How to Use RdSAP Data for Retrofit Modelling

RdSAP (Reduced data Standard Assessment Procedure) assessments provide a standardised baseline for understanding a property's current energy performance. When coordinating retrofits under PAS2035, this data becomes your starting point for modelling interventions and predicting outcomes. Understanding how to extract and apply RdSAP information effectively ensures your retrofit strategies are evidence-based and measurable.

Understanding RdSAP Assessment Data

An RdSAP assessment captures key building characteristics that directly influence energy consumption and retrofit potential:

• Construction date and building type classification
• Wall, roof, floor and window U-values and construction details
• Heating system specification and fuel type
• Hot water provision and controls
• Ventilation strategy and air tightness indicators
• Current energy efficiency ratings (SAP score and EPC rating)

This information reflects the property as it currently stands. The RdSAP report also indicates where energy is lost and which improvements would be most cost-effective, though these recommendations are generic rather than tailored to your specific retrofit strategy.

Extracting Relevant Building Data

Begin by reviewing the RdSAP assessment report systematically. The key sections for retrofit modelling are:

1. Building dimensions and fabric: Extract floor area, number of storeys, and construction period. These determine baseline heat loss and inform intervention priorities.
2. Thermal performance: Note current U-values for all building elements. Compare against Building Regulations standards and modern retrofit targets to quantify improvement scope.
3. Heating and controls: Identify the heating system type, boiler age and efficiency, and existing controls. This determines whether heating replacement is necessary or if optimisation suffices.
4. Ventilation: Understand whether the property relies on natural ventilation, has extract fans, or includes mechanical ventilation with heat recovery. This affects retrofit sequencing and specification.

Document this baseline data systematically—it becomes your reference point for modelling performance gains.

Mapping RdSAP Data to Retrofit Scenarios

Once baseline data is established, use it to model retrofit interventions. PAS2035 requires demonstrating that your proposed measures will deliver predicted energy and carbon reductions.

Fabric improvements: RdSAP U-values provide the starting point. Model the impact of wall insulation, window replacement, and loft insulation by entering improved U-values into your modelling software. Calculate the resulting SAP score improvement to quantify the effect.

Heating system replacement: If the existing boiler is old and inefficient (noted in RdSAP), model upgrading to a modern condensing boiler or renewable heating system. Calculate seasonal efficiency improvements and carbon reduction.

Ventilation strategy: If the property has poor natural ventilation or air quality risks, model introducing mechanical ventilation with heat recovery. Use RdSAP ventilation data to establish current air change rates and energy losses.

Reconciling RdSAP with Detailed Survey Findings

RdSAP assessments use standardised assumptions where detailed information is unavailable. Your retrofit survey may reveal differences:

• Cavity wall insulation may already be present, contrary to assumptions
• Actual window condition may vary from RdSAP classification
• Heating system efficiency may differ from standard tables
• Property may have non-standard construction not fully captured in RdSAP

Where discrepancies exist, update your modelling data. If improvements are justified, document why RdSAP assumptions were adjusted and how this affects predictions. This transparency supports PAS2035 compliance.

Using RdSAP for Targeting and Prioritisation

RdSAP data helps identify which interventions will yield greatest returns. The assessment typically includes an improvement ranking. However, for retrofit coordination under PAS2035:

• Prioritise measures that address the largest proportions of heat loss
• Sequence improvements logically—fabric improvements often precede heating system changes
• Consider cost-effectiveness against your client's budget and timescale
• Ensure measures are compatible—for example, low-energy ventilation may be essential if wall insulation reduces natural air infiltration

Documenting Retrofit Modelling Assumptions

PAS2035 emphasises transparency in energy performance prediction. When using RdSAP data as your baseline, document:

1. The RdSAP assessment date and SAP version used
2. Which baseline data points you accepted and which you adjusted
3. Why adjustments were made (e.g., survey findings, client requirements)
4. Which modelling software and standards you applied
5. Key assumptions about occupancy, heating patterns, and system performance

This documentation forms part of your retrofit coordination records and supports quality assurance and client communication.

Key Takeaways

RdSAP data provides a standardised, comparable baseline for retrofit modelling. Treat it as your starting point rather than definitive—ground truth comes from detailed survey. Use baseline data to establish improvement potential, model intervention outcomes, and prioritise measures. Document all assumptions and adjustments to maintain transparency and compliance with PAS2035 requirements.