From address to sunlight report in 3 minutes: how Schaduwplan works

What is Schaduwplan?

Schaduwplan is a web app that turns any Dutch address into a court-admissible sunlight report within five minutes. The tool runs entirely in the browser, uses open government data from 3DBAG, BAG and AHN4, and tests the results against the TNO standard and municipal variants. A report that costs €295 to €535 at an independent consultancy such as HoeveelZon, SchaduwSimulator or HBA runs up to €2,000 to €5,000 per report at large engineering firms (DGMR, Peutz, Nieman), with a turnaround of one to three weeks. At Schaduwplan the same report costs €29.95 and takes five minutes.

The report contains a 3D scene of the existing buildings, a drawing tool for the planned extension or roof addition, measurement points at the relevant windows and outdoor spaces, sun-hour calculations on the test dates, and a side-by-side comparison of the reference situation with the proposed situation. No subscription, no account required for the preview, payment only on download.

From address to report: the steps explained

The core claim — three minutes — refers to the active time at the computer. Reckon on five minutes if you place measurement points carefully and take the planned construction from a building drawing. The order is always the same.

1. Enter an address. You start with a Dutch address (street, house number, town or postcode). The PDOK Locatieserver geocodes it to a specific BAG building. The 3D scene loads automatically with every building within a 150-metre radius, based on 3DBAG. No 3D knowledge or CAD software required.
2. Draw the planned construction.Select your own parcel or the neighbours’ and draw the planned extension, roof addition, veranda or complete new build. The tool snaps to parcel boundaries from BAG, roof heights from AHN4, and the heights from the building drawing you have. For free-standing objects (a shed, a carport) a free-form shape is available.
3. Place measurement points. Click on the relevant windows (75 cm above floor level, as the TNO standard prescribes) and on outdoor spaces such as a terrace or garden bed. Per measurement point you automatically calculate sun hours on the TNO test dates (19 February, 21 June, 21 October) plus a date of your own choosing if you want to highlight a specific scenario, such as a garden party in August.
4. Choose a standard and run the analysis. Choose between light TNO, strict TNO, or a municipal preset such as the The Hague standard. The analysis runs at 1-hour intervals, positioned on the Dutch national grid (EPSG:28992) — the same projection the official government sources use. Result: a table of sun hours before and after the planned construction per measurement point, and a heatmap at ground level.
5. Download the report. The PDF is generated client-side. Contents: a cover with the address and 3D render, the assumptions (chosen standard, test dates, coordinate system), sunlight diagrams per test date with clock times at 1-hour intervals, the TNO test table (measurement point, reference, proposed, delta, status), a methodology appendix and a source list. You pay €29.95 and download immediately.

Which data sits underneath — and why it matters legally

Schaduwplan uses three public sources: 3DBAG for 3D building models, BAG for address and parcel data, and AHN4 for ground heights. All three are open, managed by the national government or renowned knowledge institutions, and accepted as authoritative by the Council of State and professional firms.

According to the Council of State (Almelo ruling, 18 January 2023, ECLI:NL:RVS:2023:172), TNO standards based on this type of data are “not unusual” to use. In the 2013 Ootmarsum ruling (ECLI:NL:RVS:2013:191) the Council of State in fact annulled a zoning plan precisely because no sunlight study using these sources had been carried out. The availability of authentic sources has become so self-evident that their absence is judged a procedural error.

What the PDF report contains

A sunlight report that judges and municipalities take seriously contains fixed elements. Schaduwplan generates these by default, in line with the Krimpen guideline — the most detailed official municipal template in the Netherlands. The report contains:

• A cover with the address, the date of the study and a 3D render at midsummer sun (21 June, 12:00 CEST).
• The assumptions: chosen standard (light TNO, strict TNO, The Hague, etc.), test dates, time intervals, coordinate system and all adjusted parameters.
• 3D sunlight diagrams per test date and per hour, side by side (reference and proposed), with a north arrow and a scale bar.
• Quantification per measurement point in table form: sun hours to the minute, before and after the planned construction, including the delta.
• An explicit TNO test: per measurement point a pass, a near-miss or a fail, tied to the two-hour standard or the strict three-hour standard.
• A methodology appendix: which sources (3DBAG, BAG, AHN4), which software, which assumptions (greenery and fences kept outside the formal TNO test), and a disclaimer noting that the report is indicative and that, for formal administrative proceedings, verification by a sworn expert is recommended.

The table of contents follows exactly the structure that consultancies such as Handel Bouwadvies, Blauwdruk Bouw and Bezonningsingenieur use. As a result your report reads to civil servants and judges like a familiar document, not an app export.

How accurate is the calculation?

Sun hours are calculated at 1-hour intervals across 365 days per measurement point. Per measurement point that is roughly 5,840 calculations per year. The sun path is modelled with the SunCalc algorithms, which match the official ephemeris tables of the US Naval Observatory at the level of seconds. Positioning uses the Dutch national grid (EPSG:28992), the projection of the Dutch government, and converts to WGS84 for display.

Time is computed internally in UTC and converted to CET or CEST for display, with correct DST transitions on the last Sunday of March and October. That matters: the TNO test date of 21 October falls in the week of the DST switch, so a 13:00 clock moment means something different on 20 October than on 28 October. Our model accounts for that.

In the Voorburg ruling of 5 April 2023 (ECLI:NL:RVS:2023:1329) the Council of State accepted that a height discrepancy of 3 cm (8.21 m versus 8.24 m) is negligible. The 50 cm resolution of AHN4 sits well below any reported relevant threshold, but we document our assumptions explicitly in the appendix so that any counter-expert can reproduce the inputs used.

When you still need a firm

Honest about the limits: Schaduwplan covers roughly 95% of the sunlight questions Dutch homeowners, architects and municipalities encounter. The remaining 5% call for a human firm. That is the case for:

• Large area developments with complex aesthetic-quality requirements, where a sworn expert must appear as an expert witness at a hearing.
• Municipalities that require “maximum planning possibilities” as the reference rather than the existing buildings — which demands a manual interpretation of the zoning plan.
• Historic inner cities with an unusual shadow history, where additional literature research is required.
• Situations where the building plan may still change substantially and iterative design with an architecture firm is simpler than downloading a new report each time.

In those cases we recommend using the Schaduwplan analysis as a starting point. You then already have a substantiated first estimate, and a conversation with the firm goes faster — they need not spend a week on intake and 3D modelling.

Who Schaduwplan makes the difference for

The tool was designed first and foremost for four groups. A concerned neighbour who must file a substantiated objection within six weeks. A homeowner planning an extension who wants to avoid conflicts with neighbours or the municipality. An architect or building designer who delivers sunlight studies as part of the permit application. And a municipal officer who must validate a submitted study against the local assessment framework.

For curious gardeners who simply want to know how much sun their terrace gets, the free preview is usually enough — the PDF report is meant for official use, not for hobby questions. For large developers and high-rise specialists the tool is a starting point; complex scenarios with dozens of towers call for a specialised firm.