VAMOS - Casement windows with vacuum glazing: Performance-Monitoring for Building retrofit

Knowledge consolidation of the exploratory project VIG_SYS_RENO; This project focused on the application of vacuum glass in existing casement windows for purposes of energetic performance improvement of buildings. Expected results include new insights about and a guideline for the application and utilization of vacuum glass products in existing window systems.

Short Description



Starting point / motivation

Windows are often considered to be a weak spot in buildings envelopes. Thus, building retrofit that focuses on energy performance improvements often address the exchange of existing windows. RegulaStarting point / motivationrly, existing window systems are replaced by new constructions.

While the energy performance of buildings can be improved by changing the windows, often the aesthetic performance of the overall building is neglected, resulting in existing buildings with questionable window/façade appearances.

Toward this end, we explore vacuum glazing products as a viable alternative for casement window retrofit instead of replacement with triple-glazing single shell windows. To be a convenient alternative, a structured and in-depth research- and development effort is started that relies on empiric studies as well as on deployed simulation and lab-testing efforts.

Contents and goals

The Project VAMOS addresses the retrofit of casement window with vacuum glass. Generally, Vacuum glazing is considered as two-shell glass construction, with an evacuated interstitial space in-between. These glazing products have a very good thermal performance (UG-Values of 0.4 – 0.6 W.m-2.K-1), majorly due to the widely elimination of conduction and convection in the interstitial space. As such, these products require special consideration of their properties in window construction.

In a previous project - VIG-SYS-RENO - it could be proved that these glazing products can generally be utilized for casement window retrofit, however, no realization was performed until now.

Based on the findings of VIG-SYS-RENO (and the two other projects involving vacuum-glazing products, MOTIVE and the ongoing FIVA-project) casement window designs encompassing vacuum glass will be first envisioned and designed, and then subjected to rigorous testing via empirical/physical and simulation-based models.

Based on these efforts, decisions regarding the best construction method for each type of casement window and each degree of intervention will be taken. Questions, such as the positioning of the vacuum glazing in inner, outer or both shells of the casement window construction will thus be answered. The frame-geometries, joint details, and construction specifics will be highlighted and documented.


Thereby, the project will examine for different types of casement windows (The "old Viennese casement window" / "Grazer casement window", "the Viennese casement window", etc.) and different levels of retrofit intervention (from "cosmetic" minimal-invasive refurbishment actions to total reconstruction / new construction of the corresponding casement windows) viable retrofit approaches regarding the integration of vacuum glazing. 

Methodologically, retrofit construction scenarios will be designed, tested and evaluated regarding their impact and performance both physically (laboratory) and virtually (numeric simulation), built and integrated in existing building envelopes. Subsequently, the described technology demonstrators will be subjected to a rigorous monitoring.

Aspects that will be monitored encompass local and surface temperatures, condensation risk / relative humidity, air movement/velocities, and other objective and subjective performance indicators. The project will host the first realizations of casement window retrofit with vacuum glazing in (partly historically meaningful) existing buildings.

Both the demonstration site buildings' inner spaces, affected by the retrofit, as well as the windows will be subjected to a rigorous monitoring. This will already start prior to retrofit to obtain comparison data for a before/after analysis. After retrofit the monitoring efforts will be continued.

Thus, the effect of the vacuum glazing can and will be studied in detail, and evaluated regarding indicators such as the thermal comfort, the heating demand, and others.

One further focus is the documentation and authorship of a guideline pertaining to the application of vacuum glazing products in windows within sensitive building stock.

Expected results

Expected results include not only improved thermal performances of the demo site buildings, but based on the demonstration sites an increased stock of documented experiences and knowledge regarding the specific aspects of retrofit projects encompassing vacuum glazing.

One important outcome of the efforts will be a guideline that illustrates the methods deployed during the project and the findings of the project. These shall trigger an increasing utilization of the vacuum glass technology in state-of-the-art window retrofit processes.

Project Partners

Project management

Department of Building Physics and Building Ecology, TU Wien

  • Univ.Prof. DI. Dr.techn. Ardeshir Mahdavi
  • Univ.Ass. DI. Dr.techn. Ulrich Pont (contact person)

Project- or cooperation partners

  • Holzforschung Austria - Österreichische Gesellschaft für Holzforschung
  • Ernst Prohaska - Gepr. Restaurator im Tischlerhandwerk, Tischlermeister
  • Schaden Fenstersanierung GmbH
  • Alois Svoboda GmbH
  • Tischlerei Alois Winkler
  • Zoller-Prantl Gesellschaft m.b.H Tischlerei
  • AGC Glass Europe saDept. New Business Development - Fineo

Contact Address

Univ.Ass. DI. Dr.techn. Ulrich Pont
Department of Building Physics and Building Ecology, TU Wien
Karlsplatz 13/4
A-1040 Vienna
Tel.: +43 (1) 58801 27033