Deep Retrofit Cost UK 2026: An Honest Breakdown by Element
"Deep retrofit from £X per m²" is the headline. Underneath sits a wide range of work, a wide range of qualities, and a habit in the industry of leaving the soft costs off the quote sheet until the contract is signed. This is what a deep retrofit actually costs in 2026 — element by element, three worked case studies, and the line items most quotes hide.
Why I'm writing this
Most retrofit cost articles I read fall into one of two categories. Either they quote a single number — "deep retrofit costs around £1,000 per square metre" — which is true in the same way that "a car costs around £25,000" is true. Or they pad out an article with so many caveats that the reader leaves with no usable estimate at all.
Neither helps a homeowner deciding whether to retrofit or not. When someone calls me about a Victorian terrace in Hereford or a 1960s semi in Worcester, they need a defensible number to plan against — what is the realistic budget, what does it buy, and where does the money actually go. That is what this article tries to do, with current 2026 UK prices and the assumption that you will read it once and not need a follow-up.
One thing I want to set straight before getting into the numbers: there is no such thing as "the cost of a deep retrofit". There is the cost of fabric upgrade to current Building Regulations, the cost of fabric upgrade to a level that actually changes how the building feels, the cost of an EnerPHit-targeted retrofit, and the cost of a Passivhaus-certified EnerPHit. Each of those is a real and different number. The figures in this article are 2026 UK pricing, including labour, materials and overhead, and they assume work done properly — not the cheapest available.
What "deep retrofit" actually means in 2026
For the purposes of this article I'll use four bands. They correspond roughly to the cost ranges in the latest Passivhaus Trust UK Position Paper (January 2026) and to the AtkinsRéalis retrofit costs comparison:
| Band | Description | £/m² GIA | EPC band achievable |
|---|---|---|---|
| Light retrofit | Loft, easy windows, draught proofing. The MEES C-or-better minimum. | £200–£500 | D → C |
| Medium retrofit | Adds cavity fill (where applicable) or thinner EWI, MVHR or cMEV, full window replacement, ASHP. | £500–£900 | D/E → B |
| Deep retrofit | Full fabric upgrade — IWI/EWI to 0.20–0.30 W/m²K, triple glazing, certified MVHR, ASHP, airtightness tested. Targets <50 kWh/m²/yr. | £800–£1,500 | F/G → A/B |
| EnerPHit certified | Above plus PHPP design certification, on-site verification, certified components, formal Passivhaus Institute audit. Targets ≤25 kWh/m²/yr space heating. | £1,500–£2,800+ | A |
"Deep retrofit" in everything that follows means the third row — substantial fabric upgrade without targeting formal EnerPHit certification. That is the band most private homeowners in this country actually choose when they want comfort, energy bill reduction and long-life value, but do not specifically need the certificate on the wall.
Cost by element — the line items
What follows is what each element costs in 2026 in West Midlands / Welsh borders / wider Midlands UK pricing, assuming work done properly. Cheaper is always available; cheaper rarely lasts.
1. External walls
| Approach | £/m² of wall area | Notes |
|---|---|---|
| EWI — PIR/EPS, 100–120mm, render finish | £150–£220 | Standard modern construction (post-1925 cavity, post-1965 solid blockwork) |
| EWI — wood fibre or hemp-lime, 100–140mm, lime render | £200–£300 | For traditional construction (pre-1925) |
| IWI — wood fibre 80–100mm + lime plaster | £190–£260 | Standard for traditional buildings where EWI not permitted |
| IWI — PIR + plasterboard | £80–£140 | Wrong for pre-1925 buildings — see our stone cottage article |
| Cavity wall fill (where applicable) | £15–£25/m² or £1,200–£2,000 per dwelling | Quick win on post-1925 cavity walls in good condition |
2. Roof and loft
| Approach | Cost | Notes |
|---|---|---|
| Loft insulation top-up to 300–400mm mineral wool or wood fibre | £600–£1,500 per dwelling | Quickest win; do this on day one |
| Warm roof — insulation between/over rafters, retain ceilings | £8,000–£18,000 per dwelling | Required when converting roof space, or when loft floor cannot be insulated effectively |
| Full roof recover with sarking insulation | £80–£150/m² of roof slope | Coordinate with re-roofing — significant economies if roof is due replacement |
| Airtight ceiling layer (membrane + tape) | £12–£20/m² | Critical for blower-door test result; often missed |
3. Floors
| Approach | Cost | Notes |
|---|---|---|
| Suspended timber floor — wood fibre or sheep wool between joists, breather membrane below | £35–£65/m² floor area | The right approach in pre-1925 stock |
| Solid floor — lift, insulate (PIR 100mm), re-lay screed | £180–£280/m² floor area | Expensive and disruptive; many projects skip and live with the cold floor |
| Insulating overlay on existing slab (no lift) | £80–£130/m² floor area | Reduces ceiling height by 80–100mm; check door reveals before specifying |
4. Windows and doors
| Approach | £/window or £/m² | Notes |
|---|---|---|
| uPVC triple-glazed replacement — Aluplast/Veka-class | £600–£1,000/m² window area | The 80% solution for modern construction |
| Timber or timber-aluminium triple-glazed (PH-certified) | £900–£1,400/m² | For PH-targeted projects; better thermal bridge performance |
| Slim double glazing in original sashes/casements (heritage) | £450–£650 per window unit | For listed / conservation area properties — keeps the sash, adds the glass |
| Secondary glazing (added internally) | £350–£550 per window | Sympathetic option for heritage windows; works well acoustically |
| External door — PH-certified composite or timber | £1,500–£3,500 per door | One front, one back is normal; price varies hugely with spec |
5. Airtightness
| Item | Cost | Notes |
|---|---|---|
| Airtightness consultancy + tape and membrane materials | £1,200–£3,000 | For a typical project; mostly labour time during construction |
| Pre- and post-blower door tests | £350–£800 each | Two tests minimum; one mid-works helps catch problems early |
6. Ventilation
| System | Cost installed | Notes |
|---|---|---|
| cMEV (continuous mechanical extract ventilation) | £2,500–£4,500 | For cottages and tight spaces where MVHR ducting is invasive |
| MVHR — small system, terraced/semi | £4,500–£7,500 | Ductwork in floor zones or false ceilings |
| MVHR — large system, detached | £7,000–£12,000 | Higher airflow, longer ductruns, larger heat exchanger |
7. Heating
| System | Installed cost | Net after BUS |
|---|---|---|
| Air source heat pump (5–9 kW typical) | £10,000–£14,000 | £2,500–£6,500 after £7,500 BUS grant |
| Ground source heat pump | £18,000–£30,000 | £10,500–£22,500 after BUS |
| Hot water cylinder (replacing combi) | £1,500–£3,000 | Needed when moving from combi to heat pump |
| Radiator and emitter resizing | £2,000–£6,000 | For low flow temperature (45–50°C) operation |
| Underfloor heating (where solid floor lifted anyway) | £60–£90/m² | Best paired with heat pump |
8. Renewables (optional, but increasingly common)
| System | Installed cost | Notes |
|---|---|---|
| Solar PV — 4 kWp system | £6,000–£8,500 | South or south-east/west facing roof |
| Battery storage — 5 to 10 kWh | £3,500–£7,000 | Capacity sized to evening load and demand-flexibility tariffs |
| Combined PV + battery + hybrid inverter | £8,000–£13,500 | Satisfies the MEES Smart Readiness metric from 2030 (see our 2026 MEES article) |
The hidden costs — soft fees, VAT, decants, contingency
Almost every too-cheap retrofit quote I see is missing one or more of these line items. The headline £/m² gets you to a number; these items get you to the actual cost.
| Item | Typical 2026 cost | What it covers |
|---|---|---|
| PHPP modelling / hygrothermal assessment | £2,500–£6,000 | Design-stage energy and moisture model. Higher end for EnerPHit certification process. |
| Architect or retrofit designer | £6,000–£25,000+ | Depends on scope. EnerPHit certification needs detailed thermal bridge and junction design. |
| Retrofit Coordinator (PAS 2035 schemes) | £1,500–£4,500 | Mandatory for grant-funded retrofit. Different from architect. See our PAS 2035 guide. |
| Structural engineer (if openings change) | £800–£2,500 | For new openings, lintels, beam replacements. |
| Project management | 8–12% of construction value | Either a fee charged by the main contractor or an external PM. |
| Scaffolding | £3,000–£8,000 | For EWI works, roof works, gable ends. Often shared across trades. |
| Building Control fees | £400–£1,200 | Local authority fees on regulated work. |
| Listed building / conservation area consent | £500–£2,500 | Where required; can extend project timeline by 8–16 weeks. |
| Decants (moving out during works) | £0–£30,000 | For 4–8 month deep retrofit. Often hidden because the homeowner "lives through it". |
| Contingency | 10–15% of total | Higher for traditional buildings and unknown ground conditions. |
| VAT | 0%, 5% or 20% | Reduced 5% rate often applies to qualifying energy-saving materials — depends on the work and the supplier. Check with your accountant. |
The "you live through it" bit deserves a sentence. On a deep retrofit that includes IWI, MVHR ductwork installation, window replacement and floor work, you cannot reasonably continue to live in the property. Rental for four to six months of decant accommodation in our region runs £1,200–£2,000/month plus storage. If you are pricing a retrofit and the family lives there with two children and pets, treat the decant cost as a real line item.
Three case studies with totals
Three real housing types we cost regularly. Pricing is 2026 in the West Midlands / Welsh borders / South Shropshire region. Includes labour, materials, soft costs and contingency. Excludes heat pump grant (shown net separately).
Case Study A — Victorian terrace (Hereford), 90 m² GIA
Three-bed mid-terrace, solid 9-inch brick walls, suspended timber ground floor, slate roof with empty loft, original single-glazed sash windows, gas combi boiler. EPC current band E.
Scope: wood fibre IWI to all external walls, warm roof insulation, floor insulation between joists, slim double glazing in original sashes (×7), MVHR ducted through floor zones, ASHP replacing combi, full airtightness package, redecoration.
| Element | Cost |
|---|---|
| Hygrothermal assessment + PHPP modelling | £4,500 |
| IWI — wood fibre 100mm + lime plaster (~95 m² × £215/m²) | £20,400 |
| Loft + warm roof insulation, airtight ceiling layer | £6,500 |
| Floor insulation between joists (~40 m² × £55/m²) | £2,200 |
| Slim double glazing in original sashes (×7 × £550) | £3,850 |
| Front and back doors (PH-certified composite ×2) | £4,500 |
| Airtightness work + 2× blower door tests | £2,800 |
| MVHR system (small, terraced) | £6,800 |
| ASHP 7 kW installed | £11,500 |
| Hot water cylinder + radiator resizing | £4,500 |
| Scaffolding | £3,000 |
| Project management (10% of construction) | £6,300 |
| Building Control + design fees | £3,200 |
| Contingency (12%) | £9,000 |
| Total before grant | £89,050 |
| Less BUS grant | −£7,500 |
| Net cost | £81,550 |
| £/m² (GIA) | £906/m² |
Result: EPC band C/B, indicative space heating demand 35–45 kWh/m²/yr, comfort transformation, gas off.
Case Study B — 1960s suburban semi (Worcester), 110 m² GIA
Three-bed semi-detached, cavity blockwork walls (post-1925, fillable), solid concrete ground floor, tiled roof with 100mm existing loft insulation, 1990s uPVC double glazing, gas combi boiler (8 years old).
Scope: cavity fill + EWI to all external walls, warm roof / loft top-up, retain solid floor, full window replacement (triple glazed uPVC), front and back doors, MVHR, ASHP, full airtightness package.
| Element | Cost |
|---|---|
| PHPP modelling | £3,500 |
| Cavity wall fill | £1,800 |
| EWI — 100mm PIR + render (~130 m² × £175/m²) | £22,750 |
| Loft top-up to 400mm + airtight ceiling | £3,500 |
| Solid floor — overlay insulation 80mm (~50 m² × £105/m²) | £5,250 |
| Window replacement — triple-glazed uPVC (~16 m² × £750/m²) | £12,000 |
| Doors (×2) | £4,500 |
| Airtightness + blower door tests | £2,800 |
| MVHR system | £8,500 |
| ASHP 9 kW installed | £12,500 |
| Hot water cylinder + radiator resizing | £4,500 |
| Scaffolding | £4,500 |
| Project management (10%) | £7,800 |
| Building Control + design fees | £3,000 |
| Contingency (12%) | £11,200 |
| Total before grant | £108,100 |
| Less BUS grant | −£7,500 |
| Net cost | £100,600 |
| £/m² (GIA) | £914/m² |
Result: EPC band A/B, indicative space heating demand 25–35 kWh/m²/yr, low summer overheating risk, full smart-readiness if solar+battery added (~£10,000 additional).
Case Study C — Pre-1900 stone cottage (Welsh borders), 100 m² GIA
Two-storey detached stone cottage, ~600mm solid stone walls bedded in lime mortar, suspended timber ground floor, slate roof, original timber casements with single glazing, oil boiler (rural — no gas mains). EPC current band F.
Scope: external moisture remediation (pointing, gutters, drainage), wood fibre IWI with lime plaster finish (per our stone cottage article), warm roof, floor insulation, slim DG in original frames, cMEV, ASHP at low flow temperature, larger emitters.
| Element | Cost |
|---|---|
| Hygrothermal assessment + PHPP modelling + heritage significance assessment | £5,500 |
| External moisture remediation | £4,000 |
| IWI — wood fibre 100mm + lime plaster (~120 m² × £225/m²) | £27,000 |
| Warm roof insulation + airtight ceiling | £6,800 |
| Floor insulation between joists (~50 m² × £55/m²) | £2,750 |
| Slim double glazing in original frames (×8 × £600) | £4,800 |
| Front + back doors (timber, traditional spec) | £4,500 |
| Airtightness + blower door tests | £3,000 |
| cMEV system (MVHR not practical here) | £3,800 |
| ASHP 9 kW installed | £13,500 |
| Larger radiators / UFH in kitchen + hot water cylinder | £6,500 |
| Scaffolding | £4,000 |
| Project management (12%) | £10,800 |
| Building Control + design fees | £3,500 |
| Contingency (15% — traditional building) | £15,700 |
| Total before grant | £116,150 |
| Less BUS grant | −£7,500 |
| Net cost | £108,650 |
| £/m² (GIA) | £1,087/m² |
Result: EPC band B (with traditional building "Special Considerations" applied — see our PAS 2035 article), space heating demand 40–55 kWh/m²/yr, building dries naturally, oil off, electrified.
Where the EU supply chain saves money
One of the genuine cost-saving moves available to a UK retrofit project is sourcing materials directly from established European manufacturers rather than through the UK trade chain. The reason is simple: most premium retrofit materials in the UK (wood fibre boards, PH-certified windows, MVHR units, lime products, breather membranes) originate in mainland Europe, and the UK trade chain typically adds 25–35% over the manufacturer's wholesale price by the time the material reaches a builder's merchant.
For a single deep retrofit project the materials package usually runs £25,000–£50,000 of the total. A direct-from-Europe supply can typically save 20–30% on that figure, with delivery to the UK site in 5–10 working days for most product categories. On Case Study C above, that is the difference between a £108,000 and a £100,000 project. On a larger detached or a small portfolio it scales accordingly.
The constraint is logistics and order timing — direct EU supply works best when the project programme is settled enough to commit to a delivery date 2–3 weeks ahead. For ad-hoc top-ups or last-minute substitutions, UK merchant supply is more practical. Many of our projects use a hybrid model: large structural orders (insulation, windows, MVHR) direct from Europe; consumables and finishing materials through local UK suppliers. See our materials catalogue for the routinely-stocked categories.
Grants and incentives — the 2026 landscape
The grant landscape changed materially in early 2026 with the Warm Homes Plan (21 January 2026) and the announced wind-down of ECO4. Here is what is actually available for private homeowners now:
| Scheme | What it covers | Status |
|---|---|---|
| Boiler Upgrade Scheme (BUS) | £7,500 toward an air source heat pump (£6,000 for biomass in some areas) | Active. Most reliable single-measure grant in 2026. |
| Warm Homes Local Grant (WHLG) | Up to £15,000 for fabric & renewables plus £15,000 for low-carbon heating = combined max £30,000 per property in eligible low-income areas | Active. Delivered by local authorities. Eligibility tied to property and household income. |
| ECO4 | Energy Company Obligation scheme for low-income / vulnerable households | Extended to 31 December 2026 (extension confirmed 23 January 2026). No ECO5 / successor "supplier obligation" — Warm Homes Plan replaces the framework with grant-funded delivery from 2027. |
| Reduced VAT on energy-saving materials | 0% or 5% VAT on qualifying materials (heat pumps, insulation, solar PV, etc.) | Active, with conditions. Check with your accountant for your specific project. |
| Home Upgrade Grant (HUG) | Off-grid low-income households, up to £15,000 | Continues in 2026; tighter eligibility. |
| GBIS (Great British Insulation Scheme) | Single-measure insulation for EPC D–G households | Closed 31 March 2026 as scheduled — no direct successor. |
For most private deep retrofit projects in our region, the realistic grant package is BUS £7,500 plus reduced VAT on materials. WHLG and HUG are means-tested and largely targeted at fuel poverty rather than middle-income retrofit. None of the major grants currently subsidise fabric upgrade on owner-occupied properties at meaningful scale.
What I'd do with £100k vs £200k
If a homeowner came to me with a 100 m² semi or terrace, gas combi, EPC D, and £100k of budget, here is the order I would spend it in:
- £3,000: PHPP-based pre-assessment and design.
- £8,000: Loft, floor, easy windows, draught proofing, airtightness work. Biggest comfort gain per pound.
- £25,000: Walls — IWI or EWI depending on building type.
- £15,000: Window upgrade — full replacement on modern construction, slim DG in original frames on heritage.
- £8,000: MVHR or cMEV.
- £5,000: ASHP net of BUS, with hot water cylinder and emitter resizing.
- £12,000: Soft costs — PM, scaffolding, Building Control, contingency.
- £24,000: Remaining contingency, redecoration, finishes, "while we're at it" extras.
£100k buys a properly done deep retrofit on a small-to-medium property, with EPC A/B outcome and substantial comfort improvement.
At £200k, on the same property:
- All of the above to higher specification (PH-certified windows, larger MVHR with summer bypass, thicker insulation).
- Solar PV + battery (~£12,000) for energy independence and Smart Readiness metric compliance.
- Internal layout improvements alongside the fabric work (single-story extension, kitchen remodel, opened-up living space).
- Formal EnerPHit certification process (~£8,000 additional for certifier, audit, on-site testing).
- Higher-end finishes, restored original features, careful timeline management.
£200k buys an EnerPHit-grade outcome with a properly remodelled house. Anything significantly above that on a typical UK 100 m² property is usually paying for aesthetic upgrades, not energy performance.
Where APMBuild fits
We do paid PHPP pre-assessments as the front door for most deep-retrofit projects. The deliverable is an engineered cost plan — element-by-element pricing against your specific building, U-value targets for each element, sequence of works, and a sanity-checked total. From there we either deliver the work ourselves (in Herefordshire, Worcestershire, Gloucestershire, Shropshire and the Welsh borders) or hand the assessment to a contractor of your choice.
For projects outside our site-delivery radius, we supply the materials package UK-wide through our direct EU supply chain — typically saving 20–30% on the materials portion of the budget compared with standard UK trade. The pre-assessment is portable. The materials supply is portable. The site work has to be done by someone in driving distance.
Deep retrofit cost — frequently asked questions
Why is your deep retrofit £/m² higher than the £800–£1,000/m² figure quoted elsewhere?
The lower figures usually come from social housing programmes (scale economies), exclude soft costs, exclude VAT, exclude contingency, or pre-date the construction cost inflation of 2022–2026. The £800–£1,500/m² range for properly delivered private deep retrofit in 2026, with soft costs and contingency included, is consistent with the Passivhaus Trust's January 2026 Position Paper and AtkinsRéalis cost comparison.
What does EnerPHit certification add to the cost?
Roughly 30–50% on top of an equivalent uncertified deep retrofit, primarily through tighter component specification (certified windows, MVHR, doors), more design-stage modelling, on-site testing and the certification audit fees. Whether it is worth it depends on your reasons for retrofitting — comfort and energy performance can be achieved without the certificate; resale value, planning credibility and quality assurance are the certificate's main returns.
Can I retrofit incrementally to spread the cost?
Yes, and the Passive House Institute has a formal pre-certification route for phased EnerPHit retrofit precisely for this reason. The key is to design the end-state first (with a PHPP model) and then phase the works so each step is consistent with the eventual specification. The wrong way to phase: install windows and a heat pump now, then think about insulation later — sizing will be wrong on both.
How long does a deep retrofit take?
For a typical 100 m² property with full decant, around 16–24 weeks on site, plus 8–16 weeks of design and procurement beforehand. For listed buildings or those in conservation areas, add 8–16 weeks for consent. Living through the works extends the programme by 20–40% and is rarely practical for a true deep retrofit.
What is the payback period?
Pure energy-bill payback is rarely under 15 years for a private deep retrofit and can be much longer. The honest answer is that deep retrofit pays back in comfort, indoor air quality, future-proofing against gas price volatility and 2030 MEES rules, building fabric longevity, and resale value — not in monthly bill savings alone. If pure financial payback is the goal, light retrofit (loft, draught proofing, cavity fill) has much faster payback at much smaller scope.
Should I do this myself as an owner-builder?
You can. The risk is in the details — airtightness work, thermal bridge detailing, MVHR commissioning, and getting the work signed off correctly. These are where deep retrofits fail. If you self-build, hire the design (PHPP), commission the testing (blower door, airtightness), and only self-manage the trades you understand. Do not self-manage MVHR, ASHP installation or thermal bridge detailing unless you have specific training.
What is the single most under-budgeted item?
Contingency. Then soft costs (design, PM, scaffolding). Then decants if you have a family living there. The £/m² number on the headline does not include these unless you specifically ask. Always add at least 12% to whatever total you have been quoted, and ask explicitly which line items are inside or outside the figure.