Introduction

PAS2035:2019 (Specification for the assessment of the retrofit of dwellings for improved energy efficiency) has established itself as the gold standard for retrofitting homes across the UK. Central to its framework is the requirement for thorough risk assessment before any physical work commences on site. This pre-works phase is not merely a bureaucratic formality—it is a critical foundation that protects both occupants and the integrity of the retrofit programme itself.

Why Pre-Works Risk Assessment Matters

The retrofit industry has historically struggled with unintended consequences. Improving thermal performance without properly understanding building pathology can lead to moisture problems, condensation, structural damage, and poor indoor air quality. PAS2035 addresses this by requiring practitioners to identify and evaluate risks at the design and planning stage, before work begins.

This approach reflects a shift from traditional reactive problem-solving to proactive risk management. By conducting thorough assessment upfront, project teams can:

The Core Assessment Requirements

Building Survey and Condition Assessment

PAS2035 requires a detailed survey of the building before retrofit design is finalised. This goes beyond standard energy audits and should include assessment of:

The surveyor must document findings in a condition report that informs subsequent design decisions. This is particularly important for older properties, where traditional construction methods may be incompatible with certain modern retrofit approaches.

Risk Identification and Evaluation

Once the building condition is established, practitioners must systematically identify risks associated with the proposed retrofit measures. PAS2035 requires evaluation of:

Risk evaluation should use a structured methodology—typically a risk matrix that considers both likelihood and potential consequence of identified hazards.

Thermal Modelling and Performance Prediction

PAS2035 requires thermal modelling to predict how the building will perform post-retrofit. This should account for:

The modelling must be realistic and should identify any predicted performance risks, such as overheating in summer or inadequate heating in winter.

Hazard Assessment and Mitigation Planning

Beyond general building risks, PAS2035 requires specific assessment of hazards that retrofit work might create or exacerbate. These include moisture management (the most common failure point), fire safety compliance, and ventilation adequacy.

For each identified risk, practitioners must plan specific mitigation measures that will be incorporated into the retrofit specification. These might include additional vapour control, enhanced drainage detailing, revised ventilation strategy, or alternative material selection.

Documentation and Sign-Off

All assessment findings and risk evaluations must be documented comprehensively. PAS2035 requires a Retrofit Design Specification that sets out:

This specification should be signed off by the lead retrofit designer and made available to the installer and quality assurance inspector before work commences.

Practical Implementation

For housing associations and retrofit coordinators, embedding PAS2035 risk assessment requires investment in survey resources, access to thermal modelling expertise, and time for proper design development. However, the cost of upfront assessment is typically far less than the cost of remedying problems discovered during or after construction.

Effective risk assessment also requires clear communication between surveyor, designer, installer, and quality assurance roles—each bringing different expertise to the evaluation process. Modern retrofit programmes increasingly employ dedicated retrofit coordinators to manage this complex pre-works phase and ensure PAS2035 requirements are fully met.