IFC and classification systems in the construction industry

SfB, UniClass, UniFormat, MasterFormat, OmniClass: all you need to know about IFC and construction classification systems

The term classification refers to all those activities or processes necessary for knowledge management. Processes and activities generally perform actions that fullfill order data, of whatever nature, in appropriate classifications (classes, sections, categories or species) that are associated by relationships and connections.

To be considered valid, a classification system needs to meet the following requirements:

• stability: it needs to be applicable in any context without undergoing substantial changes;
• flexibility: it needs to be extensible with the possibility of adding new parts.

Aristotle was the first to introduce a system of knowledge organization when he dealt with the classification of living beings, dividing them into two main groups, plants and animals, and then into subgroups. He was the first taxonomist (from the Greek taxis, arrangement and nomos, method or rule), organizing information in a hierarchical structure.

Today, generally speaking, taxonomy indicates any organization of entities or concepts organized hierarchically in a structure that resembles the shape of a tree. The most general category is represented by the root node. From the root node, through the parent categories to the child subcategories, you get to the leaf nodes that represent the objects in detail.

Primarily, objects can be grouped according to 2 organizational models:

• hierarchical-enumerative classification;
• analytical-synthetic classification (or faceted).

Hierarchical-enumerative classification system

The hierarchical-enumerative system is a more traditional classification system based on taxonomy. Through a rigid and one-dimensional hierarchical structure with strong vertical development, each element is classified under a single category. All categories are connected through an organization of subsets, as in a game of Chinese boxes.

Each classified element has a unique position in this hierarchy and can be found through a step-by-step path, which goes from the most general set of elements to the most specific ones.

Examples that belong to this type of classification can be family trees or the division of books into chapters, subchapters, paragraphs, sentences, words, letters. However, this system implies a certain rigidity and difficulty in the case of modifications and additions of new elements.

IFC and classification systems in the construction industry | Hierarchy enumeration tree

The analytical – synthetic classification (or faceted)

This classification system is more elastic as it leaves the enumerative and hierarchical system in favor of a methodology consisting of flexible and open schemes with horizontal development. These schemes are more easily adaptable in case of subsequent modifications.

The object to be classified is no longer described by a single pre-eminent characteristic which represents it and which determines its location in a specific place in a data hierarchy; the object is simultaneously identified and described by several non-overlapping characteristics, called “facets” .

All this establishes an open system that can always be increased with new descriptive object characteristics.

The object described is easily identifiable by multiple search accesses provided by a single feature or by the aggregation of multiple characteristics.

Example of faceted classification

IFC and construction classification systems

In pre-digital times, there have been different attempts to codify information and data classification systems in the construction industry. In some cases, they result closer to the hierarchical-enumerative model rather than to the “faceted” model, or they may have included both of them.

In this focus we’ll analyze some of the most known classification systems, such as:

• SfB (Samarbetskommitten for Byggnadsfragor)
• UniFormat;
• MasterFormat.

Check out our upcoming posts to keep updated with similar contents and get more info about UniClass and OmniClass classification systems.

The SfB classification plan

The SfB (Samarbetskommitten for Byggnadsfragor) classification plan was firstly prepared in the 1940s and was commissioned by the coordination committee for Swedish construction. Updated and further developed in the following years, this classification and coding plan for the building industry was exported to various European countries.

The SfB plan way of operating can be defined as “faceted”: practically every single part or component of the project can be broken down into 4 reading levels called “tables”.

Each characteristic, belonging to one of the 4 tables, is marked with a code.

The code assignment to each characteristic makes the identification of subjects and actions unequivocal, while the possibility of associating the tables with one another enables new combinations for data classifications that are not yet existing but possible.

A practical example of SfB classification

Let’s suppose we have a SfB code like:

52 (35) Rr1 (P)

The following information will correspond to this code:

• 52 corresponds to Show buildings and equipment from the Table o;
• (35) refers to False Ceilings from Table 1;
• R indicates slabs and panels from Table 2;
• r1 corresponds to clay, plaster, magnesium and plastic binders from Table 3;
• (P) indicates Sound and silence from Table 4.

The code consists of numbers and letters, each of which indicates a process, equipment, material, space, etc.

Those who deal with the processing (in this case creating a false ceiling) will look for the project documents which, combined with Table 1, show code (35); an acoustics engineer will take into consideration documents in Table 4 which contain the P code, and so on.

UniFormat

UniFormat was first adopted in America in 1973 as a tool for classifying construction elements and related processes. This classification system is based on 2 elements:

• the classification structure is hierarchical-enumerative;
• the classified objects were chosen based on the ratio of cost incidence and frequency of use.

UniFormat classification is based on three main levels of objects:

• level 1: collects the main groups of objects (foundations, envelope and partitions);
• level 2: represents a breakdown of the first level into subgroups;
• level 3: specifies the objects contained in the second level.

Below a table with some of the categories of the UniFormat classification system.

The elements subdivision in the table, from the widest category up to the detail element, is highlighted in different colours, for example: The Substructure category is marked with a capital letter A and is specified in the two sub-categories of the Foundations and Basement construction. The Foundations subcategory is marked with the code A10. This latter one includes the individual Standard Foundations element marked with the code A1010.

As for the other classification systems, each element is associated with an alphanumeric code based on the specific level of information.

This classification system should be given credit for having enhanced the analytical efficiency of the production process.

The image below shows how to classify any entity (for example a roof) in an IFC model.

You can try to classify the elements of any 3D model yourself (IFC, DWG, SKP, etc.), using usBIM.viewer+ for free. Simply open a file, (here you can download an example file) and select the “Edit” command in the “Classification” section from the ribbon bar.

IFC and classification systems in construction | Example of UniFormat classification with usBIM.viewer+

MasterFormat

MasterFormat was published in 1963 and updated in 1974 by the North American research institutes CSI (Construction Specification Institute) and the CSC (Construction Specification Canada).

MasterFormat is currently the most widely used classification system in the construction industry in the United States of America and Canada. This classification system has a peculiar hierarchical structure that is divided into groups and subgroups which are not numbered.

On the contrary, the “divisions” associated with the subgroups are numbered. Each division, in turn, is divided into “sections” marked by a six-digit number.

IFC and classification systems in construction | Example of MasterFormat classification with usBIM.viewer+

The ISO 12006-2 standard

Let’s now move on to analyzing ISO 12006 which we can define as the framework of all classification systems in construction. The first version of ISO12006 was written by the International Organization for Standardization and published when international systems for the standardization of classification systems were still lacking. Revised subsequently while keeping pace with technological progress and the development of different classification systems, the purpose of ISO 12006-2 is to create structures or better tables through which to classify types, elements and relationships based on a particular specialization.

The following tables describe the entire construction process of a building, from the preliminary design phase, to construction and maintenance.

A.1 Construction entities (by form)

• Buildings
• Pavements/landscaping
• Tunnels (and other underground constructions)
• Embankments, retaining walls, dams
• Tanks, silos, ecc.
• Bridges, viaducts, ecc.
• Towers, masts, superstructures
• Pipes, ducts, cables

A.2 Construction entities (by function or user activity)

• Hospital buildings
• Health centre buildings
• Footbridges
• Airport terminal buildings
• School buildings
• Ecc.

A.3 Construction complexs (by function or user activity)

Fino ad arrivare ad elementi di dettaglio

A.7 Elements (by characteristic predominating function of the construction entity)

• Floors
• Roofs
• Columns
• Ecc.

A.8 Designed elements (element bytype of work)

Alle relazioni e agli attori che legano i processi costruttivi.

A.10 Management processes (by type of process)

• Administrative management
• Financial management
• Marketing/sales management
• Ecc.

A.15 Construction agents (by discipline)

• Clients
• Architects
• Civil engineers
• Ecc.

The ISO12006-2 classification methodology is that of a hierarchical structure that branches out at different levels and proceeds gradually from more general to more detailed information. However, this system still limits itself to providing basic principles, resulting an incomplete and operational classification system.

IfcClassificationReference: IFC and construction classification systems

The IFC standard also uses data classification tools to communicate information useful in the construction process and not expressed by a standard language.

It is evident that, in many cases, it may be necessary to add information to the model, implementing the data already present expressed by the standards.

This operation involves the use of a language not encoded by the IFC standard where the vocabulary to be adopted should be agreed upon and disclosed to all interested parties (during the design, execution, maintenance and dismissal phases).

The IfcClassificationReference class is a form of “lightweight” classification that allows you to break down a building into parts (defined according to the type of classification chosen).

This classification improves model reading by adding details to its entities, while providing the possibility of selecting them in an easy manner. For example, by assigning a different classification to the single-leaf and to double- hinged windows, we could simply select them and have a more detailed picture of the information relating to “window” objects.

IFC and classification systems in construction: how to operate

How to create new classifications in an IFC model?
Below we’ll show you how to do it with a practical example. Follow these steps:

• download and install usBIM.viewer+ for free
• click on File>Open and select the IFC file to upload
• click Edit IFC>Edit to edit the model
• select (manually or with the help of selection groups) the objects to which add a classification
• click on Edit from the toolbar in the Classifications section
• from the pop-up dialog box, choose the type of classification (Masterformat, Omniclass, Uniclass, etc.) and the associated subcategories
• once concluded the operation, click on Confirm.

Setting up IfcClassificationReference in usBIM.viewer+

After you have selected the entity of your interest, you can read the information you have just assigned in the Properties toolbox on the right-hand side:

• IfcClassificationReference expresses the code that corresponds to the information that we have added
• IfcClassification expresses the type of classification adopted.

Check a classified IFC file with other software

If you receive an IFC file (generated by any software) containing object classifications, you can verify this information in the following way:

• open the file with usBIM.viewer+
• select an entity
• read the following values from the properties toolbox:
  • IfcClassificationReference contains the code
  • IfcClassification contains the classification system.

Verification of entities classification with usBIM.viewer+

In the image above you could observe how the selected window has been classified with the code Ss_25_30_95_26 that refers to the UniClass 2015 system.

Download the example file and the software to open it

IFC file example

usBIM.viewer+