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How to Measure for a Roof Lantern


Roof lanterns are a stunning addition to any home. With more natural light and an overhead focal piece, you create a bright and inviting atmosphere. With a variety of sizing options available, choosing the right roof lantern may seem overwhelming.

However, this guide will simplify the process, enabling you to confidently measure your space so you can choose the perfect roof lantern for your home.


Preparing for Measurement

To measure your roof lantern, you’ll need to gather a few key tools to ensure accurate results.

Equipment Needed:

  • Tape measure
  • Spirit level
  • Laser measure (optional, for larger openings)
  • Protective gloves
  • Non-slip shoes
  • A sturdy ladder (if measuring at height)

Additionally, make sure someone is assist if needed (especially for larger openings).


Measuring the Roof Opening (No Upstand)

If your opening doesn’t have an upstand, follow these steps to measure it:


1. Measure the External Width and Length:


  • Use your tape measure to determine the exact width and length of the hole in the roof.
  • Measure from one edge to the other on both sides to verify consistency.
  • Accurate external measurements are crucial to ensure the roof lantern fits correctly within the space.


2. Include the Necessary Overhang:


  • Factor in an overhang of around 12mm to allow for weatherproofing and an aesthetically pleasing finish.
  • This overhang ensures the roof lantern fits snugly and provides adequate protection against the elements.


3. Check Opening Is Square:


  • Measure the diagonals of the opening from one corner to the opposite corner on both sides.
  • Ensure the measurements are equal; if not, the opening is not square.
  • Make any necessary adjustments to avoid fitting issues, as a squared opening is essential for proper installation and to prevent potential leaks.

Measuring With an Upstand

An upstand is a raised frame around the roof opening that supports the roof lantern and prevents water ingress. To measure for a roof lantern with an upstand:


1. Measure External Dimensions:


  • Measure the external width and length of the upstand, including any roofing membrane.
  • Ensure the upstand is at least 150mm high to prevent water ingress.


2. Measure Internal Dimensions:


  • Measure the internal width and length of the upstand.
  • Account for the thickness of plasterboard or other lining materials to ensure a snug fit for the roof lantern.


Choosing the Right Size

When deciding on the size of your roof lantern, consider whether a standard size will fit your opening or if a custom-made roof lantern is necessary. Standard sizes are often more readily available and may be more cost-effective, but bespoke sizes offer flexibility and can be tailored to meet unique architectural requirements, ensuring a perfect fit for your space. 

To ensure compatibility and ease of installation, consult the Brett Martin manufacturer guides. These provide detailed sizing information and recommendations. Alternatively, refer to our guide to roof lantern sizes if you’re still unsure.


Ordering Your Roof Lantern

Before placing your order, double-check all your measurements and ensure that they are accurate. If you have any queries or need further clarification, don’t hesitate to reach out to us. Confirming specifications and addressing any questions beforehand will help guarantee that you receive a roof lantern that fits perfectly and meets your expectations.


Additional Considerations

Before installing your roof lantern, conduct pre-installation checks to ensure that the roof structure can support the additional weight. This step is essential to avoid any structural issues and ensure the safety and stability of your roof.

Always follow the manufacturer’s instructions carefully during installation. Adhering strictly to these guidelines is essential to maintain the warranty and ensure the roof lantern performs optimally. Proper installation not only enhances the longevity of the lantern but also guarantees its effectiveness in providing natural light and weatherproofing.


Key Takeaways

Correct measurements ensure a successful roof lantern installation. Remember these key points:

  • Measure the external and internal dimensions of the roof opening or upstand accurately.
  • Include an overhang in your measurements for weatherproofing.
  • Verify that the opening is squared to avoid fitting issues.
  • Decide between standard and custom sizes based on your needs.
  • Double-check measurements and consult us if you have any queries before ordering.
  • Ensure the roof structure can support the lantern’s weight and follow the manufacturer’s installation instructions.



What size roof lantern do I need?

The size of your roof lantern depends on the dimensions of your roof opening. Measure the external and internal dimensions accurately, including any necessary overhang. Standard sizes are available, but custom sizes can be tailored to fit unique architectural requirements perfectly.

Can a roof lantern be too big?

Yes, a roof lantern can be too big if it overwhelms the structural capacity of your roof or the aesthetic balance of the space. Ensure your roof can support the lantern’s weight and consider the room's proportions to maintain a harmonious design.

What is the minimum upstand for a roof lantern?

The minimum upstand for a roof lantern is typically 150mm. This height helps prevent water ingress and ensures the structural integrity of the installation. It also provides a proper base for weatherproofing and aesthetic finishing.

What is the minimum pitch for a roof lantern?

The minimum pitch for a roof lantern is usually around 5 degrees. This pitch allows for proper water drainage and prevents pooling on the glass, which can lead to leaks and structural issues over time. Always follow the manufacturer’s recommendations for the specific product.

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