Every Surface Counts: Why Renovation Today Must Do More Than Just Insulate
An expensive mistake is currently happening at many residential complexes: they are undergoing energy-efficiency renovations, but their energy strategy is not being rethought.
The facade is insulated. Windows are replaced. The heating system is modernized. Afterward, the building is considered "future-proof." But in reality, everything often remains the same: the house consumes energy without generating any itself.
Yet this is precisely where the great opportunity of modern renovation lies. Because while electricity prices rise, grids come under pressure, and operating costs increasingly become a social issue, vast surfaces on many buildings remain energetically unused: facades, balconies, carports, or terraces. These are surfaces that could have been doing much more than just enveloping a building for a long time now.
Energy-Efficiency Renovation: Repairs are no longer enough
Many renovations still follow an old principle: repair, renew, carry on.
However, the framework conditions have changed. Today, energy is no longer just an operating cost factor. It is increasingly becoming part of the building's infrastructure—just as natural as water, heat, or mobility. Anyone renovating a residential complex today is therefore not just deciding on insulation values or facade aesthetics. They are also deciding how a building will handle energy in the future:
- Where is electricity generated?
- When is it used?
- What happens to surpluses?
- How can heat, mobility, and common-area electricity be thought of together?
Precisely these questions are still being ignored in many renovation projects.
Photovoltaics in Multi-Family Housing: The Building Envelope as an Energy Surface
When people talk about photovoltaics, many think of the roof first. But especially in high-density housing, the roof area is often insufficient, or its structural load capacity is limited.
At the same time, the demands on modern residential complexes are changing. Today, roofs are no longer meant to be just utility spaces, but also spaces for living and gathering: featuring green roofs, community areas, or urban gardening. This creates new conflicts of use, but also new opportunities.
Because while roof areas are becoming scarcer, other areas of many buildings remain energetically unused. Balconies. Facades. Carports. Yet three things converge there: available surface area, solar radiation, and direct energy demand within the building. That is precisely what makes them interesting.
The building envelope is no longer just insulated. It is starting to work along with the system.
Photovoltaics Do Not End at the Inverter
Photovoltaics are still often thought of on too small a scale.
Yet the electricity generated today has long ceased to replace only classic household electricity. It can support heating energy, heat water, supply charging infrastructure, and reduce peak loads. In short: it can take over a large part of a building's energy supply—if it is used intelligently.
And that is exactly where the decisive difference lies. Solar power is not always generated when it is needed. Without control and prioritization, a significant portion of its potential evaporates. Modern energy management systems can prevent this: they analyze consumption profiles, automate energy flows, and ensure that surpluses are systematically directed to where they bring the greatest benefit—whether into the heating system, battery storage, or the charging station.
The decisive question is therefore no longer just: "How much electricity does the system generate?" but rather: "How intelligently is this electricity used within the building?"
Operating costs in housing: Energy as a strategic question
Rising housing costs are not just driven by construction prices. Energy is increasingly becoming an economic risk for many residential complexes.
This is precisely why the question of how much energy can be generated and used directly on-site is gaining importance. Every kilowatt-hour used locally reduces dependency on the energy market, price fluctuations, and external supply costs.
This is becoming increasingly relevant, particularly in non-profit housing and for housing cooperatives—not only from an ecological perspective, but also with a view to long-term stable operating costs. The investment costs vary greatly depending on the building, surface area, and system complexity—and are increasingly co-funded by subsidy programs at the federal, state, and municipal levels. It is well worth integrating these options into the planning at an early stage.
Practical example: Ottnang housing project – building-integrated PV in multi-family housing
A housing project by the WSO housing cooperative in Ottnang shows what this mindset looks like in practice. There, photovoltaics were consistently integrated into the energy concept—on the roof, on balconies, and on terraces. In total, 30.44 kWp were generated via the roof system and around 40 kWp of additional capacity via PV balconies—amounting to a total installed capacity of nearly 70 kWp.
The decisive factor here is not just the amount generated, but how the electricity is used.
In this project, surplus solar power is not simply fed into the grid at a low tariff, but is used specifically for water heating. An intelligent energy management system automatically controls when electricity is stored, used, or redirected—with clear priorities: first self-consumption, then heat generation, then grid feed-in.
The result: higher self-consumption, lower external energy costs, and a significantly more efficient use of the available energy surfaces. Up to 70 percent of heating costs are saved here.
Rethinking renovation: The Real Question Is No Longer "If"
The discussion surrounding energy-efficiency renovation is currently undergoing a fundamental shift. It has long ceased to be just about consuming less energy. It is also about making buildings more active, resilient, and independent.
And that is exactly why, in the future, it will often no longer be enough to just insulate or replace equipment. The decisive question will be: What role can the building itself play in the energy system? Because in the end, every unused surface is a missed opportunity.
Conclusion: The building envelope is changing its function
Facades, balconies and carports are becoming potential energy surfaces. Renovations are turning into infrastructure projects. And residential complexes are gradually becoming active components of a decentralised energy system. This is still happening on a fairly small scale. But the direction is clear.
That is why it is worth rethinking renovation – before today’s standards become tomorrow’s legacy issues.
How much energy is already stored in your building envelope?
