What is a section?
A floor plan cuts the building horizontally at roughly window height and looks down from above. A section does the same thing vertically: it splits the building with a vertical plane and you look at the cut face from the side.
A plan tells you the width and depth of the rooms. A section tells you about heights: how thick the slab is, where the ceiling is, how far above the floor the window starts, how much wall is left above the door, how the stairs climb from one floor to the next.
The A–A line on the plan
Where the section is taken is shown on the plan with a line: a chain line of alternating long and short dashes. The letters at its ends (A–A, B–B) are the section’s name; on the drawing sheet you look for the title “Section A–A” with the same letters.
The arrows at the ends show the viewing direction. In the drawing below the arrows point up: we are looking at the wall above the section line, the one with the windows. Everything on the side the arrows point to appears in the section; the side behind is not drawn.
This is the easiest way to read a plan and a section together: to find where a wall on the plan lands in the section, you draw a straight line down. A section line is sometimes stepped to pass through important places, but the reading rule is the same: everything the line passes through is cut.
Thick lines, thin lines
The key to reading a section is telling two kinds of line apart:
- Cut elements, the walls, slabs, columns and beams the knife passes through, are drawn with thick lines; they are often filled in or hatched. Architects call this poché.
- Seen elements, the walls, doors, windows and furniture beyond the cut that you see in elevation, are drawn with thin lines.
In the example, the left and right exterior walls, the wall above the door in the interior wall and the two slabs are cut, so they are solid. The two windows in the back wall are not cut; they are seen beyond, so they are drawn in thin lines. This distinction lets you read depth: thick is where the knife passes, thin is behind it.
Floor-to-floor height and clear height
Two heights are often confused in a section:
- Floor-to-floor height: the distance from the top of one slab to the top of the next. In the example, 2.80 m.
- Clear height: the space from floor to ceiling, the height you actually use in the room. It is the floor-to-floor height minus the slab thickness: 2.80 − 0.20 = 2.60 m.
A suspended ceiling, a thick screed or floor covering reduces the clear height a little further. When choosing a tall wardrobe, a bunk bed or a pendant light, the number to check is the clear height.
Doors and windows in section
If a section passes through a door or window, the wall is open at that point. Here you look at three things:
- Lintel: the piece of wall above a door or window opening. In section it appears as a solid piece above the opening. In the example, above the 2.10 m high door there is 50 cm left up to the ceiling.
- Sill: the height of the wall below the window, in other words how far above the floor the window starts. In the example, 90 cm. This height directly affects the desk, sofa or radiator you put in front of the window.
- Glass: shown with thin lines in the middle of the window opening.
Levels: ±0.00 and +2.80
The small numbers with triangles at the edge of a section are levels: the height of a surface relative to a chosen datum.
- ±0.00 is usually the finished floor level of the entrance floor; all other heights are given relative to it.
- +2.80 is the floor level of the next floor up. Negative levels show places below the datum, such as a basement.
Levels are written in metres with two decimals. In a multi-storey building you find the floor-to-floor heights by reading each floor’s level in turn: the difference between +2.80 and +5.60 is the floor-to-floor height of the second floor.
Where is a section taken?
You don’t place the section line at random, but where it gives the most information:
- Through the stairs: the relationship between the steps, the landing and the stair opening on the floor above shows best in a section.
- Through windows and doors: lintel and sill heights can only be read in a section that passes through the opening.
- Through changes in height: if there is a double-height space, a mezzanine, a sloped ceiling or floors at different levels, the section should pass through them.
- Through wet areas: to see how the counter, plumbing and ceiling relate in the kitchen and bathroom.
Most projects have at least two sections at right angles to each other: a cross section taken along the short side of the building and a long section taken along its length.
Plan, section and elevation
- Plan: a horizontal section, viewed from above. It shows width and depth.
- Section: a vertical section, a view through the inside of the building. It shows heights and how the floors relate.
- Elevation: a view of the building from outside, without cutting anything. It shows the facade and the window layout.
The difference between a section and an elevation is the knife: in a section you split the building in two and look inside; in an elevation you look from outside.
Taking a section in Nodaform
In Nodaform, the section is generated automatically from the plan you draw; you don’t need to draw it separately.
- In the editor, choose the Section tool in the Shell step (shortcut X).
- Click the start and end of the section line on the plan. Holding Shift keeps the line horizontal or vertical.
- The arrows show the viewing direction; you can reverse it with the Flip viewing direction button in the right panel.
- Check the section preview in the right panel; with Add to sheet the section goes onto the drawing sheet as a scaled box.
The section cuts through all floors. It draws cut walls, slabs, columns, beams and balconies solid; door openings and lintels, window sills and glass; doors and windows in the back wall; stair steps and the stair opening on the floor above; levels, a floor-to-floor height dimension chain and the overall width. Heights come from the values in the project (default floor-to-floor height 2.80 m, slab 20 cm) and match the 3D view. Foundations and roof parapets, which are not in the plan, are not drawn.
Checklist for reading a section
- Find the section line and its letter on the plan (A–A, B–B)
- Check which way the arrows point
- Tell thick lines (cut) from thin lines (seen)
- Read floor-to-floor height and clear height separately
- Check lintel and sill heights at doors and windows
- Follow the levels starting from ±0.00
A section taken in Nodaform is a concept drawing. Permit, structural or construction drawings require approval from a licensed architect and engineer.