Report bundle for flats on a former car park
A car park looks like an easy site until the ground investigation comes back. Here is the report bundle a residential scheme on hardstanding usually needs, and the order to commission it in.
Flats on a former car park look straightforward. No buildings to demolish, no trees, no obvious ecology, a flat site with existing access. Then the ground investigation comes back with hydrocarbons and made ground, the lead local flood authority asks for a discharge rate the site cannot achieve, and the town centre traders object to the loss of 60 spaces. The car park to flats reports bundle is driven by what is under the tarmac and what the tarmac was doing, rather than by anything visible on a site visit.
Two documents carry almost every application of this type: the land contamination work and the drainage strategy. Get those wrong and nothing else matters.
Start with the ground
Tarmac hides history. Urban car parks sit on former gasworks, foundries, railway land, bomb-damaged terraces filled with rubble, and demolished industrial buildings whose asbestos went into the made ground.
The sequence is fixed. A preliminary risk assessment assembles the site history from historic mapping, trade directories, regulatory records and aerial photography, adds a walkover, and produces a conceptual site model identifying sources, pathways and receptors. Residential with private gardens is the most sensitive end use, so the assessment criteria are tighter than they would be for a commercial scheme.
Where the model shows plausible pollutant linkages, intrusive investigation follows: trial pits, boreholes, soil and water sampling, and ground gas monitoring where made ground or infilled ground is present. A land contamination assessment at this level needs a suitably qualified and experienced author, and both national guidance and the investigation standards expect that. An AI-assisted draft can structure the report and flag what is missing, and it is a starting point for that professional rather than a substitute.
Two practical points. Vehicle fuelling and servicing areas are worth targeting specifically, because they are small, localised and easy to miss on a coarse sampling grid. And asbestos in made ground now drives more remediation cost on urban sites than almost anything else.
Surface water when the site is already sealed
A car park is already close to fully impermeable, so the greenfield runoff argument does not apply. The existing rate is the comparison, and the question becomes how much betterment the authority expects.
Work the discharge hierarchy in order: infiltration first, then a watercourse, then a surface water sewer, then a combined sewer as a last resort. Infiltration testing on made ground often fails, and a buried structure or shallow groundwater will rule it out entirely, so test early rather than assuming.
A drainage strategy for this kind of site usually combines attenuation below the podium or car park deck, permeable paving where the ground allows, green or blue roofs, and rain gardens within the soft landscaping. Include the Environment Agency climate change allowances current at the time of writing, and say which allowance you have applied.
The SuDS approval regime under Schedule 3 of the Flood and Water Management Act 2010 has been the subject of announcements and revised timetables, so check whether it is in force at the time you submit rather than relying on an older note.
Ecology on a site with almost no habitat
Sealed surface scores nothing in the statutory biodiversity metric, which means the baseline on a tarmac site is often close to zero and a 10 per cent gain is achievable through planting, green roofs and boundary treatment.
That does not remove the survey. A preliminary ecological appraisal records what is actually there, which on older car parks includes self-seeded scrub along boundaries, buddleia colonising walls, nesting birds in adjacent structures, and occasionally bats roosting in an attached building. Open mosaic habitat on previously developed land is a real and often-missed category that carries genuine distinctiveness.
Check the de minimis exemption position carefully before assuming the duty does not apply, and record the baseline properly either way.
Daylight, in both directions
Two separate assessments are needed and they are frequently confused.
Outward, the effect on existing neighbours is measured against the BRE guidance on site layout planning for daylight and sunlight, using vertical sky component, annual probable sunlight hours and no sky line. A five-storey block replacing an open car park is a large change in an urban setting, and the neighbouring windows that previously looked across open tarmac are the ones that fail.
Inward, the proposed flats need adequate daylight themselves, assessed against the current daylight standard. Deep floorplates, single-aspect north-facing units and recessed balconies are where schemes lose rooms.
Commission a daylight and sunlight assessment at massing stage, not after the planning drawings are complete. It is the study most likely to change the building.
The parking, and the evidence about losing it
If the car park is private and serves nothing else, this is simple. If it is public, or serves a parade of shops, or is the only place the flats above the high street can park, it is the objection that runs to committee.
Evidence beats argument. A parking survey run to an accepted methodology, across weekday and weekend periods and outside school holidays, shows the occupancy of the car park itself and the capacity of the surrounding streets to absorb any displacement. Pair it with a transport statement covering the trip generation of the new homes, the cycle provision and the servicing arrangements.
Where the site is a council-owned car park, the parking evidence usually has to satisfy the authority as landowner as well as planning authority, and those are different conversations with different timescales.
Servicing, refuse and access
The details that get conditioned, or refused, on flatted schemes are consistent.
- Refuse storage sized for the collection frequency, within the drag distance the authority specifies, with a bin presentation point a refuse vehicle can reach.
- Swept path analysis for the refuse vehicle and for a fire appliance.
- Fire service access and water supply under the current Approved Document, and a fire statement where the building or the scheme meets the threshold that requires one.
- Secure, covered cycle parking at the ratio the local plan sets, at ground level rather than in a basement nobody will use.
- Plant location and its noise, particularly where ventilation or heat pump equipment sits on a roof next to existing homes.
Sequencing
Order the work so each study informs the next rather than repeating it.
- Topographical survey, extended beyond the red line to pick up neighbouring window positions and levels.
- Desk study and preliminary contamination risk assessment.
- Utility searches and a drainage investigation, including infiltration testing.
- Preliminary ecological appraisal and the biodiversity baseline.
- Massing study tested against daylight to neighbours before the design is fixed.
- Intrusive ground investigation targeted by the conceptual site model.
- Transport, parking survey and servicing once the layout and unit numbers are stable.
Scale changes the list. Once the floorspace or unit count crosses the thresholds, further documents come into play, and it is worth reading what changes once the scheme passes 1,000 square metres before assuming the bundle above is complete.
You can browse the full list of report types and start a draft for the ones your site triggers.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Does a car park site always need a contamination assessment?
Almost always, because residential is a sensitive end use and car parks are frequently built over earlier industrial ground. The starting point is a preliminary risk assessment covering the site history, a walkover and a conceptual site model. Intrusive investigation follows only where that model identifies plausible contaminant linkages, which on most urban car parks it does.
If the site is already hardstanding, do I still need a drainage strategy?
Yes. The existing runoff rate is the starting point for the calculation rather than a greenfield rate, but the lead local flood authority will still want the discharge hierarchy worked through and betterment demonstrated. Local standards vary considerably, so ask the authority for its current requirement before the layout is fixed.
Does biodiversity net gain apply to a site with no habitat?
The duty applies unless an exemption is met, including the de minimis exemption for development affecting only very small areas of onsite habitat. Sealed surface scores nothing in the metric, so the baseline is often close to zero and the gain is achievable on site through planting and roofs. The baseline still has to be surveyed and recorded properly.
What evidence does the council need about the lost parking?
Where the car park serves the public or a nearby use, expect to justify the loss with occupancy evidence rather than assertion. A parking survey run to an accepted methodology across weekday and weekend periods, avoiding school holidays, shows whether the spaces are actually used and whether displacement onto surrounding streets is realistic.
When should the ground investigation happen?
After the desk study and, where possible, before the application rather than after. A conceptual site model built from the site history tells the investigation where to sample. Running intrusive work blind wastes money, and discovering a problem after permission, at the discharge of conditions stage, is when remediation costs damage a scheme.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.