Building information models (BIMs) are intelligent digital representations of facilities containing engineering data. BIMs store spatial geometric properties, bills of materials, and component structures.
Quantities extracted from BIM models can be exported directly into cost-estimating systems, enabling quicker material takeoffs and accurate 5D estimates, thus lowering risks and costs associated with project delivery.
Cost Estimation and Project Budgeting
Project scheduling and cost estimation are crucial processes in the construction process to ensure projects stay within their budgets and meet delivery schedules. Unpredictable changes in site conditions, lack of or conflicting information sources, and inaccurate estimates can wreak havoc on projects.
BIM can help keep a project on schedule by reducing costly rework, saving money through a better understanding of what will eventually be built, and providing accurate planning of materials, permits, and sourcing activities resulting in precise forecasting of costs.
BIM-enabled quantity takeoff using a coordinated 5D BIM model can save architects, estimators, and AEC companies time while mitigating errors and improving estimates.
The automated process frees estimators from manual quantification while simultaneously providing real-time parametric readjustment of costs in response to change control inputs – leading to more efficient collaboration among players who once saw themselves as adversaries; additionally, it makes clash detection and resolution simpler and helps prevent costly errors during construction.
Material Takeoff
Material takeoff is the practice of compiling an inventory list of all construction materials required to complete a project, including counts, surface area estimates, and length requirements. This can be achieved either manually or by using the software.
Cost estimators use their knowledge of materials, project scope, and design to assess costs associated with each component in an estimated takeoff and make estimates accordingly. They then add up all these costs together for an overall total.
For this study, a survey was designed that asked respondents to rank on a 5-point Likert scale the advantages and disadvantages of BIM-base takeoff on cost estimation accuracy.
Results demonstrated that verifying BIM models used for quantity takeoff was the single most critical factor in improving quality estimating (RII value of 0.813), with other vital elements including getting bids from suppliers or creating self-created databases with material costs also having significant RII values.
5D Cost Estimation
Some BIM software solutions have proven their efficiency in streamlining the estimating process and encouraging effective collaboration among architects and engineers, which leads to improved construction quality while decreasing costs and rework.
5D cost estimation is a construction management technique that connects geometric modeling (3D modeling) with cost data (4D scheduling). This allows designers to make changes during the conceptualization stage, significantly cutting budget and timeline.
By directly correlating costs with dimensions, it can also improve Bills Of Quantities (BOQ).
Time and Cost Savings
BIM allows cost managers to use automated quantity takeoff to eliminate manual calculations, saving their time for more important duties such as making more informed decisions on projects and keeping promises made to clients.
Utilizing BIM-enabled construction planning and estimating tools can drastically shorten project timelines while increasing the quality of work produced, helping teams complete projects on schedule and within budget.
But BIM can only truly succeed at cost estimation and budgeting if its users understand its inner workings. Its strength lies in being combined with real-time parametric data as well as having access to experienced professionals that can fill in any gaps that software cannot.