What "Energy Retrofitted" Really Means for a Building Portfolio

"Energy retrofitted" means the building envelope is insulated (roof, façade, basement ceiling), windows have been replaced and the heating system has been modernized, so the building meets the requirements of the Buildings Energy Act or, since July 2026, the Building Modernization Act (Gebäudemodernisierungsgesetz). What counts is the verifiable efficiency standard, not any single measure on its own.

For decision-makers and technical managers in the housing industry, that description alone rarely settles the question. Anyone trying to classify an entire portfolio needs clear criteria: which building components count, which KfW Effizienzhaus level is reached, and how the status can actually be proven.

Four factors decide whether a portfolio genuinely qualifies as energy retrofitted or has simply had a few isolated measures carried out:

What does "energy retrofitted" actually mean for an existing building?

A building is technically considered energy retrofitted once the envelope and the building services have been upgraded together to the point where they fall below statutory minimum requirements or meet a recognized funding standard. This obligation is triggered under Section 48 of the GEG whenever renovation work renews more than 10 percent of the surface area of a component such as the façade, roof or floor slab.

Since 29 July 2026, the Building Modernization Act (GModG) has replaced the previous GEG and shifted a few details along the way, most notably dropping the rigid 65 percent renewable-energy requirement for new heating systems in favor of a staggered ramp that starts at 10 percent from 2029 and reaches 60 percent from 2040. The underlying goal, a climate-neutral building stock by 2045, stays unchanged.

For the components affected, specific U-value limits apply once a renovation crosses the 10 percent threshold:

In practice, this means a fresh coat of façade paint or one replaced window does not make a building energy retrofitted, as long as the surface area involved stays below the statutory threshold.

Which components and measures count toward recognized retrofit criteria?

The recognized set of retrofit measures for existing buildings stays largely consistent across funding programs. Five components or trades sit at the center of it:

The shift on the heating side has picked up pace: the share of heat pumps in Germany's residential building stock has nearly doubled since 2019, reaching 4.3 percent in 2024, and by 2025 heat pumps already accounted for 48 percent of newly sold heating systems.

It's rare for all five measures to be implemented across an entire portfolio at once; more commonly, retrofitting happens in stages over several years. For a closer look at how individual measures can be staggered and what they cost across a whole portfolio, see our article on renovation versus operational optimization in multi-family buildings.

How do the KfW Effizienzhaus levels classify the retrofit standard?

KfW Effizienzhaus levels 40, 55, 70 and 85, plus the special Denkmal (listed building) tier, benchmark a retrofitted building's energy standard against a legally defined reference building under GEG standards. Two figures decide the classification: annual primary energy demand and the envelope's transmission heat loss (the heat lost through roof, walls and windows). An Effizienzhaus 55, for example, needs only 55 percent of the reference building's primary energy and reaches at most 70 percent of the transmission heat loss the reference building allows.

For listed or otherwise worth-preserving existing buildings, a simplified Effizienzhaus Denkmal tier applies: primary energy demand may run up to 160 percent of the reference value, and there is no fixed cap on transmission heat loss.

A full retrofit to KfW Effizienzhaus standard assesses the entire building, including all components and building services, as one package and is funded through a repayment subsidy. Individual measures such as roof insulation, a window replacement or a heating optimization instead run through the BEG EM program (BAFA's funding for individual measures), which starts with a 15 percent base subsidy and rises to 20 percent with an individual renovation roadmap.

This individual renovation roadmap (iSFP) is produced as part of subsidized energy consulting, for which 50 percent of the consultant's fee is covered, and it lays out the order in which measures pay off most for that specific portfolio.

Good to know: Some sources cite a minimum renewable-energy requirement of 55 percent for classifying KfW Effizienzhaus levels, others 65 percent. Because the BEG funding conditions changed several times during 2026, portfolio owners should always check the current KfW fact sheet for the applicable threshold rather than relying on a single quoted figure.

How do you prove a portfolio is energy retrofitted, and what does that mean for value, ESG and operating costs?

The official proof of a building's energy status is the energy performance certificate, which comes in two forms: a demand-based certificate, which calculates the standard mathematically and independently of actual occupant behavior, or a consumption-based certificate, based on real usage data from recent years. Both versions are valid for ten years and, according to the law, serve purely as information and a rough basis for comparing buildings.

From 1 January 2027, the GModG tightens the requirements for new certificates: they will need to break down consumption by energy source in more detail, and the digital energy performance certificate becomes the standard format. Since May 2026, an EU-wide, unified energy efficiency scale from A to G has also replaced the previous German scale of A+ to H, so buildings can be compared across national borders.

For portfolio owners, this certificate is more than a formality. A documented retrofit standard feeds into ESG assessments such as the Carbon Risk Real Estate Monitor (CRREM), which compares a building's carbon and energy intensity against a science-based decarbonization pathway and is used, among other things, in the GRESB rating (a global ESG benchmark for real estate portfolios) to flag stranded-asset risk early, meaning a building that loses value because it falls short of climate-pathway alignment.

Context: In the commercial office market, a so-called "brown discount" of 10 to 20 percent is already being observed for energy-inefficient existing buildings. This market observation comes from the office property sector and cannot be applied to residential portfolios one-to-one, but it does point to the direction in which ESG assessment and property value move when retrofit proof is missing.

On the operating cost side, you feel the retrofitted standard directly: you purchase less energy because the envelope and building services lose less heat, and you pass on correspondingly less through the heating cost statement to tenants.

Why does real-world consumption deviate from the calculated retrofit standard?

An energy performance certificate or a KfW Effizienzhaus level describes a calculated standard. It doesn't yet say what actually happens inside the building. An ad-hoc short study by the German Environment Agency (UBA) shows that unretrofitted existing buildings consume roughly 30 percent less energy in real operation, on average, than their calculated figures suggest, the so-called prebound effect. In thoroughly retrofitted buildings with a low energy rating, though, this effect often flips: real consumption exceeds the calculated demand, known as the rebound effect.

Combined, this can leave the actual savings a retrofit delivers up to 50 percent lower on paper than originally planned.

Numbers from the research: An IWU study commissioned by the BBSR shows that calculated energy figures based on standardized usage profiles can run up to 61 percent above actual consumption levels in multi-family buildings. Even with adjusted, more realistic usage assumptions, a gap of roughly 34 percent remains.

Anyone managing several hundred or several thousand units notices this quickly: a building's paper standard says little about how much energy it actually consumes in daily operation. Only measured operating data shows whether a retrofit delivers on its promised savings, or whether the heating curve quietly eats back into the retrofitted building's potential during live operation, often amplified by actual occupant behavior.

How does KUGU VIS Betriebstransparenz show whether a retrofitted portfolio is really running efficiently?

This is exactly where KUGU VIS Betriebstransparenz comes in (VIS stands for Visuelles-Informationssystem, or visual information system): the platform makes visible how a building actually performs after a retrofit, using real consumption and system data from live operation. For portfolio owners managing multiple Effizienzhaus levels across their buildings, this creates an ongoing comparison between the documented standard and actual operation, going well beyond a one-time look at the energy performance certificate.

Telltale patterns, such as a heating curve still running at pre-retrofit levels despite new insulation, or a flow temperature the retrofitted building no longer needs, become visible early, before they show up in the next billing cycle or the next ESG report. For a closer look at the specific levers you can pull during ongoing operation, see our article on levers, costs and savings potential in heating optimization for existing buildings.

Where retrofitting and sector coupling intersect, for instance with heat pumps and dynamic electricity prices, our article on economically viable sector coupling in existing buildings puts the connections into context. The retrofit process doesn't end once an Effizienzhaus level is decided; operation keeps getting checked afterward.

From paper standard to verified operation

The criteria for "energy retrofitted" are more clearly regulated today than ever, from the GEG's 10 percent threshold to the KfW Effizienzhaus level. What these criteria don't show is how a building actually performs, year after year, once the retrofit is done, and that gap between definition and operation is ultimately what decides a portfolio's energy costs, ESG reporting and long-term value.

If you manage a portfolio with buildings at different retrofit stages, it helps to treat the energy performance certificate and the individual renovation roadmap as the first step in a longer process. The next useful move is to look at the measured operating data from buildings already retrofitted, to check whether the documented standard actually shows up in consumption and cost structure.

Frequently asked questions about energy retrofitted buildings

Is a building with a new heating system already energy retrofitted?

No, a new heating system alone does not make a building energy retrofitted. The term refers to the combination of an insulated envelope, new windows and modern building services working together. Only once several of these components jointly meet GEG or GModG requirements does a portfolio count as retrofitted in the strict sense.

How long is an energy performance certificate valid after a retrofit?

An energy performance certificate is valid for ten years, whether it's a demand-based or a consumption-based certificate. After a comprehensive retrofit, though, it's still worth reissuing earlier, because the old certificate won't reflect the improved standard and you won't be able to demonstrate the progress to investors or tenants.

Is retrofitting individual components enough to satisfy the GEG requirement?

Yes, the GEG or GModG requirement generally applies to individual components. As soon as more than 10 percent of the surface area of a component such as the roof, façade or floor slab is renewed, the applicable U-value limits must be met for that specific component, regardless of the rest of the building.

Does "energy retrofitted" status automatically affect property value?

No, not automatically, and not to the same degree in every market. The status increasingly influences valuation indirectly, though, through ESG metrics such as the CRREM decarbonization pathway and through lower operating costs. Without a documented retrofit standard, investors face a higher risk of classifying a building as a potential stranded asset.

When does an Effizienzhaus count as fully retrofitted for KfW funding purposes?

An Effizienzhaus counts as fully retrofitted once the entire building, including all components and building services, is assessed together and reaches one of the levels 40, 55, 70, 85 or Denkmal. Individual measures such as a window replacement or roof insulation are not enough for this classification on their own, even though they can be subsidized separately through BAFA's individual-measures funding.