Architectural Drawing: Types, Scales and Conventions

An architectural drawing is a precise, conventional way of describing a building so that everyone involved, from client to contractor, understands the same thing. Long before computers, architects developed a shared visual language of projections, scales, line weights and symbols, and that language still governs the drawings produced today in CAD and BIM software.

This article explains the main types of architectural drawing, what each one shows, and the conventions that make them readable: projection, scale, line types, dimensions, levels, grids and annotation. It is aimed at students, homeowners reading drawings for the first time, and anyone who works alongside architects and engineers.

Why architectural drawing follows conventions

A drawing set is a legal and technical document as well as a design communication. Contractors price from it, authorities approve it and builders construct from it. For that to work, a dashed line, a section marker or a hatched area must mean the same thing to everyone. Conventions are what make a drawing unambiguous.

Many of these conventions are captured in international standards for technical drawing, such as the ISO 128 series on presentation and line types, and in national and company standards for symbols and CAD layer naming. Practices then add their own house style. The details vary, but the principles are remarkably consistent worldwide.

The main types of architectural drawing

Plans

A plan is a horizontal cut through the building, normally taken about a metre or so above floor level, looking down. Walls that are cut are drawn heavily; things below the cut, such as floor patterns and furniture, are drawn lightly; things above, such as beams or high windows, are shown dashed. Variations include the site plan, which shows the building in its plot with boundaries, access and levels; roof plans; and reflected ceiling plans, which show ceilings, lights and services as if seen in a mirror on the floor.

Sections

A section is a vertical cut through the building, showing floor-to-floor heights, slab and roof build-ups, stairs, voids and the relationship between levels. Section lines on the plan, with arrows and reference marks, show where each cut is taken and which way it looks.

Elevations

An elevation is a flat, orthographic view of an external face of the building, or of an internal wall in the case of interior elevations. It shows openings, materials, heights and the composition of the façade, without perspective distortion. Front elevations are often the first drawing homeowners ask about, and our article on house front elevation design looks at how they are composed.

Details

Details are enlarged drawings of junctions and components, such as a window head, a roof edge, a stair nosing or a waterproofing upstand, where small dimensions and the sequence of materials matter.

Schedules

Schedules are tables listing repeated items such as doors, windows, finishes and ironmongery, with their types, sizes and specifications. They keep plans readable by moving repetitive information into one place.

Three-dimensional views

Axonometric and isometric drawings show the building in three dimensions without perspective, so dimensions along the axes remain measurable. Perspectives and renderings show how the building will appear to the eye. These are explanatory rather than contractual.

Projection and scale

Plans, sections and elevations are orthographic projections: the building is projected onto a flat plane with parallel lines, so dimensions can be measured directly at the drawing’s scale. That is the essential difference between a technical drawing and a picture.

Scale expresses the ratio between the drawing and the real building. Common metric scales in architecture include 1:500 or 1:200 for site and location plans, 1:100 or 1:50 for general arrangement plans, sections and elevations, and 1:20, 1:10 or 1:5 for details. Larger scales show more detail; the choice depends on what the drawing must communicate. Our guide to architectural scale explains how to read and use them. Every drawing should state its scale, and a scale bar helps when drawings are reproduced at a different size.

Line weights, line types and hatching

A well-drawn plan reads at a glance because of its hierarchy of lines.

Heavy lines show elements cut by the plan or section plane, such as walls and slabs.
Medium lines show visible edges beyond the cut, such as worktops, steps and window sills.
Light lines show surface patterns, furniture and dimension lines.
Dashed lines show hidden or overhead elements, such as beams above or a roof overhang.
Chain lines (long dash, short dash) show centre lines, gridlines and section positions.

Hatching and fills indicate materials in section: concrete, blockwork, insulation, timber and earth each have conventional patterns, though these vary between offices. A legend should always accompany non-standard hatches.

Dimensions, levels, grids and annotation

Dimensions in Singapore and most metric countries are given in millimetres, without units written on the drawing. Running dimensions are usually taken to structural gridlines and to the faces of structure or finishes, as stated in the notes. A good rule is that a builder should never need to scale a dimension off a drawing; if a dimension is missing, it is a query.

Levels are shown in metres relative to a datum, with finished floor levels and structural slab levels distinguished. Structural gridlines, labelled with numbers in one direction and letters in the other, provide the common reference for architecture, structure and services, and they appear on every discipline’s drawings. North points, drawing titles, references to other drawings, revision clouds and a title block with project, drawing number, scale, date and revision complete the conventions.

Architectural drawings sit alongside the engineers’ drawings. The structural drawings use the same gridlines and levels but show the frame, foundations and reinforcement, and the two sets must agree. Discrepancies between them are one of the commonest sources of site queries.

From hand drafting to CAD and BIM

For most of history, architectural drawings were produced by hand, with pencils, pens, set squares and drafting machines. CAD replaced the drawing board from the 1980s onwards, and BIM now generates plans, sections and elevations from a single 3D model so that they stay consistent. The tools have changed, but the conventions have not: a plan produced from a model still needs correct line weights, scales, dimensions and annotation to be useful. Our companion guide to building drawings covers how a full drawing set is organised across disciplines and project stages.

Frequently asked questions

What are the main types of architectural drawing?

The main types are plans, sections, elevations, details and schedules, supported by site plans, roof plans, reflected ceiling plans and three-dimensional views such as axonometrics and perspectives. Together they describe the building’s layout, heights, appearance and construction.

What scale are architectural drawings usually drawn at?

Typical metric scales are 1:500 or 1:200 for site plans, 1:100 or 1:50 for plans, sections and elevations, and 1:20, 1:10 or 1:5 for details. The scale is chosen to show the level of detail each drawing needs and should always be stated on the drawing.

What do dashed lines mean on an architectural drawing?

Dashed lines usually represent elements that are hidden or above the cutting plane, such as beams overhead, roof overhangs or items concealed behind other elements. Chain lines with long and short dashes typically mark gridlines, centre lines and section positions.

What is the difference between a section and an elevation?

A section is a vertical cut through the building that shows its internal structure, floor levels and build-ups. An elevation is a view of a face of the building from outside or of an internal wall, showing its appearance without cutting through it.

Why are dimensions given in millimetres?

Millimetres are the standard unit for building dimensions in metric countries, including Singapore, because they avoid decimal points and give enough precision for construction. Levels, by contrast, are usually given in metres relative to a datum.

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