Open BIM Cost Estimator has been created to automatically estimate the execution cost of a construction project during its preliminary phases, in a simple and practical way, using a fast, efficient and precise design model, by taking into account the built surface, height of the building, and typological, construction, geographic and socioeconomic factors.
The Open BIM Cost Estimator user interface is divided into three tabs, which correspond to the preliminary phases of the project that are contemplated by the application:
- Phase I: Preliminary analysis
- Phase II: Draft project
- Phase III: Design project
Aim of the program
The aim of the program is to automatically estimate the execution cost of a construction project during its preliminary phases, in a simple and practical way, using a fast, efficient and precise design model, by taking into account the built surface, height of the building, and typological, construction, geographic and socioeconomic factors.
The specifications of the GSA (General Services Administration) of the USA and AIA (American Institute of Architects), indicate, depending on the phase of the project, the allowable variance in the project cost, as shown in the table below:
|Project phase||Variance (%) according to GSA||Variance (%) according to AIA|
|Preliminary analysis||10||10 - 15|
|Draft project||7 - 10||7,5 - 12,5|
|Design project||5 - 7,5||5 - 10|
Depending on how defined and developed the project is - preliminary analysis, draft project and design project -, the calculation of the execution cost of the project is more precise, and therefore, its accuracy is increased. In the case of the program, the tolerances of the deviation of the initial cost with respect to the final cost of the project, provided that the initial parameters of the project remain unchanged regarding surfaces, heights or construction properties, are summarized in the following table:
|Project phase||Variance (%)|
Open BIM Cost Estimator
|Preliminary analysis||≤ 12|
|Draft project||≤ 10|
|Design project||≤ 7|
Scope of application
The scope of application of the program covers housing, office, industry, cultural, hospitality, hospital, administrative and sport uses, amongst others, for different countries with their respective provinces or federal entities.
The following requirements must be met for the cost to be adjusted to the market:
- The construction system used must correspond to "international architecture" standards, therefore, the peculiar typologies that use artisan construction systems and/or materials, as well as singular buildings, are excluded.
- The building project must meet the minimum safety, habitability and sanitation requirements.
- The building must have the necessary infrastructure to execute the works and have accesses in an acceptable state.
- The duration of the execution must be proportional to the volume of the work. An excessively short or long term implies a deviation from the budget.
- The currency of the country should remain stable and with controlled inflation. Prices cannot be adjusted to the market when the inflation rate is high and/or the currency is fluctuating.
In no case should the estimate of the construction costs offered by the program be used to contract the project, since it requires a greater definition of the qualities, construction provisions and project quantities, which can only be obtained during the project execution phase.
Neither can it be used for valuations and appraisals, since the program only accounts for new construction buildings with current construction standards, and in these cases, there are other factors that intervene such as: the age, degree of conservation and level of maintenance of the building or the environmental aggressiveness of the environment, which influence the value of the building.
The user interface of Open BIM Cost Estimator is divided into three tabs, which correspond to the preliminary phases of the project that are taken into account by the application:
- Phase I: Preliminary analysis
The application requests the geographic and economic data related to the construction site and the general data of the building. The program then displays the amount of the execution cost of the project and the construction cost per m2.
- Phase II: Draft project
The application requests the typological properties of the building and its floor configuration. The results output, in addition to that indicated in phase I, automatically generates the budget, divided into chapters, and provides a graphto help visualise the progress of the budget.
- Phase III: Design project
Finally, the application requests more precise data on the characteristics of the building regarding the foundation, structure, construction solutions and installations. The results output, in addition to that indicated in phase II, includes sub-chapters in the chapters of the budget.
Method used to calculate the cost of the building
Definition of the geometric and construction model of the building
The program generates a geometric and construction model of the building internally, using the data entered by users and the default values based on the recommendations of the control and insurance entities, the construction solutions sanctioned by the practice and by good construction standards.
Using the geometric and construction model, the program automatically calculates the quantities of the job items involved in the project, for each chapter of the budget.
Once the quantities have been established, the program applies the prices that correspond to the job items that make up the project.
The prices that are applied are extracted from the Price Generator of each country and their corresponding federal entity or province.
In order to determine a cost in accordance with the market, the program adjusts the prices according to the geographical location, typological characteristics, execution period of the work and the market situation of the area.
Factors contemplated during price applications
Several factors, that directly or indirectly influence the final cost of the work, are taken into account to obtain the prices used to elaborate the budget. These can be grouped into the following categories:
These are factors related to the geographical and climatic situation of the area, which are intrinsically linked to the socioeconomic factors that affect the prices and performance of the workforce. These include:
- The population density
Affects the supply and demand, and therefore, the market price.
- The tourist development of the zone
Increases the demand and purchasing power of the inhabitants of the zone.
- The state and development of the transport networks
Affects the distribution and transport cost of materials, goods and services.
These factors depend on the economic, political and social situation of each zone, which influence the price of the materials, labour and machinery prices. These include:
- The net monthly salary in the construction sector
Influences the price of labour.
- The minimum interprofessional salary
Influences the price of labour.
- The gross national income per capita with purchasing power parity
Influences prices in general.
- The inflation rate
Implies a continuous price increase.
- The unemployment rate
Reflects the labour availability, and therefore, the contracting price.
- The currency exchange rate
Especially affects the import of goods and services.
- The market conditions
Provides an indication of the supply and demand relationship in the acquisition of materials, hiring of labour and rental of equipment and machinery involved in the construction process. No reference is made to the supply or demand of the real estate market, only to the demand by the contractor and the supply of materials, as well as to the labour market.
- The import of goods and services
Influences imported material prices.
- The industrial production growth rate
Reflects the availability of auxiliary measures to aid in the execution of the work.
- The corruption perception index
Affects prices in general, the greater the corruption index, the greater the cost of the work.
- The human development index HDI
Is an indicator of the health, education and economic level, which reflects the degree of competitiveness and productivity of the inhabitants of the area, and so, directly affects the performance and final cost of the building.
The adjustment coefficients associated with each socioeconomic and geographical factor have been quantified through the study and analysis of data provided by statistical sources of recognized authority, such as: World Bank, Datos Macro Expansión, IndexMundi, Preciosmundi, XE Live Exchange Rates, European Commission.
- The built surface
Affect the prices and labour performance
- The use of the building
Implies specific construction solutions and installations, and therefore, affects the final cost of the building.
- The number of floors above ground level
Increased height of the building implies more burdensome structural and construction solutions, as well as increasing difficulty to displace elements vertically, which implies a loss of performance.
- The number of floors below ground level
Building a basement implies an added difficulty, which affects the execution cost of the project, especially the land movement and foundation chapters.
- Average free height between floors
Directly affects the construction volume, especially chapters concerning façades, partitions and cladding, and with increased height, increases the difficulty to displace elements vertically.
- The type of building
Affects the configuration of the floor and façades of the building, and therefore, its construction.
- The geometric complexity of the floor
Affects the cost of the building, as it implies a general performance loss.
- Percentage façade openings
Openings in the façade imply an increase in its cost.
- The degree of floor partitioning
Affects the cost of the partitions, carpentry and indoor cladding.
- Its accessibility
The accessibility to the worksite is considered as well as the storage options.
- The topography of the site
The difficulties that are brought about due to the presence of uneven ground in the worksite, which affects the performance of machinery and labour, are quantified.
- Level of quality
It is intrinsically linked to the amount of the work execution budget. In the program, the level of quality for the whole building, constructive solutions and installations can be selected indistinctly.
The level of qualityis defined according to the characteristics of the materials, equipment and construction processes used in the project, according to the following criteria:
Strictly comply with the standards in force. Their cost lies below the 30% percentile of the set of market prices.
They exceed the minimum requirements that are prescribed by current standards and provide increased quality to the whole building. Its cost lies within the range defined by the 30-70% percentiles of the set of market prices.
They exceed the minimum requirements of the current standards and provide a significant quality bonus to the whole building. Its cost is above the 70% percentile of the set of market prices.
Depending on the selected use of the building, the program defines the project units that make up the chapters of the budget:
- Land conditioning
- Signs and equipment
- Environmental management, control, health and safety
Users can change the default options that the program offers for each use.
Climatic and seismic factors
The program also contemplates these other factors that affect the cost of the building:
- Thermal conditions
The outdoor temperature affects the design of the envelope and thermal installations of the building, particularly, regarding the cost of the insulation and exterior carpentry.
- Wind intensity
The dynamic pressure of the wind conditions the design and cost of the structure, and the exterior carpentry.
- Wind exposure degree
It has an impact on the cost of the structure and exterior carpentry, especially in buildings located near cliffs, seaside, unimpeded rural land, amongst others.
- Seismic risk
Seismic actions affect the design of the foundations and structure, therefore, the final cost of the building.
Results, checks and generated support documents
Open BIM Cost Estimator has several ways to display the values of the evaluated magnitudes, so users can analyse the results in the most efficient way according to their needs.
Execution cost of the project
The cost determined by the program corresponds to the execution cost of the project, which includes the total amount of direct and indirect costs that are incurred for its execution, where:
- Direct costs
Are the costs that are directly attributed to the execution of the project items, which include:
- Machinery or equipment
- Auxiliary measures or complementary direct costs, established as a percentage of the previous components (materials, machinery and labour).
- Indirect costs or project expenses
They consist of the costs that are not directly attributable to project items, but to the whole project: office facilities on site, warehouses, workshops, laboratories, salaries of technical staff and the manager, amongst others.
The general expenses and the industrial benefit of the contractor that correspond to the contract budget or tender budget are excluded from the execution cost of the project, as well as taxes, licenses, technical fees and other expenses that are attributable to the developer are also excluded.
Construction cost per m2
It is defined as the result of dividing the total amount of the "Project execution budget" by the "Total built surface area (S)", expressed in square metres.
"Total built surface area (S)" is the area delimited by the perimeter lines of the external enclosures and, where applicable, the axes of the dividing walls. The program computes 100% of its floor area, overhanging elements, terraces and balconies covered by a roof when they are closed laterally by walls, otherwise, only 50% of its surface is computed.
The comparison of the total amount of the execution cost of the project between two buildings, can be established with an index or ratio, which, in the case of the program, is called "Construction cost per m2".
Budget by chapters
Open BIM Cost Estimator allows users to view the decomposition of the execution cost of the project by chapters for phases II (Draft project) and III (Design project). Furthermore, in phase III, users can view these chapters and their sub-chapters.
For each chapter or subchapter the amount, the cost per m2 and its impact on the execution cost of the projectare indicated.
Open BIM Cost Estimator generates a document justifying each of the preliminary phases of the project that are contemplated by the application. This document includes the project data that has been entered and the results of the calculation of the execution cost for the project.
The report can be printed directly from the application and exported to PDF, DOCX, TXT, HTML and RTF formats.
The permits that must be included in the user license to be able to use Open BIM Cost Estimator depend on the value of the execution cost that is calculated by the program:
- Up to 1,000,000 €
Users can use the program for free.
- Up to 5,000,000 €
The user license must include the Open BIM Cost Estimator Pro permit.
- More that 5,000,000 €
The user license must include the Open BIM Cost Estimator Expert permit.