Beginner

Reading architectural plans: symbols and dimensions

06/04/2026 10 min read

You’ve just received the drawings for your future home — from a draughtsman, an architect or software like Sweet Home 3D — and you’re faced with a tangle of lines, numbers and symbols. Don’t panic: an architectural plan follows precise conventions that any self-builder can learn to decode. This article gives you all the tools to read a plan like a pro, check dimensions and spot errors before the build starts.

Types of plans you need to know

Before diving into symbols, you need to understand that a house project is made up of several types of drawings, each with a specific role:

Plan	What it shows	Common scale
Location plan	Site location within the local area	1:5,000 to 1:25,000
Site plan	Building layout on the plot	1:200 to 1:500
Floor plan	Room layout, walls, openings	1:50 to 1:100
Section drawing	Vertical cross-section of the building	1:50 to 1:100
Elevation drawings	External faces (all 4 sides)	1:50 to 1:100

Question

flowchart TD A{Which plan to read first?} -->|General context| B[LOCATION PLAN
Site location] B --> C[SITE PLAN
Plot layout] C --> D[FLOOR PLAN
Room layout] D --> E[SECTION DRAWING
Heights and levels] E --> F[ELEVATION DRAWINGS
External appearance] style A fill:#0F4C81,stroke:#0F4C81,color:#fff style B fill:#F58220,stroke:#F58220,color:#fff style C fill:#F58220,stroke:#F58220,color:#fff style D fill:#56C6A9,stroke:#56C6A9,color:#fff style E fill:#56C6A9,stroke:#56C6A9,color:#fff style F fill:#6B5876,stroke:#6B5876,color:#fff

Tip — Always start with the location plan to get your bearings, then the site plan to understand the layout, and finally the floor plans for room-by-room detail. Don’t skip steps.

Understanding plan scale

The scale is the ratio between the dimension on paper and the real dimension. It’s the first thing to check when you open a drawing.

Common scales in construction

1:50: 1 cm on the plan = 50 cm in reality (2 cm = 1 m). This is the standard scale for floor plans. Detailed enough to read wall thicknesses.
1:100: 1 cm = 1 m. Useful for large houses or overview plans.
1:200: 1 cm = 2 m. Used for site plans.
1:500: 1 cm = 5 m. For large plots.

Warning — If you print a PDF plan, make sure printing is set to 100% (actual size) and not “fit to page”. A plan printed at 95% distorts all measurements taken with a ruler. Some plans include a reference bar (for example a 1 m segment) to verify the scale after printing.

Measuring on a plan

To convert a measurement taken on the plan to a real dimension:

Real dimension = measured dimension × scale denominator

Example at 1:50: you measure 3.2 cm on the plan → 3.2 × 50 = 160 cm, i.e. 1.60 m.

In practice, use a scale rule (triangular ruler with 6 scales) which gives you the real measurement directly without calculation.

Fundamental symbols

Walls and partitions

On a floor plan, walls are represented by parallel lines whose thickness is to scale:

Load-bearing wall: thick line, often hatched or filled black (20 cm thickness typical in blockwork)
Partition wall: thin line, not hatched (75–100 mm thick in plasterboard)
Existing wall (in renovation): filled grey or hatched
Wall to be demolished: hatched with crosses

Tip — On a 1:50 plan, a 20 cm load-bearing wall measures 4 mm on paper. A 7 cm partition measures barely 1.4 mm. That’s why load-bearing walls are filled black: to distinguish them visually at a glance.

Doors

Doors are represented by an arc showing the swing (direction of opening):

Hinged door: a quarter circle showing the radius of rotation of the leaf
Sliding door: a rectangle with an arrow indicating the direction of sliding
Pocket door: the leaf disappears into the partition, shown as a dashed line inside the wall
Double door: two symmetrical arcs

The direction of opening is critical: it determines the placement of switches, furniture and circulation within the room.

Windows

Windows appear as an interruption in the wall with parallel lines representing the glazing:

Standard window: two parallel lines within the wall thickness
French door / patio door: like a window but extends to floor level (no threshold shown on plan)
Top-hung window: line with a small triangle indicating the tilt direction
Sliding door/window: two offset rectangles with arrow

Staircases

The staircase is drawn with numbered treads and an upward arrow indicating the direction of ascent. A zigzag break line indicates that the staircase continues beyond the cut plane.

Dimensions

Dimensions are the dimension lines that indicate measurements in centimetres or metres:

Internal dimensions: room sizes (length × width)
Wall dimensions: wall and partition thicknesses
Running dimensions: overall building dimensions, placed on the outside
Level dimensions: height relative to the datum (0.00 = finished floor level at ground floor)

Dimension lines consist of:

Two vertical extension lines from the elements being measured
A dimension line connecting the two
The value written above

Warning — Dimensions on the plan always take precedence over a measurement taken with a ruler. If you find a discrepancy between your measurement and the written dimension, the written dimension is correct. The drawing may be slightly distorted by printing.

Levels and heights

Advice

On a section drawing, you will find level annotations expressed in metres with two decimal places:

0.00: datum level, generally the finished floor of the ground floor
+2.50: ceiling height of the ground floor (2.50 m above finished floor level)
-0.60: foundation level (600 mm below datum)
OS (Ordnance Survey datum): absolute altitude relative to sea level (UK equivalent of NGF)

The level triangle

On plans, a small triangle with a value indicates a level:

Filled triangle (▲): finished level (tiled floor, laid flooring)
Outline triangle (△): structural level (concrete slab before screed and finishes)

The difference between the two corresponds to the thickness of the floor finish (screed + tiles = approximately 50–70 mm).

Reading a section drawing

A section drawing is a vertical view of the building, as if you cut it with a giant knife. It reveals information invisible on the floor plan:

Ceiling heights
Slab and floor thickness
Roof pitch
Foundation depth
Finished and structural levels
Cill/sill heights (the wall section below windows)

The section line on the floor plan (a line with arrows at each end) indicates exactly where the cut passes and which direction you are looking.

Good practice — When studying a section drawing, first locate the section line on the floor plan. This tells you exactly which rooms and walls you are seeing in section.

Reading elevation drawings

Elevation drawings show the four external faces of the building. Each elevation is identified by its orientation (north, south, east, west) or by a name (front elevation, rear elevation, left gable, right gable).

On an elevation, you can read:

The roof pitch (in degrees or as a percentage)
The position and size of openings (windows, doors)
External materials (render, cladding, stone) — often annotated
Regulatory heights: ridge, eaves, parapet
Roof overhangs

Common errors to detect

Before signing off your plans, check these points which cause the most problems on site:

Circulation and openings

A door that swings into a piece of furniture or a switch
A corridor less than 900 mm wide (difficult for moving furniture)
A patio door that opens onto a boundary wall 500 mm away

Critical dimensions

Ceiling height below 2.50 m (minimum regulatory height for habitable rooms)
WC width less than 900 mm
Staircase with less than 2.10 m headroom

Planning compliance

Ridge height exceeding the limit set by the local planning authority
Site coverage exceeding the permitted coefficient
Non-compliance with setbacks from boundaries

Tip — Print your plans at 1:50 and mentally walk through each room. Open each door, place the furniture, imagine the daily circulation. It’s the best way to spot problems before it’s too late.

The title block

The title block is the information panel located at the bottom right of each drawing. It contains:

Project name and address
Client name (you)
Name of the draughtsman or architect
Drawing scale
Drawing date and revision index (version)
Sheet number (e.g. PC03 = document 3 of the planning application)

Warning — Always check the revision index of the drawing. On a build, it is common to work with several versions. Display and use only the latest version. Destroy or cross out obsolete versions to avoid any confusion.

Common abbreviations

Abbreviation	Meaning
GF	Ground Floor
FF	First Floor
Bath	Bathroom
En-suite	En-suite shower room
Bed	Bedroom
Kit.	Kitchen
Liv.	Living room
Hall	Hallway / Corridor
WC	WC / Cloakroom
Util.	Utility room
GL	Ground Level
FFL	Finished Floor Level
SSL	Structural Slab Level
CH	Ceiling Height
SW	Surface Water drainage
FW	Foul Water drainage
CW	Combined Water drainage
Ht	Height
Wd	Width
Sill	Window sill height

From plan to site: setting out

Once you have mastered the plans, you will need to transfer them to the ground during setting out. This is the step that bridges paper and reality. The plan dimensions become string lines stretched between profile boards.

To find out more about setting out and compliance with planning rules, see our guide on regulatory dimensions to respect on a plan and reading the local development plan.

If you are putting together your planning application, knowing how to read your drawings will allow you to verify the consistency between the different documents before submission.