What the structural set contains
A small building's structural set runs to a handful of sheets: general notes, a foundation plan, one framing plan per elevated level and the roof, and sheets of sections and details. The general notes sheet is unusually important on structural drawings, because it carries the design loads, the material strengths, the reinforcement cover and a great deal of information that never appears on any plan.
The plans are drawn at the same scale and on the same grid as the architectural plans, which is what lets the two be read side by side. On a set produced from a shared model they will agree exactly; on any set they should agree, and checking a few points where they must agree is a fast way to test how carefully a set was coordinated.
Structural sections and details answer how members connect: a beam to a column, a joist to a beam, a slab to a foundation wall. Those are the drawings a steel fabricator and a rebar detailer work from, and they are drawn at a much larger scale than the plans.
The foundation plan
A foundation plan shows what is below the ground floor: strip footings under walls, pad footings under columns, foundation walls, piers, and the slab. Footings are drawn as dashed rectangles because they are below the cut, and each is tagged with a mark that resolves in a footing schedule giving its length, width, depth and reinforcement.
The slab itself carries notes rather than geometry: thickness, reinforcement, the vapour retarder beneath it, the sub base, and the location of any thickening, depression or construction joint. A depressed slab at an entrance or a shower is drawn with a boundary and a note giving the amount of the drop, and that boundary is worth finding because a depression missed at the pour is expensive to correct.
Read a foundation plan by first identifying every column location on the grid, then finding the pad footing at each one, then following the strip footings around the perimeter. Anything left over, a pier, a pit, a thickened edge, is a special condition and there will be a section marker pointing at a drawing of it.
- Dashed outlines: below the cut, which on a foundation plan is most of the drawing.
- A footing tag resolves in a footing schedule, not in a note on the plan.
- Slab information is carried as notes, not as drawn thickness.
- Section markers on a foundation plan point at wall sections through the foundation.
Framing plans and member callouts
A framing plan shows the structure of one level: beams, girders, joists, and the deck or slab they support. Each member carries a callout naming its size and often its grade, written as a line of text along the member itself. A steel beam callout gives the shape, the nominal depth and the weight per foot, so a reader can identify the member without any lookup at all.
Joists and other repeated members are usually shown with a single line and an arrow or a note giving the direction and the spacing, rather than being drawn one by one. That saves the drawing from becoming unreadable, and it means the number of members is a calculation from the spacing rather than a count off the paper.
The direction a member spans is important information and it is drawn deliberately. Beams span between columns; joists span between beams; the deck spans between joists. Following that chain from the deck back to the columns and down to the footings is how you read a structure, and it is the reading that tells you which walls are load bearing and which are not.
Why the grid does the locating
Structural drawings dimension to grid almost exclusively. A column is at the intersection of two grid lines, or it is offset from that intersection by a dimension that says so. A beam runs along a grid line. An opening in a slab is dimensioned from grid lines. That consistency is what allows the structural and architectural drawings to describe the same building without either referring to the other.
It also means that reading a structural plan without first reading the grid is nearly impossible. Every question you ask will be answered in grid coordinates, and if you do not know which letters run which way, the answers will not mean anything. Spend the first minute on a structural sheet learning its grid.
Where the structural grid and the architectural grid differ, which happens occasionally on a renovation, there will be a note and a drawing showing the relationship. That is a red flag worth taking seriously, because it is exactly the situation in which two trades can set out from different origins.
Where the structural drawing stops
A structural drawing shows the structure and nothing else at full weight. Walls appear only where they are structural, partitions may not appear at all, and finishes never appear. If you need to know where a partition goes, that is an architectural question and the structural sheet is not the record for it, even if a line happens to be drawn there.
Conversely, an architectural plan is not the record for a beam size, and a beam drawn as a dashed line above the ceiling on an architectural plan is a courtesy rather than an instruction. When the two disagree about a structural member, the structural drawing governs, and when they disagree about a partition, the architectural drawing governs. Knowing which document owns which fact is most of the skill.
The specification adds a third layer for materials, testing and tolerances. The drawing says a footing is three feet square and two feet deep with a given reinforcement; the specification says what the concrete must achieve and how it is tested. Neither is complete without the other.