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PAS 2035 Compliance Checklist for External Wall Insulation (EWI)

Ensuring compliance with PAS 2035 is essential for successful external wall insulation (EWI) retrofit projects in the UK. This publicly available specification, developed by the British Standards Institution (BSI), provides a structured framework to deliver safe, effective, and energy-efficient retrofits for existing domestic buildings. By following a dedicated PAS 2035 compliance checklist, homeowners, contractors, and retrofit coordinators can minimize risks, optimize energy performance, and meet regulatory requirements.

PAS 2035 emphasizes a whole-dwelling approach, integrating EWI with other measures to address issues like thermal bridging, moisture control, and ventilation. This checklist outlines key steps from initial assessment to post-installation verification, helping to achieve high-quality outcomes that contribute to net-zero goals.

Understanding PAS 2035 and Its Role in EWI Projects

The latest version, PAS 2035:2023, updates previous standards to simplify processes and enhance consumer protection. It applies to all publicly funded retrofit schemes, such as ECO4 and the Social Housing Decarbonisation Fund (SHDF), making it mandatory for EWI installations in these contexts. For EWI specifically, compliance ensures that insulation systems reduce heat loss while maintaining structural integrity and fire safety.

Key principles include risk stratification into pathways (A, B, or C) based on project complexity, with EWI often falling under Pathway B for moderate-risk retrofits. Adhering to these guidelines prevents common pitfalls like condensation buildup or inadequate airtightness, which can undermine the long-term benefits of EWI.

Pre-Project Preparation: Initial Assessments and Planning

• Conduct a Whole Dwelling Assessment: Start with a comprehensive survey of the property, including fabric condition, energy usage, and occupant needs. This involves thermal imaging and moisture mapping to identify suitable EWI applications. Reference official building regulations for external walls via the Planning Portal to ensure alignment with Approved Document L.
• Appoint Qualified Professionals: Designate roles such as Retrofit Coordinator, Assessor, and Designer early. All must hold relevant certifications, like those from TrustMark or equivalent schemes, to oversee EWI compliance.
• Risk Assessment and Pathway Selection: Evaluate potential hazards, including interstitial condensation risks unique to EWI. Use tools like the Whole House Moisture Risk Assessment to classify the project and develop a tailored Medium-Term Improvement Plan (MTIP).

During this phase, engage homeowners to discuss EWI benefits, such as up to 35% energy savings, and outline timelines. Documentation here forms the audit trail required under PAS 2035.

Design and Specification for EWI Compliance

The design stage is critical for EWI, where specifications must detail insulation thickness, fixings, and render finishes to meet U-value targets (typically 0.18 W/m²K or better for walls). Incorporate ventilation strategies to avoid airtightness issues post-installation.

• Material Selection: Choose BBA-certified EWI systems compliant with BS EN 13162 for thermal insulation products. Ensure fire performance meets BS EN 13501-1 Class B-s1,d0 for external applications.
• Integration with Other Measures: Design EWI to work alongside loft insulation or heating upgrades, avoiding conflicts like thermal bridging at junctions. Consult government best practice guidance on solid wall insulation deployment.
• Airtightness and Ventilation Plan: Develop an airtightness strategy, including testing targets (e.g., under 5 m³/h/m² at 50Pa), and specify mechanical ventilation if needed to maintain indoor air quality.

Sign off the design with all stakeholders to confirm it adheres to PAS 2035 clauses 8 and 9, ensuring scalability for archetype-based projects in larger schemes.

Installation and Quality Assurance

Execution of EWI requires PAS 2030-certified installers to handle on-site work, from substrate preparation to final rendering. Monitor progress with site visits by the Retrofit Coordinator to record any non-compliances.

• Site Preparation: Clean and repair walls, applying mesh reinforcements at vulnerable points. Adhere to weatherproofing standards to prevent water ingress during curing.
• Installation Process: Fix insulation boards mechanically and with adhesive, ensuring full coverage without gaps. Use non-combustible fixings where required by fire regulations.
• Testing and Commissioning: Perform interim checks for levelness and adhesion strength. Post-installation, conduct air leakage testing and thermographic surveys to verify performance.

Maintain detailed records, including photographic evidence, to support PAS 2035’s emphasis on traceability. Any deviations must be justified and approved.

Post-Installation Evaluation and Handover

After EWI completion, evaluate the dwelling’s performance against design predictions. This includes occupant feedback surveys and one-year follow-up monitoring for energy savings.

• Verification Checks: Confirm U-value improvements via in-situ measurements and check for defects like cracking in renders.
• Handover Documentation: Provide homeowners with maintenance guides, warranty details, and operation manuals for any integrated systems.
• Medium-Term Monitoring: Schedule reviews to assess if further measures are needed, aligning with the MTIP.

For ongoing compliance, reference resources from the Insulation Manufacturers Association (INCA) on EWI best practices. This ensures EWI projects not only meet PAS 2035 but also deliver sustained environmental and cost benefits.

In summary, a thorough PAS 2035 compliance checklist streamlines EWI retrofits, fostering energy-efficient homes across the UK. By integrating authoritative standards and expert oversight, these projects enhance building performance while safeguarding occupants.