Shadow Diagrams
Designs often continue to develop after shadow diagrams have been prepared. A revised floor plan does not automatically make the existing shadow diagrams outdated, but changes to the building geometry, position or other shadow-casting elements can alter the modelled shadow. The key question is whether the revision changes the part of the design responsible for the shadow being shown.
In Brief
Shadow diagrams represent a particular version of a proposed design. If a revision changes relevant external geometry, such as building height, footprint, setbacks, roof form or projecting elements, the modelled shadow may also change. Internal or non-geometric revisions may have no effect on the shadow. Whether revised diagrams are required depends on the nature of the change and the documentation requirements applying to the project.
A shadow diagram is based on the project geometry available when the assessment is prepared. The proposed building form, position, height and other relevant elements are represented within the model, and the resulting shadow corresponds to that version of the design.
If the design is revised later, the existing shadow diagrams do not automatically change with it. They continue to represent the earlier geometry on which they were based.
The important question is therefore whether the revision changes anything that contributes to the modelled shadow. A change to the external building form may affect the result, while a revision entirely within the building may leave the shadow condition unchanged.
Where relevant geometry has changed, the existing shadow model may need to be reviewed against the current design before the earlier diagrams are relied upon as representing the proposal.
Not every design revision necessarily changes the modelled shadow. Architectural drawings can be revised for many reasons, including changes that have no effect on the external form responsible for casting shadow.
For example, changes to internal layouts, finishes or fixtures may alter the architectural documentation without changing the building envelope represented in the shadow model.
A revision to the external geometry is different. If the building becomes higher, moves on the site, changes footprint or gains a projecting element, the geometry responsible for casting the shadow may no longer match the original model.
Whether updated shadow documentation is required should therefore be determined from the nature of the revision and the requirements applying to the project, rather than from the fact that a new drawing revision exists.
A Shadow Diagram represents a particular version of the design. The relevant question after a revision is not simply whether the plans changed, but whether the geometry responsible for the modelled shadow changed.
Changes that alter the external geometry or position of a development can affect its modelled shadow. The significance of the change depends on the geometry involved and the assessment condition being represented.
Building height is one example. Increasing or reducing the height of part of a building changes the geometry that intercepts sunlight and can therefore change the resulting shadow.
Changes to the building footprint, setbacks, upper-level massing or roof form can also alter the position or extent of the modelled shadow. Balconies, awnings and other projecting elements may be relevant where they contribute to the shadow represented in the assessment.
A change does not need to involve the entire building to be relevant. If the revised element forms part of the shadow-casting geometry, it may be appropriate to review the model against the new design.
Some design revisions can be substantial from an architectural or construction perspective without changing the geometry used to model the shadow.
Changes to internal room layouts, internal walls, fixtures, joinery or finishes generally do not alter the external massing of the building. If the position and geometry of the shadow-casting elements remain unchanged, the modelled shadow may also remain unchanged.
The same principle can apply to other revisions that affect the documentation but not the relevant external form. What matters for the shadow model is whether the geometry used in the assessment still corresponds to the current proposal.
This does not determine whether revised documentation is required for another part of the project. It only distinguishes changes that may alter the modelled shadow from changes that do not.
Shadow diagrams form part of a wider project documentation set. For the diagrams to represent the proposal accurately, the geometry used in the shadow model should correspond to the design version being assessed.
If the architectural drawings continue to develop while the shadow diagrams remain based on an earlier design, the two sets of information can become misaligned. The shadow shown may still be technically consistent with the original model while no longer representing the current proposal.
This is why drawing revisions matter even when the change initially appears minor. The relevant comparison is between the geometry represented in the shadow assessment and the geometry shown in the current project documentation.
Keeping that relationship clear helps ensure that the shadow diagrams can be understood as part of the same design package rather than as a representation of an earlier proposal.
Yes. The size of a design revision does not necessarily correspond to the size of its effect on the modelled shadow.
A relatively small change to an external edge, upper level, roof element or projection may alter part of the shadow because it changes the geometry exposed to the sun. The effect depends on the location of that element and the particular date and time being modelled.
By contrast, a substantial redesign of the internal floor plan may produce no change to the shadow if the relevant external geometry remains exactly the same.
For this reason, revisions are better reviewed according to what changed geometrically rather than simply according to whether the overall design change appears large or small.
Building height is part of the geometry used to determine a modelled shadow. If the height changes, the earlier shadow representation may no longer correspond to the revised building form.
This can apply to a change in the overall building height or to a more localised change, such as an upper level, parapet, roof form or other elevated element. The effect on the shadow depends on the location and geometry of the revised part of the building.
The relevant issue is not simply whether the building became higher or lower. It is whether the height information used in the original shadow model still represents the current design.
Where it does not, reviewing the model against the revised geometry can establish whether the shadow diagrams also need to change.
Changes to the building footprint or setbacks can also affect the geometry represented in a shadow assessment. Moving an external building edge changes the position from which part of the shadow is cast.
A revised setback may move part of the building closer to or further from a site boundary. An altered footprint may add, remove or reposition building mass. Depending on the assessment time and orientation, these changes can alter the resulting shadow extent or position.
Again, the existence of a footprint change does not by itself determine what documentation must be reissued. It establishes that geometry relevant to the shadow model may have changed.
Comparing the revised design with the geometry used for the original assessment allows that change to be identified before the existing shadow diagrams are relied upon.
A change to the proposed design does not automatically change the existing site condition. The existing shadow baseline represents the site before the proposed development and is conceptually separate from the revised proposal.
The proposed condition, however, should represent the current design geometry if it is being used to document the revised proposal. Where existing and proposed conditions are presented as a comparative set, the documentation may therefore need to be regenerated or reassembled so that the current proposal is being compared consistently against the relevant existing condition.
Keeping the assessment date, time and other relevant conditions consistent also helps ensure that the comparison reflects the design change rather than a change in the assessment conditions.
The distinction between these two conditions is explained further in Existing vs Proposed Shadow Diagrams: What Is the Difference?
Design revisions can also occur after shadow diagrams have already formed part of a submitted documentation package.
In that situation, the first issue remains the same: whether the revised design changes geometry relevant to the modelled shadow. If it does, the previously submitted diagrams may no longer represent the current proposal.
Whether revised shadow documentation then needs to be submitted depends on the nature of the change and the requirements of the relevant assessment or approval process. Those requirements can vary between projects and authorities.
For that reason, an earlier shadow diagram should not simply be assumed to remain suitable after the design changes. The relationship between the submitted assessment and the revised proposal should first be checked.
A useful starting point is to compare the revised architectural information with the design version used to prepare the original shadow assessment.
The review can focus on geometry relevant to the shadow model: building position, external footprint, setbacks, heights, roof form, upper-level massing and other shadow-casting elements. This helps distinguish revisions that may change the shadow from revisions that affect other parts of the design only.
Where relevant geometry has changed, the updated project information can be used to review or update the modelled condition. Where it has not changed, that comparison provides a clearer basis for understanding whether the existing shadow representation remains aligned with the proposal.
The drawings and site information commonly used to establish the model are discussed in What Information Is Needed to Prepare Shadow Diagrams?
A shadow diagram represents a defined development scenario at a nominated date and time. The proposed design geometry is therefore one of the fundamental conditions behind the resulting shadow.
When that design develops, the most useful question is not simply whether a new revision has been issued. It is whether anything has changed that could change the modelled shadow.
If the relevant geometry remains unchanged, the shadow condition may also remain unchanged. If the height, position, footprint, roof form or another shadow-casting element changes, the existing assessment may need to be reviewed against the revised proposal.
This keeps the shadow documentation connected to the design it is intended to represent and helps avoid relying on diagrams that describe an earlier version of the project.
Continue Reading
Design revisions are one part of maintaining an accurate relationship between project documentation and the modelled shadow condition. Explore how shadow diagrams are prepared, what they represent and how they support planning and development documentation.
Explore the Shadow Diagrams guide →Shadow Diagrams
Changes to building height, footprint, setbacks, roof form or other external geometry can alter the modelled shadow and may mean the existing diagrams no longer represent the current proposal.
Send us your current plans and the previous project information. We can review the revised design and help identify the appropriate next step for the shadow assessment.
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