Plans, sections and details

Brandt opens the third week with a pencil sketch on the board: a long rectangle with six sawtooth peaks along its top, a slab under it and two short lines for the walls. It is Callum's makerspace, drawn the way architects draw it in the first ten minutes of design. Then he asks Callum to tell him, from that sketch, how far the glazing sits from the end of the roof tooth, what the flashing is made of, and where the rain goes. Callum laughs. The sketch does not say. Brandt's point is that every drawing answers a limited set of questions at its own scale, and a set works only if each question is answered somewhere, once, at a scale large enough to answer it properly. That chain from the whole to the part is the subject of this lesson.

The hierarchy of drawings

Construction drawings work from the general to the specific. Plans and elevations at small scale show the whole building and the relationships among its parts. Building sections cut through the whole to show heights and the relationships between floors. Wall sections at a larger scale show the assembly of a wall from foundation to roof. Details at the largest scale show how individual pieces meet. Each level carries only what it can show clearly and refers the reader to the next level for the rest. A plan at 1:100 can show that a wall exists, how long it is and which wall type it is, but it cannot show how the air barrier turns the corner at the window; that belongs in a detail at 1:5 or larger.

Choosing the scale is a design decision. Too small, and the drawing cannot show what it must; too large, and the sheet fills with empty space and the set grows without adding information. Brandt adds that the scale must be chosen from the scales that the measuring tools of the trades use. Metric drawings use 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and 1:200, and odd scales such as 1:75 should be avoided because a site superintendent with a scale rule cannot read them.

Plans

A floor plan is a horizontal section cut through the building, by convention about 1.2 m (4 ft) above the floor, looking down. Everything cut by the plane, such as walls, columns and window openings, is drawn with the heaviest lines; everything seen below the plane, such as floor patterns, casework and steps, is drawn lighter; and things above the plane that matter, such as the edge of the mezzanine or the beams of the roof teeth, are drawn dashed. The line weights are not decoration. They let a reader tell in a glance what is solid and what is beyond, and a plan drawn with every line at the same weight is much harder to read even when every line is correct.

On the plans the students learn to separate what each plan is for. The floor plans of the east wing will show walls, doors, windows, stairs, the grid of columns, wall type tags, door marks, room names and numbers, dimensions and the references to sections, elevations and details. They will not show furniture, ceiling lights or finish patterns, which belong on the furniture plan, the reflected ceiling plan and the finish plan or schedule. Crowding every kind of information onto one plan is a common student habit, and it produces plans in which nothing can be found.

Dimensions deserve their own rules. Brandt asks the team to dimension the east wing from the structural grid, because the grid is set out first on site and everything else is located from it. Strings of dimensions run from grid to grid, then from grid to the face of each wall or opening, with an overall dimension outside them. Each dimension states its reference: face of framing, face of finish or centre line, with a general note saying which applies unless noted otherwise. Strings must close, so that the sum of the parts equals the overall, and no dimension should be stated twice. A plan that says a room is 6,000 in one place and 5,950 in another invites the contractor to pick the one that suits them.

Elevations, sections and wall sections

Exterior elevations show the building's faces: the openings, the materials, the joints and the heights of floors, roofs and parapets, measured from a datum such as the finished ground floor. On the east wing the north elevation is the most demanding, because the six roof teeth must be shown with their glazing, the flashing at each valley and the gutters and downspouts that carry the water away. Interior elevations, usually on the large-scale sheets, show walls with many items on them, such as the makerspace's tool wall and the washrooms.

Building sections cut through the whole building and show how the floors, roof and structure stack up, with floor-to-floor heights and roof slopes. Wall sections cut through one exterior wall at a larger scale and show every layer from the footing and the slab edge, through each floor, to the parapet or the eave, with the structure, insulation, air barrier, cladding and interior finishes labelled. In many offices the wall sections are where the building is really described; a contractor who wants to understand how the envelope works will go straight to them. Callum's wall sections for the east wing will cut through the north wall under a roof tooth, the south wall of the multipurpose wing and the brick base on the avenue.

Details show the places where the wall sections are too small to be clear: the head, sill and jamb of each window type, the valley of each roof tooth, the base of the wall at the slab, the parapet and the canopy connection. Brandt's advice is to draw a detail for every condition that is not obvious and not repeated elsewhere, and to resist the temptation to fill sheets with details copied from previous projects. A detail library is useful only if every detail is checked against this building, its materials and its dimensions. A standard detail of a parapet for a steel-stud wall placed in a set for a mass timber building is worse than no detail at all, because it looks authoritative.

References that lead the reader

The drawings are linked by reference symbols. A section cut on a plan is shown by a line with a symbol at each end: a circle divided horizontally, with the drawing number above the line and the sheet number below it, and an arrow or a filled triangle showing the direction of view. An elevation mark looks similar. A detail callout is a circle or a cloud around the area enlarged, connected by a leader to the same kind of bubble. On the target sheet, each drawing carries a title with the same bubble, its name and its scale.

References only work if they are complete and correct in both directions. Every symbol on a plan must point to a drawing that exists on the sheet named, and every section, elevation and detail should be called out from somewhere, or the reader will never know which part of the building it describes. Broken references are among the most common errors in sets, usually because a drawing was moved to another sheet late in the job. Most modelling software now updates references automatically when a view is moved, but only for views that are placed through the software; a detail drawn as linework and labelled by hand will not update.

# Check that every reference symbol points to a drawing that exists, and that
# every drawing is referenced from somewhere.
drawings = {  # sheet -> drawing numbers placed on it
    "A-201": [1, 2], "A-301": [1, 2, 3], "A-311": [1, 2, 3, 4],
    "A-501": [1, 2, 3, 4, 5, 6, 7], "A-401": [1, 2],
}
references = [  # (from sheet, drawing number, target sheet)
    ("A-101", 3, "A-301"), ("A-101", 1, "A-301"), ("A-101", 2, "A-201"),
    ("A-101", 1, "A-311"), ("A-102", 2, "A-311"), ("A-102", 3, "A-311"),
    ("A-311", 4, "A-501"), ("A-311", 5, "A-501"), ("A-311", 6, "A-501"),
    ("A-301", 7, "A-501"), ("A-101", 1, "A-401"), ("A-311", 8, "A-501"),
]
broken = [(f, n, t) for f, n, t in references if n not in drawings.get(t, [])]
called = {(t, n) for f, n, t in references}
orphans = [(s, n) for s, ns in drawings.items() for n in ns if (s, n) not in called]
print("Broken references:")
for f, n, t in broken:
    print(f"  on {f}: {n}/{t} points to a drawing that does not exist")
print("Drawings never referenced:")
for s, n in sorted(orphans):
    print(f"  {n}/{s}")
print(f"{len(references)} references checked, {len(broken)} broken, {len(orphans)} orphans")

Broken references:
  on A-311: 8/A-501 points to a drawing that does not exist
Drawings never referenced:
  1/A-201
  2/A-301
  4/A-311
  2/A-401
  1/A-501
  2/A-501
  3/A-501
12 references checked, 1 broken, 7 orphans

When the students run the check on their own early set, it finds a reference to a detail 8 on A-501 that does not exist and several details that nothing points to. Callum recognizes the orphans: they are details he drew for the first version of the roof teeth before the number of teeth was reduced from eight to six. They were never deleted, and in a real set they would have been priced.

Notes and keynotes

Drawings also carry words: room names, material labels and notes. Brandt asks for notes that are short, consistent with the specifications and written in the same terms. A label on a wall section should name the material generically, such as 'mineral wool insulation, 150 mm', and leave the product, standard and installation to the specification section that covers it. Labels such as 'rigid insulation as per spec' are useless, because they neither describe the material nor say which section to read. Many offices use keynotes: short reference codes on the drawing, often tied to the specification section number, with a legend on each sheet giving the full text. Keynotes keep the drawings uncluttered and the terms consistent, at the cost of making the reader look up each note. Whichever system is used, it must be used the same way on every sheet.

Exercise 3: following one element through the set

• Choose the north wall of the makerspace and list every drawing in the east wing set that should show it, from plan to detail.
• For each drawing, write the questions about the wall that it answers and those it leaves to the next drawing.
• Draw the reference symbols that link the drawings, and check that every link works in both directions.
• Write the labels for the wall section using generic material names that match the specification sections.

Self-check

• Does each drawing answer the questions its scale can answer, and refer the rest?
• Do my dimension strings close and state their reference faces?
• Does every reference point to an existing drawing, and is every drawing referenced?
• Are my notes generic, short and consistent with the specifications?