PAS 2035: Introduction to ventilation requirements

PAS 2035: Introduction to ventilation requirements

By Sophie Neaves on Fri 14 June 2024

PAS 2035: Introduction to ventilation requirements

In the wake of a comprehensive public consultation carried out in early 2023, the British Standards Institution (BSI) published the updated PAS 2035/2030:2023 standards in September 2023. We are currently in a transitional phase where the 2019 standards will be phased out and superseded by the updated 2023 standards on 30th March 2025. These standards represent a significant stride forward in retrofitting practices, ensuring higher energy efficiency and better living conditions across UK homes.


What is PAS 2035?

PAS 2035 is a publicly available specification (PAS) that establishes a robust, overarching framework for domestic whole-house retrofit projects. Established as part of the response to the 2015 Each Home Counts review, and first introduced in 2019, it outlines best practices for improving home energy efficiency. It provides consistent guidelines and a defined process for assessing, designing, managing and evaluating home retrofits in a holistic manner.

The standard aims to ensure retrofits are safe and effective and deliver lasting performance improvements while avoiding unintended consequences from fragmented or isolated upgrades. It covers all aspects, from initial assessments and specifications through to installation and post-retrofit evaluation. A core principle is taking a "whole-house" approach that assesses improvements best matched to individual properties.

PAS 2035 has become instrumental for housing providers, contractors and policymakers driving sustainable energy improvements across the UK's ageing housing stock. Following its risk mitigation methodology helps avoid technical issues, optimises savings, enhances occupant comfort and satisfaction, and instils quality assurance. Adherence is often a requirement for accessing public retrofit funding and financing schemes.


PA 2035 and TrustMark

The introduction of PAS 2035 also heralds the new TrustMark quality mark within the retrofit standards framework. This accreditation signifies adherence to stringent quality requirements, offering peace of mind to both property owners and occupants that retrofit works meet high standards of execution and integrity. TrustMark has integrated PAS 2035:2019 requirements into its Framework Operating Requirements, ensuring energy efficiency installations follow recognised specifications and compliance. When a business becomes PAS 2030:2019 certified, projects must adhere to PAS 2035:2019 under a registered Retrofit Coordinator's oversight, with data lodged in the TrustMark Data Warehouse for consumer confidence.


Why is PAS 2035 important?

For landlords and housing developers, PAS 2035 is a standard that demands attention, particularly regarding compliance, indoor air quality and ventilation. It covers crucial aspects such as installation accuracy, energy conservation measures, and overall property health, making it a pivotal framework for sustainable development in the housing sector.


Compliance with PAS 2035 is vital for landlords and developers as it sets a clear framework for high-quality, sustainable retrofits, helping to build consumer confidence and drive the adoption of energy-efficient housing solutions. Failure to comply with the standard could result in underperforming retrofits, negating potential energy savings and leaving properties with poor indoor air quality and inadequate ventilation. 


Ventilation requirements are crucial and can lead to failures if not fully understood. An appropriately qualified person must review the design, considering existing and proposed ventilation to ensure adequate ventilation after energy efficiency improvements. Consult retrofit coordinators, system designers, or manufacturers for guidance if unsure. Inspection findings, whether major or minor, must be rectified within the given timeframe, as failing to provide evidence can jeopardise PAS 2035 compliance,  PAS 2030 certification and Trustmark registration.

Ultimately, by adhering to PAS 2035, you can future-proof your properties, ensure compliance with regulatory standards, and provide energy-efficient, healthy, and comfortable living spaces for occupants, enhancing the value and marketability of their housing stock.

What does a fabric-first approach mean?

The fabric-first approach advocated by PAS 2035 requires prioritising the building's physical integrity before implementing energy-saving measures. This includes addressing any damp issues, enhancing the building fabric with air leakage reduction and ensuring proper ventilation. This method ensures that the efficiency measures are effective and sustainable in the long term.


The fabric-first approach advocated by PAS 2035 requires prioritising the building's physical integrity before implementing energy-saving measures. It involves prioritising the following aspects:

  • Air tightness: Improving air tightness by sealing air leakage paths through the building fabric, such as installing insulation and sealing gaps.
  • Insulation: Enhancing insulation levels of walls, roofs, floors, and windows to reduce heat loss and gain.
  • Moisture management: Addressing damp issues within the building fabric, such as rising damp, penetrating damp, or condensation problems.
  • Ventilation: Ensuring proper ventilation strategies, like heat recovery ventilation (HRV) or mechanical ventilation with heat recovery (MVHR), to maintain healthy indoor air quality.


By tackling the building fabric first, the approach creates a solid foundation for implementing energy-saving measures effectively. It ensures the building is airtight, well-insulated, and free from moisture problems, allowing subsequent energy-efficiency measures to perform optimally and deliver expected energy savings.


PAS 2035 accreditation

Unlike PAS 2030, which offers direct certification, PAS 2035:2019 cannot be certified in the same manner. Instead, it serves as a guideline that complements PAS 2030 certifications, ensuring that all aspects of a retrofit are considered and implemented effectively. PAS 2035 accreditation involves demonstrating compliance with the standard's requirements, which include a whole-house approach, addressing the building fabric, ensuring proper ventilation, and implementing energy conservation measures. 


To achieve accreditation, contractors and installers must undergo training and assessments to demonstrate their understanding and ability to adhere to the PAS 2035 framework, assuring clients that retrofits will be carried out according to best practices for energy efficiency, indoor air quality, and overall building performance.

Who is responsible for meeting PAS 2035 standards?

Delivering a successful retrofit under PAS 2035 involves a coordinated effort among several key roles.

  • The retrofit advisor is responsible for providing impartial guidance to the homeowner on recommended energy efficiency measures. 
  • The retrofit assessor conducts an in-depth evaluation of the property, identifying areas for improvement and specifying the measures required.
  • The retrofit coordinator then manages the overall retrofit process, ensuring adherence to PAS 2035 standards. They appoint and oversee the work of the retrofit designer, who produces detailed specifications for the measures, and the installer(s), who implement the physical changes to the property. 
  • The retrofit evaluator inspects and tests the completed work to certify it meets the requisite performance standards.


Each of these roles is vital, with clear responsibilities outlined in PAS 2035. Only through their collective efforts, following the prescribed methodology, can a retrofit be deemed fully compliant and the homeowner assured of its quality, safety and energy efficiency benefits. Coordination and accountability across the retrofit team are paramount.

Compliance with PAS 2035

Compliance with PAS 2035 and PAS 2030:2019 is mandatory for any government-funded retrofit projects. This includes initiatives under the Social Housing Decarbonisation Fund and the Home Upgrade Grant scheme. Local authorities may also require adherence to these standards, emphasising their importance in public housing projects. Failure to comply with these standards in government-funded or local authority-mandated projects can result in consequences, including the withdrawal of funding, fines, or legal penalties. 


Therefore, contractors, installers, and housing providers must prioritise compliance with PAS 2035 and PAS 2030:2019 to ensure that their retrofit projects meet the highest standards of quality, safety, and sustainability.


PAS 2035 ventilation assessment

The PAS 2035 ventilation assessment deems existing ventilation inadequate if there is evidence of mould, condensation, no functional ventilation system, or lack of purge ventilation for habitable rooms. An adequate and complete ventilation system includes intermittent extract ventilation, mechanical ventilation with heat recovery or mechanical extract ventilation combined with background ventilators. These systems ensure proper extraction of moist air and supply of fresh air, crucial for maintaining indoor air quality and preventing condensation issues after energy efficiency retrofits.


How Airflow can help

At Airflow, we understand the intricacies of PAS 2035 and offer certified product solutions to meet your ventilation needs. Whether your existing ventilation system needs an assessment for adequacy or a complete overhaul, our trusted expertise is here to assist. Airflow ensures that each project not only meets but exceeds the required standards, paving the way for well-equipped, more energy-efficient homes.


For more information on how we can help you comply with PAS 2035 standards, visit our website or contact us today.