The Improvement Option Evaluation (IOE) sits at the heart of PAS2035 retrofit projects. It represents the technical and financial analysis that justifies proposed energy efficiency measures to building owners and stakeholders. Getting it right is essential—not only for project viability, but for compliance with the standard itself.

Understanding the IOE's Purpose

An IOE demonstrates how proposed retrofit measures will improve a building's energy performance and indoor environment quality. It bridges the gap between the surveyed condition of a building and the desired outcome, setting clear baselines and measurable targets. The evaluation must be transparent, robust, and capable of withstanding scrutiny from clients, local authorities, and funding bodies.

Core Components of a Compliant IOE

Baseline Assessment

Begin by establishing a clear baseline of the building's current performance. This should include:

Your baseline must be evidence-based, drawing on survey data and actual performance records rather than assumptions. PAS2035 emphasises the importance of understanding as-built conditions rather than design specifications.

Technical Specification of Measures

For each improvement option proposed, specify:

Vagueness here undermines credibility. A reference to "wall insulation" is insufficient—specify thickness, type, density, and thermal resistance values. Include manufacturer technical data sheets or third-party certifications where relevant.

Performance Prediction

Demonstrate how each measure will improve performance using recognised calculation methodologies. Most retrofit professionals use SAP (Standard Assessment Procedure) or similar energy modelling tools. Your modelling should:

Be transparent about limitations in your modelling. If assumptions differ from standard practice, justify why.

Cost Analysis

Provide a detailed cost breakdown for each option, including:

Cost estimates should reflect genuine procurement research, not generic benchmarks. Building owners will scrutinise these figures closely.

Comparing Options

PAS2035 requires consideration of multiple improvement options. Your evaluation should present each option using consistent criteria:

This allows clients to make informed decisions about which options best suit their priorities and constraints.

Critical Compliance Considerations

Moisture and Condensation Risk

PAS2035 emphasises that energy improvements must not increase moisture risks. Your IOE should demonstrate:

Building Pathology

Address existing issues that retrofit work might exacerbate. If surveys reveal damp, structural movement, or other defects, your IOE should explain how proposed measures account for these.

Overheating Risk

Particularly for summer performance in improved buildings, assess whether measures could increase overheating risk. This is increasingly important for residential buildings and should be addressed explicitly in your evaluation.

Documentation and Sign-Off

Your IOE documentation should be clear enough for a competent third party to follow your logic and verify your assumptions. Include:

A compliant IOE isn't simply a technical document—it's evidence of thorough professional practice that stands up to external review.