Energy retrofit: cost by measure, the grants available and the return on investment

Energy retrofit can be done in two ways: through successive measures, one at a time over several years, or as a whole-building renovation carrying out every measure in a single operation to reach a low-energy standard. The two approaches differ in energy performance, in cost and in entitlement to grants.

• Measure by measure is cheaper in the short term and more accessible. But it does not reach the low-energy renovation standard below 80 kWh of primary energy per m² per year, which is the threshold for the best grants. It also carries a risk of defects, residual thermal bridges, condensation problems, if the measures are carried out in the wrong order.
• Whole-building renovation costs more up front, 610 to 1,220 €/m² of habitable area according to the starting point, but it is the only approach that reaches the low-energy standard, secures the maximum grants and avoids the pathologies of partial intervention. It is the approach systematically recommended by the national energy agency and by retrofit operators.

Why the order of measures matters

When retrofitting measure by measure, the order is not neutral. The recommended sequence is: first the envelope, roof, wall and floor insulation, then air-tightness, then ventilation, then the heating system. Reversing it, by replacing the boiler before insulating, leads to a heating system oversized for the real needs of the renovated building.

A building whose boiler is replaced before insulation ends up with equipment too powerful once the thermal work is done, a wasted investment of 1,000 to 3,000 €.

Measure	Cost excl. VAT, apartments	Estimated energy saving	Typical rating improvement	Gross payback, energy alone
External wall insulation, 140 mm mineral wool	120 – 200 €/m² of façade	15 – 25 %	1 – 2 grades	15 – 30 years
External insulation with rainscreen cladding	180 – 290 €/m² of façade	15 – 25 %	1 – 2 grades	20 – 35 years
Internal wall lining	40 – 80 €/m² of wall	8 – 15 %	1 grade	20 – 35 years
Loft insulation	25 – 55 €/m² of loft	20 – 30 %	1 – 2 grades	5 – 12 years
Flat roof insulation	80 – 150 €/m² of roof	10 – 20 %	1 grade	15 – 25 years
Ground floor insulation	35 – 70 €/m² of floor	5 – 12 %	0.5 – 1 grade	20 – 35 years
Window replacement, double to triple glazing	400 – 750 € per window	5 – 10 %	0.5 grade	25 – 45 years
Communal heating to air-source heat pump	4,080 – 9,200 € per dwelling	30 – 50 %	1 – 3 grades	10 – 20 years
Extract ventilation to heat recovery	820 – 1,840 € per dwelling	5 – 15 %	0.5 – 1 grade	12 – 22 years
WHOLE-BUILDING LOW-ENERGY RENOVATION	610 – 1,220 €/m² habitable	70 – 85 %	3 – 4 grades	20 – 40 years

Note: the paybacks shown are calculated on the energy saving alone, without grants or the increase in property value. With grants the net cost falls by 30 to 60 %, so the real payback is two to three times shorter. Whole-building renovation has a long gross payback of 20 to 40 years but a net payback after grants of 10 to 20 years, and generates an increase in property value of 10 to 25 %.

The ecosystem of retrofit grants is complex and changes frequently in both amounts and conditions. The table sets out the structuring schemes at the time of writing. For exact, current amounts, consult the official national retrofit service.

Scheme	Indicative amount or ceiling	Beneficiaries	Principal conditions
The national retrofit grant, supported route	20,000 – 70,000 € according to income	Owner-occupiers and landlords	At least a two-grade improvement, professional support mandatory
The national retrofit grant, single measures	500 – 15,000 € according to measure and income	Owners, with no rating-gain condition	For the lowest-income households, on a list of eligible measures
Energy saving certificates	Variable by measure and supplier	All owners, through energy suppliers	Payments are negotiable; compare offers
Reduced VAT at 5.5 %	Against the standard 20 %	All owners on eligible work	Work improving energy performance
Zero-interest retrofit loan	Up to 50,000 € at 0 %	Owner-occupiers and landlords	Income conditions; can be combined with the grant
The housing agency scheme	35 – 50 % of the works	Modest and very modest owners	At least a 35 % cut in primary energy use
Local authority grants	Variable by area	Owners, under local rules	Consult the local housing advice service; can be combined
The green fund for public bodies	30 – 40 % of the works	Local authorities and groupings	Energy retrofit of public buildings

Combining grants: the 100 % rule

Grants can be combined up to 100 % of the cost of the works. That ceiling is rarely reached in practice, but the funding structure must be carefully orchestrated before the contracts are signed.

For a whole-building retrofit of an apartment block, the effective grant rate can reach 40 to 60 % of the cost excluding VAT once the national grant, energy saving certificates and reduced VAT are combined. That rate justifies appointing a specialist retrofit adviser, whose own cost is itself grant-eligible.

The return depends on three parameters: the starting point in energy rating, the target level of renovation, and the grants secured. The table sets out that analysis for residential apartments.

Parameter	Worst-rated dwelling	Mid-rated dwelling	Already-performing dwelling
Consumption before, kWh primary/m²/year	350 – 500	180 – 250	70 – 120
Consumption after low-energy renovation	Below 80	Below 80	Below 80
Renovation cost excl. VAT, €/m² habitable	700 – 1,200	400 – 700	200 – 400
Estimated grants and certificates	260 – 510 €/m²	150 – 310 €/m²	100 – 200 €/m²
Net cost after grants, €/m² habitable	300 – 700	200 – 450	100 – 250
Annual heating saving, €/m²/year	40 – 80 €	20 – 45 €	10 – 25 €
Gross payback, energy alone	7 – 18 years	7 – 22 years	6 – 25 years
Estimated green value uplift	+ 10 – 25 % of market value	+ 5 – 12 %	Small, already efficient
Regulatory obligation	Work required before 2025–2034 according to grade	Work advisable	Compliant

The conclusion is structuring: retrofit pays best on the worst-performing dwellings, both because the energy savings are greatest and the grants highest, and because the regulatory constraint, the ban on letting the worst-rated dwellings from 2025, extending to the next grade in 2028, makes the work unavoidable.

Energy retrofit is not only an energy investment, it is a property investment. Market studies converge in showing that energy performance is now a price criterion for buyers and tenants alike.

• Housing: a dwelling rated A or B sells on average 10 to 25 % higher than an identical one rated D or E in the same area. The gap widens as the market tightens.
• Offices: a highly certified building lets 8 to 15 % higher than an equivalent uncertified one and has a structurally lower vacancy rate.
• Logistics warehouses: certification and energy performance are now selection criteria for institutional occupiers; an uncertified warehouse loses liquidity on the investment market.

That uplift belongs in the return analysis; it can shorten the payback period by 5 to 10 years according to the market and the asset type.

The construction economist works at two levels. Early on, they produce an estimate of the works to confirm the economic feasibility of the operation and identify the priority measures. At project stage they price the packages specific to the retrofit, insulation, mechanical services, joinery, and coordinate the interfaces with the existing fabric, a complexity often under-estimated.

The economist can also produce a whole-life analysis bringing together the construction cost, the grants available, the energy savings discounted over 20 years and the estimated increase in property value, the most complete decision tool for an owner or a landlord.

You have better things to do. Submit your energy retrofit project on quostra.com; estimate with grant and return analysis within 72 working hours.

Retrofit measure by measure costs from 25 €/m² for loft insulation to 9,200 € a dwelling for a heat pump, with energy savings of 5 to 50 % according to the measure. Whole-building low-energy renovation at 610 to 1,220 €/m² of habitable area is the only approach that reaches the maximum grants and eliminates the risk of defects from partial intervention. Combined support can cover 40 to 60 % of the cost of the works on the worst-performing buildings. Green value, a 10 to 25 % uplift for an A or B rating over D or E, is an economic argument often forgotten, and one that significantly shortens the real payback period.

Reference basis of the figures

These bands are orders of magnitude for framing, and their reference market is the Paris region. They serve to place a budget at the earliest stages and to compare building types with one another. They replace neither a tender exercise nor an estimate prepared on drawings, and they are not a record of prices actually charged.

The ratios per square metre and per item on this page are stated in January 2026 values. They were updated from January 2025 values, the basis adopted for the whole cocoon, using the BT01 all-trades index published monthly by INSEE on its 2010 base: 132.0 in January 2025, 134.7 in January 2026, a rise of about 2 %.

The global amounts quoted as examples, and any rents, charges or receipts expressed per year or per night, remain on their own basis: a building cost index does not apply to them.

To bring the ratios forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7). The index has kept rising since: it stood at 138,3 in June 2026, the last value published when this page was checked, that is 2,7 % above the reference base. BT01 measures contractors' input costs, wages and social charges, materials, plant and energy, not the prices actually tendered.