Sun Path and Solar Access Studies Explained

Quick answer: A sun path study shows where the sun sits over a site across the day and across the year. A solar access study uses that geometry to answer a specific question: how much direct sunlight a given window, yard, plaza or solar panel receives before and after a proposed building exists. The deliverable is normally a set of dated and timed images or an animation, plus a written statement of the location, the time zone, the dates tested and whether daylight saving was applied. Those four statements are what makes the study checkable.

What the two studies are, separately

The terms get used interchangeably and they are not the same product.

A sun path study is about the site. It describes the solar geometry: the altitude and azimuth of the sun at a given latitude, through the day and across the seasons. It is useful early, when massing is still moving, and it tells a designer where south is in a way a site plan never does.

A solar access study is about a receiver. It asks whether a particular thing keeps the sunlight it currently has. The receiver might be a neighbour window, a school playground, a public plaza with a stated hours of sun requirement, a rooftop array, or a garden the planning code protects. The question is narrow, and the answer is a number of hours or a yes.

Both rest on the same geometry. They differ in what gets measured, and the difference matters because a board that asked for solar access and received a sun path diagram has been given background rather than an answer. See shadow study deliverables and what reviewers check.

The four statements that make a study verifiable

Any competent study carries four facts on the sheet, and a study missing them cannot be audited by anybody.

• Geographic position. Latitude and longitude to a sensible precision, not a city name. Solar angles change measurably across a metropolitan area.
• True north. Stated, and distinguished from the project north used on the drawings. Nearly every serious error in this work is a north error, and it is invisible in the output because wrong shadows look exactly like right ones.
• Dates tested. Normally the two equinoxes and the two solstices as a minimum, plus any date the local code names.
• Times and time basis. Clock times with the time zone, and an explicit note on whether daylight saving is applied. A study run in standard time and presented with summer clock times is an hour wrong all the way through.

Write those four on the sheet rather than in a covering email, because the sheet is what ends up in the record and the email does not.

Which dates and hours actually get tested

The default set is March 21, June 21, September 21 and December 21, at three hours each: mid morning, noon and mid afternoon. That grid covers the extremes and the mean, and it is enough for most hearings.

It is not always enough. Where a code protects a specific condition, the code names the date and the hours, and that naming overrides the default. A protected hours of sun rule on a public space will state the season and the window, for example a number of hours between stated clock times on a stated date, and the study has to answer that rule in its own terms rather than present a general picture and leave the board to interpolate.

December is where proposals usually fail and where applicants are most tempted to be quiet. A winter low sun throws very long shadows, so a scheme that looks harmless in June can be severe in December. Present December plainly. A board that finds the winter case missing stops believing the rest of the set, and recovering that credibility costs more than the finding would have.

Hourly increments rather than three snapshots are worth producing when the question is duration rather than presence. A neighbour does not usually care that a shadow touches their window; they care how long it stays.

How the geometry gets built

The study is only as good as the model under it, and the model is mostly context rather than proposal.

The proposed building comes from the design model, simplified. Balcony rails, mullions and reveals change nothing at this scale and cost render time, so they come out. What must stay is anything that casts a real shadow: parapets, lift overruns, plant screens, stair cores and roof equipment. A proposal modelled to the parapet and presented without its rooftop plant understates its own shadow, and that is the single most common honest looking error in this work.

The context comes from survey, aerial survey or public datasets, and its heights must be real heights rather than storey counts multiplied by an assumed floor to floor. Where context height is estimated, say which buildings were estimated and on what basis.

Ground level is the other thing people get wrong. A sloping site changes where a shadow lands considerably, and a study run on a flat plane over a site with a fall across it produces shadows that are confidently in the wrong place. Use the survey surface. See massing study, what it shows and what it proves and context massing studies for urban sites.

Existing condition and proposed condition, side by side

A solar access study that shows only the proposed condition is almost useless, because nobody can tell how much of the shadow is new.

The pairing is the whole argument. Same viewpoint, same date, same hour, existing on the left and proposed on the right, with the difference available as a third image where the change is subtle. On many urban sites the honest finding is that the receiver was already shaded at that hour by a building that has stood for decades, and the proposal adds very little. That finding is worth far more to an applicant than a flattering single image, and it only exists if the existing condition was produced.

Where the proposal does take sunlight, say how much and for how long, in plain numbers. Boards are considerably more tolerant of a quantified loss than of a qualitative reassurance, and a study that volunteers its own worst case is treated as evidence rather than advocacy. See visuals for hearings versus community meetings.

What the deliverable contains

A complete package normally holds the following.

• A sheet per date, each carrying the three or more times, existing and proposed paired.
• A key plan locating the receivers tested and the viewpoints used.
• The four statements above, on every sheet rather than once at the front.
• A short written summary in sentences, naming the receivers, the hours lost and the worst case date.
• An animation where duration is the point, since a moving shadow communicates duration in a way stills do not.
• A statement of what was excluded: vegetation, future permitted development on adjacent sites, or context whose height was estimated.

That exclusions note is the item most often dropped and the one most often asked about in the room. Writing it down converts a weakness into an acknowledged limit. See sight line and story pole studies explained.

Where solar access meets the other studies

Sun path work, massing work, view analysis and sight line work answer four different objections and are regularly commissioned as one package because the same context model carries all four.

If the model is built once with real heights, a real ground surface and a stated true north, then massing images, shadow sheets, view corridor plates and sight line sections all come out of it. Building four models separately is how applicants end up with four sets of drawings that disagree with each other, which is the fastest way to lose a board. See view analysis and view corridor studies and visual evidence for land use attorneys.

The sequencing that works is massing first, while the scheme can still change cheaply, then solar and sight line work once the envelope is settled, then presentation imagery last. Running presentation imagery first is common and expensive, because the pretty views get redone after the shadow study forces a setback. See planning a 3D rendering around a hearing date and the land entitlement process guide.

What it costs and how to scope it

There is no published rate for solar access work, because the cost sits almost entirely in the context model and the number of receivers, not in the sun calculation itself. A single receiver on a flat site with three dates is a small job. Fourteen neighbour windows on a sloping site with hourly increments and an animation is not.

Published figures on the 3D rendering cost page cover visualization deliverables, and they are the right reference where the package includes presentation imagery: standard exterior stills run $750 to $1,250 and upwards, premium exteriors $1,250 to $2,500 and upwards, and walkthrough or animation work $3,500 to $15,000 and upwards. Study work itself is scoped after the site, the receivers and the code requirement are reviewed.

Four lines make quotations comparable: the receivers to be tested, the dates and hours required by the code, whether existing condition pairing is in scope, and whether an animation is needed. Leave any of them unstated and you will receive prices for different jobs.

The honest summary

Solar access is the easiest part of an approvals package to get technically right and the easiest to get quietly wrong, because a wrong north or an assumed context height produces output that looks completely credible.

State the position, the true north, the dates and the time basis on every sheet. Model the plant on the roof and the fall across the site. Produce the existing condition so the change is measurable. Include December. Write down what you excluded. A study built that way survives the one question that matters in the room, which is how anybody else could check it.

Rendimension has produced this work since 2004, architect led, across more than 1,000 projects. See 3D visualization for land use attorneys and what to send for a hearing.

Frequently asked questions

What is the difference between a sun path study and a solar access study?

A sun path study describes the solar geometry over the site across the day and the year. A solar access study uses that geometry to answer a narrow question about a specific receiver, such as how many hours of direct sun a neighbour window or a public plaza keeps once the proposal exists.

Which dates should a study test?

The usual minimum is the two equinoxes and the two solstices, at three times each. Where the local code protects a condition it will name its own date and hours, and that naming overrides the default set. December is the case that matters most and the one most often left out.

Why does true north matter so much?

Because a north error produces output that looks entirely credible. Wrong shadows are the same shape as right ones, so nothing in the image reveals the mistake. State true north on the sheet and distinguish it from the project north used on the drawings.

Does daylight saving time affect the result?

Yes, by a full hour. A study run in standard time and presented with summer clock times is wrong throughout. Every sheet should state the time zone and whether daylight saving was applied, so a reviewer can reproduce the angles independently.

What has to be in the model?

Anything that casts a real shadow: parapets, lift overruns, plant screens, stair cores and rooftop equipment, plus context at real measured heights and the actual ground surface. A proposal modelled only to the parapet understates its own shadow, which is the most common honest looking error in this work.

Why show the existing condition as well?

Because without it nobody can tell how much shadow is new. On many urban sites the honest finding is that the receiver was already shaded at that hour by an existing building, and the proposal adds very little. That finding only exists if the existing condition was produced.

When is an animation worth it?

When the question is duration rather than presence. A neighbour rarely objects that a shadow touches their window; they object to how long it stays. A moving shadow communicates duration in a way that three still images cannot.

How is this work priced?

Against the context model and the number of receivers, not against the sun calculation, which is trivial. Scope it by naming the receivers, the dates and hours the code requires, whether existing condition pairing is included, and whether an animation is needed.