AEC definitions
A building section is a drawing of the building as if it were cut through on a vertical plane, with the portion in front removed. It shows floor-to-floor heights, the structure, and how roofs, floors, and walls stack. The cut line is marked on the floor plan.
Definition
Sections are the vertical counterpart of the floor plan. Where the plan locates a wall, the section shows how tall it is and, at larger scales, what it is made of. A building section cuts through the whole volume. A wall section enlarges one assembly. A detail enlarges a joint. The section mark on the plan, a line with arrows and a sheet reference, is the only reliable way to know where the cut was taken.
In depth
A section mark shows where the cut is and which way you are looking. The sheet number and the detail or section number sit in the mark. If the mark says 1/A-301 and sheet A-301 has no section 1, the set is broken.
Direction matters. A cut looking north shows a different face than the same line looking south. State the direction in the answer to a question, not only the sheet number.
Building sections are often at 1/8 or 1/4 inch to the foot. They establish heights and relationships. They are a poor place to read a flashing lap. Wall sections and details exist so that information has a sheet at a scale where it can be drawn.
If a flashing or a firestopping condition appears only on a small-scale section, and no detail is called, the document is thin. The RFI should ask for the detail, not invent the lap.
Structure, stairs, elevators, ducts, and the reflected ceiling all depend on the floor-to-floor dimension in the section. A plan note that implies a different ceiling height has to be checked against that section before anyone coordinates.
Datums should be explicit: finish floor, top of slab, or top of steel. A dimension that does not say which one it measures from will be read both ways.
A wall section strings the roof, the floor, the window, and the foundation in one vertical cut, and it keys each piece to a detail and a specification. It is where ratings, insulation, and cladding come together.
The wall type on the plan should match the wall section. A plan tag that says Type A, when the only wall section drawn is Type B, is a coordination miss. Do not assume they are the same wall with a wrong tag.
The architect's section shows occupied heights and the envelope. The structural section shows framing depths and elevations of steel or concrete. Both can be true and still conflict if one moved and the other did not.
Coordination of a section is a comparison of those two cuts at the same grid. A deeper beam that appears only on the structural section changes the plenum the architect drew.
Examples
Section 1/A-301, looking north at grid C, shows 14 foot floor-to-floor. The mechanical main is coordinated to the plenum that height leaves under the beam.
A wall section at grid 4 shows a 2-hour shaft wall. The plan tag at the same grid says 1-hour. The tag is corrected before permit.
A bidder scales a flashing from the building section at 1/8 inch and orders the wrong lap. The detail at 3 inches to the foot was the sheet that dimensioned it.
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