The Role of Concrete Estimates in Controlling Project Costs

[edit] Introduction

Accurate estimation of concrete quantities and associated costs is an important part of construction cost planning and cost control. Concrete is widely used in foundations, ground-bearing slabs, suspended floors, structural frames, walls and other elements, and errors in estimating quantities or costs can affect procurement, programming and the overall project budget.

Concrete estimates generally consider the volume and specification of concrete required, as well as associated costs such as reinforcement, formwork, labour, plant, transport, pumping, testing and finishing. The level of detail required will depend on the stage of the project and the purpose of the estimate.

Estimates should be reviewed and developed as the design progresses and more detailed information becomes available. Early estimates may be based on approximate quantities and comparable project data, while later estimates can be based on detailed measurement from drawings, specifications or building information models.

[edit] Estimating concrete quantities

The starting point for estimating concrete work is to identify the elements that require concrete and determine their dimensions and specifications. Quantities are commonly measured by volume, although other units of measurement may be used for associated work.

The estimate should take account of factors including:

• The dimensions and geometry of foundations, slabs, columns, beams and walls.
• Concrete strength and other performance requirements.
• Reinforcement requirements.
• Formwork and temporary works.
• Construction joints and sequencing.
• Access and delivery arrangements.
• Placing, compaction and finishing methods.
• Curing requirements.
• Testing and quality control.
• Allowances for waste, overbreak or other project-specific factors where appropriate.

Accurate measurement can help to reduce the risks of over-ordering or under-ordering materials. However, estimates should distinguish between measured quantities and appropriate allowances, rather than assuming that all construction work can be predicted precisely before work begins.

[edit] Supporting cost planning and budgeting

Concrete estimates contribute to wider construction cost planning by identifying the likely costs of individual elements and work packages. This allows project teams to compare estimated costs with the available budget and assess the financial implications of design decisions.

Construction cost estimates generally become more detailed as the project develops. Early cost appraisals may be based on limited information, while later estimates can incorporate measured quantities, detailed specifications and current market information.

An accurate estimate can provide a basis for:

• Establishing and monitoring project budgets.
• Comparing alternative design and construction solutions.
• Identifying elements with significant cost implications.
• Planning procurement and material deliveries.
• Preparing tender and pricing information.
• Assessing the financial implications of design changes.
• Monitoring anticipated and actual costs during construction.

Cost estimates should also identify the assumptions on which they are based. Changes in design, quantities, specifications, programme, market conditions or procurement arrangements can affect the reliability of an earlier estimate.

[edit] Material, labour and plant requirements

Estimating concrete work involves more than calculating the volume of concrete. The resources required to complete the work may include labour, plant, equipment, formwork, reinforcement and specialist services.

Labour requirements can vary according to the scale and complexity of the work, site conditions, access, construction methods and programme. Plant requirements may include equipment for excavation, concrete transport, pumping, placing, compaction and finishing.

Estimating these requirements can assist with resource planning and programming. However, actual productivity and costs may be affected by weather, site constraints, sequencing, labour availability and other factors that should be considered when preparing and reviewing estimates.

[edit] Reducing waste and avoiding delays

Accurate quantity information can support efficient procurement and reduce unnecessary material waste. Concrete has a limited working life after batching, and ordering significantly more than is required can result in additional cost and the need for appropriate management of surplus material.

Conversely, insufficient quantities or poor coordination of deliveries can disrupt construction activities. Estimates can therefore support programme planning by identifying anticipated material requirements and helping to coordinate deliveries, labour and plant.

Good estimating alone cannot prevent project delays. Effective programme management, procurement, site coordination and quality control are also required. Estimates should therefore be integrated with other project planning and control processes.

[edit] Tendering and cost control

Measured quantities are commonly used in tendering and cost management. A bill of quantities, where used, provides project-specific measured quantities of work identified in drawings and specifications, allowing tenderers to prepare prices on a consistent basis.

Accurate quantities can improve the comparability of tenders and provide a basis for monitoring costs. They may also assist with the valuation of variations, interim payments and the preparation of the final account, depending on the procurement and contractual arrangements.

During construction, estimated costs can be compared with actual costs to identify significant variances. Where differences arise, project teams can investigate their causes and consider appropriate corrective action. Variances may result from changes in quantities, design alterations, productivity, material prices, programme changes or unforeseen site conditions.

[edit] Digital estimating and measurement

Digital tools can assist with the measurement and analysis of construction quantities. Estimators may take quantities directly from digital drawings or building information models, subject to appropriate checking and verification.

Digital systems can improve the speed of measurement and make it easier to update estimates when design information changes. However, the accuracy of the output depends on the quality and completeness of the information entered into the system.

Automated measurement does not remove the need for professional judgement. Estimators must understand the design information, specifications, measurement methodology and assumptions used in preparing the estimate.

[edit] Long-term benefits of accurate estimating

Reliable estimating can contribute to improved financial control throughout a construction project. It provides information that can support design decisions, procurement, tendering, programming and the monitoring of costs.

The accuracy of an estimate should always be considered in relation to the information available at the time it is prepared. As the design develops and uncertainties are resolved, estimates should be reviewed and updated to reflect current project information.

Effective cost control therefore depends not only on preparing an initial estimate, but also on maintaining and developing cost information throughout the project lifecycle.

[edit] Related articles on Designing Buildings

• Construction costs
• Approximate quantities cost plan
• Approximate quantities
• Bill of quantities BOQ
• Approximate bill of quantities
• Priced bill of quantities
• Firm bill of quantities
• Quantity
• Cost breakdown structure
• Bill of quantities v Schedule of rates

Comments

Concrete estimates are one of the most overlooked tools for controlling construction costs. Accurate quantity calculations help reduce material waste, improve budgeting, prevent costly shortages, and support better project planning from day one. The earlier project teams understand their concrete requirements, the easier it becomes to avoid unexpected expenses and keep projects on track.