Old or poorly functioning roof windows can cause drafts, leaks, and reduced natural light in your attic or loft space, making rooms uncomfortable and less energy-efficient. Whether you are renovating your home, converting your loft, or simply upgrading existing fixtures, knowing how to replace old Velux window units correctly is essential to maintain comfort, prevent energy loss, and ensure long-term durability.
This guide provides detailed instructions on roof window sizes, building codes, and best practices for replacement. It also explains how to use a roof window sizes chart, walks through a replacement skylight guide, and offers practical tips for upgrading old windows effectively. For homeowners exploring modern alternatives, you can view our collection of roof window options to find high-quality solutions that improve natural light, ventilation, and energy efficiency in your attic space.
Why Replace Old Roof Windows?
Replacing old roof windows has several advantages. Modern windows improve energy efficiency, increase comfort, enhance property value, and require less maintenance. Older units often allow heat to escape in winter and let in excessive heat during summer, leading to higher energy bills and less comfortable living spaces.
Many homeowners choose to replace old Velux window units because Velux is a common brand with widely available replacements. However, these steps apply to any standard-sized roof window, regardless of brand.
Upgrading your windows ensures your loft or attic is safe, functional, and visually appealing. It also allows you to incorporate modern features, such as improved ventilation, noise reduction, and advanced glazing options.
Understanding Roof Window Sizes
Accurate sizing is critical for a seamless replacement. If your new window does not fit correctly, you risk leaks, reduced insulation, and alignment issues. Most roof windows come in standard widths and heights, making replacement straightforward if you reference a roof window sizes chart.
Standard Roof Window Sizes
Here is a chart of common roof window sizes for Velux and other major brands:
| Width (mm) | Height (mm) | Typical Use |
|---|---|---|
| 550 | 780 | Small attics, bathrooms |
| 550 | 980 | Single bedrooms, compact spaces |
| 780 | 980 | Larger bedrooms, home offices |
| 1140 | 1180 | Spacious lofts, living areas |
| 1340 | 1400 | Panoramic views, multi-room conversions |
Panoramic views, multi-room conversions
Using this chart ensures the new window matches the existing opening or helps identify if adjustments are required. If you are upgrading to a larger or more efficient unit, you may need to modify the roof opening to accommodate it.
Replacement Skylight Guide
Replacing a skylight or roof window is more than simply swapping panes of glass. Proper measurement, code compliance, and sometimes structural adjustments are required to guarantee safety, efficiency, and long-term performance.
The first step is to measure your existing window frame carefully. Measure the width and height, and check the distance from the roof battens. This ensures the new window sits flush and aligns correctly with your roof’s pitch. Hinge types such as centre pivot or top hung can also affect which models are suitable for your replacement.
Next, review local building codes. Regulations often specify minimum distances from the floor for safe egress, ventilation requirements, energy efficiency standards, and fire safety. Following a replacement skylight guide ensures your installation meets all requirements and avoids potential problems.
For homeowners looking for reliable options to upgrade their attic or loft windows, you can explore the full range of products on the Skylights Roof Lanterns collection page to find units designed for long-lasting performance, comfort, and improved natural light.
How to Upgrade Old Windows
Older roof windows may lack features that make modern units more convenient and energy-efficient. Upgrading allows you to improve ventilation, security, noise reduction, and thermal performance.
Using a roof window sizes chart ensures your new window fits the old frame or identifies whether modifications are required. Modern upgrades often include trickle vents for continuous airflow, automated opening mechanisms, and enhanced locking systems for safety. These improvements make a noticeable difference in comfort and energy efficiency, particularly in bedrooms, offices, or living spaces.
Step-by-Step Replacement Process
Replacing a roof window requires careful planning and execution. The process can be handled by professionals or experienced DIYers.
Step 1: Preparation
Clear the area, gather tools, and protect interior surfaces from dust and debris.
Step 2: Remove the Old Window
Carefully detach the existing window, noting hinge type and seal placement for reference.
Step 3: Inspect the Frame
Check the roof opening for rot, leaks, or structural damage. Any issues should be repaired before installing the new window.
Step 4: Fit the Replacement Window
Install the new window according to the manufacturer’s instructions, ensuring it aligns correctly with the roof pitch.
Step 5: Seal and Flash
Proper flashing is essential to prevent leaks. Use a flashing kit compatible with your replacement window.
Step 6: Test Operation
Open and close the window to ensure smooth functionality.
Step 7: Finish Interior and Exterior
Reinstall trims, insulation, and any interior finishes to complete the installation.
Following these steps guarantees a secure, weatherproof installation and maximizes the window’s performance and lifespan.
Choosing the Right Replacement Option
Deciding whether to perform a direct replacement or upgrade your window depends on your budget, the room’s function, roof compatibility, and energy efficiency goals. Bedrooms or offices may benefit from modern features like improved ventilation, noise reduction, and high-performance glazing.
Balancing cost and long-term benefits ensures you select the most suitable replacement. Using a roof window sizes chart helps avoid installation errors and ensures the new unit fits your space correctly.
Common Pitfalls to Avoid
When replacing roof windows, homeowners often make several mistakes. These include using incorrect measurements, ignoring local building codes, poor sealing, and choosing a replacement that is incompatible with the existing roof structure. Avoiding these pitfalls ensures your new roof window performs efficiently and lasts for decades.
Energy Efficiency Considerations
Attic spaces are particularly prone to heat loss in winter and overheating in summer. High-quality pitched roof windows from Skylights Roof Lanterns help regulate indoor temperatures and reduce energy costs.
Double glazing is standard in most replacement installations, while triple glazing offers better insulation and noise reduction. Low-emissivity coatings and laminated safety glass increase comfort and durability, making your attic more livable and energy-efficient.
Conclusion:
Replacing old roof windows is more than a simple swap. It is an opportunity to improve energy efficiency, comfort, and aesthetics. Using a roof window sizes chart, following a replacement skylight guide, and upgrading old windows when possible ensures your loft or attic space becomes brighter, safer, and more functional. Proper planning and professional installation maximize long-term benefits and increase your property’s value.
Create your account today with Skylights Roof Lanterns to access exclusive updates, track your orders, and get tailored recommendations for your attic and loft projects. Sign up now and start improving your home today!
