Shadow length and sun exposure shift with season and latitude — this tool estimates shading, sun position, and daylight hours for a given site.
| Month | Sunrise | Sunset | Daylength | Solar Noon Altitude |
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| Time | Solar Altitude | Solar Azimuth | % Floor Shaded |
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| Month | Sunrise | Sunset | Daylength | Peak Altitude |
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How to Work Out Sun Position, Shadow Length, and Shading Requirements by Hand
Understanding how the sun moves across a site through the seasons, and how to calculate the shadows and shading that result, is one of the more genuinely rewarding pieces of landscape science to learn, because the underlying geometry is consistent and predictable everywhere on earth, even if the specific numbers change with latitude and season. This guide walks through the core reasoning.
Why the sun’s path changes so much between winter and summer
The sun’s height above the horizon at any given time of day depends on latitude, season, and time of day working together, and the practical consequence for design purposes is that the sun sits noticeably lower in the sky throughout the day during winter than during summer at the same location, which is exactly why winter shadows are so much longer than summer shadows cast by the very same object. At the winter solstice, the shortest day of the year in the northern hemisphere, the sun reaches its lowest maximum height above the horizon of the entire year, producing the longest shadows a site will experience at any point in the annual cycle, which is precisely why winter solstice conditions are the reference point designers use when checking whether a space will receive adequate winter sun.
How shadow length is actually calculated
Shadow length from a vertical object such as a building, wall, or tree trunk is calculated from the object’s height and the sun’s current angle above the horizon, using a simple trigonometric relationship where shadow length equals object height divided by the tangent of the sun’s altitude angle, meaning a lower sun angle, mathematically corresponding to a smaller altitude angle and therefore a smaller tangent value, produces a proportionally longer shadow for the exact same object height. This is why a modest two-storey building can cast a shadow reaching many times its own height across an adjacent courtyard during the depths of winter, even though the same building’s shadow barely reaches beyond its own footprint at the height of summer, and understanding this relationship lets a designer check, well before construction, exactly which parts of an adjacent outdoor space will fall inside or outside a building’s winter shadow at different times of day.
Why trees behave completely differently to buildings in this calculation
A deciduous tree’s shadow behaves in a genuinely useful way that a building’s shadow cannot replicate, because its shading effect changes dramatically between seasons entirely independent of the sun’s own seasonal movement, casting a light, minimal shadow through winter while bare of leaves, precisely the season when a design typically wants to preserve access to low winter sun, and then developing a substantially denser, more effective shadow once fully in leaf through summer, precisely the season when shade is genuinely wanted. This seasonal self-adjustment is exactly why deciduous trees are such a consistently favoured design tool for seating areas and courtyards that need to welcome low winter sun while still providing effective shade during hot summer conditions, an outcome a fixed structure alone cannot achieve without some form of adjustable or seasonal shading device.
Sizing an overhead structure for a target shading percentage
Pergolas, louvre structures, and similar overhead elements are generally sized around a target shading percentage rather than complete shade, since a genuinely comfortable outdoor seating area in summer conditions typically wants somewhere in the region of fifty to seventy percent shading coverage, a benchmark consistent with guidance published by the Chartered Institution of Building Services Engineers, rather than either full, unbroken shade or no shade at all, and this target percentage translates directly into decisions about louvre spacing or slat width relative to the gaps between them, since a wider gap relative to slat width naturally produces a lower overall shading percentage and a narrower gap produces a higher one.
Estimating usable daylight hours through the year
Total daylight hours at a given location vary through the year in a pattern that mirrors the sun’s changing altitude discussed above, with meaningfully shorter days around the winter solstice and meaningfully longer days around the summer solstice, and this seasonal daylight variation is worth checking explicitly for any outdoor space intended for year-round use, since a space that feels perfectly well lit during a long summer evening may need supplementary lighting considered far earlier in the evening during winter months, a genuinely useful thing to establish at design stage rather than discover after the space is already built and in use.
Disclaimer
The information and any results referenced on this page are provided for general educational and design exploration purposes only, using simplified solar geometry and general reference benchmarks including CIBSE AM11. This content does not account for site-specific obstructions, atmospheric conditions, or precise geographic and topographic data the way specialist solar modelling software does. For planning applications, daylight and sunlight rights assessments, or formal overshadowing reports, consult a qualified daylight and sunlight consultant.