Unlocking the value of air testing in social housing retrofits

For landlords and retrofit co-ordinators aiming to lift properties into EPC Band C and beyond, this development offers a crucial opportunity to evidence building performance, secure funding and reduce the need for additional measures.

With hundreds of successful retrofit schemes delivered across the UK, AES is well-placed to demonstrate the strategic and practical benefits of air testing.

A recent project we did with McBains, on behalf of Cambridge Housing Society, showcases how measured airtightness can help bridge the often-crucial gap between EPC Bands D and C, which enables access to WH:SHF funding.

Measured performance as a catalyst for EPC gains

Several properties in Cornish Close Cambridge, surveyed, assessed and tested by AES, exemplify the transformational role of air testing. Each property in the scheme had already undergone a full suite of fabric-first and services upgrades: improved insulation, upgraded windows, additional ventilation and in some cases replacement heating or hot water systems. However, despite these significant interventions, EPC ratings for several dwellings remained just below the Band C threshold.

These were well-executed retrofits in every respect, but without measured airtightness data, the EPCs didn’t fully reflect the quality or benefit of the work. We knew the buildings were performing better than the default models were crediting them for.

AES’ compliance and testing department conducted airtightness testing across the dwellings, producing data that was fed into the EPC modelling. The impact was immediate: properties previously scoring 67 (Band D) under RdSAP default values rose to scores of 69 or 70 (Band C) when actual air permeability rates were applied.

The properties therefore became eligible for WH:SHF funding without requiring further capital investment in technologies like photovoltaic (PV) systems. We’re now adopting this approach for other retrofit properties.

Alignment with PAS 2035 and RdSAP10

This approach is fully aligned with PAS 2035 principles, which emphasise evidence-based delivery and post-installation verification. The use of measured airtightness serves several purposes under this framework:

· Demonstrating retrofit effectiveness beyond visual inspection

· Supporting accurate ventilation design based on real leakage rates

· Providing transparent, auditable performance data for funders and regulators

Under RdSAP10, airtightness testing has become quantifiable in EPC assessments and real permeability data is now accepted, enabling recognition of quality fabric upgrades. RdSAP9.94 had constrained assessors to default values, which often penalised well-sealed homes.

RdSAP10 therefore gives landlords the ability to model EPCs based on how the building actually performs, not just what it was designed to achieve. That’s a significant shift for retrofit co-ordinators trying to deliver cost-effective Band C outcomes.

Implications for retrofit strategy and portfolio planning

For housing associations, asset managers and delivery partners, incorporating airtightness testing into retrofit strategies delivers wide-ranging benefits:

· Improved EPC ratings without requiring additional capital works

· Robust, data-driven performance validation in support of PAS 2035 compliance and funding applications

· Smarter sequencing of interventions, which means potentially avoiding installations such as PVs if the fabric performance is sufficient

· Greater confidence in ventilation design, reducing the risk of condensation and mould.

These outcomes strengthen the case for WH:SHF funding eligibility and support compliance with Minimum Energy Efficiency Standards (MEES), local authority net zero strategies, and tenant expectations.

As the social housing sector continues to pursue decarbonisation and funding compliance, airtightness testing emerges as a cost-effective, high-impact intervention that has historically been overlooked. With the implementation of RdSAP10 and the rollout of WH:SHF Wave 3, there is now a strong case to make airtightness testing a standard component of all retrofit programmes.

AES Sustainability has demonstrated that this is a practical and proven strategy, not merely a theoretical advantage. By adopting airtightness testing, landlords can unlock EPC improvements, reduce capital expenditure and chart a clearer path to zero-carbon housing.

For those managing complex property portfolios, the message is clear: do not allow assumed performance to limit your buildings’ potential. Measure it, verify it, and reap the strategic and financial benefits.

Jonathan Platt, existing buildings service lead, AES Sustainability