What Do SC1, L1, GB1 Mean on Steel Drawings?

Marks like SC1, L1, GB1, F1, and WF1 on structural drawings are schedule references — short labels that point to a separate schedule sheet where the actual size, material, and details are listed. The mark itself doesn't tell you the section size. The schedule does.

Decoding the Letter Prefix

Different prefixes signal different schedule categories. Common conventions on US commercial drawings:

| Prefix | Stands For | Schedule Type | Section Type | |--------|-----------|---------------|--------------| | SC | Steel Column | COLUMN (SC) SCHEDULE | HSS, W-shapes | | C or COL | Column (older convention) | Same as SC | Same | | L | Ledger | LEDGER (L) SCHEDULE | Steel angles | | GB | Grade Beam | GRADE BEAM SCHEDULE | Concrete + rebar | | F | Footing (isolated) | ISOLATED FOOTING SCHEDULE | Concrete | | WF | Wall Footing (continuous) | CONTINUOUS FOOTING SCHEDULE | Concrete | | B | Beam | BEAM SCHEDULE | W-shapes, channels | | J | Joist | JOIST SCHEDULE | OWSJ, K-series |

Engineers don't follow a strict convention — different firms use different prefixes — but these are the most common across US drawing packages.

How the Number Works

The number after the letter is just an index. SC1 is "Steel Column type 1," SC2 is type 2, etc. Two columns with the same mark are the same section (same size, same length, same base plate). Different marks = different specs even if they look similar on the plan.

Some drawings use suffixes (SC1A, SC1.1, SC-1) to indicate variants — same general design, different detail. The convention varies by firm.

How to Look Up a Mark

Find the schedule sheet (usually S008 or similar in the structural set)
Locate the relevant schedule (e.g. COLUMN (SC) SCHEDULE)
Find the row matching the mark
Read the section across to the right

For takeoff: every callout of SC1 on every plan page is the same column type — same section, same weight, same price. You count every callout and multiply.

What If the Mark Isn't in the Schedule?

That's a real problem. Possible causes:

The mark on the plan is a typo (engineer wrote SC1 but the schedule only has SC2-SC4)
The schedule sheet is missing from the issued drawing set
The mark is on a revision sheet that supersedes the schedule

Software-aided takeoffs flag unresolved marks for review. Steelflo shows them as "Schedule? — Possible: HSS10X10X5/16" so you can confirm or correct without losing the count.

FAQ

Q: Are SC and SC1 the same mark? No. SC alone is rarely a mark — it's just the prefix. The schedule will only have numbered entries like SC1, SC2, etc. If you see a callout that's just SC without a number, it's likely a generic note ("verify with SC schedule") and not a specific column.

Q: Why don't drawings just write the section size on the plan? On large drawings the same section appears 50+ times. Writing HSS10X10X5/16 everywhere makes the drawing unreadable. The schedule consolidates all the specs into one place.

Q: Can I find these marks myself or do I need software? You can manually — open the schedule sheet, write down each mark + section, then go through plan pages counting. For a 60-column job this is 30-60 minutes. Software automates this entirely.