In this comprehensive episode of Beyond the Glass, host Jan Verhoeven tackles one of the most critical—yet often overlooked—aspects of window performance: the installation itself. While homeowners and builders focus on choosing premium PVC windows with triple glazing and advanced hardware, the uncomfortable truth is that even the best window can perform like a cheap one if the installation fails.

Jan delivers a practical, step-by-step compliance checklist that covers every phase of a high-performance PVC window installation: what to verify before the frame arrives on site, what to document while the work is happening, and what evidence you need after the job is finished to prove it was done correctly.

What You'll Learn

This episode breaks down the three pillars of window performance—the Performance Triangle:

1. Airtightness (comfort and energy efficiency)
2. Water management (durability and mold prevention)
3. Thermal continuity (preventing cold bridges and condensation)

Jan emphasizes a critical insight: most window failures happen at the interfaces—the junctions between the wall and frame, the sill connections, and the reveal transitions. Not the glass. Not the PVC profile. The edges.

The Three-Phase Compliance Checklist

Phase 1: Before Installation

• Site and opening verification (measuring at multiple points, checking substrate condition)
• Product and spec confirmation (matching install method to wall type)
• Materials planning using the 3-Layer Concept: inner airtight layer, middle insulation layer, outer weather layer
• Setting client expectations and documentation standards

Phase 2: During Installation

• Frame positioning with proper packer placement at load transfer points
• Fixings and anchoring without over-tightening (a common mistake that warps frames)
• Airtightness layer continuity—the most critical segment of any install
• Thermal bridge prevention at reveals and sills
• Water management details including sill pans, end dams, and proper drainage paths
• Movement and expansion allowances for PVC's thermal behavior

Phase 3: After Installation

• Functional verification (operability, gasket compression consistency)
• Creating an evidence pack with comprehensive photo documentation
• Optional but powerful testing (smoke pencil, thermal imaging)

The 7 "Looks Fine, Fails Later" Mistakes

Jan identifies the seven most common installation errors that pass visual inspection but lead to callbacks within months:

1. Foam-only sealing without a continuous airtight layer
2. No sill drainage plan
3. Over-tightening fixings
4. Ignoring corner detailing
5. Thermal bridges at reveals or sills
6. Exterior seals that trap moisture
7. Handover with zero documentation

Real-World Case Study

The episode includes a detailed callback scenario: a new build with premium triple-glazed windows that developed drafts, noise issues, and condensation within three months. The problem? Airtight tape that stopped 50mm short of the corners on both sides. The fix cost three times what it would have cost to do it right the first time—and could have been prevented with proper documentation and testing.

Homeowner Takeaway

For listeners planning window replacements, Jan provides 10 essential questions to ask any installer—from "How do you ensure airtightness around the full perimeter?" to "What documentation will I receive at handover?" These questions help homeowners separate professional installers from those relying on "trust me" assurances.

Why This Matters

As Jan emphasizes throughout the episode: performance is installed, not purchased. Whether you're working with a specialized window supplier in Overijse or any other provider, the quality of the installation determines whether your investment delivers the promised energy savings, comfort, and durability—or becomes a source of callbacks and complaints.