MasterFormat (CSI)

In short

• MasterFormat is the system of the Construction Specifications Institute (CSI) for numbering and organising the specifications of US and Canadian construction projects. It has 50 divisions, numbered 00 to 49. Only 16 divisions existed before 2004, and many numbers are reserved for future expansion. CSI calls it the construction industry’s shared and standardized language for project documentation.

• Section numbers have three to five levels, which means 6 to 10 digits. The digits are written in pairs, one pair per level. Division 00 is Procurement and Contracting Requirements, and Division 01 is General Requirements. The divisions for building services are 21 Fire Suppression, 22 Plumbing, 23 Heating, Ventilating, and Air Conditioning (HVAC), 26 Electrical, 27 Communications and 28 Electronic Safety and Security.

• The current edition is MasterFormat 2026. It is available through CSI Dynamic Standards, together with UniFormat and OmniClass.

Example

The project manual for a US hospital puts all plumbing requirements, including the named products and the “or equal” clauses, into Division 22 sections. A distributor quoting the plumbing fixtures works through those sections and the submittals they require.

Specification sections in a project manual are numbered and grouped by MasterFormat, so a section number is the first thing to look up when you need the requirements for a product line.

What to watch for

• Section numbers show where a product is specified, not which product.

• The spec section usually lists the submittals that are required.

• Older projects may use the numbering from before 2004, when there were 16 divisions.

Not to be confused with

• STLB-Bau: the German standard texts for LV positions.

• Bill of quantities: US construction specifications often have no quantities.

• UniFormat: classifies a building by its elements over its life cycle, not by the work result.

• OmniClass: a classification structure for databases and software.