Section Drawing in Architecture: How to Read and Use It

A section drawing shows a building as if it had been sliced vertically and opened up, revealing floors, walls, roofs, stairs and the spaces between them. Where a plan explains how a building is arranged on each level, a section explains how those levels relate to one another, how high the rooms are and how the building meets the ground.

This article explains how sections are cut and referenced, how to read their line weights and levels, the different kinds of section used at each stage of design, and why sections are among the most important drawings for engineers and builders. It complements our guides to reading floor plans and to architectural drawing generally.

What a section drawing shows

Imagine a vertical plane passing through a building along a chosen line. Everything the plane cuts, such as slabs, walls, beams, roofs and foundations, is drawn with heavy lines and often filled or hatched. Everything beyond the cut, seen in the distance, is drawn with lighter lines in elevation: doors in far walls, windows, stairs and furniture.

The result shows heights and vertical relationships that a plan cannot: floor-to-floor and floor-to-ceiling heights, the depth of beams and slabs, the build-up of roofs and floors, the size of voids, and the relationship between inside and outside. Sections reveal how light enters, how spaces connect across levels, and how the structure carries load down to the ground.

How sections are referenced on plans

Every section is located on the plans by a section line, often drawn as a heavy chain line with arrows at each end. The arrows show the direction of view, which is the side of the building you are looking at. A reference bubble at the end gives the section’s identifier, such as A-A or 1, and the sheet on which it appears.

When reading a set, find the section line on the floor plan, note which way the arrows point, and then turn to the section. Grid lines run through both drawings and are the easiest way to orient yourself: the column on grid C in plan is the same column on grid C in section.

Section lines do not have to be straight. A stepped section line can jog to pass through the most informative parts of a building, such as a stair and a double-height space, in one drawing.

Reading line weights, hatching and levels

Line weight is the key to any section. The cut elements carry the heaviest lines, so the profile of the building’s structure stands out immediately. Hatching distinguishes materials: concrete, masonry, insulation, earth and timber each have conventional patterns, though offices vary and a legend should confirm them.

Levels are given relative to a datum. On Singapore drawings, levels are commonly referenced to a survey datum and to finished floor levels, marked with a small triangle or cross and a figure in metres. Floor-to-floor heights, ceiling heights, window heads and sills, and the top of parapets are all dimensioned vertically.

Ground lines are drawn heavily, with the earth below often hatched. Foundations may be shown below ground in simplified form on architectural sections and in detail on structural sections.

Types of section drawing

General arrangement sections

These cut through the whole building, typically at 1:100 or 1:200, to show overall levels, storey heights and the relationship between floors and site. They are part of the planning and building plan submissions and are used to check height controls and setbacks.

Wall sections

Wall sections, usually at 1:20 or 1:50, cut through an external wall from foundation to roof. They show the construction build-up, the junctions between wall, floor and roof, window positions and waterproofing. They are the bridge between general arrangement drawings and detailed design.

Detail sections

At 1:5, 1:2 or full size, detail sections resolve specific junctions: a window head, a balcony threshold, a roof parapet. Many leaks and defects begin at junctions that were never drawn in section.

Perspective and sectional models

Architects also produce sectional perspectives and section models to communicate space. These are design tools rather than construction documents, but they can make vertical relationships far easier to grasp.

Why engineers depend on sections

For a structural engineer, a section is often more revealing than a plan. It shows how loads travel down through slabs, beams, columns and walls to the foundations; where a transfer structure picks up columns that do not continue; where a slab steps, cantilevers or spans a void; and how deep beams need to be to fit within the available ceiling zone.

Clashes between disciplines are frequently caught in section. A beam may conflict with a duct, a ceiling height may not allow for services, or a step in the slab may interrupt waterproofing. Coordinated sections, increasingly produced from a shared building model, are one of the most effective tools for avoiding these problems before construction. Our article on structural drawings explains the engineer’s own section conventions.

Sections also matter in renovation. Lowering a floor for a sunken bathroom, opening a slab for a stair, adding a mezzanine or raising a roof all change the vertical structure. A section through the existing building, based on a survey, is usually the starting point for the engineering assessment.

Section drawing versus elevation

Elevations and sections are easy to confuse because both are vertical views. An elevation shows the outside of a building as seen from a direction, without cutting anything. A section cuts through it. The giveaway is line weight: an elevation has no heavy cut profile, while a section does.

Both are needed. The elevation, such as those discussed in our guide to house front elevation design, explains appearance and facade composition. The section explains how the building is built and how its spaces relate. For an overview of how all these drawings fit together, see our guide to building drawings.

Frequently asked questions

What is a section drawing?

A section drawing shows a building as if cut vertically along a line and viewed from one side. It reveals floor heights, structure, roof and floor build-ups and the relationship between levels.

How do I find where a section is taken?

Look for the section line on the plans, usually a chain line with arrows and a reference bubble. The arrows show the direction of view and the bubble gives the section identifier and sheet number.

What is the difference between a section and an elevation?

An elevation shows the exterior of a building without cutting it, while a section cuts through it. Sections show cut elements with heavy lines and reveal internal heights and construction.

What scale are section drawings drawn at?

General sections are often at 1:100 or 1:200, wall sections at 1:20 or 1:50, and detail sections at 1:5, 1:2 or full size, depending on the level of information needed.

Why do engineers need section drawings?

Sections show how loads pass down through the structure, where slabs step or cantilever, and whether beams and services fit within the available depth. They are essential for coordination and for assessing alterations.

Planning a mezzanine, slab opening or sunken floor in an existing building? Talk to our consultancy or get in touch.