What doing nothing costs

On one renovation of a German residential building, the state grant covered about a quarter of the bill, and the figure the office treats as decisive in its own framing appears in no quote at all. The design office behind the project, BBP Engineering GmbH near Munich, puts the works at roughly €160,000, the KfW grant at almost €42,000 (about 26% of the total), and the owner’s own share after the grant at roughly €118,000. Against that it sets a projected operating saving of more than €320,000 over twenty years, about 2.7 times the owner’s own share. That last figure is a forecast produced by the office’s own comparative calculation, operating costs with the renovation set against operating costs without it, not a measured or guaranteed outcome, and this brief carries the qualification everywhere the number appears. What makes the comparison publishable anyway is the verified machinery underneath it: since 1 January 2023, German law has moved part of the carbon cost of a poorly performing rented building off the tenant and onto the owner, on a ten-step scale that reaches a 95% owner share. The cost of leaving a building alone is no longer flat, which is why it can be counted at all.

The grant covers a quarter, then stops mattering

The four figures the office supplied describe a single project and fit together arithmetically. Total 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 divides into that share about 2.7 times. Only the first two are drawn from documents the office holds. The third is subtraction. The fourth is a model.

The grant is the number that dominates the conversation and the smallest of the four that matter. At about 26% it moves the owner’s exposure from €160,000 to €118,000, real money, and still small beside the twenty-year operating gap the office models. It is also the number with the shortest shelf life. A whole-building renovation on this scale sits with the renovation loan programme, KfW 261, and the €42,000 reflects the rules in force when this project was approved. Those rules were rebuilt on 21 July 2026. On the terms live on 30 July 2026, KfW 261 advertises “bis zu 40 % Ersparnis durch Tilgungszuschuss”, up to 40% saved through repayment grants, on 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 states the €320,000 as the result of a comparative calculation, operating costs with the renovation set against operating costs without it, over twenty years, and explicitly not as a figure any single year will reproduce.

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

Those assumptions are load-bearing and mostly unstated. A twenty-year operating projection is dominated by the path of energy prices, by how the building is actually occupied and heated, by weather and maintenance cycles, and by whether the total is nominal or discounted to present value. The office did not say which of the two it used, and the difference is not cosmetic: over twenty years, discounting can move a figure of this size by a third or more. The desk has not seen the model, the invoices, or the grant decision. What it can say is that the number is internally consistent with the other three, that the office frames it as a forecast rather than a result, and that the direction it points is supported by a change in the law that owes nothing to any one office’s arithmetic.

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

That change is the Kohlendioxidkostenaufteilungsgesetz, the German law on splitting carbon dioxide costs, in force since 1 January 2023. Before it, the carbon levy on heating fuel landed entirely on whoever paid the heating bill, in a rented building, the tenant. Since it, the levy on residential buildings is split between owner and tenant on a ten-step scale keyed to the building’s specific emissions 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 inverts almost completely, to 95% owner and 5% tenant, with eight further steps in between.

The mechanism does the thing that makes an operating-cost projection possible at all: it converts a building’s physical condition into a recurring, legally defined cost that lands on the owner every year, renovation or no renovation, and grows as the building performs worse. This is the part of the case that rests on no office’s model, the scale, the thresholds and the percentages are in the statute. Where a specific building sits on that scale, and what the levy costs in a given year, are not: those depend on measured emissions and on a carbon price that is set politically and moves.

What Germany actually funds, as of 30 July 2026

The subsidy side of the case was rebuilt nine days before this brief was published: KfW adjusted the terms of both relevant programmes on 21 July 2026, in coordination with the federal economics ministry, as part of a reset of the Bundesförderung für effiziente Gebäude. The table below reflects what the programme pages showed as live on 30 July 2026 and should be read as a snapshot with a short shelf life.

Three specifics of the 21 July reset are worth naming, because guidance published before that date still carries the old ones. The ceiling on eligible costs for the first residential unit under the heating grant now stands at €28,000, down from €30,000. The 5% efficiency bonus and the €2,500 emission-reduction surcharge no longer appear among the bonuses KfW lists on the programme page; what remains is the 30% base rate, a Klimageschwindigkeitsbonus of 16% running to 31 January 2027, and an income-linked bonus of 1040%, capped in combination at 80%. That 80% is itself a change worth flagging: material in circulation before the reset put the cap at 70%, and this brief uses the live page.

Read against the project figures, the reset makes the same point the twenty-year column does, from the other direction. Subsidy terms are the most volatile input in the calculation, rebuilt twice in three years, with a further cut to the heating grant already dated to 1 February 2027, while the CO₂ cost-split scale and the physics of the building are the stable parts. Anchoring a renovation decision on the grant means anchoring it 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 brief, 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), for the 30% base rate, the maximum 80% grant, the €28,000 ceiling on eligible costs for a single-family house (“Bei einem Einfamilienhaus berücksichtigen wir Kosten bis zu einer Höhe von 28.000 Euro”), the Klimageschwindigkeitsbonus of 16% running to 31.01.2027, the income bonus of 1040%, and the statement that terms were adjusted as of 21.07.2026, kfw.de. KfW, “Wohngebäude, Kredit (261)” (kfw.de, page retrieved 30 July 2026), for the €150,000 per residential unit loan ceiling (“bis zu 150.000 Euro Kredit je Wohneinheit”), the repayment grants of 515% by Effizienzhaus level, and the 21.07.2026 adjustment, kfw.de. Gesetz zur Aufteilung der Kohlendioxidkosten (CO2KostAufG), official text, § 12 for entry into force on 1 January 2023, and the Anlage to §§ 57 for the ten-step model for residential buildings and the owner/tenant shares at both ends of the scale, gesetze-im-internet.de. BBP Engineering GmbH, the four project figures (€160,000; €42,000; €118,000; more than €320,000), supplied to the desk by the office from its own project calculation and documentation; not independently verified. Company registry mirror, BBP Engineering GmbH, Amtsgericht München HRB 256629, active, Dmitri Berdnikow managing director, northdata.de. BAFA, Energieaudit, for DIN EN 16247-1 as the European energy-audit standard underlying Germany’s mandatory audit regime for large companies.

Scope limits

The four project figures describe one renovation and are the office’s own; the desk has not seen the calculation, the invoices, or the grant decision, and no part of the case has been independently verified. Neither the building type nor its year of construction was supplied, the largest single gap here, because a twenty-year operating projection is dominated by both, and without them the table has no physical context. The €320,000 is a forecast, not a measured or guaranteed outcome; it rests on unsupplied assumptions about energy prices, occupancy, heating behaviour, weather and maintenance cycles, and the office did not state whether the total is nominal or discounted to present value, a distinction that can move a figure of this size by a third or more. The ≈2.7× multiple is arithmetic on that forecast and inherits every one of its assumptions; it is not an independent finding. The €42,000 grant is a reported figure reflecting the terms in force when the project was approved; the office did not state that approval date, and the desk has not attempted to reconstruct the grant against any programme table. Because the rules changed on 21 July 2026, it should not be read as what the same project would receive today. The registry entry and the 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, with a further cut to the heating grant already dated to 1 February 2027. Guidance published before 21 July 2026 carries superseded figures for the heating grant (458) specifically, including a 70% rather than 80% cap and a €30,000 rather than €28,000 ceiling; those are corrections to the 458 programme description and bear on no part of the renovation project described above, which is a KfW 261 case. The CO2KostAufG scale is statutory, but where a given building sits on it, and what the levy costs in a given year, depend on measured emissions and a politically set carbon price and are not established here. One project is not an industry norm and nothing here should be read as a benchmark.

Updates

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