Structural drawings show how a building stands up: the foundations, the frame of columns, beams and slabs, and how those parts are connected. To read them, start with the general notes (codes, loads, materials), then the foundation plan, then the framing plans level by level, and use the schedules and details that the plans point to. Every member on a plan is a short code: W12x26 is a steel wide-flange beam about 12 inches deep weighing 26 lb per foot, and "#5 @ 12" o.c. EW" means 5/8-inch bars every 12 inches in each direction. Below is how a structural set is organised, how to decode the common callouts in US and UK notation, and how to check the structure against the architectural drawings.
How a structural set is organised
Most sets follow the sheet numbering of the US National CAD Standard: the discipline letter S, then a digit for the type of sheet, then a sequence number. In the NCS order of disciplines, structural sheets come after civil and landscape and before architectural, although many offices put the architectural sheets first.
| Sheet | Usually contains |
|---|---|
| S-0xx | General notes, design loads, materials, abbreviations, legend, special inspections |
| S-1xx | Plans: foundation plan first, then floor and roof framing plans |
| S-2xx | Elevations, for example braced frames |
| S-3xx | Sections |
| S-5xx | Details: connections, footings, slab edges, openings |
| S-6xx | Schedules: footings, columns, beams, piers |
Read the S-0 sheets first. They set the defaults (concrete strength, steel grades, bolt types, "unless noted otherwise" rules) that apply wherever a plan is silent. Our guide to general notes on construction drawings explains what they contain.
The foundation plan
The foundation plan shows what sits in or on the ground. Footings carry marks such as F1 or F2 that point to a footing schedule, where each row gives the size (length × width × depth) and the reinforcement, for example "#5 @ 12" o.c. EW BOT": 5/8-inch bars at 12-inch centres, each way, in the bottom of the footing. Piles or caissons are tagged by cap, with grade beams running between the caps. Look for the elevation of the top of each footing (often written T/FTG), the slab-on-grade thickness and reinforcement note, stepped footings where the ground changes level, and depressed slabs (showers, entrance mats, equipment).
Framing plans
Each framing plan shows one level seen from above: the grid, the columns at grid intersections, and every beam and girder with its size. A steel beam callout can carry three pieces of information. A callout such as W21x44 (14) c=3/4" means a W21x44 beam, 14 shear studs, and 3/4 inch of camber (the slight upward curve built into the beam so it ends up level under load).
- Top of steel (TOS) is the level of the top of the top flange. A general note usually gives it for the whole level, with exceptions marked at individual beams. Framing is set out from the top of steel, not from the finished floor.
- Symbols on the plan mark moment connections, braced frames, slab openings, stepped or depressed slabs and the direction a slab or deck spans. Offices draw them differently, so check the legend on the S-0 sheet.
- Repeated beams may be tagged once with a span tag ("type @ spacing") instead of a tag on every beam. Revit, for example, offers both styles.
Columns, grids and the column schedule
Grid lines run one way with letters and the other way with numbers, and a column is named by its intersection: column C-4 sits where grid C meets grid 4. The column schedule lists the grid positions across and the levels up, showing where the section size changes (often at a splice), and the base plate and anchor rod marks. Concrete columns show their size, the vertical bars and the ties.
How to read steel member sizes
| Callout | Shape | How to read it |
|---|---|---|
| W12x26 | Wide flange (I-shape) | Nominal depth 12 in, weight 26 lb per foot. The actual depth differs slightly from the nominal one. |
| HSS5x4x3/8 | Rectangular hollow section | 5 in × 4 in outside, 3/8 in nominal wall. HSS replaced the older "TS" (tube steel) name. |
| HSS5.563x0.258 | Round hollow section | Outside diameter × wall thickness, in inches |
| L4x4x1/2 | Angle | Leg × leg × thickness, longer leg first |
| C10x15.3 | Channel | Depth × weight per foot |
Unless the notes say otherwise, AISC lists ASTM A992 as the usual material for W shapes and A500 Grade C (or A1085) for hollow sections; the general notes state what the project uses. UK sets name steel sections by the British series (UB and UC), continental European sets by series such as IPE, HEA and HEB, with the grade such as S355 given in the notes.
How to read concrete reinforcement
In US notation the bar number is its diameter in eighths of an inch for bars #3 to #8: a #5 bar is 5/8 inch (larger bars are close to, but not exactly, eighths). Common abbreviations around a bar callout:
- o.c.: on centre, the spacing between bars.
- EW: each way, bars in both directions. EF: each face, bars near both faces of a wall. They are easy to confuse.
- T&B or TOP/BOT: top and bottom of a slab or beam.
- CLR: clear cover, the concrete between the bar and the surface. TYP: typical, the same wherever the condition repeats.
UK drawings follow BS 8666 and the IStructE Standard Method of Detailing. A callout such as 12H16-03-150 B1 reads as: 12 bars, high-yield steel (H), 16 mm diameter, bar mark 03 in the bar schedule, at 150 mm centres, in the outer bottom layer (B1; B2 would be the next layer in). Bar shapes are given by shape codes in the bar schedule.
| Meaning | US | UK (BS 8666) |
|---|---|---|
| Bar size | #5 (5/8 in) | H16 (16 mm high-yield) |
| Spacing | @ 12" o.c. | -150 (mm centres) |
| Position | TOP / BOT, EF, EW | T1, T2, B1, B2 (layers from the face) |
| Which bar exactly | Schedule or detail | Bar mark (03) in the bar schedule |
Welding symbols, the basics
A welding symbol is an arrow with a horizontal reference line. A weld symbol drawn below the line means the weld is on the side the arrow points to; above the line, on the other side; on both sides, both. A small flag where the arrow meets the line means a field weld (made on site), and a circle there means weld all around. For a fillet weld, the size is written to the left of the symbol and the length and spacing to the right. These conventions come from AWS A2.4; anything beyond the basics should be read against the standard and the project's welding notes.
For CJP and PJP groove welds, supplementary symbols and the differences between AWS and ISO, see our full guide to welding symbols.
Sections and details
Plans point to sections and details with reference bubbles: the number on top is the detail, the number below is the sheet. Follow every bubble that touches the area you are checking. Our guides to construction details and plans, sections and elevations explain the symbols.
How to check structure against architecture
- Grids: the structural and architectural grids must match, with the same letters, numbers and dimensions. Check whether both sets dimension to the grid line or to a column face.
- Levels: structural levels are usually top of slab or top of steel, architectural levels often finished floor. The difference is the floor build-up and must be consistent everywhere.
- Slab edges and openings: every stair, shaft, duct and riser opening on the architectural and MEP drawings needs a matching opening on the structural plan.
- Depressed and raised slabs: showers, mats, ramps and equipment pads must be located on both sets.
- Thicknesses: if the architectural section shows a 6-inch slab and the structural drawing 8 inches, raise a request for information rather than choosing one.
Common mistakes
- Scaling off the PDF instead of reading written dimensions.
- Reading top of steel or top of slab as finished floor level.
- Confusing EF (each face) with EW (each way).
- Reading the weld on the wrong side of the joint.
- Missing camber on beam callouts.
- Applying a "typical" detail where the condition is not quite typical.
- Working from a superseded revision of the structural sheets.
- Mixing imperial and metric bar sizes on international projects.
Frequently asked questions
What does W12x26 mean?
A wide-flange steel beam with a nominal depth of 12 inches and a weight of 26 pounds per foot.
What does TOS mean on structural drawings?
Top of steel: the level of the top of the beam's top flange. Framing is set out from it.
What is the difference between EF and EW?
EW (each way) means bars run in both directions. EF (each face) means bars are placed near both faces of a wall or thick element.
What order should I read structural drawings in?
General notes, foundation plan, framing plans from the lowest level up, then the schedules and details each plan refers to.
What do structural drawings include?
General notes and loads, foundation and framing plans, elevations of frames, sections, details of connections and reinforcement, and schedules of footings, columns and beams.
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Related: general notes on construction drawings, how to read construction drawings, Ncored for structural engineers.
All product names, standards and organisations mentioned on this page are trademarks or registered names of their respective owners and are used for identification only. Ncored is an independent product by Noir architects and is not affiliated with, sponsored by, or endorsed by any of them. This page explains common drawing conventions and is not engineering advice; the project's drawings, specifications and engineer of record govern. Individual experiences may vary.