What is a Retrofit Assessment? How PAS 2035 Protects Homes from Bad Insulation

What is PAS 2035?

PAS 2035 is the national publicly available specification for the energy retrofit of domestic buildings in the UK. Published by BSI (the British Standards Institution) and mandated by DESNZ for government-funded retrofit schemes including ECO4 and the Great British Insulation Scheme, it establishes the processes and standards that must be followed when improving the energy performance of an existing home.

PAS 2035 was introduced in 2019 following a widespread failure of cavity wall insulation and solid wall insulation installations under earlier government schemes, where insulation was installed in properties with pre-existing damp, structural problems, or unsuitable wall construction. The resulting damage, mould growth, structural deterioration, failed render, affected tens of thousands of homes and led to the Cavity Insulation Guarantee Agency (CIGA) being overwhelmed with complaints.

The Retrofit Assessment

A Retrofit Assessment is the formal survey carried out at the start of the PAS 2035 process, before any improvement measures are specified or installed. It must be carried out by a qualified Retrofit Assessor, an individual holding a recognised qualification (typically Level 3 or 5 in Domestic Retrofit Assessment) registered with TrustMark.

The assessment covers:

• The current condition of the building fabric, walls, roof, floors, windows, and doors
• The current heating and ventilation systems
• Signs of damp, mould, condensation, or structural issues
• Occupancy patterns and the health or vulnerability of residents
• The current EPC rating and recommendation report
• Any pre-existing problems that could be made worse by insulation

The assessor produces a written report that identifies risks and sets out conditions that must be met before each measure is installed.

The Medium Term Improvement Plan

Following the Retrofit Assessment, the Retrofit Assessor produces a Medium Term Improvement Plan (MTIP), a whole-house plan setting out which measures should be installed, in what order, and with what preconditions.

The MTIP is designed to ensure that improvements work together as a system rather than being installed piecemeal. For example:

• Insulation must not be installed if ventilation is inadequate, doing so traps moisture and causes condensation
• A heat pump should not be installed until the building is sufficiently insulated to allow it to operate efficiently
• Cavity wall insulation should not be specified for a property with ongoing damp without addressing the damp source first

The Role of the Retrofit Coordinator

A Retrofit Coordinator is a separately qualified individual responsible for overseeing the entire retrofit project from design through to completion. They are distinct from the Retrofit Assessor and the installer, providing an independent check that work is specified and carried out correctly.

For government-funded projects, the Retrofit Coordinator must hold a TrustMark-recognised qualification and must sign off the project on completion. Their involvement is mandatory under ECO4, the Great British Insulation Scheme, and the Social Housing Decarbonisation Fund.

Why This Matters for Homeowners

If a contractor offers you free insulation funded through ECO4 or another government scheme but does not mention a Retrofit Assessment or PAS 2035 compliance, treat this as a warning sign. Installation without a prior assessment is a breach of scheme requirements and leaves you without the protections the standard provides.

You should ask any installer to confirm:

• That a qualified Retrofit Assessor will survey the property first
• That the project will have a named TrustMark-registered Retrofit Coordinator
• That all installers are TrustMark-registered
• That you will receive copies of the Retrofit Assessment and MTIP

Checking Your EPC Before a Retrofit Assessment

Before engaging a Retrofit Assessor, it is useful to review your property's current EPC certificate and recommendation report. Property Passport UK displays the current EPC data and recommendations for every UK address, giving you a starting point for understanding what improvements may be available and what an assessor is likely to find.