A window installed before 1990 in a typical Berlin Altbau loses roughly three to four times more heat than a modern replacement system – a gap of about 2 W/(m²K) in thermal performance that shows up directly on the annual heating bill. Foreign buyers who fall for the high ceilings and stucco mouldings tend to budget carefully for the kitchen and the bathroom, then treat the windows as an afterthought. That’s the mistake. The windows are usually the single biggest energy leak in the building, and getting them wrong is expensive for a very long time.
Key Takeaways:
- Windows in a pre-1990 Berlin Altbau typically have a Uw-value of 2.5-3.0 W/(m²K) – three to four times worse than a modern system (e.g. from 0.76 W/(m²K)).
- Heritage protection (Denkmalschutz) rarely blocks window replacement outright – a like-for-like profile matching the original sightlines is usually enough.
- Private homeowners can get a 50% BAFA grant (EBW) toward new windows if the Uw-value is 0.95 W/(m²K) or better – capped at €30,000 per unit, €60,000 with an iSFP.
- Ground-floor/low-floor Altbau windows without RC-2 certification are a common, overlooked security gap.
- Replacing windows without adding controlled ventilation (per DIN 1946-6) raises the risk of condensation and mould on cold walls.
What Kind of Windows Do Berlin Altbau Buildings Actually Have?
Most Altbau apartments built before 1990 still have single-glazed or early double-glazed timber windows with a Uw-value – the technical measure of how much heat a window lets through – of roughly 2.5 to 3.0 W/(m²K), three to four times worse than a modern window system. Berlin’s housing stock is dominated by Gründerzeit buildings from the 1870s to 1918, and a large share of them were never fully modernised at the window level, even when the kitchen or bathroom was renovated decades ago.
The wooden frames themselves are often part of the charm, but the seals around them dry out, shrink and let cold air straight through the joints. That’s why an Altbau flat can feel draughty even with the heating running constantly, and why condensation collects on the inside of the glass on cold mornings – an early warning sign of a window that’s no longer doing its job.
A Quick Way to Check Your Own Windows
Run a finger along the frame on a cold day. If you can feel moving air at the joints, or the glass is noticeably colder than the wall next to it, the window is very likely underperforming by current standards – not just old-fashioned.
| Window type | Uw-Value (W/(m²K)) | Typical era | Security rating |
| Original single/early double glazing | 2.5 – 3.0 | Before 1990 | None |
| Modern PVC triple-glazed system (e.g. OKNOPLAST PAVA) | from 0.76 | Current standard | RC-2 (ift Rosenheim) |
| Passive-house-grade system (e.g. Winergetic Premium Passiv) | from 0.67 | Current, premium | RC-2 (ift Rosenheim) |
Can You Even Replace Windows in a Heritage-Protected Altbau?
Around 14,500 buildings in Berlin carry heritage protection (Denkmalschutz), yet this rarely means owners are stuck with draughty single-pane glass forever. Modern window systems can replicate a historic frame’s sightlines and glazing-bar pattern while meeting current energy standards, which is exactly the detail a heritage office (Bezirksamt / Landesdenkmalamt) usually cares about most.
A straightforward like-for-like replacement – same opening, same visual division of the panes – is often permit-free or handled through a short informal enquiry to the district office. Structural changes, such as enlarging an opening or altering the façade, are the cases that genuinely require sign-off. Profile lines designed with slim, classic sightlines, such as OKNOPLAST Grande Classic or Konzept, exist specifically to bridge this gap: traditional appearance on the street-facing side, current insulation values on the inside.
How Much Heat – and Money – Do Old Windows Really Lose?
A pre-1990 Altbau window rated around Uw 2.8 W/(m²K) loses close to four times as much heat as a modern system such as OKNOPLAST PAVA, with Uw values starting from 0.76 W/(m²K). Multiplied across a whole flat’s worth of windows, that difference is often a bigger lever over winter heating costs than switching the heating system itself.
The comparison only works when both sides are measured the same way. A 1980s single-glazed window and a current triple-glazed PVC or aluminium-composite system are tested to the same DIN EN standard, which is what makes the Uw figures directly comparable rather than marketing shorthand.
What Subsidy Is Actually Available for Window Replacement in Germany?
Private homeowners in Germany can claim a 50% grant toward the cost of new energy-efficient windows through BAFA’s EBW programme – Bundesförderung für effiziente Gebäude, Einzelmaßnahmen – provided the new windows reach a Uw-value of 0.95 W/(m²K) or better. That single figure is worth remembering: 50%, not the 80% rate that sometimes circulates online, which actually applies to non-residential buildings (EBN) rather than private flats and houses.
The grant caps out at €30,000 of eligible costs per residential unit, rising to €60,000 if the renovation is guided by an individual renovation roadmap (iSFP). It’s aimed at owner-occupiers and landlords who own the building fabric – tenants can’t apply for it directly, though a landlord passing on a partial cost after a subsidised renovation is common in practice.
| Condition | Requirement |
| Subsidy rate (EBW, residential) | 50% of eligible costs |
| Maximum Uw-value of new windows | 0.95 W/(m²K) |
| Funding cap per residential unit | €30,000 (up to €60,000 with iSFP) |
| Applies to | Private homeowners, owner-occupiers, landlords |
| Non-residential rate (EBN, for comparison) | 80% – not applicable to private flats |
Are Old Berlin Windows a Security Risk on the Ground Floor?
Ground-floor and low first-floor Altbau windows without RC-2 certification are a recurring weak point flagged by police crime-prevention advisors, because the simple hook-and-catch locks common before the 1990s offer almost no resistance to a forced opening. RC-2, tested and certified by ift Rosenheim, requires mushroom-head locking bolts (Pilzkopfverriegelung) set into a reinforced frame – a feature that’s now standard on current window systems but was never fitted to original Altbau joinery.
It’s a detail that rarely makes it onto a viewing checklist, but it’s worth asking about directly if the flat you’re buying sits below the second floor.
Will New Windows Cause Mould in an Old Building?
Replacing only the windows in a poorly insulated Altbau can increase condensation risk on cold exterior walls, because airtight new frames remove the accidental draughts that used to carry moisture out of the flat. DIN 1946-6, the German standard covering ventilation in renovated dwellings, exists precisely for this reason: once a building is made airtight at the window, moisture has to be managed on purpose rather than by accident.
The fix isn’t complicated. Modern window systems come with built-in comfort-ventilation positions – OKNOPLAST’s FOUR Seasons tilt setting is one example – that allow a controlled trickle of fresh air without a wide-open sash and without the heat loss of the old draughts. Owners planning a window replacement should ask their installer about ventilation in the same conversation, not as an afterthought once mould has already appeared on a cold wall.
What Foreign Owners Get Wrong, in Short
They budget for the kitchen and forget the windows are the bigger energy problem. They assume Denkmalschutz rules out replacement entirely, when a like-for-like profile usually solves it. They don’t ask about the BAFA grant, or repeat the wrong percentage when they do. And they replace the glass without planning for ventilation, which is how a well-intentioned renovation ends up with mould six months later.
If there’s one line item worth increasing in an Altbau renovation budget, it’s this one. Few other upgrades pay part of themselves back through a government subsidy – most Altbau renovation costs don’t.
