Dry riser inlets and where they land on an elevation

The dry riser inlet position planning question arrives late and always in the same form: the fire engineer has specified an inlet, the contractor needs it within reach of the appliance standing position, and the elevation the planners approved has no box on it. Changing the facade after permission means a non-material amendment at best and a section 96A or section 73 application at worst.

It is a building regulations requirement that becomes a planning matter the moment it appears on an elevation. Which means it belongs on the drawings at submission, not at technical design.

When a fire main is required at all

Approved Document B triggers a fire main where the floor of the topmost storey sits above a stated height over fire service vehicle access level. Dry mains are accepted up to around 50 metres, above which a wet main with stored water and pumps is required.

The trigger heights differ between the volume covering dwellings and the volume covering other buildings, and they have been amended more than once since 2019. Read the current edition rather than working from a remembered figure, and record which edition you relied on. For residential buildings the 18 metre and seven storey thresholds in the Building Safety Act 2022 framework sit alongside the Approved Document heights and bring a separate set of duties, so a building can cross one threshold without crossing the other.

Three things follow for the design team. The height measurement is taken from fire service vehicle access level, which is not the same as finished floor level at the entrance on a sloping site. A single-storey basement can push the measurement in an unhelpful direction. And a roof terrace or plant deck above the top occupied storey does not usually count, though an occupied storey disguised as plant does.

Where the inlet has to sit

BS 9990 governs the siting, and the controlling dimension is the distance from the inlet to the position where the pumping appliance will stand. Eighteen metres is the figure the standard works to, measured as a hose run rather than as the crow flies, and the inlet has to be visible from that position.

That constrains the elevation in a way architects often underestimate:

• the inlet must be on the face of the building nearest the appliance standing position
• it cannot be behind a locked gate, inside a bin store or in a courtyard the appliance cannot see
• it cannot be screened by planting that will grow
• a fire hydrant has to be available within 90 metres of the inlet, which is a separate conversation with the water undertaker
• the route from the appliance to the inlet must be trafficable by a firefighter carrying hose

On a perimeter block with a single street frontage, that puts the inlet on the principal elevation, usually within a few metres of the main entrance. On a scheme with a shared surface courtyard, the standing position may be inside the site and the inlet on an internal face, which is better architecturally and needs the courtyard designed for appliance loading.

Settle the appliance standing position first, with the fire engineer and the highway authority together. Everything else follows from it.

The cabinet and the elevation

The inlet itself is a connection on the end of a pipe. What appears on the elevation is a wall box with a hinged, marked door, set at about waist height, large enough for a firefighter in gloves to open and couple two hoses to.

Four moves make it sit comfortably:

1. Recess the box into the wall construction rather than surface-fixing it, which needs the structural opening coordinated early
2. Align it with a vertical in the facade, a pier, a reveal or a downpipe line, rather than centring it on a blank panel
3. Match the door finish to the adjacent material where the marking requirements allow, and keep the required signage on the door rather than on the wall around it
4. Keep it clear of the entrance canopy, the letterbox bank and the intercom, all of which compete for the same stretch of wall

The marking is not negotiable. The box has to be identifiable as a fire main inlet from the appliance, which rules out the flush, unmarked, colour-matched solution that looks best in a visual.

Show the box on the submitted elevation at the right size and in the right place. An officer who sees it drawn once will not query it again. An officer who finds it added later will.

Outlets inside the building

Outlets matter to planning only through their effect on the plan, and that effect is real. Approved Document B works from a hose coverage distance that combines the length of hose a crew will run with the reach of the jet, and every point on a floor has to fall within that distance of an outlet.

On a deep plan or an L-shaped floorplate, one riser rarely achieves it. A second riser means a second shaft through every storey, which takes area from every floor and may force a second core. That is a planning consequence, because it changes the unit mix and the floor area schedule.

Test the coverage on the planning drawings rather than at technical design. A 30 minute exercise with a compass on the floorplate tells you whether the scheme needs one riser or two, and the answer changes the viability of a small floorplate scheme. Structural choices interact with it too, and our note on mass timber schemes and the questions planners now ask covers how material selection changes the fire case on the same floorplate.

Wet risers and the water they need

Above the dry main threshold the system changes character. A wet riser is charged permanently, which means a stored water supply, duty and standby pumps, and a pump room.

Three planning consequences. The tank is large and heavy, so it usually sits at the lowest level, which competes with parking, cycle storage and plant. The pump room needs ventilation, access for maintenance and a route for equipment replacement, which may mean a door onto a public elevation. And the standby pump needs a power supply arrangement that survives a fire, which the electrical strategy has to accommodate.

None of that is visible on a planning drawing unless someone draws it. Where a scheme is close to the wet main threshold, test the height carefully, because designing for a dry main and discovering at Gateway Two that a wet main is required is an expensive late change.

Conservation areas and listed facades

A marked steel box on a listed frontage is a conservation problem with a fire safety answer that cannot be waived.

Three approaches tend to be accepted. Site the inlet on a secondary elevation where the appliance standing position allows it, which usually means arguing the standing position rather than the box. Recess the box behind a door matching the joinery, with the required marking on the door face. Or place the inlet in a boundary wall or a freestanding pillar within the hose distance, which keeps the historic facade clear.

Listed building consent is needed for the opening and the fixing, and the conservation officer will want to see a drawing at a sensible scale rather than a note on a plan. Bring the fire engineer into that conversation. An officer resisting a box on a principal elevation will often accept it once someone explains what happens without it.

Getting the detail into the planning submission

Five items, none of which takes long:

• the appliance standing position marked on the site plan, with the hose run dimension to the inlet
• the inlet box drawn on the elevation, to scale, with a note of its dimensions and finish
• the riser position shown on each floor plan, with the hose coverage radii if the floorplate is awkward
• hydrant positions within 90 metres marked or noted as to be agreed with the undertaker
• a paragraph in the Fire Statement explaining fire service access and water supply, where the building is one for which a statement is required

The Fire Statement requirement under Article 9A of the Development Management Procedure Order applies to relevant buildings only, and it is the document where this material belongs. Where the building falls below the threshold, the same content fits in the design and access material or in a Fire Safety Strategy prepared by someone with fire engineering competence.

For basement levels the access and escape questions interact with flood risk, which our note on basement light wells, escape and flood risk deals with directly.

Browse the report types to see which fire and structural documents a scheme of this height usually carries.

This is general guidance, not legal advice. A Fire Statement and a fire safety strategy must be prepared by someone with the necessary fire engineering competence, and PlanScope's draft is a starting point for that professional rather than a substitute. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.