Plan sheet numbers - Explained

The sheet numbers assigned to the plans and drawings identify them with their classification, context, and purpose. Architects and Engineers use a numbering system to organize the sheets that pertain to different divisions of work, drawing types, the subject they depict, and more. Companies follow numbering system conventions that may differ from one region to another. To mitigate confusion created at various levels, it becomes evident to follow standard systems. 

There are many standards, such as the United States National CAD Standard, National BIM Standard, British CAD standards, Eurocode CAD standards, etc. By and large, these standards follow a similar pattern. However, there are some differences between them.

This article explains the numbering scheme per the US National CAD standard, with the prefixes and abbreviations used for the sheet numbering.

The sheet number comprises a sequence of alphanumeric characters with segments identifying the classification of the sheet in a hierarchical structure.

The US National CAD standard follows a three-segment structure containing the discipline designator, the sheet type, and the sequence number.

1. Discipline Designators

The first segment of the sheet number with one or two characters. These identify the construction discipline or the division of work that the sheet pertains to, for e.g., architectural, plumbing, electrical, and structural. For instance, "A" represents architectural drawings.

The discipline designator is crucial for organizing drawings by type of work. For example, sub-contractors find it helpful to have plumbing drawings grouped together, eliminating the need to sift through unrelated electrical or structural drawings.

The discipline designator can be a single-letter or a double-letter. The single-character discipline designator would suffice for projects with less number of sheets, where sheets pertaining to a single division can be further classified with the sequence numbers. 

Large and complex projects where a large number of sheets are involved require two character discipline designators. The second character serves to subdivide the discipline identified by the first character. For example, in a big shopping mall renovation, it makes sense to separate lighting and power drawings across multiple electrical sheets. But for a small home renovation, it's often easier to put them on the same or consecutive sheets. This flexibility suits the needs of various projects.

Level 1 Discipline Designator

The first letter designator typically signifies the discipline or category to which the drawing/information pertains. It serves as a quick reference to the primary focus of the content. The following table gives a list of first-letter designators with their disciplines. The list is in the order of how the sheets pertaining to the different disciplines are arranged in the plan set.  

Level 2 Discipline Designator

The second letter designator provides additional specificity within the broader discipline indicated by the first letter. It refines the focus of the content, allowing for more detailed categorization. For example:

• EL denotes an Electrical Lighting plan within the electrical discipline.
• EP denotes an Electrical Power layout plan within the same electrical discipline.

By incorporating a second letter, the system becomes more nuanced, allowing for a more granular classification of drawings and documents and facilitating efficient organization and retrieval in complex projects. Please see the table below for the standard 2-level discipline designators.

Delimiter

The discipline designator is followed by a delimiter, usually a space or a hyphen, to separate it from the next segment, namely the sheet type identifier. For example, A-101.

2. Sheet Type

The sheet type identifier plays an important role in bringing order to the diverse array of drawings within a single discipline, strategically organizing drawings from the most general to the most specialized.

Organizing Hierarchy

• Plans (Most General) - Plans take the lead as the most general drawings. They provide a bird's-eye view, offering a comprehensive understanding of the project's overall design.
• Elevations and Sections (More Specific): As we zoom in, elevations and sections come into play. These drawings offer a more detailed perspective, focusing on specific areas or aspects of the project.
• Details and Schedules (Most Specific): The final act belongs to details and schedules—the most specific type of drawings. Here, every minute detail is outlined, ensuring nothing is left to chance.

To simplify, picture it as telling a story. You start with the big picture, then zoom in to highlight important scenes, and finally, you delve into the intricate details that bring the narrative to life.

The following table shows the standard numbers used for different sheet types in alignment with the US National CAD Standard:

Delimiter

In usual practice, the sheet type identifier continues with the sheet sequence number without any delimiters in between. For example, A-101.

3. Sequence number

The sheet sequence number is a two-digit identifier assigned to each sheet in a series of drawings within the same discipline and sheet type. 

• The numbering starts from 01, followed by 02 through 99.
• Although many projects may only need single-digit numbers, the standardized two-digit sequence number facilitates efficient sorting.
• The numbering can be non-sequential, with gaps in the order. This allows seamless incorporation of future additions between the existing sheets in a set. 
• User-defined suffixes can be added to the sheet sequence numbers with delimiters, like hyphens and dots. This is useful to mark a sheet as a supplemental sheet or a partial revision. For Example, A-101-R1.

Commonly used 2-level Discipline Designators