Historic England guidance sets out key design considerations when transforming heritage properties into residential in bid to tackle the housing crisis
Labour’s pledge to build an extra 1.5 million homes in five years might seem optimistic given the challenges faced by developers and the planning system, but a report commissioned by Historic England aims to show how a significant gap, of up to 670,000 homes, can be plugged by repurposing historic buildings for residential use.
Heritage Works for Housing was drafted by Deloitte and gives SME developers and their project teams practical step-by-step guidance on the process of converting historic buildings, from feasibility testing, stakeholder engagement, heritage appraisal, and design development, through to building consent and ongoing maintenance.
According to Historic England, redundant heritage buildings could create up to 670,000 new homes – textile mills in Yorkshire and Lancashire alone could create around 42,000 – emphasising the scale of the reuse opportunity.
The better a heritage building is understood, the less risky the development process is likely to be, the report states, a heritage appraisal involving the local authority and heritage experts should build upon an initial assessment at purchase to identify the areas of highest heritage significance.
An iterative design process should ‘robustly discount alternative uses’, particularly if they require less intervention and cause less harm to the significance of the building. Layout options should be tested ‘to achieve the required number of homes needed to make a viable scheme with minimal harm to the significance.’
The guidance sets out the typical interventions required to make historic buildings suitable for residential use. Listed Building Consent is likely to be required for these, as detailed in Listing Building Consent Advice Note 16, and some listed buildings are exempt from meeting certain building regs in recognition of their national significance.
Key design development considerations include mechanical, electrical and plumbing (MEP), with a focus on minimising interventions by making use of existing openings and risers, or routing the MEP through any new build elements, also factoring in practical considerations for end users, such as location of radiators or ventilation extract.
Some historic buildings have non-typical floor-to-ceiling heights, the report states. If heights are too low, significant intervention may be required, such as the removal of every other floor. High ceilings may reduce energy efficiency, but also create an opportunity to introduce mezzanines and duplex apartments
According to Historic England, how a heritage building is sub-divided into multiple homes needs careful consideration, balancing the original planform and the building’s special interest with ‘market expectation, regulations, policy and guidance’. Unless there is a robust justification, all residential developments are expected to comply with Nationally Described Space Standards, including those created through permitted develpment rights.
The provision of affordable housing is often not viable on heritage projects (a viability statement is nevertheless required under local planning policy and the NPPF), and according to the report there may also be ‘complexities around a Registered Provider occupying the building due to potentially unusual layouts and long-term maintenance costs.’ However, working collaboratively with registered providers can sometimes unlock grant funding for restoration and viable use as affordable housing.
Turning to sustainability, the report notes that embodied and operational carbon should be understood together to ensure decisions have the maximum effect with the least impact on the special interest of the building. For example, the return on carbon savings may not be justified by fabric interventions to the roof, floor, walls, or windows, due to their high embodied carbon, including construction impacts, switching the focus to operational carbon.
Conversions may require an element of new build to 'cross-fund' the works to bring the historic building into long-term viable use, and if the site interfaces with brownfield land a new build residential element may be a more suitable use.
Affordable housing policy at the Local Planning Authority may require submission of a viability statement, says Histroic England, to demonstrate the need for a new build element that could cause harm to a historic building. Design development exercises are often required to demonstrate that the new build element has been sensitively designed.
The report states that the design for an extension to a historic building should give specific attention to the structural integrity of the building and the interventions required to allow it, with consideration for areas of higher heritage significance.
The report also underlines the importance of stakeholder engagement during design development to ‘help mitigate unforeseen comments at the formal planning application or listed building consent stage’.
The ongoing transformation of the Grade II*-listed Park Hill estate, in Sheffield, is highlighted as a best practice example where early engagement with key stakeholders, including Historic England, was crucial to success and modernising it for current use.
Phase 2 of the Park Hill regeneration, by Mikhail Riches, is one of six projects shortlisted for this year's RIBA Stirling Prize.