PAS FAQs

WHAT IS PAS2035

PAS 2035 (Publicly Available Specification) is the UK's standard for whole-house retrofit projects. It mandates a 'whole-house' approach to ensure quality, durability, and energy efficiency, and is required for all government-funded retrofit works.

What’s the difference between PAS 2030 and PAS 2035?

PAS 2035 is the national standard for managing domestic retrofit projects in the UK. It sets out the process for assessing, designing and coordinating energy efficiency improvements to ensure they are safe, effective and appropriate for each home.
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PAS 2030 sets the technical and quality requirements for installers carrying out energy efficiency improvements. It covers the installation of measures such as insulation, heating systems and renewables, ensuring all works are delivered safely, competently and in accordance with best practice standards.
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Together, PAS 2030 and PAS 2035 form the framework that ensures all retrofit projects are delivered to consistent, high standards of quality and compliance.

What is the Whole House or Fabric First Approach?

The whole house or fabric first approach is central to PAS 2035. It means looking at the building as a complete system rather than focusing on single measures. The aim is to improve the building fabric first, such as insulation, airtightness and ventilation, before adding heating or renewable technologies.
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This approach ensures that improvements work together effectively, reduce energy demand and prevent problems like damp, mould or condensation. By understanding how each element of the building interacts, the retrofit process delivers long-term performance, comfort and value for both the homeowner and the environment.

What is the role of Trustmark?

Trustmark is the UK Government-endorsed quality scheme for work carried out in and around homes. The Department for Energy Security and Net Zero (DESNZ) supported Trustmark to become the established Quality Mark for the retrofit sector.
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Businesses operating under Trustmark must comply with a Code of Conduct, a Code of Practice and a Customer Charter, ensuring high standards of technical competence, compliance and customer care. Under PAS 2035 and PAS 2030, all retrofit projects must be delivered by Trustmark registered organisations.
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Trustmark also operates the central Data Warehouse where all project evidence is lodged, providing oversight, accountability and transparency across every retrofit project.

What is BS 5250?

BS 5250 is the British Standard for managing moisture in buildings. It provides guidance on controlling condensation, damp and mould by balancing insulation, ventilation and material choices. The standard promotes a whole-building approach that helps maintain healthy indoor environments, reduce moisture-related defects and protect the long-term durability of the property.
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The Level 3 Award in Damp, Mould and Condensation in Buildings (Damp And Mould Qualification Online | Environment Study Centre) is built on the principles of BS 5250, supporting a clear understanding of how moisture interacts with building fabric and how to prevent associated risks through effective design, assessment and management.

What is BS 7913?

BS 7913 is the British Standard for the conservation of historic, traditionally constructed and protected buildings. It sets out best practice for maintaining, repairing and improving older properties, ensuring that energy efficiency upgrades are sympathetic, compliant and appropriate for each building’s character and construction, while protecting historic value.
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A key part of BS 7913 is the Significance Assessment, which identifies what is important about a building and often forms the basis for any Heritage Impact Assessment required for planning or design approval.
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The Level 3 Award in Energy Efficiency for Older and Traditional Buildings (Traditional Buildings Retrofit Course | Environment Study Centre) is built on the principles of BS 7913 and is a recognised qualification for professionals working on traditional buildings, and a requirement under PAS 2035.

What measures can be installed under PAS 2035?

PAS 2035 covers a wide range of energy efficiency measures designed to improve the performance, comfort and sustainability of existing homes. These typically include:
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Fabric measures: Loft insulation, Cavity wall insulation, Internal wall insulation, External wall insulation, Floor insulation, Window and door upgrades

Ventilation measures: Extract fans, Background and trickle vents, Undercuts
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Heating measures: Air-source heat pumps, High efficiency boilers, Heating controls and smart thermostats, Hot water cylinder and pipework insulation, Electric Storage Heaters
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Renewable and low-carbon technologies: Solar photovoltaic, Battery storage
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The final combination of measures is agreed collaboratively between the Retrofit Coordinator, Designer, Installers, Funders and Occupants. Working together ensures that all upgrades are appropriate, practical and deliver real improvements in comfort, efficiency and sustainability.

What are an IOE and an MTP?

The Improvement Option Evaluation (IOE) is the stage in the PAS 2035 process where the Retrofit Coordinator reviews all possible energy efficiency measures for a property. Each option is assessed for cost, performance, suitability and interaction with other measures to identify the best whole-house solution.
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The Medium-Term Plan (MTP) sets out a long-term improvement strategy for the property, typically over 20–30 years. It outlines which measures should be installed now and which could follow in future phases, helping to manage budgets while maintaining a consistent, fabric-first approach to achieving net zero.