Architectural sheet numbering: the NCS standard and what A-101 means

How the NCS sheet numbering system works

The United States National CAD Standard (NCS), published by the National Institute of Building Sciences, takes its sheet numbering from the Construction Specifications Institute's Uniform Drawing System (UDS). Every sheet number has three parts:

1. Discipline designator. One or two letters for the discipline: A for architectural, S for structural, M for mechanical.
2. Sheet type designator. One digit for the kind of drawing: 1 for plans, 2 for elevations, 5 for details.
3. Sequence number. Two digits, 01 to 99, that order sheets of the same discipline and type.

So A-101 reads as architectural, plans, first sheet, and A-201 is the first elevation sheet. The standard also allows user-defined characters after the sequence number, for example to mark a construction phase.

Why there is a hyphen in A-101

The discipline field is two characters wide. The second character is an optional modifier that splits a discipline, such as AD for architectural demolition or AS for architectural site. When there is no modifier, the hyphen holds its place, so A-101 and AD101 are both correct and every number in the set stays the same length. Modifiers help on large projects; most smaller sets use the single letter.

Discipline designators: the NCS letter codes

These are the Level 1 discipline designators in the order the NCS lists them, which is also the usual order of the bound set.

Sheet type designators: what the digit after the letter means

The first digit after the discipline says what the sheet holds, and it means the same thing in every discipline.

So P-101 and E-101 are both plans, and many firms line up sequence numbers across disciplines so the first floor is 101 in architectural, structural and mechanical alike. Small sets often combine plans and elevations on one sheet; number it for its main content and name it for everything on it.

A typical architectural sheet index

The architectural part of a modest set might read like this. Building sections and wall sections share a type digit but start their own runs at A-301 and A-311, leaving room to grow.

The usual discipline order in a drawing set

Sets are commonly bound in the NCS order above: general information, then hazardous materials, survey and the site, then structural, architectural and interiors, then equipment and the building systems. Within a discipline, the type digits run the sheets from general to specific on their own.

Office standards vary. Some firms put architectural ahead of structural, and the order of plumbing, mechanical and electrical differs from office to office. Where an owner or permit office sets an order, follow it; some electronic plan review systems require the sheet index in NCS discipline order, so check with your authority having jurisdiction. Our permit submission checklist covers the rest of what a permit set needs.

Common alternatives to A-101

Plenty of firms number sheets their own way. The variants you will meet most often:

• A1.01: a series digit before the decimal and a two-digit sequence after it. Often follows the firm's own series, so A2.01 may be a plan rather than an elevation.
• A-1.1: the same idea with a one-digit sequence. Past nine sheets in a series, the numbers stop sorting cleanly.
• A101: the NCS number without the hyphen.
• A-1, A-2, A-3: a plain sequence. The number says nothing about the sheet, and A-10 lands before A-2 in most file lists.

Any of these works if it is applied consistently. Agree the scheme with your consultants at kickoff, so nobody reads your A2.01 plan as an elevation, and write it into the project standard. Some permit offices require NCS discipline letters but leave the digits after them to the designer, so a decimal scheme can still comply.

Canadian sets commonly use the same discipline letters, and some Canadian owners, such as the University of Calgary, publish drawing standards adapted from the NCS. As in the US, the owner's standard wins where there is one.

How to choose and keep a sheet numbering system

• Pick the standard before construction documents. Title blocks, the sheet index template and your consultants' sheets all depend on it, and changing it later means touching every sheet.
• Check the owner's and the jurisdiction's requirements first. Public owners, universities and some permit offices publish their own formats, and they vary. Confirm with the authority having jurisdiction before you lock the scheme in.
• Leave gaps in the sequence. Number floor plans A-101 to A-104 and start partial plans at A-111, and an added level never pushes later sheets along.
• Keep the sheet index and the title blocks in agreement. If your authoring tool builds the index from the sheets themselves, let it. If not, check the two against each other before every issue.
• Use the same string everywhere. Title block, index, callouts, PDF file names and bookmarks should all carry the identical number, hyphen included.

What goes wrong when sheets are renumbered late

The number is how everyone else finds a sheet, so changing it after issue costs more than it looks.

• Callouts break. Section marks, detail bubbles and elevation tags point at nothing, or at the wrong sheet, including on consultants' sheets you never see.
• History splits. RFIs, submittal reviews and permit comments cite the old number. Electronic plan review systems that match revisions by sheet number or file name treat a renumbered sheet as a new one, not a revision.
• The index and the title blocks drift. Renumbering is when they fall out of step, and that mismatch is exactly what a plan reviewer writes up.

To add a sheet after issue, use a gap in the sequence or a suffix, such as A-201A, or A-201.1 in a decimal scheme, so no existing number moves. Retire a dropped sheet's number rather than reusing it. For keeping each sheet's versions straight, see how to track drawing revisions.

How SketchWeave uses your sheet numbers

SketchWeave runs in the browser, works alongside Revit, AutoCAD or Archicad, and is built around the sheet number, whichever scheme you use.

• Import reads numbers off the title block. Import the set as one PDF or a folder of one PDF per sheet, and show SketchWeave once where the sheet number and name sit on your title block; it reads both off every page. Pages that didn't read, such as a cover page, are flagged before anything is imported, so you can untick them or correct the number in place.
• The number is how a drawing finds its sheet. A page whose number a sheet already has becomes that sheet's next drawing version; the rest become new sheets. So a renumbered page arrives as a new sheet, one more reason to settle numbers early.
• The set is a deck in sheet-number order. Each sheet carries its name, status, notes and attachments, so the deck reads like your sheet index. See Drawing Set Management.
• Submissions follow the same order. Order a submission by sheet number in one click, and Assemble merges each sheet's current drawing into one PDF in that order, recording which version of every drawing went out. See Submission assembly.

Frequently asked questions

What does A-101 mean on a drawing?

A-101 is the first architectural plan sheet in a set numbered to the US National CAD Standard: A for architectural, 1 for plans, and 01 for the first sheet of that type.

What is the standard for architectural sheet numbering?

In the US it is the National CAD Standard, which uses the Uniform Drawing System format: a discipline designator, a one-digit sheet type and a two-digit sequence number. Many firms use a variation, and owners or permit offices can set their own, so check each project's requirements.

Should sheet numbers have a hyphen?

Under the NCS the hyphen holds the place of the optional second discipline character, so A-101 has one and AD101 does not. Writing A101 instead is fine if the whole set, the sheet index and every callout do the same.

What sheet number does the cover sheet get?

In an NCS set the cover sheet falls under the General discipline with sheet type 0, so it is commonly G-001. Some firms leave it unnumbered.

How do you number a sheet added after the set is issued?

Use an unused number in the right series, or a suffix such as A-201A. Avoid renumbering issued sheets, because callouts, RFIs and permit comments all cite the old numbers.