Retrofitting of the existing building stock is one of the strategies for the European Union's goal to reach net zero carbon emissions. This alteration has prompted revisions in regulatory frameworks and technical recommendations to enhance the energy efficiency of existing structures. 

The fabric-first approach remains significant and often recommended; however, optimal long-term outcomes can also be achieved through a comprehensive whole-house strategy that integrates insulation, ventilation, and renewable technologies like solar photovoltaics and heat pumps, if the context allows for this.

Retrofitting is an important step towards Net Zero, but it comes with significant challenges, such as a lack of clarity within existing regulations, along with the limitations of technical solutions. Retrofitting strategies need to consider the historical significance, construction method, and typology.

Policy and regulatory challenges

PAS 2035 is the main framework guiding the domestic retrofit industry in the UK. It outlines the responsibilities and requirements for delivering retrofit projects. However, it sometimes fails to address the diversity of the UK's building stock, as each structure has distinct performance characteristics and limitations.

Alongside PAS2035, retrofit design also must comply with national building regulations, including Part L (Conservation of Fuel and Power), Part F (Ventilation), and Part J (Combustion Appliances and Fuel Storage Systems). These regulations can sometimes conflict, leading to uncertainties. For instance, PAS 2035 outlines specific ventilation requirements; however, the Building Regulations may restrict the simultaneous use of dMEV (Decentralised Mechanical Extract Ventilation) systems and closed-room heaters within same room.

Properties built prior to 1919, particularly those situated in conservation areas or classified as locally or nationally listed, require additional approvals for any alteration. The procedure for obtaining planning consent or assessing the necessity of it is sometimes unclear. Maintaining communication with local authorities is crucial to avoid these issues, as they may lead to delays in project execution, complicating retrofit design.

Technical challenges

The success of a retrofit project depends on a comprehensive understanding of the existing building fabric. This involves evaluating the structural style, materials implemented, wall thickness, insulation effectiveness, and moisture behaviour.

Before implementing the fabric-first approach, it is essential to address prevalent issues such as cracks, vegetation growth, and dampness. Necessary remedial works may include roof maintenance or replacement, gutter repair, or the treatment of moisture growth before the start of further development.

Traditional and non-traditional buildings demonstrate similar challenges concerning survey accuracy, data gaps, and the need for interdisciplinary coordination. Due to their architectural significance, traditional structures, particularly those constructed before 1919, require higher levels of attention.

Non-traditional buildings, characterised by cavity walls or post-war steel and concrete frames, often present challenges including thermal bridging and shallow cavities. A carefully performed technical analysis enables more accurate design decisions in both cases. Building age, typology, and internal floor area are critical factors in determining suitable interventions.

Stakeholder and communication challenges

Retrofitting is successful only through effective collaboration among three key stakeholders:

1. the client or homeowner,
2. the contractor, and
3. funder or authority.

Each group has unique responsibilities, and a lack of communication between them often results in project delays or performance gaps. Homeowners, for instance, may not fully understand what retrofit involves, find it financially challenging, or be unaware of the whole-house approach. Many tends to install internal wall insulation as an isolated measure without considering ventilation. This oversight can result in issues like condensation, dampness, and poor indoor air quality.

Contractors face different pressures. A lack of understanding of building typologies and technical knowledge may lead to poorly executed insulation and other interventions. In funded schemes, additional challenges arise. Contractors are less likely to do pre-retrofit repairs since there is usually no specific budget for them. These problems can make the recommended measures less effective.

Towards an integrated approach

Retrofitting should always be approached comprehensively. To achieve successful results, it is essential to establish effective communication and collaboration among all stakeholders. Any intervention that is implemented without the active involvement of occupants is at risk of underperformance and is unlikely to produce sustainable results.

Local authorities could play a vital role by prioritising homes most in need of retrofit and allocating dedicated funding for essential pre-retrofit remedial works. In addition, consistent monitoring through pre- and post-retrofit evaluations is necessary to ensure that quality and accountability are maintained. Strengthening collaboration between authorities, funders, and contractors would help ensure that these improvements are carried out to a robust and durable standard, preventing repeated interventions caused by poor initial conditions.