Step 1 — Find the property
Search an address, or pan/zoom the map manually and click to drop the structure.
Step 2 — Describe the structure
Enter its dimensions — this could be a shed, house, flagpole, or steeple. For an L-shaped house, a lean-to extension, or any building with more than one roof line, use Add Another Wing below: each block is its own box with its own roof, positioned independently on the map, and shadows from all of them are combined together.
Structure on the property
Drag each shaded footprint to reposition it — if you've added extra wings, each one moves independently. Use the button below to mark a neighbouring area you want to check for sun access.
Step 3 — Choose the assessment date
Defaults to the winter solstice (21 June) — the standard "worst case" date used in Australian shadow diagrams.
Run the assessment
Calculates shadow shape at 9am, 12pm, and 3pm, and — if you've marked an assessment zone — how many hours of direct sun it keeps.
How this works
For any location and moment in time, the sun sits at a specific height above the horizon (altitude) and compass direction (azimuth). A structure's shadow points directly away from the sun, and its length is the structure's height divided by the tangent of the sun's altitude — the lower the sun, the longer the shadow. This tool calculates that precisely for your property's real latitude and longitude, using the same solar position mathematics used in astronomy and solar design software.
Australian councils commonly assess overshadowing using a shadow diagram at 9am, 12pm, and 3pm on 21 June — the winter solstice, when the sun is lowest and shadows are longest, making it the "worst case" test for the year. Requirements typically centre on whether neighbouring private open space or living room windows keep a minimum of 2–3 hours of direct sun somewhere in that 9am–3pm window, though the exact figure and which spaces count varies by state and council.
What this tool assumes
- Flat ground. Slopes and elevation changes aren't modelled — on a sloped block, real shadows will differ from what's shown here.
- Your browser's local time zone is used for 9am/12pm/3pm, rather than looking up the property's actual time zone. For Australian properties viewed from an Australian device, this is accurate.
- Only the structure(s) you add. Existing trees, fences, and neighbouring buildings aren't included in the shadow calculation.
- Each block is modelled as a simple box with an optional gable or skillion roof. For a building with more than one roof line — an L-shaped house, a lower lean-to extension, a carport at an angle to the main roof — add each part as its own block with Add Another Wing, positioned independently; their shadows are combined. Hip roofs still aren't modelled directly, so approximate a hip as a gable (a close, slightly conservative match).
Frequently Asked Questions
Use it to understand and refine your design before engaging a professional. Most councils expect a shadow diagram prepared or certified by a town planner, architect, or surveyor for an actual DA submission — this tool is for exploring the impact yourself first, not a replacement for that certification.
It's the winter solstice in the Southern Hemisphere — the day the sun is lowest in the sky and shadows are at their longest. If a design keeps adequate sun access on this "worst case" day, it will keep it (or more) on every other day of the year.
Whatever you're checking sun access for — commonly a neighbour's private open space (backyard, courtyard) or a specific window. Mark it on the map roughly where that area sits, and the tool checks its centre point against the shadow at regular intervals through the day.
Yes, and which direction the ridge runs matters too. A tall ridge running toward the shadow side of the building extends the shadow further than the same ridge running side-to-side, even at the same pitch — this tool accounts for that rather than just using the wall height.
A flat roof has no slope at all. A gable roof is the classic triangular house shape — two slopes meeting at a central ridge line. A skillion roof (sometimes called a mono-pitch or lean-to roof) has just one slope running from a low side to a high side, common on sheds, garages, and modern-style extensions. See the small diagrams above the roof type dropdown for a visual comparison.
Eave height is where the wall ends and the roof begins — the height you'd measure with a tape measure standing next to the wall. For a flat roof, that's also the building's full height. For a gable or skillion roof, the actual highest point (the ridge, or the high edge of a skillion) sits above the eave height by an amount that depends on the roof's width/depth and pitch — this tool calculates that automatically from the numbers you enter, you don't need to work it out yourself.
Rotation is a compass bearing — 0° faces due North, and it turns clockwise from there (90° = East, 180° = South, 270° = West). If you want the structure's edge to run parallel with a boundary line, you need that boundary's actual bearing, which is normally printed on your property's survey plan or title documents (often written as something like "N 15°30' E"). Click "How do I find the right angle?" next to the Rotation field on the form above for a visual compass reference and a quick estimate method if you don't have a survey handy.