What doing nothing costs

On one renovation of a German residential building, the state grant covered about a quarter of the bill. Yet the figure the office treats as decisive appears in no quote at all. BBP Engineering GmbH near Munich puts the works at roughly €160,000 and the KfW grant at almost €42,000, about 26% of the total. That leaves the owner with a share of roughly €118,000.

The office sets against this a projected operating saving of more than €320,000 over twenty years, about 2.7 times the owner’s share. This is the office’s forecast, based on a comparison of operating costs with and without the renovation. It is not a measured or guaranteed outcome, and that qualification appears everywhere the number is used.

The comparison still rests on a verified mechanism. Since 1 January 2023, German law has shifted part of a poorly performing rented building’s carbon cost from the tenant to the owner. The ten-step scale reaches a 95% owner share. Leaving a building unchanged no longer has a flat cost, which is why that cost can be modelled.

The grant covers a quarter, then stops mattering

The four figures supplied by the office describe one project and fit together arithmetically. Works of about €160,000, less a KfW grant of almost €42,000, leave an owner’s share of about €118,000. The projected saving of more than €320,000 is about 2.7 times that share. Only the first two figures come from documents held by the office. The third is subtraction. The fourth is a model.

The grant dominates the conversation, yet it is the smallest of the four figures that matter. At about 26%, it moves the owner’s exposure from €160,000 to €118,000. That is real money, but still small beside the twenty-year operating gap modelled by the office.

The grant also has the shortest shelf life. A whole-building renovation on this scale falls under the KfW 261 renovation loan programme. The €42,000 reflects the rules in force when this project was approved. Those rules were rebuilt on 21 July 2026.

Under the terms live on 30 July 2026, KfW 261 advertises a saving of up to 40% through a repayment grant. The German line on the page is “bis zu 40 % Ersparnis durch Tilgungszuschuss.” That applies to loans of up to €150,000 per residential unit. The same building, submitted today, would be calculated against a different table.

The number that decides the case is a forecast

Everything that makes the €320,000 interesting also makes it unverifiable from outside. It compares two futures: one in which the building is renovated and one in which it is not. The first has invoices attached. The second does not and never will, because it does not happen. No audit can settle it; the most anyone can do is inspect the assumptions.

The office presents the €320,000 as the result of a comparative calculation over twenty years. It compares operating costs with the renovation against costs without it. The office explicitly says that no single year will reproduce this figure.

Dmitri Berdnikow, Managing Director, BBP Engineering GmbH; position as supplied to the desk, reported rather than quoted verbatim

Those assumptions carry the whole calculation and are mostly unstated. Energy prices, occupancy, heating, weather and maintenance cycles all shape a twenty-year operating forecast. So does the choice between a nominal total and one discounted to present value.

The office did not say which approach it used. The difference is substantial: over twenty years, discounting can move a figure of this size by a third or more. We have not seen the model, invoices or grant decision.

We can say that the number is internally consistent with the other three. The office presents it as a forecast, not a result. A change in the law supports the direction of the forecast independently of the office’s arithmetic.

Since 2023 the owner carries part of the tenants’ carbon bill

That change is the Kohlendioxidkostenaufteilungsgesetz, Germany’s law on splitting carbon dioxide costs, in force since 1 January 2023. Previously, the carbon levy on heating fuel fell entirely on whoever paid the heating bill. In a rented building, that was the tenant.

The law now splits the levy between owner and tenant on a ten-step scale tied to the building’s specific emissions. Those emissions are measured in kilograms of CO₂ per square metre per year. Below 12 kg, the tenant still pays 100% and the owner nothing. At 52 kg and above, the split becomes 95% owner and 5% tenant, with eight steps between.

This mechanism turns a building’s physical condition into a recurring, legally defined cost for the owner. The cost applies every year, whether or not the building is renovated, and grows as its performance worsens. No office model determines the scale, thresholds or percentages; they are written into the law.

The law does not establish where a specific building sits on the scale or what the levy costs in a given year. Those figures depend on measured emissions and on a politically set carbon price that changes.

What Germany actually funds, as of 30 July 2026

The subsidy rules changed nine days before this review was published. KfW adjusted both relevant programmes on 21 July 2026 in coordination with the federal economics ministry. The changes formed part of a reset of the Bundesförderung für effiziente Gebäude.

The table reflects what the programme pages showed as live on 30 July 2026. It is a snapshot with a short shelf life.

Three details of the 21 July reset matter because older guidance still carries the previous figures. The ceiling for the first residential unit under the heating grant is now €28,000, down from €30,000.

The 5% efficiency bonus and €2,500 emission-reduction surcharge no longer appear on KfW’s programme page. The page still lists a 30% base rate and a 16% climate-speed bonus (Klimageschwindigkeitsbonus) running to 31 January 2027. It also lists an income-linked bonus of 10-40%, with a combined cap of 80%.

That 80% cap is itself a change. Material circulated before the reset gave a 70% cap, while this review uses the live page.

Read against the project figures, the reset makes the same point as the twenty-year column from the other direction. Subsidy terms are the calculation’s most volatile input. They were rebuilt twice in three years, and another heating-grant cut is already dated to 1 February 2027.

The CO₂ cost-split scale and the building’s physics are more stable. Anchoring a renovation decision on the grant means relying on the one variable guaranteed to change.

Practitioners quoted in our analysis supply domain expertise, not the underlying data. The data is assembled by the editorial desk. Contributors do not see or approve the conclusions drawn from it. This is a data review, not engineering, tax or financial advice. Subsidy terms, eligibility rules and carbon prices change; anyone assessing a specific building should consult current KfW and BAFA guidance and a qualified adviser.

Methodology

Sources

KfW, “Heizungsförderung für Privatpersonen, Wohngebäude (458)” (kfw.de, page retrieved 30 July 2026). This page supports the 30% base rate, maximum 80% grant and €28,000 cap for eligible costs on a single-family house. It states: “Bei einem Einfamilienhaus berücksichtigen wir Kosten bis zu einer Höhe von 28.000 Euro.” That is the single-family cost cap. The same page supports the 16% climate-speed bonus through 31.01.2027. It also supports the 10-40% income bonus and the adjustment dated 21.07.2026. Source: kfw.de.

KfW, “Wohngebäude, Kredit (261)” (kfw.de, page retrieved 30 July 2026). This page supports the €150,000 loan ceiling per residential unit. The German wording is “bis zu 150.000 Euro Kredit je Wohneinheit.” The page also supports the 5-15% repayment grants by Effizienzhaus level. It records the 21.07.2026 adjustment. Source: kfw.de.

Gesetz zur Aufteilung der Kohlendioxidkosten (CO2KostAufG), official text. Section § 12 gives the entry into force on 1 January 2023. The Anlage to §§ 5-7 gives the ten-step residential model and the owner and tenant shares at both ends. Source: gesetze-im-internet.de.

BBP Engineering GmbH supplied four project figures from its own calculation and project documentation: €160,000, €42,000, €118,000 and more than €320,000. The figures were not independently verified.

The company registry mirror lists BBP Engineering GmbH under Amtsgericht München HRB 256629. It shows the company as active and names Dmitri Berdnikow as managing director. Source: northdata.de.

BAFA, Energieaudit, identifies DIN EN 16247-1 as the European energy-audit standard behind Germany’s mandatory audit regime for large companies.

Scope limits

The four project figures describe one renovation and come from the office. We have not seen the calculation, invoices or grant decision. No part of this case has been independently verified.

The office supplied neither the building type nor its year of construction. This is the largest gap because both strongly shape a twenty-year operating forecast. Without them, the table lacks physical context.

The €320,000 is a forecast, not a measured or guaranteed outcome. It rests on undisclosed assumptions about energy prices, occupancy, heating behaviour, weather and maintenance cycles. The office did not say whether the total is nominal or discounted to present value. That choice can move a figure of this size by a third or more.

The ≈2.7× multiple is arithmetic based on that forecast and inherits all of its assumptions. It is not an independent finding.

The €42,000 grant is a reported figure based on the terms in force when the project was approved. The office did not provide the approval date. We have not tried to reconstruct the grant from a programme table.

The rules changed on 21 July 2026, so the figure does not show what the same project would receive today. The registry entry and DIN EN 16247-1 reference describe the office, not this project.

KfW terms are reported as they stood on 30 July 2026, nine days after a scheduled reset. A further cut to the heating grant is already dated to 1 February 2027.

Guidance published before 21 July 2026 carries old figures for the heating grant (458). These include a 70% rather than 80% cap and a €30,000 rather than €28,000 ceiling. Those changes concern the 458 programme description, not the renovation above, which is a KfW 261 case.

The CO2KostAufG scale is set by law. This review does not establish where a building sits on it or what the levy costs in a given year. Those values depend on measured emissions and a politically set carbon price.

One project is not an industry norm and should not be read as a benchmark.

Updates

This review will be revised as new data is published. Corrections are handled under our corrections policy.