Retrofit means modifying an existing building to improve its energy performance – anything from loft insulation to a full fabric-first overhaul paired with solar PV and a heat pump. Most of the UK’s building stock was built before modern energy efficiency standards existed, and retrofit is one of the most direct ways any building owner can cut both running costs and carbon.
In this blog, you’ll learn:
- What retrofit is
- The benefits of retrofitting
- What an energy efficient retrofit actually involves, with real examples
- The different types of building retrofit
What is Retrofit?
So, what is retrofit? In simple terms, a building retrofit is the process of modifying an existing building to improve its energy performance. This can encompass a wide range of upgrades, from insulation to solar panels. With many buildings constructed before modern energy efficiency standards were in place, retrofitting has emerged as a vital solution for bringing these structures up to today’s standards.
How Retrofit Is Regulated: PAS 2035 and PAS 2038
Retrofit work on homes is governed by PAS 2035, the framework that sets out how a domestic retrofit is assessed, coordinated and designed – from initial risk pathway through to installation and evaluation. Non-domestic and commercial buildings, from offices to schools and community halls, fall under a related but distinct standard: PAS 2038. It follows a similar whole-building process, but without a Retrofit Coordinator – instead, a Retrofit Lead Professional oversees the project, reflecting the added complexity of commercial building services and occupancy patterns.
Which standard applies depends on the building, not the scale of the works: a single flat retrofit and a 300-unit domestic portfolio require a PAS 2035 retrofit assessment, while even a small community hall requires a PAS 2038 retrofit assessment since it’s non-domestic.
Whether either standard is mandatory depends on how the work is funded. Retrofit delivered through publicly funded schemes – such as the Warm Homes: Social Housing Fund or the Warm Homes: Local Grant for domestic properties, and the Public Sector Decarbonisation Scheme for non-domestic buildings – must comply with PAS 2035 or PAS 2038 to secure and retain that funding. For privately funded retrofit outside these schemes, neither standard is a legal requirement, but both are increasingly treated as best-practice guidance: green lenders and ESG-linked finance providers use PAS 2038 compliance as evidence a commercial retrofit will deliver real-world carbon reduction, and homeowners, landlords and contractors working to PAS 2035 on privately funded projects get the same quality management discipline – proper risk assessment, coordination and evaluation – that funded schemes are held to, without being tied to a specific scheme.
Why is Building Retrofit Important?
Much of the UK’s building stock predates modern insulation standards, and it shows in the bills. Retrofit brings a genuinely wide set of benefits, both for your running costs and the building itself:
- Lower energy bills: reducing the amount of energy a building needs in the first place cuts costs directly – upgrading insulation, windows and heating systems can mean substantial savings.
- Better comfort and health: insulation and air sealing reduce leaks in the building envelope, keeping temperatures more consistent, cutting draughts, and reducing the damp and mould risk that poor ventilation and ageing fabric can cause.
- Property value and compliance: EPC ratings increasingly carry real financial consequences, from MEES compliance risk on rented properties to lower resale and letting value – a retrofitted building protects against both.
- Better returns on further investment: a heat pump or solar PV array added to a leaky, poorly-insulated building rarely performs as well as the same technology paired with a genuinely retrofitted fabric – fabric-first sequencing matters more than which technology you choose.
Energy Efficient Retrofit: What Does It Actually Involve?
An energy efficient retrofit isn’t a single upgrade – it’s a sequence of measures, prioritised in the right order. In practice, that means starting with the building envelope – insulation, air tightness and glazing – before addressing heating systems and renewables, so the fabric is actually capable of making the most of whatever technology goes in afterwards. A handful of real projects show how that sequencing plays out on an actual building, not just in theory:
- Retrofit West: a three-part home energy assessment for a chronically cold Bristol semi – air tightness testing, thermal imaging and a ventilation review – identified quick, low-cost fixes alongside the more fundamental step of resolving ventilation before any further airtightness work went ahead.
- St Werburghs City Farm: diagnostic testing and energy modelling sequenced before any technology decisions, building the evidence base for what low carbon investment would actually be worthwhile.
- St Mungo’s: the same sequencing principle applied at portfolio scale – a fabric-first hierarchy across 300 units in Bristol and London.
What’s next?
Retrofitting your building doesn’t just make it more efficient and comfortable – done in the right order, it’s the difference between a heating upgrade that pays for itself and one that doesn’t.
We carry out the retrofit assessment and testing work that identifies exactly where a building is losing energy, the coordination that sequences the fix, and the design that specifies it.
Keep Informed
Get practical insights on retrofit, decarbonisation and compliance, delivered straight to your inbox.
"*" indicates required fields