The picture shows an example of a timber-aluminium window with a fully filled glazing rebate base; no opening that can pass through as a result of testing the glass connection (picture: ift Rosenheim)

Burglar resistance on windows

Improvement through bonding between glass and frame

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Multi-pane insulating glass units have been bonded into sash frames and fixed glazing as standard for around 20 years. Even before that, there were systems in which the base of the glazing rebate was partially filled to improve burglar resistance, particularly as resistance to attack via the glass connection.

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As this process was usually carried out without knowledge of the interactions with the glass edge seal, the investigation and description of glass bonding in the frame was tackled more systematically from around 2005; the adhesive manufacturers were brought on board on the pages of the window manufacturers.

Adhesive positions

The pioneers here were the plastic system houses. The sash and thus the profile widths of the window frames should become narrower and narrower, but the stability and resistance of the sash should at least remain the same despite higher glass weights. Depending on the system houses, the adhesive system used (liquid adhesive or adhesive tapes) and the objective (improved properties), different bonding positions are favored (Photo 1).


Prerequisites for the full effectiveness of bonding

Various reasons are given for using bonding:

  • Reduction of frame face widths, no need for steel reinforcement in standard sizes of plastic windows;
  • Increased light incidence due to smaller frame sections;
  • "Oversizes" can be built as the glass stabilizes the frame;
  • Hinge-passage mechanical manufacturing also for glazing processing steps;
  • Improvement in burglar resistance, achieving Classes RC 2 or RC 3 according to DIN EN 1627 [3];
  • Improvement in the rigidity of the sash, no more re-blocking/re-setting required;
  • Easier assembly due to good frame stability. This means no additional visits on site to readjust the hardware or re-blocking.
The table below shows examples of bonding positions (source: ift Guideline VE 08/4 [1] or RAL-GZ 716 Part 2 [2])
Figure 1: Examples of bonding positions (source: ift Guideline VE 08/4 [1] or RAL-GZ 716 Part 2 [2])
The picture shows an example of a timber-aluminium window with a fully filled glazing rebate base; left (sketch): Cross-section, right (photo): no passable opening as a result of testing the glass connection (Image: ift Rosenheim)
Figure 2: Example of timber/aluminium window with fully filled glazing rebate base;
left: Cross-section,
right: no passable opening as a result of testing the glass connection
(Image: ift Rosenheim)

The benefits, especially in terms of burglary resistance, only become effective under certain regulations: the bonding must be carried out using the same manufacturing process and the same materials as for the bonding, for which the test led to successful Evidence of Performance with the corresponding classification. E.g,

  • the geometries and the position of the bonding must be the same.
  • The substrates used must be the same in order to ensure the required adhesion.
  • the glass product described with the corresponding classification must be used.
  • the bonding must be manufactured by trained specialist personnel and documented.
  • the curing of the adhesive, especially when using 1-component products in the rebate base, must also be warranted in the production process.

Systems as illustrated in Photo 2 can only be produced with adhesive systems which, according to the situation in the glazing rebate, can also fully react in depth. Fission products resulting from the reaction must not damage the edge-sealing of insulating glass units. Other interactions (keyword: migration of ingredients) between the bonding in the edge-sealing of insulating glass units and the adhesive in the rebate base, which negatively affect one or the other product, are also undesirable.

Bonding to coated wood surfaces

Bonding in wooden windows was usually only carried out on untreated wooden surfaces due to the very different surface coating materials (varnishes and glazes with different combinations and pigment types and parts). Since bonding on untreated wood does not fit into the production flow of wooden window manufacturing, systematic use has been almost non-existent. It is therefore necessary to find a method for a sensible pre-selection of substrates that reduces the scope of testing and gives the manufacturer of the bonding more leeway.

In Part 5 of the ift-Guideline VR-08/4 "Assessment principles for bonded glazing systems" [1], a concrete method was described together with several adhesive and adhesive tape manufacturers as well as a manufacturer for surface coatings. On the basis of simple preliminary tests, this allows a representative selection of at least three adhesive systems, consisting of wood type - surface coating - adhesive/adhesive tape - glass and enables an assessment and direct responsibility transfer to other adhesive systems in compliance with the "extrapolation rules" according to Part 5 of the ift-Guideline. This requires responsible and trained bonding specialists who are able to evaluate, document, review and use variants with direct responsibility.



  1. ift guideline VR-08/4 Assessment basis for bonded glazing systems
    Part 1 Characterization of the bonding system
    Part 2 Tests on the window system (component testing)
    Part 3 Compatibility
    Part 4 Quality assurance
    Part 5 Supplement to Part 1 - Bonding on coated wood.
    ift Rosenheim, March 2017
  2. Quality Assurance RAL-GZ 716, Special Quality Regulations and Test Specifications for plastic window and door systems Part 2: Systems with bonded glazing. Gütegemeinschaft Kunststoff-Fensterprofilsysteme e.V., Bonn, April 2019
  3. DIN EN 1627:2021-11 Doors, windows, curtain walls, grilles and shutters - Burglary resistance - Requirements and classification DIN Media GmbH, Berlin


Karin Lieb

ift Rosenheim

After graduating from high school, education in carpentry and studies at the Rosenheim University of Applied Sciences as a graduate engineer (FH) in the area of wood technology, Karin Lieb has been working in the testing division of ift Rosenheim since 1989. Since then she has been involved with materials testing, which at ift Rosenheim means dealing with all the individual parts that can occur in building components. This activity has built up over time from the position of Test Engineer, to Head of Testing Department, to Product Management. There she is now available to customers for enquiries of all types regarding the services provided by ift Rosenheim. She also works as an expert for the ift Centre of Technical Experts.

These activities have always been accompanied by technical cooperation in national and European standards committees as well as working groups for various associations.

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