18,000 Homes 'Lost' Because of the Second Staircase Rule? Here's the Real Maths
The 18m second staircase rule is reshaping mid-rise development economics in the North. What it actually means for Sheffield and Northern property investors — and which strategies remain viable.
Disclaimer: This article reflects publicly available information and professional analysis at the time of publication. Building safety regulations, planning policy and the second staircase rule are subject to change. Always check current government guidance, seek advice from a planning consultant, and take professional advice before making any development or investment decisions.
The government’s second staircase rule — requiring a second protected staircase in new residential buildings over 18 metres — has generated significant commentary about its effect on housing supply.
Research firm Place Base claims the rule removes approximately 18,000 homes per year from development pipelines. The government argues housing targets of 1.5 million homes can still be achieved without compromising fire safety.
Both positions contain elements of truth. For investors and developers active in Northern cities, the more useful question is: what does this actually change for the deals you’re looking at?
What the rule requires
Since 2023, new residential buildings exceeding 18 metres in England must incorporate a second protected staircase. Place Base contends this removes:
- Around 17,960 homes per year
- Approximately 90,000 homes over five years
They advocate raising the threshold to 50 metres, citing international precedent. The government’s position is that the requirement reflects post-Grenfell fire safety priorities.
The policy is unlikely to shift significantly in the near term — this isn’t primarily about economic optimisation. It’s about liability management following a major fire safety failure.
The actual development economics
The impact isn’t simply “add a staircase and carry on.” The redesign consequences cascade:
- Reduced net internal area (NIA) — the space lost to the second staircase is space that was previously sold or let
- Unit count reduction — some schemes lose units entirely
- Layout compromises — not every building can accommodate the requirement without significant design changes
- Scheme viability — some projects, particularly marginal ones, become unviable
For a typical 9-storey, 27m block:
- NIA loss: 3–8% (195–520 sqm on a 6,500 sqm scheme)
- Build cost uplift: £600,000–£1.5m+
- Programme delays: months of redesign and resubmission
That translates to: yield-on-cost dropping 50–150 basis points, weakened stabilised returns, and refinancing assumptions that no longer stack.
Why Northern markets feel it harder
London can sometimes absorb these additional costs because residual land values and exit prices per square foot remain high enough to maintain viability. In Sheffield, Leeds, Manchester, and Liverpool, the margins are thinner.
A 5% NIA loss that a London developer can absorb may kill the financing viability of a Sheffield scheme where construction costs are relatively fixed but sale or rental values per square foot are substantially lower.
The 18m–30m range — typical mid-rise city centre projects — experiences the greatest pressure because the redesign requirements don’t generate compensatory value.
Which strategies are most affected
Most at risk:
- Mid-rise BTR (Build to Rent) and PBSA (Purpose Built Student Accommodation) at 8–12 storeys/22–35m
- Schemes that were marginal before the rule
Mixed impact:
- Office-to-residential conversions (depends on building height and structure)
Largely unaffected:
- Sub-18m blocks (6 storeys typically stays under)
- Small blocks over shops
- HMO investments
- BRRR stock (standard residential refurbishment)
- Terraced house conversions
What this means in practice
If you’re evaluating a development scheme or a commercial conversion in the North:
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Confirm the finished height early — before detailed underwriting. A scheme at 19–30m with tight margins will likely have viability problems built in.
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Prioritise sub-18m models — 6 storeys typically offers simpler fire strategy, more lender confidence, and fewer design complications.
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Expect land price repricing — sites zoned for mid-rise development at heights that trigger the requirement should be priced to reflect the additional cost and risk. Many aren’t yet.
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For HMO and BRRR investors — this rule doesn’t directly affect standard residential refurbishment, existing terraces, or sub-18m blocks. Your core strategy is not disrupted.
The political reality
This rule exists because of Grenfell. The political conditions for relaxing it are extremely limited. Planning for a world where the 18m threshold rises significantly in the near term is unlikely to be the right assumption.
For most investors operating in Sheffield and the North — doing standard BTL, HMO, or small-scale refurb — this rule doesn’t change your immediate position. For anyone looking at mid-rise development schemes, it’s now a fundamental underwriting consideration.
Sources:
- Place Base research on second staircase rule impacts (cited in property trade press)
- GOV.UK — Building Safety Act guidance
- Planning Portal