Risers, hydrants and the core layout at planning stage

Dry riser planning core layout decisions get made at planning stage whether or not anyone writes them down. Rising mains, their inlet boxes and the external hydrants that feed them fix where the fire service pulls up, which part of the ground floor frontage is unavailable for anything else, and how much floor area the core consumes on every level. Get it wrong and the fix is a redesign, because an inlet needs a hard standing within reach of a pump appliance and that is a site planning constraint rather than a technical detail.

Why riser provision shows up on a planning drawing

Fire mains are a Building Regulations matter, set out in Approved Document B, and they are not something a planning officer assesses. The consequences are planning matters all the same.

An inlet box has to sit on an external wall where a fire appliance can reach it. The appliance needs hard standing, and the guidance in Approved Document B puts the pumping appliance within 18 m of the inlet, with the inlet visible from the appliance. That dictates a stretch of accessible frontage, a surface built to take appliance loading, and a clear line of sight that cannot be planted out.

Inside, a firefighting shaft eats plan area on every floor it serves. On a small flatted site that can be the difference between four units and three on the upper levels, which changes the viability of the whole scheme. Architects who leave it to technical design find out at Gateway Two, long after the planning drawings were approved.

Dry and wet main thresholds

The trigger is height above fire service vehicle access level, not storey count.

A wet main brings a pump room, a water store and a maintenance regime, so the floor area and the plant allowance change as soon as the top floor passes 50 m. BS 9990 covers the design and installation of non-automatic firefighting systems and is the standard the detail is tested against.

Sprinkler provision moves on a different threshold again. New blocks of flats above 11 m in height require sprinklers under the current Approved Document B, which adds a tank and pump room to the ground floor or basement. And the second staircase requirement for taller residential buildings has been confirmed by government with transitional arrangements, so check the current Approved Document B and the transitional dates on gov.uk before fixing a single-stair core on a scheme above 18 m.

Inlet position and the street frontage

The inlet is a steel box, roughly the size of a meter cabinet, with a wired glass or breakable panel and signage. It has to be visible, reachable and obstruction free.

That rules out several popular frontage treatments. A continuous planter, a cycle hoop run or a bin store across the only accessible elevation will have to move. On a corner site the inlet usually belongs on the secondary frontage, which is normally where the designer wanted the service riser anyway. On a listed building or in a conservation area the box becomes a design issue in its own right, and the answer is usually a recessed position with a painted face, agreed with the conservation officer rather than imposed later.

Where the main elevation is set back behind a courtyard, check the appliance route before you commit to the layout. A 4.5 m wide access with a tight turning head may satisfy refuse collection and still fail on appliance swept path, and the two vehicles have different requirements.

Hydrants and the water undertaker

Hydrants are not building control's job. They are installed in the public highway or on private land by the water undertaker, and the fire and rescue authority's duty to secure an adequate water supply for firefighting sits in the Fire and Rescue Services Act 2004. The Water Industry Act 1991 governs the undertaker's obligations and the recovery of costs.

Approved Document B expects hydrants within 90 m of a dry main inlet, and hydrants spaced no more than 90 m apart where a development has no fire main. On a greenfield or large brownfield site that often means new hydrants on the new estate roads, which means an application to the water undertaker, a quotation, a lead time and a connection programme that is entirely outside your control.

Two practical points. The quotation process is slow, so start it at the same time as the water connection application rather than after permission. And the fire and rescue service will comment on hydrant provision as a consultee on larger schemes, so the hydrant plan is worth submitting even where it is not a validation requirement.

Core space take and unit planning

A firefighting shaft is a protected stair, a firefighting lobby, a firefighting lift and the rising main, all in one enclosure. The lobby is the element people underestimate, because it has to be a real room with doors in and out, not a widened landing.

On a single-core block the cumulative effect is a core of a size that only works above a certain floor plate. Below that, the net to gross ratio collapses and the scheme stops stacking. This is why a 9 storey point block on a tight urban plot sometimes has to become 6 storeys with a different core, and why that conversation belongs in the pre-application meeting. The structural implications run alongside, and the questions raised in mass timber schemes land on the same drawing.

Below ground, a basement that puts a floor more than 10 m below access level brings a firefighting shaft of its own. Light wells, escape and flood risk then have to be resolved together, which is the problem set out in basement light wells, escape and flood risk.

Where risers collide with cycle stores and refuse routes

The ground floor of a flatted block is a queue of competing requirements, and the ones that routinely clash are:

• the fire main inlet and its clear zone
• the sprinkler tank and pump room, if sprinklers are required
• the cycle store, sized to the local plan standard, with a route that does not pass through the protected core
• the bin store, within the carry distance the waste authority specifies and within reach of the collection vehicle
• the substation or switch room, with its own access and ventilation requirements
• the lobby and any concierge or post provision

The resolution that usually works is to give the fire main and the appliance standing first call, because they are the least flexible, then place the sprinkler plant adjacent, then fit cycle and bin stores around them. Doing it the other way round produces a layout where the bins have to cross the protected core, which no building control body will accept.

Note: cycle and bin store standards are local plan matters and vary by authority, so take the figures from the adopted plan rather than from the last scheme you did.

Showing the arrangement in the submission

A planning submission does not need a full fire engineering design. It needs enough to show the arrangement is possible.

1. A ground floor plan marking the inlet position, the appliance standing, the 18 m reach and the sightline.
2. A typical upper floor plan showing the shaft, the lobby and the main.
3. A site plan with existing and proposed hydrants, with distances annotated.
4. A short note on the main type, dry or wet, with the height above access level that justifies it.
5. For relevant buildings, a Fire Statement on the published form.

That last item is a legal requirement rather than good practice. Article 9A of the Development Management Procedure Order 2015 requires a fire statement for applications for relevant buildings, and the Health and Safety Executive is a statutory consultee at Planning Gateway One. A fire statement must be prepared by someone with the necessary fire engineering competence, so PlanScope's draft is a starting point for that professional rather than a substitute for them. The same applies to a Fire Safety Strategy to BS 9991 or BS 9999, which is a fire engineering document throughout.

Illustrative example. A 7 storey residential block with the top floor at 20 m above the access road. It needs a fire main, a firefighting shaft, sprinklers, an inlet on an elevation with hard standing within 18 m, and a hydrant within 90 m. Put those five things on the drawing before you count units, and the unit mix that survives is the one that was always going to be buildable.

This is general guidance, not legal advice; the competent designer and the building control body determine what is required for your building. Browse the PlanScope report types to see what a fire-related submission usually includes.

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.