Common Window Installation Mistakes & How We Avoid Them [Bishop's Stortford]

7 Common Window Installation Mistakes & How We Avoid Them in Bishop’s Stortford

Investing in new windows is a significant decision for any homeowner. But here’s a truth I’ve learned over 38 years in the industry: the quality of the installation is just as important as the quality of the windows themselves. A poor installation can turn top-of-the-range windows into a source of draughts, leaks, and frustration.

I’m Oliver Greene, and today I’m pulling back the curtain on the most common window installation mistakes I see right here in Bishop’s Stortford. My goal is to arm you with the knowledge to spot a quality installer from a cowboy, ensuring your investment is protected.

From inaccurate measuring to failing to comply with regulations, I’ll show you the pitfalls and, more importantly, the professional standards we insist on to guarantee a perfect fit every time.

Want to guarantee your installation is done right the first time? Speak to our FENSA-certified experts who are committed to avoiding these common mistakes.

Mistake #1: Inaccurate Measuring

This is the original sin of window installation. Everything flows from the initial survey.

The Problem: Windows are ordered based on incorrect measurements. They arrive on-site and are either too small (leaving large gaps that need to be filled, compromising insulation and security) or too big (requiring costly and damaging structural alterations).
The Cause: Rushed or inexperienced surveyors.
Oliver’s Take: “In my career, I’ve been called to ‘rescue’ jobs where windows were measured incorrectly. It’s a heartbreaking and completely avoidable situation. A professional surveyor will measure each opening in at least three different places (top, middle, bottom and left, right, middle) and check for squareness. It’s a 15-minute process per window that prevents a six-week delay and thousands in wasted costs. We use laser measures and double-check everything on-site.”

Mistake #2: Not Installing the Window Plumb, Level, and Square

This sounds basic, but you’d be surprised how often it’s done wrong.

The Problem: The window frame is installed slightly crooked. This prevents the opening sashes from operating smoothly, puts stress on the hinges and locking mechanism, and breaks the airtight seal.
The Result: Draughts, difficulty locking the window, and premature failure of the hardware.
How We Avoid It: “Every single window we fit is checked with a spirit level on all four sides before it’s permanently fixed. We make micro-adjustments using packers to ensure it is 100% plumb and level. This guarantees a perfect seal and effortless operation for the next 25 years.”

Mistake #3: Improper Sealing and Insulation

A window is only as good as its seal against the elements.

The Problem: Installers use cheap silicone or insufficient foam insulation around the frame. This creates gaps where air and water can penetrate.
The Result: Heat loss, cold draughts, and potentially damaging water ingress that can lead to damp and mould inside your walls.
The Professional Standard: “We use a ‘belt and braces’ approach. First, we apply a high-performance expanding foam to fully insulate the cavity between the window frame and the brickwork. Then, we finish with a premium, low-modulus silicone sealant on the exterior, tooled to a smooth, weatherproof finish. This creates a completely airtight and watertight barrier.”

Mistake #4: Failing to Secure the Frame Correctly

The window needs to be a secure, integral part of your home.

The Problem: Not enough fixings are used, or they are the wrong type for the wall construction (e.g., using standard screws in thermalite blocks). The frame is not securely anchored into the brickwork.
The Result: The window can move or warp over time, breaking seals and compromising security. In the worst-case scenario, it can become a serious safety hazard.
Our Method: “We follow the window manufacturer’s and FENSA’s precise guidelines, which specify the number and spacing of fixings based on the window’s size. For a typical Bishop’s Stortford brick and block construction, this means using frame fixings that penetrate deep into the structural brickwork, not just the plaster.”

Mistake #5: Damaging Surrounding Plaster and Brickwork

A good installation should be clean and tidy.

The Problem: The old window is removed carelessly, causing excessive damage to the internal plaster, external render, or brickwork. The mess is then poorly patched up.
The Result: You’re left with an unsightly finish and the additional cost and hassle of hiring a plasterer or decorator.
Oliver’s Take: “This is a sign of a crew that doesn’t respect the customer’s home. Our teams are trained to remove old frames with minimal disruption. We protect all surrounding surfaces and have the skills to ‘make good’ any minor damage to a high standard. We leave your home as tidy as we found it.”

Mistake #6: Ignoring Building Regulations (Part L)

This is a huge red flag and can cause serious issues when you come to sell your home.

The Problem: The new windows don’t meet the minimum energy efficiency standards required by Part L of the Building Regulations, and the installation isn’t registered with the local council.
The Result: An illegal installation. You won’t receive a FENSA certificate, which can cause major problems during the conveyancing process when you sell your house.
How We Guarantee Compliance: “As a FENSA-approved company, every installation we carry out is guaranteed to meet or exceed Part L regulations. We handle all the paperwork, register the installation with the council, and you receive your FENSA certificate by post, giving you complete peace of mind.”

Mistake #7: Lack of Post-Installation Checks

The job isn’t finished until the window is tested and the customer is happy.

The Problem: The installers pack up and leave without properly testing the window’s operation or cleaning up.
The Result: You discover a stiff handle, a misaligned lock, or protective film still left on the glass after they’ve gone.
Our Completion Process: “Before we leave, we perform a multi-point check on every window: we test the opening and closing action, check every lock, and ensure there are no scratches or blemishes. We then demonstrate the operation to you, the homeowner, and only consider the job finished when you are 100% satisfied.”

Frequently Asked Questions

What is the most common window installation mistake?

From my experience, the most common and costly mistake is incorrect measuring. Inaccurate measurements lead to windows that don’t fit, causing major delays and requiring complete remanufacturing. This is why a professional survey is non-negotiable.

How can I tell if my windows have been installed poorly?

Signs of poor installation include visible gaps around the frame, difficulty opening and closing the window, draughts, water leaks, and messy sealant. A FENSA certificate is your best guarantee of a quality installation that meets building regulations.

Can a bad window installation be fixed?

Some minor issues like poor sealing can be fixed, but major problems like an out-of-square frame or incorrect fitting often require a complete removal and re-installation, which can be as expensive as the initial job. It’s crucial to get it right the first time.

Does a FENSA certificate guarantee a perfect installation?

A FENSA certificate guarantees that the installation complies with building regulations, is energy efficient, and is registered with the local council. FENSA installers are regularly assessed, which ensures a high standard of work and provides you with crucial homeowner protection.

Your Guarantee of a Quality Installation

Avoiding these mistakes isn’t difficult—it simply requires professionalism, experience, and a commitment to quality. When choosing an installer for your Bishop’s Stortford home, ask them directly how they prevent these specific issues. Their answers will tell you everything you need to know.

After 38 years, my philosophy is unchanged: do it right, or don’t do it at all. Your home is your biggest asset, and your new windows should enhance it for decades to come.

Want an installation that avoids every one of these mistakes? Contact our team of FENSA-approved installers in Bishop’s Stortford today. We pride ourselves on meticulous, professional installations that stand the test of time.