EnerPHit Retrofit in the UK: The Complete Guide for Homeowners (2026)
If your UK home is cold, draughty and expensive to heat, EnerPHit is the only retrofit standard with the building physics to fix all three permanently — and 2026 is the year the economics finally make sense.
Why EnerPHit, why now
The economic and regulatory case for deep retrofit in the UK changed quietly between 2022 and 2026. Gas prices doubled, then settled at a new structural baseline. The forthcoming Future Homes Standard (now scheduled to come into force on 24 March 2027) moves Building Regulations Part L further toward fabric-first, low-carbon heating thinking. And the new consultation proposing EPC C for private rented homes by 2030 (with new tenancies from 2028) — and the broader direction of travel for owner-occupied properties — means cosmetic upgrades no longer cut it.
For UK homeowners, the question has shifted from "should we improve our home's energy performance?" to "how deep do we go, and which standard do we follow?" The cheapest answer (top-up loft insulation, a few draught strips, a new boiler) gives you a 10–20% improvement at most. The deepest answer — EnerPHit — gives you an 85–90% reduction in heating demand and a property that is verifiably future-proof against any energy price scenario.
At APMBuild, based in Hereford and serving the West Midlands and Wales, the typical client coming to us in 2026 is not a passionate eco-builder. They are a homeowner who has done the maths, looked at the next 20 years of fuel bills, and concluded that doing the work properly once costs less than doing it incompletely three times.
What EnerPHit actually is
EnerPHit is a building certification standard issued by the Passive House Institute (PHI) in Darmstadt, Germany — see the official Passive House Institute EnerPHit criteria. It is the retrofit counterpart to full Passive House. Where new-build Passive House targets a heating demand of 15 kWh/m²a, EnerPHit relaxes the heating-demand criterion to 25 kWh/m²a in the cool-temperate UK climate (energy-demand method), or alternatively the project can be qualified via the component method by meeting per-element PHI U-value and efficiency requirements — recognising the practical constraints of existing buildings. See the Criteria for Buildings: Passive House – EnerPHit – PHI Low Energy Building (PDF) for the full criteria.
In plain terms, EnerPHit asks you to upgrade five things in a coordinated, physics-aware way:
- The fabric — walls, roof, floors brought up to U-values around 0.15 W/m²K, with continuous insulation that eliminates thermal bridges.
- Windows and doors — triple-glazed units with a whole-window U-value typically below 0.85 W/m²K. APMBuild specifies German and Polish triple-glazed windows that meet this comfortably.
- Airtightness — measured by blower door test, typically achieving 1.0 air changes per hour at 50 pascals or better.
- Mechanical ventilation with heat recovery (MVHR) — a balanced ventilation system that recovers 75–92% of the heat from outgoing air.
- Thermal bridge detailing — every junction designed and built to avoid cold spots and condensation risk.
The difference between EnerPHit and a "good" UK refurbishment is not the components — it is the integration. EnerPHit treats the building as a single physics system. UK refurbs typically treat it as a list of products.
Is your home suitable? A practical checklist
Around 90% of UK housing stock can reach EnerPHit. The other 10% — typically very small terraces with extreme geometric constraints, or Grade I listed buildings where external alterations are forbidden — cannot. Here is the suitability checklist APMBuild uses at first enquiry:
Building fabric
- Solid masonry, cavity masonry, or timber frame — all workable.
- Steel frame and reinforced concrete — workable with extra design attention to thermal bridging.
- Cob, straw bale, hempcrete — possible but specialist (we would partner with a conservation specialist).
Form factor
Form factor is the ratio of external envelope area to internal floor area. A detached house has more external surface per m² than a mid-terrace, so it loses more heat — and therefore needs more insulation to compensate. Detached bungalows are the hardest type of home to retrofit to EnerPHit; mid-terraces are the easiest.
Orientation and overshadowing
South-facing glazing is a gift — it gives free solar heat in winter. Heavily north-facing or overshadowed homes still work but require more insulation to balance lower solar gains.
Planning constraints
Conservation areas and listed buildings are not deal-breakers, but they shift the strategy from external wall insulation toward internal wall insulation, which is more involved. APMBuild handles the design choices and planning negotiation as part of the standard service.
The seven stages of an EnerPHit retrofit
From the first phone call to handover, an APMBuild EnerPHit project runs through seven stages. The whole programme typically takes 9–14 months.
- Initial enquiry and free 30-minute consultation. We look at your address, EPC, photos and your goals. We give you an honest first read on feasibility and indicative cost band.
- PHPP pre-assessment. We model your home in the Passive House Planning Package — see our PHPP service page for what the report covers — to verify EnerPHit is achievable and to scope the fabric specification.
- Design. Architectural drawings (with our architect partner), detailed fabric build-ups, MVHR layout, window schedule, thermal bridge details.
- Planning permission and Building Control. Submitted in parallel where possible. Most APMBuild projects also follow PAS 2035 protocols voluntarily — see our PAS 2035 explainer.
- Materials procurement. APMBuild orders direct from Polish, German and Austrian manufacturers. Materials are CE/UKCA-marked and typically arrive in 5–10 days from order.
- Build. Sequenced fabric works, airtightness layer installation, window installation, MVHR commissioning, internal finishes. On-site duration is typically 4–8 months.
- Commissioning and handover. Blower door test, MVHR commissioning report, full documentation pack, and our 24-month workmanship warranty.
Realistic UK costs in 2026
The honest answer most homeowners want: how much per m². For a complete EnerPHit-route deep retrofit delivered by APMBuild, the 2026 range is £1,800–£2,600 per m² of treated floor area. The variation depends on building type, condition, level of finish and how much fabric work is required.
| Project type | Typical cost range (per m²) | What's included |
|---|---|---|
| EnerPHit retrofit (terraced / semi) | £1,800–£2,200 | Fabric, windows, MVHR, airtightness, finishes |
| EnerPHit retrofit (detached) | £2,000–£2,600 | As above + larger envelope |
| Passive House new build | £2,400–£3,200 | Full new-build to PH standard |
| Standard UK refurb (comparison) | £1,400–£2,000 | Cosmetic + partial upgrades, no PH targets |
| Design-build full A–Z | £2,800–£3,800 | Including architectural design (via UK architect partner) and interior fit-out |
What is included: external or internal wall insulation, roof and floor insulation, triple-glazed windows, MVHR system, all airtightness works, new internal finishes, full project management, planning, Building Control, PHPP pre-assessment.
What is not included: structural alterations, new kitchens or bathrooms beyond like-for-like, heating system (heat pump typically costs £8–14k installed on top), garden and external works, VAT for non-zero-rated work.
If your home is in a particularly poor structural condition, expect the upper end of the range. If it is well-maintained and you choose modest finishes, the lower end is realistic.
Energy savings — what to actually expect
The headline figure across the APMBuild project pipeline and across published EnerPHit case studies in the UK is consistent: 85–90% reduction in space heating demand. In real numbers, that takes a typical pre-retrofit semi-detached home from around 180–220 kWh/m²a of measured heating demand down to 20–30 kWh/m²a.
Bill savings depend on fuel:
- Gas to retained gas boiler: bills drop by roughly the same 85% as heating demand.
- Gas to heat pump: bills drop by an even greater proportion because the heat pump itself runs at a coefficient of performance of 3.5–4.5, multiplying the fabric savings.
- Electric heating retained: bills drop the most in absolute terms, given the higher unit cost of electricity.
The non-financial benefits are often what surprises clients most: a steady 20–22°C indoor temperature regardless of weather, no cold spots, no condensation, much improved indoor air quality from MVHR filtration, and dramatically reduced external noise.
Planning, Building Control and PAS 2035
An EnerPHit retrofit touches three regulatory frameworks. Most homeowners only think about the first.
Planning permission
External wall insulation almost always requires planning permission. Triple-glazed window replacements that match the existing appearance are often permitted development. Conservation areas and listed buildings need a more careful design approach — typically internal wall insulation paired with conservation-style windows. APMBuild prepares and submits the planning application as part of the standard scope.
Building Regulations
All works require Building Regulations approval, particularly under Part L (energy) and Part F (ventilation). The latest UK guidance is published by UK government. EnerPHit specifications comfortably exceed Building Regulations minimums.
PAS 2035 and ECO
PAS 2035 is the UK retrofit quality framework. It is mandatory for ECO4-funded works and increasingly used as a quality marker on private retrofits. We cover this in detail in our PAS 2035 guide. Even on fully private projects, APMBuild typically follows PAS 2035 documentation protocols because they prevent the most common retrofit failures (moisture risk, ventilation gaps, inadequate U-values).
Common mistakes UK homeowners make
After 20+ years on European construction sites and a growing UK retrofit pipeline at APMBuild, the patterns are clear. Here are the five most expensive mistakes — listed in rough order of frequency.
1. Choosing windows on price alone
A cheap "triple-glazed" window from a UK volume supplier often has a whole-window U-value of 1.3–1.4 W/m²K. A proper Polish or German PHI-listed window comes in at 0.7–0.85 W/m²K. The price difference is around 20–30%; the heat-loss difference is nearly 2×.
2. Ignoring airtightness
You can insulate to perfection and still lose 30% of your heating energy through air leakage. Airtightness is the cheapest single upgrade to specify (it is mostly tape, membranes and detailing) and the most commonly skipped.
3. Skipping MVHR
An airtight home without MVHR is a moisture trap. MVHR is non-negotiable for any EnerPHit-route retrofit. The decent units start around £3,500 installed for a small house.
4. Mixing trades without a single coordinator
Insulation contractor, window installer, electrician, plumber, plasterer — each working to their own schedule, with no single person accountable for thermal bridges or airtightness lines. This is how retrofits fail. APMBuild operates as a single point of accountability for the entire fabric envelope.
5. Phasing without a master plan
Phasing an EnerPHit retrofit over 5–10 years is fine — but only with a master plan that knows where every future detail will land. Random phasing locks you out of the airtightness layer permanently.
How to choose a contractor
EnerPHit is unforgiving of poor execution. A contractor who builds a "near-passive" house to 80% of the spec gets 30% of the benefit. So the contractor question matters more here than in any other type of construction.
Look for these four things:
- PHPP training. Has someone in the firm actually trained on PHPP? If they cannot read a PHPP report, they cannot build to the model. Paweł at APMBuild is PHPP-trained, and our full PHPP service includes both pre-assessment and certified modelling via our PHI-accredited partner.
- References on similar UK projects. European Passive House experience is valuable but not sufficient — UK climate, planning rules and supply chain are different.
- Direct material supply. Contractors with direct European supply chains (APMBuild ships Polish, German and Austrian materials with typically 5–10 day delivery) save you 20–30% on materials cost without compromising on specification.
- Workmanship warranty. Any serious retrofit contractor backs their work for at least 2 years. APMBuild's standard warranty is 24 months on workmanship, on top of the product warranties (50 years roofing, 10 years windows, 5 years insulation systems).
If you would like a free 30-minute conversation about your specific property, get in touch with APMBuild. You can also browse our full service list or retrofit calculators first.
EnerPHit retrofit — your questions answered
How much does an EnerPHit retrofit cost in the UK in 2026?
An EnerPHit-route deep retrofit in the UK typically costs £1,800–£2,600 per m² of treated floor area in 2026, depending on building type, condition, level of finish and regional labour rates. APMBuild's costings include full fabric upgrade, triple-glazed windows, MVHR installation and airtightness works.
Can I get an EnerPHit retrofit on a Victorian terrace?
Yes. EnerPHit was designed specifically to handle hard cases like Victorian solid-wall terraces. The standard recognises that historic buildings have geometric and planning constraints, so it relaxes the criteria slightly while still targeting 85–90% reduction in heating demand. Most UK Victorian and Edwardian masonry homes are suitable.
Do I need planning permission for an EnerPHit retrofit?
It depends. External wall insulation almost always requires planning permission, especially in conservation areas or on listed buildings. Internal wall insulation, new MVHR, and like-for-like window replacements often fall under permitted development. All works require Building Regulations approval. APMBuild handles planning submissions and Building Control liaison as part of our service.
How long does an EnerPHit retrofit take from enquiry to handover?
Allow 9–14 months end-to-end. The design and PHPP modelling phase typically takes 8–12 weeks, planning 8–13 weeks (often in parallel), procurement 4–6 weeks (European materials typically arrive in 5–10 days once ordered), and on-site works 4–8 months depending on house size and whether you remain in occupation.
Can EnerPHit get my home to EPC A?
In most cases yes. EnerPHit-route retrofits delivered by APMBuild typically achieve EPC A or high B, with measured heating demand reduced by 85–90%. The actual SAP/EPC rating depends on the heating system specified — pairing fabric upgrades with a heat pump usually secures EPC A.