Case study 11: Plastic windows

Incorrect design and installation of PVC windows - causes, consequences and assessment by the expert - expert reports for PVC windows - typical damage and incorrect installation

Mission and initial situation

A private building owner commissioned me due to recurring problems with several newly installed PVC windows. The anomalies occurred shortly after the building was first occupied and concerned leaks, warped sashes, malfunctioning fittings and condensation forming in the lower frame area.

During the site inspection, I discovered that these were modern multi-chamber PVC-U window systems with triple glazing that had been installed as part of a renovation project. The first functional check already revealed several significant execution errors.

Damage pattern detected

Typical defects that have been identified:

  • Warped sashes and frame profiles - due to incorrect storage and faulty assembly
  • Leaking connection joints - Missing or inadequate internal and external sealing
  • Condensation and moisture in the lower frame area
  • Faulty locking and stiff fittings
  • Incorrect measurement → Insufficient installation clearance and pressures in the frame
  • Insufficiently bolted or incorrectly positioned fixing points
  • Damaged glass edge seal (often due to improper insertion of the glass)
  • Thermal bridges due to missing insulation in the soffits

These defects led to malfunctions, draughts, increased heat transfer and local moisture problems.

Root cause analysis

Incorrect measurementThe measurement was carried out inadequately. In several cases, the frames were under tension or had too little installation clearance. This regularly leads to warped sashes and malfunctions.

Improper sealing: The sealing did not meet the specifications of the RAL installation guidelines (RAL-GZ 695) and non-DIN-compliant installation requirements:

  • - Inner seal (airtight) not present
  • - External waterproofing (driving rain-proof, open to diffusion) inadequate
  • - Lack of separation between inner and outer seal

Moisture was able to penetrate unhindered into the connection areas.

Faulty fasteningIn some cases, too few frame dowels were used or incorrectly positioned. This results in warping, leaks and a lack of stability.

Improper installation of the fittingsNon-adjusted or incorrectly installed hardware parts led to functional problems.

Errors during glazing installation: Pressings were found on the glass edge seal as well as incorrectly placed glass blocks.
This jeopardizes the service life of the insulating glazing.

Normative evaluation

Relevant regulations:

  • DIN EN 14351-1 - Performance characteristics of windows and doors
  • RAL installation guideline - Guidelines for installation
  • DIN 4108-7 - Airtightness of the building envelope
  • VOB/C ATV 18360 - Metal construction work / Window work
  • DIN EN 1627-1630 - Burglar resistance (relevant for burglar-resistant PVC-U windows)

The audit showed that several of these standards and codes of practice not observed in particular:

  • Lack of airtightness
  • Insufficient impermeability to driving rain
  • Lack of thermal bridge-free design
  • Faulty mechanical fastening

Consequences of the defects

I recommended the following steps:

  1. Removal of faulty window connections incl. complete restoration of the inner and outer sealing according to RAL.
  2. Correction of the fastening Subsequent, standard-compliant fastening in accordance with the manufacturer's specifications.
  3. Function and fitting correction Readjustment of all fittings, replacement of defective components if necessary.
  4. Elimination of thermal bridges Adaptation of the insulation in the reveal area.
  5. Documentation Photo documentation and acceptance report after completion.

Recommendation For future projects I recommend a Quality control during construction, to avoid execution errors at an early stage.

Summary

The case shows typical damage to plastic windows caused by non-standard installation and a lack of sealing.
The combination of incorrect measurement, insufficient sealing, faulty fastening and Fogging problems led to considerable functional and moisture damage.

Professional execution according to DIN EN 14351-1, DIN 4108 and RAL installation guidelines would have prevented this damage.

Note from the expert

As a publicly appointed and sworn expert for the metalworking trade, I provide independent expert opinions on PVC, aluminum and metal windows - including testing of installation quality, tightness, thermal insulation and hardware technology.

Further information

Overview of the case studies:

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