Evidence base for a data centre on an employment allocation
The allocation's job numbers came from offices or light industry, and a data centre cannot match them. That gap, plus generator testing, shapes the whole evidence base.
Data centre planning evidence on an allocated employment site turns on a policy problem rather than a technical one. The allocation was in all likelihood justified by job numbers taken from office or light industrial floorspace, and a data centre delivers a fraction of those jobs per square metre. That gap is the first thing the authority will raise, and no amount of noise modelling answers it. The technical issues that follow, standby generator testing and the continuous sound of heat rejection plant, are the two that decide the objections.
Use class and the employment policy test
There is no settled classification. Authorities and inspectors have variously treated data centres as Class B8 storage and distribution, as Class B2 general industrial, and as sui generis, and the answer matters because it determines whether the allocation's policy wording covers the proposal at all.
Do not assume. Read the allocation's supporting text, see which use classes it names, and if the classification is arguable, address it in the planning statement with reasons rather than asserting a class in a single line. Where the allocation is drafted around former Class B1 uses, remember that class no longer exists and the saving provisions mean the old wording is read against the classes as they stood.
The employment test then has two limbs. Whether the use is one the allocation supports, and whether the site's contribution to the authority's employment land supply is maintained. An Employment Land Assessment is the document that addresses the second, and it should engage with the authority's own employment land review rather than restating national policy.
National policy supports advanced digital infrastructure, and the current Framework is organised by policy codes rather than paragraph numbers, so take the code from gov.uk at the time of writing.
Power and water demand information
Authorities now ask about both, and the answers shape the application.
On power, set out the design load, the connection voltage, the point of connection, the distribution or transmission operator's position in writing, and the on-site substation and switchroom requirements with their footprint and access. In parts of the country grid capacity is the binding constraint and connection dates run years ahead of the planning programme, which is a material fact about deliverability rather than a commercial secret.
On water, state the cooling technology and whether it is evaporative, adiabatic or closed-circuit, because the water demand differs by an order of magnitude between them. Give the peak and annual demand figures, the water undertaker's capacity response, and the discharge arrangements including blowdown quality. Where the site sits in a water-stressed catchment or an area subject to water neutrality requirements, this becomes a determinative issue and a water supply assessment is the place to deal with it.
Closed-circuit cooling removes the water argument and costs more in energy. Say which you have chosen and why.
Noise from chillers, dry coolers and generators
Two noise sources, two different assessments, and conflating them is the commonest weakness in these applications.
The continuous plant, chillers, dry coolers and air handling, produces steady and often tonal sound at all hours. Assess it under BS 4142 with a background sound survey covering night-time periods at the nearest noise-sensitive receptors, manufacturer sound power data for the plant actually specified, and the character corrections the standard requires. A Noise Impact Assessment based on generic plant data will be conditioned tightly or refused.
Standby generators are the contentious part. They are tested regularly, the testing is audible, and residents experience it as an event rather than a background. Describe the testing regime explicitly: how many generators, how often each is tested, for how long, at what time of day, and whether tests are staggered or simultaneous. Then assess the tested condition as well as the emergency one. The emergency condition is rare. The testing is regular, and it is what neighbours hear.
Expect conditions fixing rating levels at named receptors, restricting testing hours, requiring a post-commissioning verification survey and requiring the testing regime itself to be agreed.
Air quality from standby generation
Diesel standby plant produces nitrogen oxides and particulates, and the assessment has to cover both testing and emergency running. An Air Quality Assessment with dispersion modelling of the stack arrangement is the normal requirement, and it needs the stack heights and locations to be fixed, which means coordinating with the architect early.
Where the site lies in or near an air quality management area, the authority's environmental health team will engage closely, and the mitigation usually involves stack height, selective catalytic reduction or a move to lower-emission plant.
Separately from planning, generators above the relevant thermal thresholds fall within the specified generator and medium combustion plant controls in the environmental permitting regime, so an environmental permit from the Environment Agency may be required. Establish that in parallel, because permit conditions on emission limits and operating hours can conflict with what you have told the planning authority.
Security fencing, lighting and boundary design
Data centres are secure compounds and they look like it. The design issues are the ones that generate amenity objections on an allocated site next to housing.
Fencing type and height, its visual treatment and any landscape buffer in front of it. Lighting, which has to be presented as a layout with spill contours assessed against the obtrusive light guidance for the relevant environmental zone, with detection-activated rather than continuous lighting wherever security allows. A Lighting Assessment covers this. Camera column positions and heights. And the blank elevations, which need treating as elevations rather than as the back of the building.
Employment density and the economic case
Meet the job numbers argument head on. The honest position is that a data centre employs relatively few people directly for its floorspace, and that the economic case rests elsewhere: construction employment over a long build programme, specialist maintenance and supply chain activity, business rates, and the role the facility plays in enabling employment in the businesses that depend on it.
An Economic Impact Assessment should set out net additional operational jobs after displacement, construction person-years, and the rates position, and it should state the gross and net figures separately. A report that presents only enabled employment in the wider economy invites the response that any building could claim it.
Where the authority's allocation depends on a job target, consider whether part of the site can deliver a different employment use to bridge the gap. That answer has closed more of these applications than any technical report.
Heat rejection and a heat network opportunity
Rejected heat is a planning opportunity and increasingly a policy requirement. Where a heat network exists or is planned nearby, set out whether the facility can export heat, at what temperature, and what safeguarding of plant space and connection points is proposed if export is not viable from day one.
Even where export is not feasible, saying so with evidence is better than silence, because the question will be asked and an unanswered question becomes a condition.
Construction traffic and phasing
Transformers, chillers and generator sets arrive as abnormal indivisible loads, and the build runs over a long period with heavy deliveries. A construction traffic management plan has to cover the abnormal load route agreed with the highway authority, the escorting and any temporary works, delivery hours, wheel washing and the compound layout.
Phasing matters too, because these schemes are often built in halls over several years. Say which plant is installed at which phase, because the noise and air quality assessments have to be presented for the final built condition as well as for the first phase.
Enter your postcode on PlanScope to see which reports your site is likely to need, and the 12 flat brownfield report list shows the same exercise on a smaller scheme. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance rather than legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Which use class does a data centre fall into?
There is no settled answer. Authorities and inspectors have treated data centres as Class B8 storage and distribution, as Class B2 general industrial and as sui generis. The classification matters because it determines whether an employment allocation's policy wording covers the proposal, so address it with reasons in the planning statement rather than asserting a class.
How should generator testing noise be assessed?
As the condition that will actually occur, rather than treating it as an emergency scenario alone. State how many generators there are, how often each is tested, for how long, at what time of day, and whether tests are staggered. Then assess that regime at the nearest receptors alongside the continuous plant assessment, because residents experience testing as an event.
Do standby generators need an environmental permit as well?
They may. Generators above the relevant thermal thresholds fall within the specified generator and medium combustion plant controls in the environmental permitting regime, so a permit from the Environment Agency can be required. Run that in parallel with the planning application, because permit limits on emissions and operating hours can conflict with planning commitments.
How much water does a data centre need?
It depends entirely on the cooling technology, and the difference between evaporative, adiabatic and closed-circuit systems is an order of magnitude. State which you have chosen, give peak and annual demand, supply the water undertaker's capacity response and describe the discharge arrangements. In a water-stressed catchment this becomes a determinative issue.
How do I answer the employment density objection?
Directly. Accept that direct operational employment is low for the floorspace, and set out the case that does exist: construction person-years over a long build, specialist maintenance and supply chain activity, and business rates. Report gross and net figures separately, and consider whether part of the site can deliver a different employment use.
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.