontractors, 2017. https://srfm.com/business-insurance/8-
steps-to-vet-construction-subcontractors/ (accessed November 24, 2020).
Ji Sae-Hyun, Ahn Joseph, Lee Hyun-Soo, & Han Kyeongjin. Cost Estimation Model Using
Modified Parameters for Construction Projects. Advances in Civil Engineering, 2019(1), 1-10.
Laryea, S. Impact of tendering procedure on price formation in construction contracts: case
study of the competitive negotiation procedure. Proceedings of WABER Conference, Accra, Ghana, 16-18 August 2017; University of the Witwatersrand, Johannesburg, 2017.
Varghese, S. & Kanchana, S. Modeling the parametric construction project cost estimate using
bootstrap and regression technique. International Journal on Engineering Technology and Sciences, 2(5), 47-50.
