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Toughened standard for government-funded whole house retrofits

Words:
Stephen Cousins

New national standard PAS 2035/2030:2023 require a medium-term improvement strategy for home undergoing retrofit, an airtightness strategy and site visits by Retrofit Co-ordinators

The front of a 125-year old semi-detached Victorian townhouse on Manchester’s Zetland Rd, renovated by property developer and environmental consultancy Ecospheric in 2019 and transformed into a Passivhaus-compliant home.
The front of a 125-year old semi-detached Victorian townhouse on Manchester’s Zetland Rd, renovated by property developer and environmental consultancy Ecospheric in 2019 and transformed into a Passivhaus-compliant home. Credit: Rick McCullagh

Best practice in providing ‘whole house’ retrofits for domestic dwellings, from project inception to handover and evaluation, has been set out in the new national Publicly Available Specification PAS 2035/2030:2023 – developed by the British Standards Institute (BSI) in collaboration with the government which will require it for domestic retrofits under its own energy efficiency schemes.

The update supersedes PAS 2035:2019+A1:2022, which will be withdrawn in March 2025 and, says the BSI, addresses the ‘urgent need to decarbonize 27 million UK homes’ by improving their energy efficiency.

The standard covers end-to-end energy efficiency, rather than piecemeal fixes, and minimises the risk of poorly executed and therefore ineffective retrofits. Compliance with the standard, and TrustMark registration, are required for domestic retrofit under government energy efficiency schemes.

The revision introduces a simplified risk assessment process and more references to the main contractor to reflect the emphasis on whole dwelling, rather than measures-based, retrofit. Clauses have been added to allow retrofit design based on assessments of ‘archetype’ to enable retrofitting at scale.

The Retrofit Co-ordinator is defined as a specialist qualified retrofit project manager (potentially an architect) who takes final responsibility for the suitability of the design and oversees aspects such as the assessment of dwellings, and the identification, specification and evaluation of energy efficiency measures for installation.

 

Detail of the Zetland Rd ground floor bay window. Once retrofitted, new inner walls encroached on room space by only 50mm.
Detail of the Zetland Rd ground floor bay window. Once retrofitted, new inner walls encroached on room space by only 50mm. Credit: Credit Ecospheric

PAS 2035/2030:2023 introduces the requirement that the Retrofit Co-ordinator conducts either in‑person or virtual/ remote site inspections during construction to verify compliance with the standard during installation. Inspections should cover the interaction of energy efficiency measures (EEMs), air barrier and thermal bridge details and installation, and airtightness or air leakage testing, also verifying that the correct products are being installed in line with the design.

The Retrofit Co-ordinator must ‘make a written record of quality and progress from all inspections’, including photographic evidence and record any evidence of non‑compliant work on site. Non-compliant work must be reported in writing to the main contractor or retrofit installer and the client in order to agree a schedule for rectification.

The update makes medium‑term retrofit improvement plans a requirement, rather than guidance, even if only limited house improvements are carried out in the short term. The plans are a responsibility of the Retrofit Co-ordinator and guide the phased improvement of a dwelling by identifying the overall scope and appropriate order for improvements over a period of time, also highlighting the critical interactions between them. Furthermore, plans should be updated ‘to respond to changes in standards or the availability of new technologies, and to record improvements as they are made.’

Six recently- retrofitted homes in Swansea, Wales. Formerly off the mains gas grid, very energy inefficient and expensive to heat, with damp, mould and low SAP ratings, a whole-house zero carbon retrofit by Swansea City Council took their EPC from G to A.
Six recently- retrofitted homes in Swansea, Wales. Formerly off the mains gas grid, very energy inefficient and expensive to heat, with damp, mould and low SAP ratings, a whole-house zero carbon retrofit by Swansea City Council took their EPC from G to A. Credit: Swansea Council/ Welsh School of Architecture

Where the retrofit design includes EEMs to the building fabric, such as insulation, airtightness, or replacement windows, the Retrofit Designer or Retrofit Co-ordinator must now develop an airtightness and air leakage testing strategy as part of the retrofit design.

This should include airtightness target/s, especially for a whole-house retrofit, and recommend any other airtightness or air leakage testing required before, during or after installation of EEMs.

An air leakage test verifies the absence of major air leaks through installed EEMs. ‘Ideally’ this should be carried out before and after any major insulation project to verify that leakage has been reduced through the external envelope.

Among the other changes included in the update are the requirement for building performance monitoring and evaluation from inception through to completion, referencing the new BS 40101 on Building Performance Evaluation. 

In addition, where a ‘distressed replacement’ of heating appliances is being designed, the standard acknowledges that a whole‑dwelling assessment and the involvement of a Retrofit Co-ordinator might not be possible.

Significant improvements to building energy efficiency are vital if the UK is to meet its statutory targets for emissions reductions. The government’s Net Zero Strategy includes a commitment to improve energy performance certificate scores in existing dwellings. However, critics slammed its decision last month to scrap a plan to require landlords to upgrade properties to EPC band C, questioning its commitment to climate policy.

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