Second staircases will be required in new residential buildings over 18 metres after ministers confirmed the measure following consultation. The decision closes months of industry uncertainty, with many designers and funders already pivoting schemes towards dual means of escape. The move is expected to draw planning and building control into closer alignment, reduce ambiguity for insurers, and set a clearer baseline for fire strategy on high-rise housing. Transitional routes are anticipated for schemes already well advanced, but new applications and tenders above the threshold will now need to evidence compliant layouts. Housebuilders, build‑to‑rent clients and student accommodation providers are reviewing cores, lifts and net‑to‑gross impacts in response. Attention is turning to viability, programme and supply chain capacity as second cores are priced, detailed and sequenced into live pipelines.
TL;DR
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– New high-rise housing schemes above 18m will need two staircases, with transitional arrangements expected for projects already in train.
– Design teams face core reconfiguration, potential net‑to‑gross losses and possible re‑massing to maintain unit numbers.
– Contractors should anticipate re‑tendering, resequencing and longer lead‑ins for cores, doorsets and fire‑critical elements.
– Funders and insurers are likely to align rapidly with the new baseline, raising the bar for any non‑compliant legacy proposals.
Design, viability and procurement under an 18m rule
/> For architects and fire consultants, the confirmed threshold resets the brief for towers just over 18 metres where single-core configurations had been explored during the policy limbo. Dual-stair solutions will typically enlarge or duplicate cores, with knock‑on effects for circulation, risers and unit planning that can reduce saleable or lettable area. Some teams are expected to adjust massing, move amenities, or rationalise apartment mix to claw back efficiency while maintaining daylighting and accessibility standards. Early engagement with building control and fire authorities will be vital to agree strategies that integrate evacuation, smoke control and wayfinding around the new core arrangements.
Cost plans are being re-opened. Additional structure, wall linings, doorsets, balustrades and associated services can meaningfully shift preliminaries and build cost, and may alter frame selection or bathroom‑kitchen stacking. Contractors report that re‑marketed packages could see repricing where the scope expands to include second cores, temporary works or revised scaffold and hoist strategies. Procurement teams will need to lock in longer lead items earlier and coordinate with façade and MEP partners to avoid clashes at shaft and lobby interfaces.
Developers and their funders are re‑assessing risk. Where previously a single stair could pass locally with mitigation, market sentiment has swung firmly towards the more conservative standard. Lenders and insurers are widely expected to ask for clear evidence of compliance or a credible transitional position, and planning committees are likely to scrutinise legacy layouts more tightly. For clients on narrow sites or constrained footprints, the new baseline could prompt a switch to fewer, larger buildings or a stepped‑height approach to keep some blocks under the threshold.
# Caveats
/> Important details still matter. Industry attention is fixed on the precise transitional cut‑offs, how “start on site” is defined for eligibility, and how mixed‑use lower floors or ancillary spaces will be treated under the threshold. The interface between planning permissions already granted and building control approvals yet to be secured may create grey areas that require case‑by‑case handling. Designers should also watch for clarifications in guidance that could influence stair width, protected lobby arrangements and interaction with evacuation strategies.
Delivery timelines, transition and on‑site realities
/> Programme risk is the immediate operational concern. Where a scheme tips over the 18m mark, redesign cycles, re‑submissions and fresh fire statements can push key dates, with potential to disrupt land conditions and funding drawdowns. Construction managers are mapping resequenced logistics to accommodate two permanent stair cores, rethinking tower crane placement, and re‑allocating vertical transportation during build. Supply chains for fire doors, smoke control equipment and stair balustrades may tighten as demand jumps, increasing the value of early orders and framework agreements.
A plausible UK scenario is a regional high‑rise scheme transitioning from a single to a dual core at late design stage. The client instructs a targeted redesign to hold the façade line while reclaiming net area by consolidating plant and adjusting amenity locations. The contractor re‑packages core trades, revises the temporary works design and extends the preliminaries allowance to maintain safe access routes. Planning officers are briefed on the layout change and accept amended drawings that retain massing and materials. The lender requests an updated fire strategy and confirms continued support once the new compliance path is shown.
For local authorities and housing associations, the rule may drive earlier gateway discussions to avoid late changes, particularly where sites are finely balanced on viability. Smaller developers might respond by capping building heights just below the threshold, but the market shift towards two staircases is already visible, and planning committees may view sub‑threshold proposals with greater scrutiny if they rely on slender design margins.
# What to watch next
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– Publication of detailed transitional criteria and definitions that determine which in‑flight schemes can proceed without major redesign.
– How planning authorities handle amendments to consented schemes where massing and external appearance are largely unchanged.
– The pace at which funders, insurers and warranty providers standardise around the 18m threshold in their lending and coverage terms.
– Market evidence on build cost uplifts, net‑to‑gross outcomes and delivery timelines as dual‑stair projects return from tender.
The industry now has a clearer signal to design and price to a dual‑stair standard for tall housing. The direction of travel is towards earlier, more conservative fire strategy decisions; the key question is whether transitional flex and supply chain capacity can keep delivery moving without derailing viability.
FAQ
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What exactly changes with the 18m threshold?
Residential buildings above 18 metres will be expected to include two staircases as part of a compliant fire strategy. This formalises a direction already adopted by many schemes and reduces discretion around single‑stair solutions in tall buildings. The aim is to provide a more robust means of escape and firefighting access.
# When is the requirement likely to bite on live projects?
/> Projects early in design or pre‑application should work on the basis that two stairs will be needed if they exceed 18 metres. Transitional arrangements are anticipated for schemes already significantly advanced, but details typically depend on definitions such as when construction is deemed to have started. Teams should seek timely advice from their building control body once the final criteria are published locally.
# Does this affect schemes already in planning or consented?
/> Many planning authorities are expected to accept amendments that introduce a second stair without treating them as substantive design departures. However, where permissions are old or designs rely on tight internal layouts, a fresh application or re‑consultation may be required. Whether a consented scheme can proceed as‑is will depend on how transitional rules and building control approvals intersect.
# How will this impact costs and layout efficiency?
/> Adding a second stair generally increases core area and associated structure, doorsets and finishes, which can reduce net‑to‑gross efficiency. Some of this can be mitigated through careful planning of risers, amenities and plant, but most teams should expect a measurable cost and area impact. Tender returns will provide the best read‑across for each project’s specifics.
# What should contractors and clients do now?
/> Confirm building heights, review core strategies and engage early with designers and building control to map a compliant route. Revisit procurement plans to secure longer lead items and anticipate resequencing where cores and vertical access need re‑planning. Where relying on transitional protection, document the project’s status clearly and align funder expectations before committing to major spend.
