As the UK accelerates toward its 2050 net-zero goals, the importance of retrofitting the nation’s ageing housing stock has never been clearer. At the heart of this transition is PAS 2035, the government-backed specification for domestic retrofit. Introduced to bring structure, quality, and consistency to retrofit projects, PAS 2035 continues to evolve, and 2025 marks the full arrival of a significantly updated version of the standard.
PAS:2035 forms part of the UK Government’s TrustMark quality assurance framework and outlines the standards and processes required for retrofitting domestic properties. It works alongside PAS:2030, which specifies the installation of energy efficiency measures, and together they underpin schemes like ECO4 and SHDF.
The three retrofit risk pathways (A – low risk, B – medium, C – high have been overhauled to be more practical and aligned with project types. In 2025, the selection of a risk pathway no longer exists by the ‘A/B/C’ ratings; instead, it simply depends on the type and number of interacting measures to reduce confusion and ensure more consistent risk assessments across the industry.
The standard now clearly defines traditional construction as:
This clarity ensures better planning and appropriate energy efficiency measures for older buildings.
Assessors must now include enhanced ventilation assessments, and SAP 10 will become the new standard methodology. This brings assessments closer to Full SAP and includes key metrics like air permeability.
Coordinators must also collect more robust compliance evidence, including:
The focus on ventilation under PAS2035:2023 has been sharpened to include a detailed record and assessment of existing systems in dwellings, in line with PAS2035’s core remit to prevent any harmful consequences of retrofit.
The update introduces clearer guidance for large-scale retrofit projects, helping local authorities, housing associations, and major contractors apply best practices consistently across multiple properties.
Projects must now include post-retrofit evaluation, such as:
A feedback questionnaire for residents (within 3 months of completion)
A full record of inspections and photographic documentation