Plan, Elevation, Section and Detail: What Each View Cuts
Why this matters
Every drawing in a set is one of four kinds of view, and each kind answers some questions and is silent on others. A plan cannot tell you how high anything is. An elevation cannot tell you what is inside the wall. A section is only true where it was cut. A detail does not say where it applies. Most field arguments that start with "the drawings don't show that" end with somebody finding it on a view the crew never opened, because they were looking for a height on a plan. Know what each view cuts, and you know which sheet to pull before the question turns into a ceiling full of duct that does not fit.
The four views, by where the cut is
Plan. A horizontal slice through the building, looked at from above. On a floor plan the slice is commonly taken about four feet above the floor, high enough to pass through doors and windows so they show as openings. Walls the slice passes through are drawn heavy; things below it (floor, fixtures, counters) are drawn as seen; things above it (upper cabinets, soffits, skylights) are commonly dashed. MEP plans use the architect's plan as a backdrop and draw their routing on it as if seen from above. A reflected ceiling plan is a plan of the ceiling drawn as though reflected in a mirror on the floor, so it keeps the floor plan's orientation; see Reflected Ceiling Plans and What Lives Above the Grid.
Elevation. No cut at all: you stand in front of a face and look straight at it. Exterior elevations show what is on the outside of the building (louvers, wall penetrations, meters, equipment seen above a parapet). Interior elevations show one wall of a room, with the heights of counters, casework and often devices. An elevation shows heights and widths but has no depth: it cannot tell you what is behind the face.
Section. A vertical slice, looked at from the side. A building section cuts through the whole building and shows floor and roof levels, ceiling heights and the structure in between. A wall section cuts one wall at larger scale and shows the assembly from footing to roof. Sections are where heights and stack-ups live. The catch is the word "where": a section shows what is true at its cut line, which is marked on the plan with a section symbol, and the building may be different twenty feet away.
Detail. A small area of a plan or section redrawn much larger, commonly 1-1/2" or 3" to the foot, so the assembly can be built: flashing, fasteners, sleeve, sealant, support. A detail shows how, at a size nothing else can. It does not show where; the callout bubble on another view, or a note calling it typical, carries that. See How to Tell Where a Typical Detail Applies, and How to Cross-Reference Between Drawing Sheets for reading the callout symbols.
Which way you are looking
Elevations and sections are seen from one side, and reading one from the wrong side swaps left and right.
- Elevations are commonly named for the face, not for your direction of view. The north elevation is the face of the building that faces north, so to see it you stand north of the building looking south. Interior elevations are often keyed by a symbol on the plan with an arrow or a pointed tag aimed at the wall being drawn.
- A section symbol on the plan has arrows on its ends pointing the way the viewer looks. A cut line running north-south with its arrows pointing east means you are looking east, so north is on your left on the drawing. Standing in the room, face the way the arrows point and the section reads the right way round.
- Check against something asymmetric. A door, a window or a column that sits off to one side of the drawn wall will tell you within seconds whether you have the view the right way round, before you mark a penetration on the wrong end of a wall.
Which view holds which answer
| Question | Look on | Not on |
|---|---|---|
| Where does it run, and how long | Plan | Section (only shows one cut) |
| How high is the ceiling | Reflected ceiling plan, section | Floor plan |
| How deep is the structure, and which way it spans | Wall section, structural framing plan | Architectural floor plan |
| What is inside this wall | Wall section, detail | Plan, elevation |
| What is mounted on the outside face | Exterior elevation | Plan (shows only what the slice hits) |
| How high is the device or counter | Interior elevation, general notes | Plan |
| How the penetration is sealed or supported | Detail | Anything at plan scale |
Read the table as a habit, not a lookup: when a question involves a height, your first sheet is never a plan.
A worked case: will the duct fit under the joists
A mechanical crew is about to hang a 14x10 supply duct across an open office: 14 inches wide, 10 inches deep, wrapped in external insulation. The mechanical plan shows the route running east-west down the middle of the room and a note: "run duct below structure, above ceiling." Nothing on that plan says whether it fits. Three other sheets and the specification do.
From the building section on A-301: top of roof deck at 12'-0" above finish floor at this location, which is 144 in.
From the wall section and the structural framing plan: 1-1/2 in roof deck on open-web steel joists 24 in deep, and the framing plan shows the joists spanning north-south. The duct runs east-west, so it crosses every joist at right angles and cannot slip between them.
From the reflected ceiling plan on A-102: ceiling at 9'-0", which is 108 in.
From the mechanical specification: external duct wrap 1-1/2 in thick, so the duct's outside depth with insulation is 10 + 1.5 + 1.5 = 13 in.
BUILDING SECTION AT THE DUCT ROUTE (schematic)
=============================== TOP OF DECK 144 in
| roof deck 1-1/2 in |
|\/\/\/\/\/\/\/\/\/\/\/\/\/\/\| joists 24 in deep,
| | span north-south
------------------------------- BOTTOM OF JOIST 118.5 in
| space for duct: 10.5 in |
=============================== CEILING 108 in
| |
| - - - - - - - - - - - - - - | PLAN CUT, about 48 in
| |
=============================== FINISH FLOOR 0 in
The arithmetic, each step shown: bottom of joist is 144 minus 1.5 minus 24, which is 118.5 in (9'-10-1/2"). The space between bottom of joist and ceiling is 118.5 minus 108, which is 10.5 in. The wrapped duct needs 13 in, so it is 13 minus 10.5, or 2.5 in, too deep before counting hangers, the ceiling grid's own hanger wires, or any recessed light fixture underneath it.
The decision is not the crew's. Three ways out exist and each belongs to someone else. Passing through the joist webs depends on the openings the joist manufacturer and the structural engineer allow, and nobody cuts or notches a joist chord or web to make room. A wider, shallower duct of similar capacity is the mechanical engineer's resize. A lower ceiling is the architect's change. The crew's job is to stop before the first hanger goes in and send an RFI with these four numbers and the sheets they came from. See How to Write an RFI That Gets a Usable Answer.
What would change the answer. If the framing plan had shown joists spanning east-west, parallel to the duct, the duct could run up between two joists in the 24 in joist space and the 10.5 in figure would never have mattered. If the section had been cut somewhere else, say at a raised roof over the entrance, its 144 in could be wrong for this route; check that the section's cut line on the plan actually crosses your run, or that the roof is flat between the two.
How each view misleads when used alone
- A plan read for height. MEP plans often carry a height note (BOD, bottom of duct, or "tight to structure") in one place and nowhere else. Absent a note, the plan says nothing about elevation, and drawing a pipe over a duct on a plan does not mean the pipe is physically higher.
- A section treated as universal. It is a statement about one cut line. Roofs slope, slabs step, beams deepen at long spans. Before carrying a section's heights to your run, find its cut line on the plan.
- A detail applied everywhere. A detail labeled for one wall type can be wrong at a rated wall or an exterior wall. The callout and the "typical" note govern where it applies.
- An elevation read for depth. A louver on an exterior elevation tells you its size and height, not what is behind it or how deep the plenum is. That is a section or a detail.
- A diagrammatic route read as a dimension. MEP routing is often drawn along a convenient line rather than at its true offset, which is why coordination drawings exist. See Coordination Drawings and Who Gets the Ceiling Space.
Checking you have all the views a question needs
Before answering any question that involves fitting one thing into a space, list the dimensions the answer depends on and write beside each the view and sheet it came from. In the case above that list has four lines (deck height, structure depth and direction, ceiling height, duct outside size) from four sources (the section, the framing plan and wall section, the reflected ceiling plan, the specification). If any line reads "assumed" instead of a sheet number, the answer is not finished. Acceptance: every dimension has a source sheet, the section's cut line is confirmed to apply at your location, and the result either fits with room for supports or goes out as an RFI before the work starts.
References
- United States National CAD Standard (NCS), National Institute of Building Sciences, drawing types and view conventions
- Joist manufacturer load and web opening data, through the structural engineer of record
- See related: Reading Floor Plans + Basic Drawings Reference; How to Cross-Reference Between Drawing Sheets
- See related: How to Read a Wall Section Before Cutting a Hole; Reflected Ceiling Plans and What Lives Above the Grid