Renovation / refurbishment of historic windows: Historic window constructions – especially box-type windows – are widespread throughout the German-speaking world and beyond and have been considered tried and tested constructions for more than 200 years. Their good usage and functional properties as well as their high aesthetic value speak for their preservation.

As a traditional Berlin window construction company, Hans Timm Fensterbau offers the renovation / refurbishment (window renovation / window refurbishment) of single, composite and box-type window constructions in accordance with the holistic principle.

In a two-year research project – supported by the Berlin Senate, monument protection authorities and the European Union – we developed the necessary work steps for the complete refurbishment/renovation of historic box-type windows in 2000 and presented them in the VFF-Guideline HO.09 published by the Window and Facade Association, which today today one of the recognized rules of of technology throughout Germany.

Thanks to our many years of expertise, our comprehensive refurbishment leads to a considerable improvement in the thermal, sound and weather protection of your window constructions from the period of construction by effectively eliminating historical weak points.

Our refurbishment is carried out with a focus on sustainable low-tech principles and results in a holistic refurbishment with significant functional improvements. As a result, your box-type windows are optimally adapted to the requirements of today’s use and are given a new life cycle.

All in all, retreading is an investment that pays off in the short term. It leads to considerable savings in heating energy costs and increases comfort through improved tightness and sound insulation. The functional and functional properties as well as the high aesthetic value of the historic windows are fully retained.

Stock Retreaded
Thermal insulation U-value [W/m²K] 2,5 – 3,0 1,3 – 0,9
Sound insulation Rw [dB] acc. DIN 4109 approx. 34 46
Air permeability class 1 3

Put your trust in the inventor of rebated box windows

Through a research project – supported by the Berlin Senate and the European Union – we developed the necessary work steps for the renovation / refurbishment (window renovation / window refurbishment) of box-type windows in 2000 and wrote them down in the VFF guideline HO.09, which is now one of the recognized rules of technology throughout Germany.

In 2014, we revised the guidelines – after more than a decade of experience with retreading – in the working group of the technical committee of the Window and Façade Association.

Our work is also based on the
specifications of the monument conservationists
in order to preserve the historical building substance in the best possible and professional way.

TIMM Fensterbau specializes in holistic window refurbishment

The renovation / refurbishment (window renovation / window refurbishment) of box-type windows is a complex process involving several trades (carpenters, painters, glaziers, plumbers). We therefore take a holistic approach. As a specialized window construction company, TIMM offers you all the necessary work across all trades for an upcoming box-type window renovation / retreading.

In contrast, individual renovation measures separated by trade (so-called brush renovations) usually only lead to a short-term visual improvement of the windows, as the “weak points” of the historical construction and thus the causes of damage are not eliminated.

You can therefore rely on our many years of experience and the processing in our Plant 1, which is specially equipped for refurbishment/retreading and has specially trained personnel. Our impressive list of references speaks for our work.

TIMM’s awards in recognition of our listed windows

Both our passion for historic windows and our love of detail, as well as our commitment to finding individual and creative solutions for listed buildings, are reflected in various awards:

  1. Federal Prize for Craftsmanship in Monument Conservation 2004 and 2009
  2. Hans Timm was awarded the Medal of Merit of the Order of Merit of the Federal Republic of Germany in 2004 and 2010 for his services to the preservation of historical monuments.
  3. In recognition of ecologically responsible entrepreneurial action and the associated contribution to environmental and climate protection, TIMM Fensterbau is presented with the Green Buddy Award for the “retreading” product in 2013.
  4. In 2014, Hans Timm was awarded the Ferdinand von Quast Medal, the Berlin Monument Preservation Prize, for special services to monument preservation.
  5. In 2017, Hans Timm is awarded the Berlin Energy Saving Champion for his efforts to renovate historic box-type double windows.

Photo: Hiepler, Brunier



Carpentry overhaul of the window constructions

One of the core work steps in the refurbishment/renovation (window refurbishment/window refurbishment) is a carpentry overhaul of the blind and sash frames . In particular:

  • Open parapet joints and wood cracks closed by carpenters
  • Corner joints reattached
  • Damaged and no longer repairable weatherboards replaced.

Special new paint structure for durability

A 100% paint stripping and color recoating of all wooden parts is required. The sashes are processed in our factory during renovation / refurbishment (window renovation / window refurbishment), the frames on site. We carry out 100% paint stripping exclusively using the hot air process. This is because chemical paint stripping causes damage to the window and is rejected by us. All untreated wood is impregnated with solvent-based primers during the renovation of the box-type windows on site using the brush method and twice in the factory using the immersion method. A color coating is then applied in accordance with the technical requirements of the VFF-HO.09 guidelines.

New glazing for improved thermal insulation

To improve energy efficiency, the inner sashes will be modernized with thin insulating glazing in line with listed building requirements. This creates the possibility of a significant energy improvement to 1.5 to 0.9 W/m²K (previously UW value 3.0 W/m²K).

Ensuring suitability for use and moisture protection

The brittle, cracked putties with partially insufficient adhesion are completely renewed. The glazing rebates are repainted and the new glazing is sealed with elastic, improved sealant so that moisture protection is once again guaranteed.

Reworking the historical fittings

As part of the retreading process, the historical fittings are refurbished by us using special processes. The old olives are polished. Furthermore, the The hinges are realigned and the fittings readjusted so that the historic windows can be operated and closed again. If necessary, historical fittings are replaced.

Improvement of driving rain tightness

To improve the driving rain tightness – one of the historical weak points of the constructions – the box-type window is given a revised stepped rebate on the lower section, including a water nose developed by us in research projects.

Improved tightness and increased sound insulation

As a measure to improve tightness, thermal and sound insulation, a circumferential seal is fitted to the inner sash. This also significantly improves the susceptibility to condensation on the inside of the outer pane.

Procedure – Individually adapted to your property

The refurbishment (window renovation / window refurbishment) of box-type windows can be carried out in two different processing sequences. As a rule, the sashes are completely refurbished in the factory and the frames are refurbished on site. However, the box-type windows can optionally be refurbished by completely removing the building elements and completely refurbishing them in the factory.

Support program

As a qualified specialist company, the refurbishment we offer is eligible for the nationwide funding program “BEG EM – 5.1 Individual measure on the building envelope” with a current subsidy of 15%.

Please note!
The application requires the involvement of an energy efficiency expert (EEE). We will be happy to assist you in your search for the right energy efficiency expert.



Holistic revision of a box-type double window


De-glazing of the sashes in the factory and removal of the existing fittings


Re-milling the glass rebates after devitrification


100% paint stripping using the hot air process


Reconditioning or replacing wooden parts that are not intact


Reattaching the corner brackets to stabilize the corner joint


Closing open parapet joints and cracks in the wood


Milling the seal on the inner sash


Installing the driving rain seal on the frame on site


New coating in the factory by spraying


New glazing and sealing with elastic sealant


Reworking and cleaning the fittings




Die innovativsten Lösungen der Branche

Auf rund 850 m² Ausstellungsfläche präsentieren wir Ihnen in unserem Showroom an über 60 Exponaten die aktuellsten und innovativsten Lösungen der Branche aus den Bereichen Aluminiumfenster, Holzfenster, Holz-Alu Fenster und Stahlfenster sowie Sicherheitsfenster und Fassaden.

Architekten, Bauherren und Partnern im Objektgeschäft bieten wir die Möglichkeit, alle Arten und Designsprachen von Fenstern und Fassaden zu erleben und sich von unserem vielseitigen Produktportfolio begeistern zu lassen. Wir laden Sie herzlich ein, diese Erlebniswelt für Ihre Bauvorhaben und Planungen zu nutzen.

Hinweis: Bitte besuchen Sie uns nach einem vorab mit uns vereinbarten Beratungstermin, da unser Showroom nicht auf Publikumsverkehr und spontane Besuche ausgerichtet ist.



Hans Timm Fensterbau GmbH & Co. KG
Motzener Str. 10
D-12277 Berlin

Beratungs- & Angebotsanfragen:
+49 30 720 831-70

Service-, Reparatur- und Wartungsanfragen:
+49 30 720 831-60
+49 30 720 831-0


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