Architecture and construction
How to simulate shadows from a planned building
A planned wall, extension, garage, or new building can change light far beyond its footprint. The useful question is not only where the structure will stand, but where its shadow will go.
By Peter Szucs Last updated: July 14, 2026
Short answer
To simulate shadows from a planned building, place a virtual mass on the map, set its width, depth, height, and rotation, then review shadows across the day and across seasons. SunCast Construction Mode is built for this early shadow-planning workflow.
Why shadow simulation matters
Building shadows are easy to underestimate because they move. A small structure can miss a garden at noon but shade it in the morning. A taller mass can affect a window in winter even if it seems harmless in summer.
For early planning, the useful view is simple: show the proposed shape, move the time, and check the surrounding streets, windows, yards, parks, or neighboring lots. That gives you a faster read before spending time on formal drawings.
This kind of preview is best used as a planning aid. It helps you spot obvious issues, compare options, and prepare better questions for architects, planners, or solar professionals.
How to run a building shadow check
1. Pick the site on the map
Start from the real location. Zoom in enough that streets, rooflines, and nearby lots are easy to inspect.
2. Place the virtual building
Use Construction Mode to put a simple mass where the planned structure would stand.
3. Set height, width, depth, and rotation
Approximate the planned form. For early review, a simple block is often enough to reveal the main shadow pattern.
4. Scrub through the day
Check morning, noon, and afternoon. Many shadow issues only appear for part of the day.
5. Compare seasons
Review winter and summer. Low winter sun usually creates longer shadows and is often the stricter test.
6. Save the questions, not just the image
Use the preview to decide what needs a professional check: affected windows, garden beds, solar panels, or neighboring properties.
What SunCast adds
SunCast keeps the workflow visual. You can test a building mass where it belongs instead of trying to imagine the shadow from a flat drawing.
| SunCast feature | How it helps |
|---|---|
| Construction Mode | Place a configurable building block on the map and adjust the basic dimensions and rotation. |
| Time travel | Move through hours and seasons to see when shadow impact is most noticeable. |
| 3D map context | View the planned mass in relation to nearby streets, lots, buildings, and terrain. |
| Solar position data | Use azimuth, elevation, and shadow direction to understand why the shadow falls where it does. |
Mistakes to avoid
Testing one date
One sunny day is not enough. Check solstice periods and the months when people use the affected space.
Forgetting height
Height changes shadow length quickly, especially when the sun is low.
Treating a preview as approval evidence
A visual preview is useful for planning, but formal approvals need the correct professional process.
Limits
SunCast is suitable for preliminary shadow review. It is not a certified planning, surveying, engineering, or permitting tool.
Check it in SunCast
Planning a structure or extension? SunCast helps you preview shadow direction and seasonal impact before the formal design work starts.
Frequently asked questions
Can SunCast simulate a future building?
Yes. Construction Mode lets you place a virtual building block and adjust its size and rotation to preview likely shadows.
What dates should I check for building shadows?
Check winter, summer, and the months when the affected space matters most. Winter often creates the longest and most sensitive shadows.
Can I use this for a planning application?
Use SunCast for early review and communication. For a planning application, use the required professional studies, drawings, and local process.
