Estimating Calculations
24 February 2024
ETL Transform application of validation rules and transformation
26 February 2024

Construction schedules

Of the hundreds of different business processes that affect the survival of a company operating in the construction industry, some of the main ones, as they were thousands of years ago, are the processes of qualitative calculation of element group quantities, project costing and time.

It was commodity-money relations that were one of the main reasons for the emergence of written language. And it was commodity-money relations thousands of years ago that formed the first legally significant clay tablets of calculations of materials and works in construction projects.

While for tens of thousands of years estimating processes remained unchanged and calculating project scope was a manual process, with the advent of ERP and CAD tools, the traditional world of estimating is becoming automated.

The main interest of a construction business is centred on the time and cost data of the work in a project. Estimating and costing departments pump up their calculation skills with each project in order to reduce the calculation error. Historical cost and process time data is collected during the construction of past projects throughout the life of a construction company and recorded in systems databases. The availability and quality of this data is a major competitive advantage for any construction organisation.

To understand the process of creating estimates, costings, and schedules in construction, we will draw a parallel to costing and calculating the cost of dinner at a restaurant.

To determine the total cost of an evening at a restaurant, a manager would need to make a grocery list and calculate the preparation time for each dish, then multiply the resulting costs by the number of guests. Similarly, in construction, we develop itemized costings for each category of project elements (entities), resulting in a total project cost by summing the costs of all categories-entities in the final estimate.

Calculations in the world of construction are kitchen recipes from building resources and materials.

In the very first stage of calculating the cost of the entire project and in the form of calculations and schedules, it is necessary to first collect in the form of a table all the items, work and resources that the company operates in the execution of its construction projects.

Information on all elements that can be used in construction projects is collected in the company's "Construction Resources, Materials and Works Database" and this database (or table) is a key source for all subsequent cost and time calculations.

Database of construction resources, materials and works

Database or table of construction resources, materials and works - includes detailed information about each entity element – article, material, work or service, including its name, description, unit of measurement and unit cost recorded in a structured form.

 

Everything from the variety of fuel and stock materials used in projects to detailed descriptions of professionals in various categories by hourly wage can be found in this table.

"Resource database" is akin to an online store's product catalog, in which each product has a detailed description of its attributes. This makes it easier for estimators to select the right resources needed to calculate specific construction processes - works.

"Building Resource Database" can be thought of as a listing of all the ingredients in a restaurant cookbook. Each building material, equipment and service is similar to the ingredients used in recipes. "Resource database" is a detailed list of all ingredients - building materials and services, including their cost per unit: piece, meter, meter, hour, liter, etc.

New entity items can be added to the «Construction Resource Databases» table in two ways: manually or automatically by integrating with the company's inventory control systems or supplier databases.

To keep up with changing market conditions such as inflation, the "cost attribute" for each unit of an entity (good or service) in the system is updated regularly, which can be monthly, quarterly or annually, ensuring that costing and estimates are up-to-date and accurate.

A typical medium-sized construction company uses a database containing thousands to tens of thousands of such elements-entities. These minimum units - described entities serve as the basis for estimators who prepare estimates based on them.

Calculation items and composition of works

Having filled the "Construction Resource Database" with entities, we can now proceed to the creation of calculations that are calculated for each process on the construction site for specific units of measurement: for example, for one cubic meter of concrete, one square meter of gypsum board wall, per meter of curb or for the installation of one window.

To build a 1m² brick wall requires approximately 65 bricks (entity «Sand lime brick»), attribute a cost of $1 each (attribute "Cost per unit"), which adds up to $65. We also need to use construction equipment (entity «JCB 3CX loader») for 10 minutes, which will place the bricks near the work area. Since it costs $150 per hour (attribute "Cost per unit") to rent the machinery, 6 minutes of using it will cost about $25. In addition, 2 hours of labor by a mason-laying contractor will be required, with an hourly rate of $30, for a total of $60.

The composition of the recipe-calculations are formed on the basis of the accumulated experience of the company, which has a track record of performing these works: laying tens of thousands of cubic meters of concrete, erecting hundreds of thousands of square meters of gypsum cardboard structures, installing kilometers of curbstone or hundreds of windows.

Just as a recipe describes the necessary ingredients and quantities to prepare a dish, a costing sheet provides a detailed list of all the construction materials and services needed to prepare a particular work.

Dozens and hundreds jobs performed dozens and hundreds of times - give workers, foreman and estimator data on the approximate representation of the work in resources, materials, liters of diesel and labor hours per unit of measurement. These volumetric and quantitative attributes of the entities are entered into the costing systems in the form of tables describing each individual task and work consisting of minimal entities from the resource base.

To obtain the total cost of each entity in the work costing, the cost attribute of the entity is multiplied by its quantity and a Bid Factor. Bid Factor can take into account various factors such as complexity of the work, risks, expected overheads and profit.

Thus, the total price of the entire minimum entity per unit of measurement (square meter, cubic meter or piece) made up of articles reflects both the direct costs of materials and labor and the company's additional costs and margins.

The estimator, acting as an analyst, translates the words of the site foreman into repetitive estimates and describes construction processes through resource entities in the form of a table.

Depending on the size of the company, the number of task-work calculations can reach hundreds or thousands. Created calculations are stored in the form of tables - templates for typical projects, which are directly linked to the resource base. If the price attribute of an entity (product, material) changes in the resource base, this attribute is automatically changed in the costing table, which allows estimators to update only the resource base (Figure 3.1-6), while work and task costings can remain unchanged for a long time.

These costing templates are not immutable - a copy of the standard costing template is taken for a new project, and then in this copy certain activities are adjusted to meet the needs of the specific project without affecting the standard costing template. Calculations in order to adapt to individual client requirements and opportunities to increase profitability through speculation, maintaining a balance between maximizing revenue, meeting client needs and maintaining a good reputation for the company.

In some countries, such costing templates, accumulated over decades on a national scale, in order to standardize mark-ups and ensure transparency of the cost of works, are turned into state standards (costing recipes) to be followed by all companies operating in the construction market of a given region in projects with state participation.

 

Construction schedules and 4D project data

A construction schedule is a visual representation of the plan for executing the various phases of a project. It is created from detailed calculations such as the one above, where each task-job is timed and sequenced.

To determine the dates for the construction schedule in a Gantt chart, we take the values of the time volume attribute for each item from the foundation block costing and multiply them by the number of blocks (in this case, concrete foundation blocks). This calculation gives the duration of each task. We then plot these durations on a timeline, starting from the project start date, to construct a graph and the result is a visual representation showing when each task should start and finish.

The schedule helps project managers and workers clearly understand when and in what sequence the various phases of construction should be performed, ensuring efficient use of resources and meeting deadlines.

Let's present the scheduling of work for the installation of three concrete foundation blocks using the costings from the table above, starting May 1, 2024.

Using the costing table from the example above, let's ask ChatGPT to schedule the installation of the 3 foundation block elements from the first of May 2024. In order to send the costings to ChatGPT, we can either upload the costings table in XLSX format or simply insert a screenshot of the costings. ChatGPT will independently find a library to visualize the graph and by multiplying the time attributes of works from table by their volume will add all the data into a graph.

 

❏ Text request to ChatGPT:

Construct a schedule of work using the costings from the table to install 3 pieces of foundation block beginning 01/05/2024. ⏎

 

➤ ChatGPT Answer:

The resulting graph is divided into horizontal bars, where each bar corresponds to a certain stage of work on the block. The colors distinguish the stages such as preparation, excavation, formwork, reinforcement, concrete pouring, finishing work and concrete curing. The duration of each stage is shown by the length of the corresponding-colored bar on the graph.

This schedule not only helps to estimate how long each phase will take, but also shows how work on one block overlaps with work on another. For example, when concrete pouring for the first block is finished, preparations for the installation of the second block begin. This scheduling method allows for optimal allocation of labor and equipment, reducing overall project completion time and improving site efficiency.

Using costing, we can, thanks to the attributes of volumes from 3D geometries, automatically calculate the time characteristics of groups in the form of tables or graphs for different project variants

Modern ERP systems employ automated methods for calculating time, which substantially shorten the decision-making process. This enables swift and precise planning of work schedules and the computation of the total time required for completing project tasks.

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