Decoding the changes to PAS certification

Risk pathway removed

The 2019 version grouped projects into risk paths A, B or C, which dictated how much assessment and oversight each needed. In 2023, that model has been removed.

Now, every retrofit project follows a unified process, involving the following steps:

·       Retrofit assessment

·       Improvement option evaluation

·       Medium-term improvement plan

·       Retrofit design

·       Retrofit installation

This simplified, streamlined approach reduces complexity while still allowing for property-specific detail.

BS 40104: a new assessment standard

Replacing Section 7 of PAS 2035, BS 40104, a new standard specifically for retrofit assessment, strengthens alignment with building regulations and introduces smarter auditing practices. 

The changes include stricter requirements around the equipment used during assessment, a heightened focus on health and safety and new obligations to consider long-term climate risks. Assessments must now factor in ground conditions, topography, site exposure and shelter, as well as more rigorous evaluations of ventilation and occupancy.

Responsibility for ensuring these assessments meet the required standard lies with the retrofit co-ordinator, who must also maintain a robust audit trail for every decision made.

A new approach to retrofit assessment

Assessors can now carry out initial desktop surveys to gather contextual data ahead of a site survey, saving time and improving planning. Each retrofit assessment must include a condition survey, a ventilation survey, an occupancy assessment and an Energy Performance Report (EPR). External influences, such as sun exposure, prevailing winds, proximity to roads or industrial activity and party wall constraints, must also be taken into account.

‘Traditional buildings’

The definition of a traditional building has been expanded. It’s no longer limited to homes built before 1919. Now, any dwelling constructed using solid brick, stone, earth or pre-1919 timber frames is classed as traditional.

This change brings new training and competency requirements. All professionals working on traditional buildings must now hold a Level 3 Award in Energy Efficiency for Older and Traditional Buildings. Retrofit assessors must complete a Significance Assessment. If the retrofit work could impact the building’s historic fabric, a Heritage Impact Assessment is also required. Only chartered professionals with appropriate heritage expertise can sign off this work.

Ventilation and moisture strategy

Ventilation must now be assessed on every project, particularly where fabric upgrades are planned. Properties are categorised based on the sufficiency of their current ventilation. Category A properties are considered adequate and need no changes, while Categories B and C require designed and implemented ventilation upgrades.

For more complex solutions, such as mechanical ventilation with heat recovery (MVHR) systems, design input from a specialist is required. Site assessments must now include measured data covering humidity, airflow and moisture levels to ensure adequate moisture control across the building fabric.

Mandatory retrofit co-ordination site visits

Retrofit co-ordinators are now required to conduct in-person site visits either before, during or after installation. While virtual inspections or the use of third-party evidence is permitted in some cases, we strongly advocate for on-site visits to maintain quality and consistency.

Each measure must be logged through a Pre-Installation Building Information pack, and must contain photographs and detailed checklists to document the condition and readiness of the property.

New guidance for retrofit design

One of the most notable changes is that airtightness testing is no longer mandatory. However, when used, the results can still contribute to SAP scores and energy performance benchmarking.

The government now provides funding for airtightness improvements, making this a potentially valuable addition to many projects.

PAS 2035 also introduces a more detailed design framework, with requirements based on the complexity of the measures involved. For single-measure retrofits, qualified installers can carry out the design. For two or more non-interacting measures, a retrofit co-ordinator or chartered professional must be involved.

If measures are interacting, especially if they’re fabric-related, or if the building is system-built, high-rise or traditional, only a chartered professional may design the works.

Archetype designs now accepted

A significant efficiency gain comes from the allowance of archetype designs. Under the new standards, a single retrofit design can be applied across multiple properties, provided they are of the same archetype. These designs must clearly list all applicable properties on the cover page and must still include any property-specific adaptations as needed.

While this approach has the potential to streamline design work, there’s a risk of on-site issues where individual property defects diverge from the norm. That’s why clear communication and careful co-ordination remain essential.

A positive step for retrofit

The 2023 PAS updates are a welcome move for the sector. They provide greater alignment with regulatory goals, improve project quality and co-ordination and will ultimately drive better outcomes for residents. Far from being a cause for concern, these updates represent a valuable opportunity for the industry to evolve and improve. 

With the right partners in place, and a collaborative mindset between clients, contractors and co-ordinators, these standards will help drive long-term energy savings, better health outcomes and future-proofed compliance. For us, this is not just a compliance exercise, and we are looking to embrace the quality standards. It’s a step forward in delivering quality retrofit in partnerships that work.

Gary Lawson, managing director, Sustainable Building Services