Retrofit revisit

Retrofit revisit
Retrofit revisit
UKCMB Web Admin

Retrofit Revisit

Moisture balance and long-term performance

Retrofit Revisit was led by Julie Godefroy (CIBSE) and Marion Baeli (10 Design, formerly Studio PDP). The project revisited ten homes approximately ten years after deep retrofit, many of which formed part of the original Retrofit for the Future programme.

The aim was to assess whether the interventions had stood the test of time and to extract lessons for future retrofit practice. The work combined building performance evaluation (BPE), carried out in accordance with BS 40101:2022, fabric assessment and occupant feedback. The moisture investigations were part-funded by Historic England.

The UKCMB contribution focused on long-term moisture balance. The objective was to understand whether retrofit strategies — particularly in case of internal wall insulation and complex junctions — were functioning as intended when considered as whole-building systems.

We began with structured screening of each home. This included visual inspection, fungal and allergen testing, and targeted fabric moisture measurements. The purpose was to identify potentially critical areas without destructive investigation.

The screening findings were interpreted alongside the wider BPE analysis, including airtightness testing, heat transfer assessment, ventilation review and energy use data. This allowed moisture performance to be considered within the full building system rather than as an isolated defect issue.

Where screening indicated increased risk, the analysis was enhanced. Additional in-situ monitoring and hygrothermal simulations were undertaken to assess drying potential and longer-term moisture behaviour. This approach provided evidence on moisture balance with minimal disruption.

Across the sample, the majority of homes demonstrated moisture balance ten years after retrofit. Where issues were identified, they were generally associated with maintenance, water ingress or detailing at interfaces.

Lessons learnt

The work highlighted that:

  • Early treatment of water damage is critical to reducing biological growth and limiting fabric deterioration.

  • Maintenance plays a decisive role in long-term moisture balance.

  • Ventilation systems must be verified periodically to ensure continued effectiveness.

  • Internal wall insulation can perform robustly when correctly specified, detailed and installed.

  • Drying capacity is fundamental, particularly in exposed and non-protected masonry walls.

  • Hygrothermal simulations can provide valuable insight into the factors influencing long-term moisture balance.

The Retrofit Revisit report is available free of charge on the CIBSE website. More information here.

Publicly available webinars include:

 

 

  • Combining BPE results with screening and detailed moisture analysis: UCL Webinar

The learning from Retrofit Revisit has also been incorporated into the second edition of Residential Retrofit by Marion Baeli, strengthening the original case studies with building performance evidence.

The UKCMB team for Retrofit Revisit comprised Spyros Efthymiopoulos, Toby Cambray and Valentina Marincioni.