Understanding PAS2035

PAS2035:2019 is the Publicly Available Specification that sets out the framework for the retrofit of dwellings. Developed by the British Standards Institution (BSI) in collaboration with industry experts, it provides a standardised approach to planning, delivering and quality-assuring building energy efficiency retrofit projects across the UK.

The standard recognises that every building is unique. Rather than prescribing specific technical solutions, PAS2035 establishes a process-based methodology that retrofit coordinators must follow to ensure quality outcomes, regardless of the building type or measures installed.

Why PAS2035 Matters

Building retrofits are complex projects involving multiple trades, technologies and design considerations. Without a coordinated approach, risks emerge:

• Incompatible measures that reduce overall effectiveness
• Quality assurance gaps leading to poor installation
• Unintended consequences such as moisture problems or thermal bridging
• Inconsistent performance across retrofit programmes

PAS2035 addresses these challenges by requiring coordinators to assess buildings holistically, consider interactions between measures, and maintain quality standards throughout delivery.

The PAS2035 Process Framework

Stage 1: Project Initiation and Building Assessment

The retrofit coordinator must establish project objectives and gather comprehensive building data. This includes:

• Condition surveys of structure, services and building fabric
• Energy performance analysis and baseline consumption
• Assessment of occupant health and comfort needs
• Identification of existing hazards (asbestos, lead paint, etc.)
• Documentation of any previous retrofit work

Stage 2: Retrofit Strategy Development

Using assessment data, the coordinator develops a tailored retrofit strategy specifying:

• Target energy performance levels
• Measure selection and sequencing
• Expected performance and cost-benefit analysis
• Risk assessment and mitigation plans
• Quality assurance and testing protocols

Critically, the strategy must consider interactions between measures. For example, improved insulation and airtightness require adequate ventilation to prevent moisture accumulation.

Stage 3: Design Development and Technical Specifications

Detailed technical specifications are produced for each measure, covering:

• Materials and products (with evidence of performance)
• Installation methods and sequencing
• Quality standards and acceptance criteria
• Commissioning and handover requirements

The coordinator ensures designs are buildable and specifications are compatible across trades.

Stage 4: Quality Assurance and Construction

Throughout installation, the coordinator:

• Inspects work against agreed specifications
• Carries out testing (air permeability, thermal imaging, etc.)
• Manages non-conformances and remedial action
• Maintains detailed records of all works and testing
• Coordinates between contractors to prevent conflicts

Stage 5: Commissioning, Handover and Evaluation

On completion, the coordinator ensures:

• All systems are properly commissioned and perform as designed
• Occupants receive training and clear documentation
• Post-completion performance is monitored and evaluated
• Lessons learned are documented for future projects

Key Principles Underpinning PAS2035

Several core principles guide PAS2035 implementation:

• Building science understanding: Coordinators must apply principles of heat transfer, moisture management and air movement
• Holistic assessment: Considering the building as an integrated system rather than isolated elements
• Evidence-based decision making: Using data from surveys and testing to inform retrofit choices
• Quality assurance: Verification through inspection and testing at critical stages
• Occupant-centred approach: Addressing health, comfort and usability alongside energy performance

The Retrofit Coordinator Role

PAS2035 requires appointment of a qualified Retrofit Coordinator responsible for:

• Overseeing the entire retrofit process from assessment to handover
• Ensuring compliance with the PAS2035 framework
• Managing technical coordination between different measures and contractors
• Quality assurance and defect management
• Maintaining documentation and records

Coordinators must demonstrate competence in building science, retrofit technologies, project management and quality assurance. Many retrofit coordinators undertake formal accreditation programmes to evidence this competence.

Common Retrofit Measures Addressed by PAS2035

Typical measures coordinated within PAS2035 retrofits include:

• Fabric improvements (insulation, air sealing, window replacement)
• Heating system upgrades (heat pumps, boiler replacement, district heating)
• Ventilation improvements (mechanical ventilation with heat recovery)
• Hot water systems and storage
• Renewable energy technologies (solar thermal, photovoltaic)
• Water efficiency measures

The coordinator ensures all measures work together effectively and meet the retrofit strategy objectives.

Getting Started with PAS2035

For those new to PAS2035, understanding the following helps:

• Read the full PAS2035 standard document from BSI
• Familiarise yourself with complementary standards (PAS 2030 for installation quality)
• Understand your building type and common retrofit challenges
• Engage with professional bodies and industry guidance
• Consider formal training and accreditation if coordinating retrofits

PAS2035 represents a significant shift towards professionalised, quality-assured retrofit delivery in the UK. By following its framework, retrofit projects deliver better outcomes for buildings, occupants and the environment.