By adding a roof window or skylight, you can dramatically transform your roof spaces, and bring more light and ventilation not just to these rooms, but to your entire property. 

As a result, both roof windows and skylights are extremely popular investments among property owners. 

If you’re planning on adding one of these windows to your property, keep reading. 

Below, our expert glaziers have shared their top tips for measuring for the addition of a window to a flat roof (a skylight), and for a pitched roof (a velux window).

What tools will you need?

In order to measure the required area, you will need:

• Tape measure 
• Spirit level
• Step ladder (if you don’t already have loft access)
• Pencil and notepad (or a notes app on your phone)

How to measure for a flat roof skylight

Measure the internal opening of your roof deck

Measure both the length and width of your opening, from timber to timber (you don’t need to include the upstand or kerb).

We recommend measuring at multiple points in the opening, to check whether there is any variation across the area. If these measurements do vary, use the smallest measurement for future reference.

Decide whether an upstand will be needed 

In some cases, the skylight comes with its own upstand. However, others require an upstand to be built and added separately. 

So, determine which is the case for your skylight. You will need to do so, in order to confirm whether the product dimensions refer to the unit’s internal dimensions, external kerb dimensions, or the overall frame size. 

Once you have confirmed this point, you can check whether the skylight will fit in the available area.

Check the pitch of your roof 

Use your spirit level to check the pitch of your roof, and confirm that the skylight is compatible with this angle. 

Even if your roof is a flat roof, these roofs are typically designed to feature slight pitches, in order to ensure a sufficient level of drainage. 

How to measure for a pitched roof Velux window

Measure the width between roof rafters 

Velux windows sit between roof rafters, and are angled so that they are flush with the roof line. 

So, you will need to start by measuring the width of the gap between your roof rafters. 

Again, we suggest measuring this area at multiple points, to check whether there is any variation. If these measurements do vary, use the smallest measurement for future reference.

Check the height of your window

To ensure the area is safe and suitable for the addition of a velux window, you will need to measure the distance from the floor to the base of your window.

Then, check against the manufacturer’s instructions, to confirm that there is enough height available. 

Other key considerations

Other key points that you will need to confirm include: 

• How will the window open? (E.g. will it be top-hung or centre-pivot)
• What building regulations will your windows need to be compliant with? 
• What type of glazing will your window need?

If you’re unsure on any of these questions, or want to ensure the best possible end result for your roof installation, enlist the professionals. 

To find out more, or to enlist the support of our team, get in touch with Abbey Glass.