How to Read a Shadow Diagram

In Brief

To read a shadow diagram, first establish the date and time shown, the orientation of the site and the condition being represented. Then identify the existing and proposed shadows and follow their extent across the site and surrounding context. The legend, drawing title and annotations explain how each condition is represented. A shadow diagram shows where shadow falls; whether that shadow satisfies a particular planning or solar-access requirement is a separate assessment question.

How do you read a Shadow Diagram?

The easiest way to read a shadow diagram is to establish the drawing conditions before interpreting the shadow itself. Start by identifying what view or plan you are looking at, then check the nominated date and time and locate the north point or other orientation information.

Next, determine which shadow represents the existing condition and which represents the proposed development. Depending on the drawing, these may be distinguished through different tones, hatching, outlines or other graphic treatments.

Once those elements are clear, follow the shadow across the drawing. Look at where it begins, the direction in which it extends, whether it remains within the subject site and which surrounding areas or structures it reaches.

Reading the diagram in this order helps separate the information shown on the drawing from the planning interpretation that may follow from it.

Start with the date and time

A shadow diagram represents a particular moment rather than a permanent shadow condition. The date and time shown on the drawing therefore provide essential context for everything else you see.

As the position of the sun changes, the direction and extent of the shadow change as well. A morning diagram should not be expected to show the same shadow as a midday or afternoon diagram, even though the building itself has not changed.

You may also see several diagrams prepared for the same date. These allow the shadow condition to be viewed at different nominated times rather than treating one moment as representative of the entire day.

In Australian planning documentation, 21 June is commonly used as a winter reference date, although the required date depends on the project and applicable planning requirements. For more on this distinction, see Why Is 21 June Used for Shadow Diagrams in Australia?

A Shadow Diagram is a snapshot of cast shadow under defined conditions. Before interpreting the shadow itself, establish the date, time, orientation and scenario shown on the drawing.

Find north and understand the site orientation

Once you know the date and time, find the north point on the drawing. This establishes how the site is oriented and helps you understand the direction in which the modelled shadow is extending.

Orientation is particularly useful when reading a site plan containing several neighbouring properties. It allows you to relate the shadow shown on the page to the actual arrangement of the site, street, boundaries and surrounding buildings.

You do not need to calculate the solar position yourself. The purpose of locating north is to give the drawing a physical reference so that the direction of the shadow can be understood in relation to the development.

Where orientation information is unclear, the title block, site plan or accompanying project drawings may provide additional context.

Identify the existing and proposed shadows

Shadow documentation may show an existing condition, a proposed condition or a comparison between the two. Establishing which condition you are looking at is essential before drawing conclusions from the shaded areas.

Where existing and proposed shadows appear on the same drawing, different graphic treatments may be used to distinguish them. This can make it easier to see the shadow already created by existing buildings and the change associated with the proposed development.

There is no reason to assume that a particular colour or hatch always means the same thing across every drawing set. Graphic conventions can vary between consultants, projects and documentation formats.

Use the legend, annotations and drawing title to confirm what each shadow treatment represents before comparing the conditions.

Follow the extent of the shadow

After identifying the condition being shown, follow the shadow from the building across the drawing. Its shape reflects the form of the elements casting it and the solar position at the nominated date and time.

Look at whether the shadow remains within the subject site or crosses a property boundary. Where surrounding context is shown, you can also see which adjoining areas, buildings or other relevant features fall within the modelled shadow.

If both existing and proposed conditions are shown, the comparison can help distinguish shadow that already occurs from shadow associated with the proposed development. The drawing may make that difference visible through overlays, separate diagrams or other graphic conventions.

This tells you where the shadow falls. It does not, by itself, determine whether the resulting condition is acceptable under a particular solar-access or planning requirement.

Compare Shadow Diagrams at different times

Where a drawing set includes several times of day, read the diagrams as a sequence rather than as unrelated images. This allows you to see how the shadow moves across the site and surrounding context as the solar position changes.

For example, a set may include morning, midday and afternoon conditions. The shadow may extend in one direction earlier in the day, become shorter or change position around the middle of the day, and extend in another direction later in the afternoon.

When comparing the sequence, check that you are looking at the same development condition and assessment date. This helps ensure that the change you are seeing is caused by the change in time rather than by comparing different scenarios.

The particular times required for an assessment can vary between projects and planning authorities, so the drawing set should be read in the context of the requirements that apply to that development.

What do property boundaries and neighbouring buildings tell you?

The lines and buildings surrounding the proposed development give the shadow its physical context. Without that context, it may be possible to see the shape of a shadow without understanding where it falls in relation to the site.

The subject site boundary helps establish whether the shadow remains within the development site or extends onto adjoining land. Surrounding building outlines can then help show how that shadow relates to nearby built form.

Depending on the purpose of the assessment, other relevant site features may also be identified. The amount of surrounding information shown should reflect what the particular shadow documentation needs to communicate.

Not every surrounding property or feature needs to be interpreted in the same way. At this stage, the objective is simply to understand where the modelled shadow sits within the context represented on the drawing.

What does the legend tell you?

The legend is the key to the graphic language used in the drawing. Before assuming what a shaded area, hatch or line represents, check how it has been defined in the documentation.

Depending on the drawing set, the legend may distinguish existing shadow, proposed shadow, additional shadow, the proposed building footprint, site boundaries or surrounding built form. Date and time information may appear in the title, annotation or directly beside each diagram.

The exact presentation can vary. One set of diagrams may use tones or hatching, while another may use outlines, overlays or separate drawings to communicate the same underlying conditions.

Reading the legend first prevents a common mistake: interpreting the visual appearance of the diagram before confirming what the drawing actually says those graphics represent.

Can you tell whether a development complies from the Shadow Diagram alone?

Not necessarily. A shadow diagram primarily documents where cast shadow falls under the nominated conditions. Whether that condition satisfies a particular planning requirement can involve a separate assessment.

Planning controls may consider particular areas, periods of sunlight, existing conditions or other project-specific criteria. Those requirements need to be identified before the significance of the shadow can be assessed against them.

This distinction is important when reading the drawing. Seeing proposed shadow on a neighbouring property does not, on its own, establish whether the proposal complies or fails to comply with an applicable control.

The shadow diagram provides the graphical evidence. Any assessment of solar access, overshadowing performance or planning compliance should then apply the requirements relevant to the particular development.

Reading Shadow Diagrams within the wider assessment

A shadow diagram becomes much easier to understand when you read the information in a consistent order rather than starting with the darkest area on the page.

Establish the date and time. Find north and understand the orientation of the site. Confirm which existing or proposed condition is being shown. Then follow the shadow across the site boundary and surrounding context using the legend and annotations to interpret the drawing correctly.

That process tells you what the shadow documentation is showing without asking the diagram to answer a different question. The diagram establishes the location and extent of the modelled shadow; the wider planning assessment determines what that condition means for the project.

Understanding that distinction makes it easier to compare drawings, identify meaningful changes between conditions and read shadow documentation as part of the wider development assessment.