When Should Windows Be Installed In A New Build?

Debating at what stage to install windows for your new build project? We’ve got you covered - learn more from our team of experts.

When constructing a new build in the UK, ensuring each stage of the process is completed in the right order is essential for efficiency, quality, and compliance. One key consideration is when to install windows. Getting the timing right ensures the structure remains protected from the elements while allowing construction work to progress smoothly.

At Dale Joinery, we have extensive knowledge of new-build projects and have worked with many developers, architects, and self-builders across the UK. We offer award-winning timber windows and tailored guidance to ensure your project meets your vision and, most of all, your budget.

Ideal Stage for Window Installation

In the UK, windows are typically installed during the second fix stage of construction. This usually occurs after the structure is watertight, meaning the roof is on and external walls are complete, but before internal finishes like plastering and flooring begin.

Why Is Second Fix the Best Time?

Weatherproofing - Installing windows too early in the build can leave them exposed to rain, wind, and dust, which could affect their performance and durability. Waiting until the structure is enclosed reduces the risk of damage.

Security - Windows installed too soon may be at risk of damage or theft on an open construction site. Ensuring doors and other security measures are in place before window installation can help protect these valuable components.

Airtightness & Energy Efficiency - Properly installed windows contribute to the airtightness of the building, which is crucial for meeting UK Building Regulations regarding thermal efficiency. Installing them during the second fix stage allows for effective proper sealing and insulation.

Minimising Site Damage - Construction sites can be busy, and if windows are installed too early, they risk being scratched, cracked, or covered in debris. Delaying installation until the interior is nearing completion helps keep them in pristine condition.

Factors That May Affect Installation Timing

Build Schedule and Project Phases

Each new build project will have its own schedule. While the second fix is generally the preferred time for window installation, some projects may need adjustments based on specific timelines or requirements.

Weather Conditions

In the UK, unpredictable weather can impact installation. If heavy rain, frost, or extreme temperatures are expected, it may be best to delay installation to prevent sealants from failing or materials from contracting and expanding incorrectly.

Energy Performance and Airtightness Testing

Windows play a key role in achieving airtightness targets for new builds. If an airtightness test is required, installing windows before this stage ensures an accurate assessment of the building’s overall efficiency.

Early vs. Late Installation: Weighing the Pros and Cons

Early Installation (During First Fix or Before Roof Completion)

Allows early airtightness testing

Ensures faster overall progress

Greater risk of weather exposure

Increased potential for site damage

Later Installation (After Interior Finishes Begin)

Protects windows from site damage

Easier access for tradespeople working inside

Potential delays if installation clashes with other finishing work

It may require additional weatherproofing measures if the building is already enclosed

Conclusion

For most UK new builds, installing windows during the second fix stage, after the roof is complete but before the interior finishes, strikes the right balance between protection, security, and efficiency. However, considerations such as weather conditions, build schedule, and airtightness testing may influence the final timing.

By carefully planning window installation, builders can avoid costly delays, maintain high-quality finishes, and ensure the property’s long-term durability and efficiency. If in doubt, consult our experts at Dale Joinery, and we will be more than happy to determine the optimal installation schedule for your specific project.

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