Post-Retrofit Monitoring: What PAS2035 Requires

Post-retrofit monitoring is a critical component of PAS2035 compliance. It ensures that retrofit measures perform as designed, identifies any deficiencies, and provides evidence that the Standard's requirements have been met. This guide outlines what monitoring is required and how to implement it effectively.

Why Monitoring Matters Under PAS2035

PAS2035 recognises that building performance in reality often differs from predictions. Monitoring serves three key functions:

• Verifies that retrofit measures achieve their intended energy performance improvements
• Identifies underperformance early, enabling corrective action
• Demonstrates compliance and provides accountability to building owners and regulators
• Gathers data to refine future retrofit designs and predictions

What Must Be Monitored

The Standard requires monitoring of key performance indicators that directly relate to the retrofit's objectives:

Energy Consumption

• Whole-building energy use (gas, electricity, renewable generation)
• End-use breakdown where practicable (heating, hot water, appliances)
• Comparison against baseline and predicted performance

Indoor Environmental Quality

• Temperature and humidity levels in representative spaces
• Ventilation effectiveness, particularly in properties with mechanical ventilation
• Indoor air quality indicators where relevant to the retrofit

Building Envelope Performance

• Surface temperatures of upgraded elements
• Evidence of condensation or moisture issues
• Performance of new windows, doors, or insulation where critical to design

System Performance

• Heat pump efficiency (where installed)
• Solar PV or thermal system output
• Controls and automation functioning as designed

Establishing a Monitoring Plan

A robust monitoring plan should be developed during the design and specification phase, before any retrofit work begins. This plan forms part of the retrofit coordination documentation.

Key Elements of a Monitoring Plan

1. Baseline measurement: Establish pre-retrofit performance where possible, or use historical data and predictions as reference
2. Measurement locations: Specify exactly which spaces, systems, or components will be monitored
3. Monitoring frequency: Define how often data will be recorded (continuous, daily, weekly)
4. Measurement methods: Detail whether smart meters, sensors, or manual readings will be used
5. Data management: Plan how data will be collected, stored, and analysed
6. Reporting schedule: Set intervals for analysis and reporting to stakeholders
7. Success criteria: Define what constitutes acceptable performance against the retrofit's stated objectives

Practical Implementation

Effective monitoring requires practical consideration of how data will be captured and used:

Data Collection Methods

• Smart meters: Essential for electricity and gas consumption; provide granular data remotely
• Building management systems: Integrate with new heating systems, ventilation, and renewable energy installations
• Wireless sensors: Cost-effective for temperature, humidity, and CO₂ in representative rooms
• Manual readings: Still required in some cases; document protocols clearly

Duration and Frequency

Monitoring must run long enough to capture seasonal variation and normal occupancy patterns. Minimum requirements include:

• At least 12 months of continuous monitoring post-completion
• Monthly analysis and reporting during this period
• Extended monitoring (2-3 years) recommended for complex retrofits or heat pump installations to establish long-term performance

Addressing Performance Gaps

If monitoring reveals that the retrofit is underperforming against predictions, PAS2035 requires investigation and corrective action:

1. Analyse data to identify the cause: commissioning issues, occupant behaviour, design assumptions, or construction quality
2. Document findings and inform the building owner and retrofit coordinator
3. Implement remedial measures where necessary (recalibration, repairs, occupant engagement)
4. Continue monitoring to verify improvements
5. Update the retrofit's actual performance record

Documentation and Reporting

All monitoring data and analysis must be documented as part of the PAS2035 compliance record:

• Retain raw monitoring data in a structured format
• Produce monthly performance reports during the initial 12-month period
• Compare actual performance against baseline and predictions
• Document any anomalies, interventions, or changes affecting performance
• Provide a final report summarising the retrofit's actual performance against objectives

Building Owner Engagement

Effective monitoring requires building owner and occupant cooperation. The retrofit coordinator should:

• Explain the monitoring plan and its purpose clearly during project handover
• Provide accessible performance dashboards or regular summaries
• Help occupants understand how their behaviour affects energy performance
• Ensure meters and sensors are accessible for maintenance
• Collect feedback on indoor comfort and any issues affecting performance

Key Takeaways

• Develop your monitoring plan before work commences; it forms part of PAS2035 compliance documentation
• Monitor energy consumption, indoor environmental quality, building envelope, and system performance as relevant to the retrofit
• Use smart meters and sensors to minimise manual intervention and ensure data reliability
• Run minimum 12 months of monitoring; extend to 2-3 years for complex retrofits
• Act on findings: investigate and address underperformance through documented corrective measures
• Keep comprehensive records and engage building owners throughout the process

Post-retrofit monitoring transforms retrofit programmes from one-off interventions into data-driven improvement cycles. By implementing robust monitoring under PAS2035, retrofit coordinators can verify performance, build the evidence base for future improvements, and deliver genuine value to building owners and the wider retrofit sector.