Budgeting a daylight and sunlight evidence base

Daylight and sunlight evidence is priced by the number of windows analysed and the number of times the massing changes, not by the size of the scheme. A 40 unit infill block overlooked by three Victorian terraces generates more assessment work than a 200 unit scheme on an isolated brownfield site, and budgets built from a cost per unit will be wrong in both directions.

Price the work by stage, and make the design team aware that every massing revision after the model is built has a number attached to it.

Early massing testing

The least costly daylight work is the work done before the massing is fixed. At concept stage an assessor can take a block model, the surrounding buildings from published mapping and a rough window survey from the street, and report where the problems will be.

That is a short exercise. It tells you whether the top two storeys of the north block are going to cost you the scheme, and it does so while moving them still costs nothing but a drawing revision.

Scope it explicitly as screening. What you are buying is a set of vertical sky component figures for the worst affected windows, a note on which neighbouring properties will drive the assessment, and an opinion on whether a full study will be needed. What you are not buying is a report you can submit.

The single biggest saving available on the whole evidence base is making this call early and acting on it.

Full assessment scope and model building

The full assessment is a modelling exercise, and the cost sits in three places.

Survey comes first. Someone has to establish the position, height and window arrangement of every relevant neighbouring building. Published mapping and aerial data get you part of the way, and a measured survey is needed where accuracy matters, which it does whenever a result is close to a threshold. Where interior room uses cannot be established from outside, assumptions have to be made and stated, and a letter drop asking neighbours to confirm room uses is sometimes worth the effort.

Model building comes second. The existing context, the existing baseline condition and the proposed scheme all have to be modelled, and the baseline is the part people forget to price.

Analysis and reporting come third, and this is where the window count drives everything. Vertical sky component and no sky line analysis are run per window and per room, so 300 windows across six neighbouring properties is a materially different job from 40 windows across one. Ask for the fee to be expressed as a base plus a rate per additional property, so a late discovery does not become a variation argument.

Internal daylight for the new homes

This is a separate piece of work with a separate cost, and it is the one that catches development managers who budgeted for neighbour impact only.

Assessing daylight within the proposed dwellings follows BRE 209 and the UK national annex to BS EN 17037, using target illuminances achieved over half the room area for half the daylight hours. It is climate based daylight modelling, which needs the internal layouts, the glazing specification, the balcony arrangements and the surrounding context. The work therefore cannot start until the unit layouts are reasonably settled, and it has to be redone if they change.

The results have design consequences. Single aspect north facing units, deep plan flats and rooms behind a balcony are where schemes fail, and the remedies are larger windows, shallower plans or fewer units. Running this analysis before the accommodation schedule is fixed is worth far more than the fee.

Additional runs when the massing changes

Every serious massing change after the model is built costs money, and this is the line most budgets omit entirely.

Expect at least two re-runs on a scheme of any complexity: one after the pre-application feedback, one after the design review panel or the officer's comments, and often a third after a committee deferral. Each re-run means updating the proposed model, re-running the analysis and reissuing the report with revised tables.

The way to control it is contractual rather than technical. Agree a fee that includes a stated number of re-runs, with a rate for additional ones, and make the design team aware of that rate. Nothing disciplines optional massing tweaks like a known cost per iteration.

Keep the assessor on the distribution list for drawing issues. Discovering at the eleventh hour that the report describes a superseded scheme is an avoidable and expensive embarrassment.

Rebuttal work and committee material

Where an objector commissions their own daylight report, the rebuttal is a distinct piece of work: reading their methodology, identifying where the assumptions differ, and producing a comparison. Assumption differences are usually the whole story. Room uses, whether a window serves a habitable room, the treatment of balconies and whether the baseline reflects an existing consented scheme rather than what is standing today.

Budget for it on any scheme with organised local opposition, and budget for the assessor's attendance at committee where the daylight case is a live issue. Committee material is its own line: a short presentation, clear before and after images, and a plain English explanation of what a vertical sky component number means to someone who has never seen one.

Where amenity space rather than windows is the issue, the Overshadowing Study reporting sun on ground is a separate document again, and it costs less than the window analysis.

Rights of light is a separate line

Rights of light is not a planning matter. It is a private law right, typically acquired by twenty years of uninterrupted enjoyment under the Prescription Act 1832, and it is enforced by injunction or damages rather than through the planning system.

The tests are different, the thresholds are different, and a scheme that is acceptable in planning terms can still give rise to a claim. Rights of light advice comes from a specialist surveyor and often a solicitor, and the mitigation is commercial: negotiated releases, a light obstruction notice, or insurance.

Put it in the development appraisal as its own line, at its own stage, and do not let anyone tell you the planning daylight report covers it. Two different professionals, two different reports, two different purposes.

Budgeting the whole amenity evidence base

Build the budget as a table of stages rather than a single figure, and attach each stage to a programme date.

Then ask each quote to price the stages separately with a rate per additional property and per re-run. Fee comparisons between assessors are meaningless otherwise, because the scopes will not match.

A Daylight and Sunlight Assessment is a report type councils expect to be authored by someone suitably qualified, so professional review is strongly advised. Drafting the policy narrative and report structure in advance, then having the assessor supply and check the modelling, is a reasonable division of labour, and it is the same approach that works for the documents covered in what drives the price of a Planning Statement and what a design and access statement costs to produce.

For the drafting side, PlanScope pricing is one free report, £50 per report, or £150 per month for the Professional tier aimed at architects, planning agents and consultants. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.