Car park ventilation and charging bays in a layout

Car park ventilation fixes your elevations. Approved Document B treats a car park as open-sided only where the openings at each parking level reach a stated proportion of the floor area at that level, distributed between opposing walls, and an enclosed or basement car park needs mechanical ventilation instead, with plant, ducts and discharge points that have to go somewhere. Decide which route the scheme takes before the elevations are drawn, because retrofitting a 5 per cent opening area into a designed facade means losing habitable frontage or adding louvres nobody wanted.

Electric vehicle charging has made the same point about layout. Where the charging bays sit, and what separates them from escape routes and from the rest of the parking, is now a planning-stage question on any enclosed car park.

Why car park design appears at planning stage

Two things force it up the programme. The first is that ventilation openings and plant are visible, so they are a design and access matter and a neighbour amenity matter. The second is that on a relevant building the fire statement submitted at Planning Gateway One has to describe the fire strategy, including the car park, before permission is granted rather than at building control.

A Fire Statement is a document where competence is legally expected, under the Building Safety Act 2022 framework and Article 9A of the Development Management Procedure Order 2015. It must be prepared by someone with the necessary fire engineering competence, and an AI-assisted draft is a starting point for that person rather than a substitute for them.

The third reason is more mundane. Changing a car park from naturally ventilated to mechanically ventilated after permission usually changes the elevations, the roof plant and the floor-to-ceiling heights, which means a section 73 application or a fresh one.

Ventilation openings and the elevational effect

For a car park to be treated as open-sided, Approved Document B expects permanent openings at each parking level with an aggregate area of at least one twentieth of the floor area at that level, with a substantial share of that provided between two opposing walls so that cross-ventilation works. A naturally ventilated car park that is not open-sided is expected to achieve a smaller but still material proportion.

Those numbers translate directly into design decisions:

• the opening has to be permanent and unobstructed, so decorative screens, planting and acoustic louvres all reduce the effective area and need the free area calculated rather than assumed
• cross-ventilation needs two opposing elevations, which conflicts with a podium car park built into a slope or against a boundary
• the openings sit at the level of the street, where they are visible, audible and a route for vehicle emissions into the street

Where the car park is below residential accommodation, the openings also become a noise and air quality path. The ventilation strategy, the acoustic treatment and the emissions dispersion are one problem, and splitting them between three consultants without a coordinating section drawing produces a scheme that fails on all three. Where plant noise is in play, the assessment belongs in the Noise Impact Assessment with the louvre specification attached.

Check the current edition of Approved Document B for the figures before you fix the design, since the document is amended.

Charging bay location and separation

National building regulations require charging provision in new development through Approved Document S, with a charge point for dwellings that have associated parking and provision scaled to the parking count in other buildings. Planning conditions commonly go further, and local plan policies often require active and passive provision.

The fire question is separate and unresolved at national guidance level. Fire and rescue services and insurers have taken a cautious position on charging within enclosed and basement car parks, and the practical responses that appear in fire strategies are consistent even though the guidance is not:

1. Locate charging bays on the upper deck or in the open air where the site allows it.
2. Where charging must sit in an enclosed area, place it away from escape routes, stair cores and the building's structural elements, and away from the single means of escape in a compact car park.
3. Keep charging bays within sight of an access point for firefighting, and avoid positions remote from the entry.
4. Consider separation by distance, by a non-combustible barrier, or by locating charging in a dedicated compartment, and record the reasoning rather than the conclusion.

None of that is a code requirement, which is why the fire strategy has to explain the basis for the chosen arrangement. An authority reading a strategy that simply asserts the layout is acceptable will ask the fire engineer for the reasoning, and the answer is easier to give before the layout is fixed.

Enclosed and basement parking questions

A basement car park needs mechanical ventilation, designed for normal operation and for smoke clearance after a fire, with the extract split between high and low level and the system arranged so that failure of one part does not remove all capacity.

That brings plant, risers and discharge locations into the design. Discharge points need to be away from openable windows, balconies, intakes and the public footway, which on a tight urban site usually means a vertical route to roof level. The riser then has to be coordinated with the residential layout above, and this is the coordination that is most often missed between planning and technical design.

Below ground there is a second set of questions about groundwater, heave and the effect on neighbouring structures, which belongs in the Basement Impact Assessment and is a report councils expect from a suitably qualified author, with professional review strongly advised.

Sprinkler and detection consequences

Suppression and detection change the planning drawings less than ventilation does, but they change the plant and the water supply.

A sprinkler installation needs a tank and pump room with access, and the tank size is driven by the hazard classification and the design density. On a basement scheme the tank room competes for the same space as the ventilation plant and the substation. Where the authority or the fire strategy relies on suppression as part of the justification for the layout, the space for it has to be shown on the submitted plans, not left to the technical design stage.

Detection and alarm in a car park serving residential accommodation also affects the management arrangements, which may be secured by condition or by the agreement.

Access for firefighting

Appliance access, fire main locations and the route from the appliance to the riser inlet all sit in Approved Document B, and they constrain the site layout rather than the building. A basement car park with a single entry from a narrow mews is a different proposition from one entered from an adopted road with turning space.

Three items should appear on the planning layout. The appliance standing position and access route, with the swept path shown. The location of fire main inlets and the distance from the standing position. And the firefighting shaft or stair serving the basement, with its relationship to the car park entry.

The information box that supports an operational response has its own design and location requirements worth settling early, and how a secure information box is handled at planning stage sets out the usual approach.

What the drawings should show

Annotate rather than imply. A reviewing officer and a consultee should be able to read the strategy from the drawings alone:

• each parking level plan with the floor area stated, the opening positions marked, and the aggregate free opening area shown as both an area and a percentage
• elevations showing louvre extents with the free area of the chosen louvre type noted
• a section through the car park and the accommodation above, showing the riser route and discharge location
• the charging bay positions, with any separation measures and the compartment extent
• the appliance access, standing position, fire main inlets and firefighting shaft
• plant room locations for ventilation, suppression and the water supply

Keep the same information in the fire statement and in the design and access statement, and make sure the numbers match. A scheme where the elevation shows 4 per cent of opening and the fire statement claims an open-sided car park will be picked up, and the correction is almost always a design change rather than a drafting one.

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, and this article is general guidance rather than advice on a specific building. Enter your postcode on PlanScope to see which reports your site is likely to need.