Poorly Installed Windows? Signs, Consequences, and What to Do Next

Introduction: When Window Installation Goes Wrong

Investing in new windows should be a long-term improvement, enhancing insulation, security, and aesthetics. However, when installation is rushed or carried out incorrectly, it can lead to gaps, draughts, moisture infiltration, and even structural damage.

A recent case involved a homeowner who had 15 windows installed over two days by a small installation team. They later noticed gaps, insufficient foam coverage, persistent odours, and a lack of accountability from the installer.

This article outlines the key warning signs of poor installation, explains best practices for window fitting, and offers guidance on how to address substandard work.

Related: The Importance of Professional Window and Door Installation

Common Signs of Poor Window Installation

If you’ve had new windows installed and suspect an issue, look for these red flags.

1. Gaps Between the Window and the Wall

A properly installed window should fit snugly within the opening. Large gaps—especially those filled with excessive foam—indicate a sizing issue. Best practices recommend that external gaps should not exceed 10mm on each side.

What to Look For:

• Visible gaps around the window frame
• Overuse of foam or trims
• Draughts when holding a candle or tissue near the frame

2. Insufficient or Uneven Foam Insulation

Expanding foam tape and foam insulation is crucial in sealing air leaks and improving energy efficiency. A rushed installation and using low-quality products can result in patchy or minimal foam application, leading to draughts and moisture issues.

What to Look For:

• Uneven or missing foam along the edges
• Gaps in expanding foam tapes
• Missing fixings (screws or anchor brackets)
• Difficulty maintaining room temperature

3. Misalignment or Poorly Fitted Frames

Windows should sit level within the opening and be properly adjusted using professional equipment. If the frame is misaligned, it can cause operational and aesthetic issues.

What to Look For:

• Windows that do not close properly
• Gaps between the frame and the sash
• Poor external sealings
• No external EPDM membrane
• Increased noise levels

Best Practices: How Windows Should Be Installed

To ensure long-lasting, energy-efficient, and weather-resistant windows, professional installers follow these key practices.

1. Correct Sizing and Placement

• Measure window openings in multiple points precisely to ensure a perfect fit.
• Allow for a minimal expansion gap (typically 10mm) to accommodate thermal expansion.

2. Proper Sealing and Insulation

• Use high-performance expanding foam tape (such as ISO-BLOCO ONE) rather than relying solely on silicone or just expanding foam.
• Apply weatherproof EPDM at the bottom section of the frame and cover with an aluminium powder-coated sill to prevent water ingress.
• Seal both the internal and external perimeters of the window frame using correct materials.

3. Structural Integrity and Finishing

• Ensure windows are level and properly anchored within the frame.
• Use correct weather and UV resistant exterior materials to prevent leaks.
• Conduct an airtightness test or use a thermal camera to check for air and thermal leaks.

What To Do If Your Windows Were Poorly Installed

If you suspect substandard installation, take the following steps.

1. Document the Issues

• Take clear photographs of gaps, insulation, and misalignment.
• Record draught tests or temperature fluctuations as evidence.

2. Contact the Installer

Send a formal written complaint with photos attached. Clearly outline the problems and request rectification under warranty.

3. Check Local Building Regulations

Some UK councils require permissions and inspections for window and door installations. Contact your local authority’s building control office or FENSA for advice.

4. Seek Legal or Consumer Protection Support

If the installer refuses to address the issue, you have several options to escalate your complaint.

Trading Standards UK

Trading Standards is a government-backed organisation that helps protect consumers from unfair or substandard business practices. They can:

• Provide guidance on your rights and possible next steps
• Investigate complaints about faulty goods or services
• Take action against businesses that repeatedly breach consumer laws

You can contact Trading Standards through Citizens Advice for assistance in reporting the installer.

The Glass and Glazing Federation (GGF)

The GGF is the leading trade association for glazing companies in the UK. If your installer is a GGF member, it means they have:

• Met industry standards for professionalism and competency
• Agreed to follow a consumer code of practice
• Access to a complaints resolution service, which can help mediate disputes between customers and installers

If your installer is a GGF member and refuses to correct the installation, you can file a complaint with the GGF, which may offer a resolution process or advice on further action.

By working with certified professionals and using consumer protection services, you can increase your chances of resolving poor workmanship issues effectively.

Legal Disclaimer

The information provided in this article is for educational purposes only and does not constitute legal advice. If you require legal assistance, consult a qualified solicitor or consumer protection agency.

Final Thoughts: Don’t Settle for Poor Workmanship

Window installation is a significant investment, and poor workmanship can cause long-term damage. If you’re experiencing gaps, draughts, or installation defects, act quickly to document the issues, contact the installer, and seek professional advice if needed.

Related: The Importance of Professional Window and Door Installation

Have you had a similar experience? Share your thoughts below—your insights could help others navigate their own installation challenges.