How to Choose the Right Roof Window Flashing Kit

A roof window is only as good as its installation – and the flashing kit plays a crucial role in ensuring a watertight seal. Choosing the correct roof window flashing kit prevents leaks, improves insulation, and ensures long-term performance.

Here’s what you need to know.

What Is a Roof Window Flashing Kit?

A flashing kit creates a waterproof seal between the roof window frame and the surrounding roofing material.

Without the correct flashing:

• Water can penetrate the roof structure
• Draughts may occur
• Manufacturer warranties may be void

1. Match the Flashing to Your Roofing Material

Flashing kits are designed specifically for different roofing materials.

Profiled Roof Coverings (up to 45mm)

• Roof tiles
• Corrugated metal sheeting

High-Profile Roof Coverings (up to 90mm)

• Deep roof tiles
• Corrugated metal sheets

Low-Profile Roof Coverings (up to 10mm)

• Roofing felt
• Bitumen
• Flat sheet metal

Plain Tiles (Non-Interlocking / Peg Tiles)

• Suitable up to 36mm

Always check the maximum profile height before selecting your kit.

2. Check the Roof Pitch Compatibility

Flashing kits are pitch-specific. Common pitch ranges include:

• 10° – 75°
• 15° – 90°
• 20° – 90°
• 25° – 90°

Using a flashing kit outside its approved pitch range risks water ingress.

3. Understand Fitting Depth Options

Flashing kits are available in different installation depths:

• N – Elevated (+3cm)
• V – Standard depth
• J – Recessed (-3cm)

A recessed installation can:

• Improve thermal performance
• Create a more streamlined appearance
• Reduce cold bridging

Your installer will usually advise which depth best suits your project.

4. Consider Thermo Flashing Options

Some manufacturers, including FAKRO, offer thermo flashing kits designed to enhance insulation around the window frame.

These can improve overall U-values and are worth considering for energy-efficient builds or renovations.

Why Choosing the Right Flashing Kit Matters

Even the highest-quality roof window can fail if installed with the wrong flashing kit.

Correct flashing ensures:

• Long-term weather protection
• Compliance with manufacturer guidelines
• Improved insulation
• Professional finish

For UK homes exposed to heavy rainfall and changing weather conditions, correct flashing selection is essential.

Final Thoughts

When choosing a roof window flashing kit, always check:

• Roofing material
• Profile height
• Roof pitch
• Installation depth

If you’re unsure, consult your installer or supplier before ordering.

A properly selected flashing kit ensures your roof window performs exactly as it should – watertight, insulated and built to last.

Explore our range of FAKRO roof windows and centre pivot windows and find the perfect solution for your home. If you have any questions about our products, our friendly advisors will be here to help you. You can chat with a BPF Online product advisor through our website, or call us on 01295 678614.

Learn More About Roof Windows:

• How to Choose the Right Roof Window for Your Home