A Whole House Retrofit (WHR) is a systematic approach to upgrading all major energy-consuming elements of a residential property simultaneously. Unlike piecemeal improvements, WHR integrates:
- Building fabric enhancements (insulation, airtightness, thermal bridge mitigation)
- Mechanical services upgrades (heating, ventilation, renewables)
- Monitoring & controls (smart systems, user interfaces)
This methodology aligns with the UK’s SHDF Wave 2.2 objectives (2024-2027) and Future Homes Standard 2025 requirements, typically achieving 60-80% energy demand reduction in pre-1980s housing stock.
Synonym(s): Whole-building retrofit, holistic retrofit, deep energy retrofit.
Key Components #
- Fabric-First Principle
- Example: A 1920s terrace receives external wall insulation (EWI), triple-glazed windows, and insulated suspended floors – reducing heat loss by 65%.
- Regulation: Approved Document L1B (2023) mandates U-values ≤0.18 W/m²K for retrofit walls.
- Ventilation Strategy
- Best Practice: Hybrid ventilation systems (MEV + humidity-controlled trickle vents) in airtight retrofits (<3.0 m³/h.m² @50Pa).
- Case Study: Nottingham City Homes installed dMEV in 500 retrofitted properties, eliminating condensation issues while maintaining <1.5 air changes/hour.
- Heating Transition
- SHDF Requirement: Heat pumps must achieve SCOP ≥2.8 in WHR projects.
- Example: Bristol City Council’s WHR programme saw ASHP installations achieve 320% efficiency when combined with fabric upgrades.
Regulatory Framework #
| Document | Relevance to WHR |
|---|---|
| Approved Document L (2023) | Sets retrofit insulation standards and DER/TER calculations |
| Part F (2021) | Mandates ventilation rates post-retrofit (6-8 l/s per bedroom) |
| PAS 2035:2023 | Requires retrofit coordinators for WHR projects >£15,000 |
Practical Challenges #
- Moisture Management
- Issue: 38% of poorly executed WHR projects develop interstitial condensation (BRE Report 2024).
- Solution: Hygrothermal modelling + vapour control layers in >0.5 W/m²K upgrades.
- Ventilation Compliance
- Conflict: Achieving <3 ACH airtightness often requires mechanical ventilation, yet 42% of UK retrofit installers lack MEV commissioning skills (NIBE 2025 survey).
Related Essential Terms #
- Fabric Efficiency Ratio – Measures insulation performance relative to building geometry
- Ventilation Heat Recovery Efficiency – Critical metric for MVHR in retrofits (≥85% for SHDF funding)
- Thermal Bypass Risk – Hidden gaps allowing heat escape, requiring infrared thermography
- Retrofit Moisture Risk Index – PAS 2038:2024 assessment criterion
- Energy Followback Effect – Post-retrofit energy use rebound phenomenon