Elevation and section, and how to tell which you are looking at
An elevation is an orthographic view of a face. Nothing is cut, so you see finishes, openings, the ground line, the parapet and any change of plane, drawn flat with no perspective at all. Because there is no perspective, a window twenty feet away is the same size on the paper as an identical window right in front of you, which is exactly what makes an elevation measurable and a photograph not.
A section is a vertical cut. The cut elements are drawn heavy and poched in the same way a plan draws its cut walls, and everything beyond the cut is drawn lighter, in elevation, because that is what you see once the near half is removed. So a building section usually looks like a slice of poche with a room drawn behind it. If you can see the thickness of the floors, you are in a section. If the building has a face and no visible thicknesses, you are in an elevation.
Both views are drawn at the same scale as the plans on a small building, which lets you carry a measurement between them and lets an elevation sit directly beneath a plan of the same building without either being adjusted.
How the plan points at them
A section marker on a plan is a circle split across the middle, with the drawing number above and the sheet number below, attached to a tail with an arrowhead. The arrow is the part people skip, and it is the part that matters: it states the direction of view after the cut is made. A cut line usually runs across the plan between a pair of markers, showing exactly where the slice is taken, and it may jog to catch two interesting conditions in a single drawing.
Exterior elevations are named by compass direction, and the naming refers to the face rather than to where the viewer stands: the north elevation is the face that looks north. That is a convention worth stating out loud because it is easy to reverse, and reversing it puts the entrance on the wrong side of the building in your head for the rest of the day.
Interior elevations are located by a four armed marker sitting in the middle of a room, each arm carrying its own drawing number and pointing at one wall. One symbol therefore sends you to four drawings, and the arm pointing at a wall is the drawing of that wall. If a room only needs two of its walls drawn, only two arms will carry numbers.
Level datums, and why heights are not a dimension string
Vertical positions are given as datums rather than as a chain of dimensions. A datum is a horizontal line across the drawing with a symbol and a label giving a name and a height, and every other vertical fact is read relative to those lines. The Level 1 finish floor is normally set at zero, and the other levels read as distances above it: a second floor at fourteen feet, a roof bearing at twenty six, a top of parapet at twenty nine.
The reason datums are used instead of a running dimension string is that heights are set out independently on site. A surveyor establishes a benchmark and every floor is shot from it, so an error at one level does not accumulate into the next. Reading a section the same way, from the datum rather than by adding up thicknesses, keeps you honest about what is actually controlled.
Floor to floor and floor to ceiling are different numbers and both matter. Floor to floor is the distance between two floor datums and includes the structure. Floor to ceiling is what you experience in the room, and the difference between the two is the depth of the structure plus the ceiling void, which is where every duct, pipe and cable tray in the building has to live.
- Level 1 finish floor at zero is the origin for the building drawings.
- Floor to floor includes the floor structure; floor to ceiling does not.
- Roof bearing is where the roof structure lands on the wall, and the parapet continues above it.
- A civil sheet may use real survey elevations rather than zero, and the two systems must never be mixed silently.
What the section shows that a plan cannot
A plan can tell you that a corridor is six feet wide and a duct runs along it. Only a section can tell you whether that duct, the beam it crosses, the sprinkler main and the ceiling all fit in the space between the floor above and the ceiling below. That question, called coordination, is settled in section, and it is the single most common reason a drawing that looks fine gets rebuilt on paper before it gets built in the field.
Sections also show how the building is put together at the large moves: how the floor structure bears on the wall, how the roof drains and where the parapet finishes, whether there is a slab on grade or a suspended ground floor, and what happens where two roof planes meet. Each of those transitions may then carry a detail bubble sending you to a much larger drawing of the same joint.
One habit repays itself constantly: when a question contains a height, a clearance, a slope or the word above, stop reading the plan. The answer is on a section, an elevation or a schedule, and continuing to stare at the plan will produce a guess.
Reading an elevation for openings and materials
On an elevation, windows and doors appear at their real proportions and at their real heights, which makes it the natural place to check head and sill heights, transoms, and how openings line up across a facade. Material changes are shown by hatch or by a note with a leader, and a change of material usually coincides with a change of plane or a control joint, which the elevation will also show.
Elevations carry level datums too, usually as horizontal lines with labels at one edge, so a head height can be read against the floor line without any arithmetic. Where a dimension is given on an elevation it is normally to the head or the sill of an opening, because those are the numbers a window installer needs and they are not obtainable from the plan at all.
Finally, count. Counting the openings on an elevation and counting the same openings on the plan is a genuine coordination check that takes under a minute and catches real errors. The two drawings were produced from the same model on a modern set, but sets get edited, and a window deleted in plan and left in elevation is exactly the kind of thing a careful reader finds first.