(Photo credit: Rui Tang)
Here are six ways BIM improves construction estimating.
By Rui Tang
Construction estimating is a tedious, time-consuming and error-prone process that starts with scouring pages of drawings to categorize pricing or bid items, calculate quantities, quote unit pricing and much more. Building Information Modeling, also known as BIM, has been utilized for years in the planning and construction of buildings and is proven to increase efficiency, prevent human error and cut overall construction costs and transform construction estimating into an accurate process.
There are many benefits a well-coordinated BIM model can provide and below we explore six scenarios where BIM can be utilized to help save time and money throughout the construction estimating process.
Master Catalog of Utilities and Materials
Using Revit, project teams can establish categories and sub-categories of utilities and materials, such as pipe variations, pipe sizes and what types of connections and fixtures are needed for the project. Revit families can then be set up within the model and act as the master catalog that general contractors will utilize to set up bidding sheets.
Total Quantity and Unit Price Calculations
BIM can assist in calculating the pricing of different family types by taking advantage of family parameters and formulas. Family types are a sub-component of a Revit family. For example, a door family could contain multiple types with various height/width combinations and varying head geometries and combinations. With all these choices in family types, estimators will find differences in price.
Utilizing BIM, separate unit pricing can be stored for the different family types and when used in combination with a calculated parameter enable the total price for all options to be calculated.
If there is varied pricing within a family, the parameters can be set up utilizing formulas to accurately calculate the unit price for the specific family and deliver a total cost.
Additionally, price quotes received from vendors can be physically linked to the BIM model giving general contractors easy access to the figures during the final bidding stages.
Jobsite Geographic Conditions
One of the most important aspects of estimating for underground pipe laying work, for instance, is to calculate how much earth material to dig out and refill. Each type of earth material – asphalt, aggregate, soil and rock – can have different overall costs associated with the dig and refill in terms of per square foot and per cubic foot. A well-coordinated BIM model of the existing and finished conditions of the jobsite that includes the information about each separate material can be helpful in calculating earth-moving costs. The same concepts can be applied to paving, which can require different types of materials and varying costs for each item.
When it comes time to refill the land, project teams may be allowed to reuse the existing material that was dug-out. However, other situations may require the project team to purchase new material for refill. If that is necessary, vendors will need to be sourced, trucks rented and calculations configured to see how many truckloads based on total volume will be needed.
When dealing with rock and railroad construction or repairs, project teams could be faced with huge project delays and price inflation depending on the level of difficulty associated with removing rock material. During estimating, rock profiles can be compared against pipe profiles to calculate how much needs to be dug out in order to calculate costs accordingly. With the help of BIM, rock boring logs can be translated into a 3D rock contour and volumes can be calculated with ease.
Railroad construction requires permits and only allows for work to be done during certain timeframes and in very specific areas due to the railroad tracks being live. Using BIM, project teams can rule out any construction costs within the forbidden areas near the railroad and aid with determining the very specific scheduling parameters for equipment usage.
Project Pricing Adjustments
Estimating is not only Unit Price times Total Quantity. Unfortunately, there are more factors that play into the calculations and often adjustments need to be made. For instance, every time a designed utility pipe is knowingly run across an existing utility line, additional time and costs should be accounted for.
The traditional way of documenting these changes allows room for human error which causes the need for rework and results in a loss of time and money. The implementation of BIM can eliminate the possibility of mistakes and should remove the need to cross check different sets of drawings for crucial information. BIM provides a single source of truth, giving all project participants access to project information in real time.
Regular days, half days, weekends, holidays, nightshifts – they all have impact on the actual workhours of each calendar day. Each project’s schedule consists of a varied amount of these days and can affect the expected completion date if they aren’t calculated up front. Using BIM software such as Navisworks, estimators can import work schedules and create time-lapse animation for proper planning.
Periodical Project Cost Tracking and Projection
Using project parameters together with Dynamo scripts, timestamps can be applied to the design and as-built BIM model. This allows project teams to compare the actual cost, materials used and progress against the planned timeline.
In addition, a “Daily Job Report” can be electronically generated and standardized with the help of BIM360 Field. From there, with very little effort, that information can be imported into a live as-built Revit model and provide a single source of truth for all project participants. These daily job reports also provide vital evidence for any extra cost claims which helps general contractors manage reimbursements throughout the project.
Rui Tang is part of the Construction Solutions Specialist team at Microdesk, a global AECO consultancy. Rui helps clients with the construction coordination process, providing technical support and managing the model exchange between consultants and clients. Rui holds a Master of Construction Engineering and Management from Columbia University.