Sheet numbering
A sheet number is an address, not a label. A letter says whose drawing it is, the first digit says what kind of drawing it is, and the rest is a sequence. Once you can read the address you can find a drawing in a set you have never opened, which is the whole reason the convention exists.
The discipline designator
The letter at the front names the discipline that produced the sheet, and therefore whose scope the answer lives in. That is the fastest way to narrow a search: a footing size is structural, a duct size is mechanical, a setback is civil, and none of those questions belongs on an architectural sheet even though the geometry may appear there as a background.
| Letter | Discipline | What it holds |
|---|---|---|
| G | General | Cover sheet, sheet index, symbols legend, abbreviations, general notes, code information. |
| C | Civil | Site plan, grading, drainage, paving, site utilities, erosion control. |
| L | Landscape | Planting, hard landscape and irrigation, on projects large enough to need them. |
| S | Structural | Foundations, framing plans, structural sections and details, structural notes and schedules. |
| A | Architectural | Floor plans, ceiling plans, elevations, sections, wall sections, details, schedules. |
| I | Interiors | Furniture, finishes and interior detail, where they are separated from the architectural set. |
| Q | Equipment | Owner supplied and specialist equipment layouts, such as kitchen or laboratory fit out. |
| F | Fire protection | Sprinkler and standpipe layouts, alarm devices where they are not on the electrical set. |
| P | Plumbing | Supply and drainage plans, fixture schedules, riser diagrams. |
| M | Mechanical | Ductwork, equipment, controls, mechanical schedules and details. |
| E | Electrical | Power, lighting, home runs, panel schedules, single line diagrams. |
| T | Telecommunications | Data, voice and audio visual pathways and outlets. |
The sheet type digit
The first digit after the letter says what kind of drawing the sheet holds, and the order runs from far away to close up: general information, then plans, then elevations, then sections, then large scale views, then details. Schedules and diagrams sit at the end because they are tables rather than drawings.
| Digit | Type | What it holds |
|---|---|---|
| 0 | General | Notes, legends, schedules of general application and code information for that discipline. |
| 1 | Plans | Horizontal views: floor plans, roof plans, foundation and framing plans, site plans. |
| 2 | Elevations | Vertical views with nothing cut, exterior and interior. |
| 3 | Sections | Building and wall sections, where the drawing cuts through the building. |
| 4 | Large scale views | Enlarged plans, enlarged elevations and enlarged sections of a part of the building. |
| 5 | Details | Assemblies and joints at a large scale, usually with hatch doing most of the naming. |
| 6 | Schedules and diagrams | Door, window, room finish, equipment and panel schedules, and riser diagrams. |
| 7 | User defined | Whatever a project needs that the other categories do not cover. |
| 8 | User defined | A second category available to a project for the same reason. |
| 9 | Three dimensional | Isometric, axonometric and perspective views, where a set includes them. |
The Millbrook set as a worked example
The sixteen sheets below are the set used throughout this site. Read the number of each one before you read its title and you will find that the title rarely surprises you. That is the test of whether you have the convention: the number should be a prediction, and the title should confirm it.
| Sheet | Reads as | Title |
|---|---|---|
| G-001 | General, general | Cover Sheet, Sheet Index, Project Data |
| G-002 | General, general | Symbols, Abbreviations and General Notes |
| C-101 | Civil, plans | Site Plan |
| A-101 | Architectural, plans | Level 1 Floor Plan |
| A-102 | Architectural, plans | Level 2 Floor Plan |
| A-121 | Architectural, plans | Level 1 Reflected Ceiling Plan |
| A-201 | Architectural, elevations | Exterior Elevations |
| A-301 | Architectural, sections | Building Sections |
| A-401 | Architectural, large scale views | Wall Sections and Details |
| A-501 | Architectural, details | Enlarged Plans and Interior Elevations |
| A-601 | Architectural, schedules and diagrams | Door, Window and Room Finish Schedules |
| S-101 | Structural, plans | Foundation Plan |
| S-201 | Structural, elevations | Level 2 Framing Plan |
| M-101 | Mechanical, plans | Level 1 Mechanical Plan |
| P-101 | Plumbing, plans | Level 1 Plumbing Plan |
| E-101 | Electrical, plans | Level 1 Power and Lighting Plan |
Where the convention bends
Offices vary. Some sets use two digits for the type on very large projects, some prefix a level or a building designation, and renovation sets often carry a demolition series of their own. The sheet index on the cover is always the authority on what a given set actually contains, and where a project defines its own numbering it says so on a general sheet.
One rule is close to universal: a sheet number is not renumbered after a set is issued. Doing so would invalidate every callout, submittal and record that referenced it. A sheet added late takes the next number in its own series, and the index is reissued to record it.