Expert Panel Outputs for 2025: Retrofit & Conservation Expert Panel

Summary by Expert Panel Chair Andrew Henriques, BGY

The NLA Expert Panel on Retrofit & Conservation (R&C) set out to consider the underlining challenges with said topic.

Session 1 debated the key challenges to R&C around the following headings:

Planning reform.
Sustainability and energy-performance targets
Heritage constraints.
Regulatory codes.
High construction costs.
Viability pressures.

HEADLINES

Planning Reform:

Inconsistent retrofit policies between London boroughs.
Need to streamline pre-planning processes.
Positive moves: City of London’s SPD (Feb 2025), Westminster’s draft retrofit policy
Concerns: NPPF (Dec 2024) and the Mayor’s Growth Plan lack strong retrofit focus.
Enabling the use of permitted development rights for certain low-impact retrofit works.
Case Study: Westminster project where standardised fabric improvements pre-agreed with the local authority reduced need for multiple planning applications.

Sustainability, Heritage & Regulation:

Heritage stakeholders often resist the changes needed to meet sustainability goals.
Balancing conservation with environmental performance remains a significant huddle for all retrofit.

Cost, Risk, & Viability:

Rising development costs, high inflation and macro global forces is fuelling weak market confidence.
Retrofit carries higher risk than new-build due to likelihood of unknowns and potential discoverables.
On-site investigations/fabric surveys are difficult to fully administer within occupied buildings.
Delivering residential retrofit at scale is complex due to fragmented ownership, differing construction types and varied household finances.
Discussion around potential incentives: existing domestic green grants are helpful; removing VAT on domestic & commercial retrofit could provide a major boost to sector.

Session Two examined the key ingredients for successful heritage retrofit reflecting on building fabric, historical, social, cultural significance and technical application.

Four Main Focus Areas

Approach to heritage fabric
Robust construction methods
Appropriate material selection
Navigating conservation vs sustainability through planning policy

Approach for Heritage Fabric

Presumption against restoration.
Minimum intervention—avoid unnecessary alteration.
Juxtaposition of old and new to ensure legibility.
Reversibility of interventions.
Use of knowledge, experience, craftsmanship to ensure authenticity.
Narrative—retrofit as a new, sensitive, contextual chapter in a building’s story.

Robust Construction Methods – Consideration for:

Structural movement: cracking, deformation, subsidence from removed loadbearing walls.
Water/moisture ingress due to incompatible modern materials.
Poor ventilation from blocked chimneys, vents, cupolas.
Timber decay, especially in roofs and embedded wall locations.
Moisture-increased vulnerability to insects/fungal attack; timber should remain <20% moisture.
Steel corrosion, particularly in external walls; pavement vault leakage.
Degraded below-ground drainage (e.g., cracked ceramic pipes, root intrusion).
Retrospective structural justification and strengthening.
Need for sensitive, compliant and certified floor fire protection.
Employing the specialist skills required for authentic repairs, particularly when undoing poorly executed past alterations.
Regular maintenance is essential—prevents decay, improves energy efficiency, and keeps fabric dry (damp walls up to one-third less energy efficient).

Appropriate Material Selection

Authenticity requires matching materials and traditional repair techniques.
Modern materials may be suitable in specific cases (e.g., synthetic resins for timber repairs).
Materials should be sustainably sourced.
Breathable materials crucial for longevity (e.g., lime render, wood fibre, vapour-permeable membranes).
Importance of capturing good data and knowledge of heritage fabric.
Using Conservation Management Plans (CMPs) that capture/enable;

I. Condition surveys
II. Significance categorisation
III. Cost assimilation
IV. Delivery planning
V. Data-driven change management and visual risk mapping.

Navigating Conservation vs Sustainability Through Planning Policy

Westminster City Council (WCC) retrofit-first policy expected Q1 2026:
- Requires justification for extensions/demolition.
- Sequential test before demolition.
- Strong emphasis on planning balance.
Critical to identify which building elements are significant vs less sensitive.
Policy intent: To support conservation of energy and buildings and give weight to public benefits of improved environmental performance.
Important recognition that heritage buildings must remain adaptable to stay valuable.
Discussion that the GLA/London Plan should incorporate retrofit-first policy.
Planning policy itself is not the barrier—implementation and planning balance are the core challenges to successfully navigating heritage retrofit.

Impact and Industry Relevance
Amid broader industry conversations around investment, housing delivery, and infrastructure, retrofit stands out as both an environmental necessity and a strategic economic opportunity. The panel discussed the hurdles around domestic retrofit at scale with there being limited guidance available for the public, the diverse
range of building types and varied forms of construction.

Whilst easier said than actioned, a citywide retrofit approach, underpinned by government support, could simultaneously advance climate goals, boost energy security, drive job creation and development of skills, raise productivity, foster innovation, and support long-term sustainable growth for London.

Focus for 2026

As a sounding board for industry initiatives the panel’s priorities for 2026 will be set around the following themes.
NLA Heathy Cities – How does retrofit support healthy buildings?
- Healthy buildings = Healthy people = Less impact on NHS.
- Healthy buildings create education and employment opportunities. This is key to raising productivity.
- The healthy city with retrofit to deliver economic growth.
- Source retrofit case studies that underpin the principles of health and wellbeing.
London Plan 2026 - Review of new London plan in context of promoting city retrofit / conservation.
NPPF 2026 – Review of NPPF in respect of conservation retrofit.