Lesson 4.3
The Section: The Most Honest Drawing
Turn the plan's cut on its side. Slice the building vertically and look at the face you've exposed. Suddenly you see heights, how floors meet walls, how a roof actually sits — the truths a plan and elevation both hide.
Start hereA plan hides height. An elevation hides what's inside. A section hides nothing — it cuts the building open like a dollhouse and shows you the guts.
That's why builders trust sections. You can't fake how a wall meets a floor when you've sliced straight through it.
01 — The vertical cut
Slice down, look across
A section is made by a vertical cut plane through the building. You remove one half and look horizontally at the cut face. Where the plane slices solid material — floors, walls, roof, ground — you draw heavy cut lines. Things beyond the cut that you can see (a far wall, a staircase) are drawn lighter, as seen lines.
The section reveals the building's vertical story: floor-to-ceiling heights, the thickness of a slab, how a window's head and sill sit, where a roof pitches. None of this is visible in plan. Tap below to see what a section uniquely exposes.
Each truth here — height, slab, sill and head, roof pitch — is invisible in plan. The section is where vertical space is designed.
02 — Cut vs seen in section
Poché: the filled-in cut
In a section, the cut material is often filled solid or heavily hatched — a technique called poché (from the French for “pocketed”). It makes the cut walls and floors read as massive and immediately separates them from the lighter spaces and the seen elements beyond. Poché is lineweight hierarchy taken to its logical end: the cut isn't just heavy, it's solid black.
| In the section | Treatment |
|---|---|
| Walls, floor slabs, roof, ground — cut through | Heavy cut line, often poché (filled/hatched) |
| Far wall, stairs, furniture beyond the cut | Medium seen lines |
| Things above/behind, implied | Light or dashed |
03 — Where the cut goes
Cut through the interesting part
A section is only as useful as the line it's cut along. Slice through a blank wall and you learn little; slice through the stair, the tall window, the change in level, and the section earns its place. On the plan, a section line with arrows marks exactly where the cut is taken and which way you're looking — so the section and plan always agree. Choosing that line well is a real design skill.
Beyond documentation, the section is where architects design the experience of height and light. A double-height living space, a clerestory window throwing light deep into a room, a stepped floor, a sloping ceiling — these are all section ideas, invisible in plan. Many celebrated buildings are essentially brilliant sections. When you learn to think in section, you stop designing flat floor layouts and start shaping three-dimensional volume. It's the drawing that most rewards imagination, because it shows the dimension people actually move through vertically: up.
12 minutes
- Use the toggles above: name one thing the section shows that a plan never could.
- By hand, draw a simple section of a one-storey room: ground line, two walls cut, floor slab, a roof, and a window with its head and sill heights. Poché the cut walls solid.
- On a plan of that room, draw the section line with arrows showing where your section was cut.
Key terms — added to the Drawing Atlas
- Section
- An orthographic drawing from a vertical cut, looking across. Reveals heights and how the building is constructed.
- Poché
- Filling or heavily hatching cut material solid in a section or plan, so cut walls and floors read as massive.
- Section line
- A line with arrows on a plan marking where a section is cut and which direction the view looks; keeps section and plan in agreement.
- Cut line vs seen line
- In plan and section, material sliced by the cut plane is drawn heavy (cut); things beyond, still visible, are lighter (seen).
- Vertical experience
- The dimension of height and light that only a section reveals — double heights, clerestories, level changes — designed in section.
Check yourself
2 quick questions — pick an answer to see why.
Q1A section is made by…
Q2What is “poché”?
- A section is a vertical cut — slice down, look across — revealing heights and how things are built.
- Cut material is drawn heavy, often poché (filled/hatched); things beyond are lighter seen lines.
- The section is where vertical experience — double heights, light, level changes — is designed.
- A section line with arrows on the plan marks where the cut is taken and which way you look.
Plan and section both slice the building open. The third drawing cuts nothing at all — it just looks at the outside face. What can an uncut view still tell you?