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One size matters: the daylight size.

You order a skylight or flat roof window by daylight size, meaning the clear light opening at the top of the curb. The curb is the raised edge on your flat roof that supports the skylight. The hole in your roof, the roof opening, depends on your curb.

Side view - Daylight size, roof opening & height

Example of a sloping curb 16/20: 16 cm high, with the roof opening 20 cm larger than the daylight size. The daylight size is the opening at the top and the size you order. With a vertical curb, the roof opening is equal to the daylight size.

Top view - Measuring daylight size

Do you already have an existing curb? Then measure the daylight size: the clear opening at the top of the curb, both width and length. So do not measure the outside of the curb, only the opening on which the skylight or flat roof window is placed.

Which size do you order?

The right size depends on your situation. If you are replacing an existing skylight or flat roof window, start from the daylight size of your current curb. If you are making a new opening, first choose the desired daylight size and adjust the roof opening accordingly.

You already have a Skylux curb

Measure the daylight size: the clear opening at the top of your curb, width × length. That is the size you order for a skylight or flat roof window.

You are making a new opening

First choose your daylight size. Then make the roof opening to size: equal to the daylight size for a vertical curb, larger for a sloping curb.

You have a non-Skylux curb

No problem. With an adapter frame, you can still install a new Skylux skylight or flat roof window on your existing curb.

Frequently asked · how large is the skylight itself?

The skylight has an 8 cm flange all around that rests on the curb. The total skylight size is therefore always daylight size + 16 cm - 8 cm on each side. Example: A skylight with a daylight size of 100x100cm has a total skylight size of 116x116cm.

Roof opening by curb

How large you make the hole in your roof depends on your curb.

Vertical curb

Roof opening = daylight size

A vertical curb runs straight down. As a result, the opening at the top is the same size as the hole in your roof. So the roof opening is equal to the daylight size.

  • 16/00: 16 cm high · roof opening = daylight size
    Suitable only for skylights, not for flat roof windows.
  • 20/00: 20 cm high · roof opening = daylight size
    Suitable for skylights and flat roof windows.

Vertical curb range

Sloping curb

Roof opening = daylight size + extra

With a sloping curb, the walls slope outward. As a result, the opening at the bottom is larger than the daylight size. So the roof opening is equal to the daylight size + extra.

  • 16/20: 16 cm high · roof opening = daylight size + 20 cm
  • 35/30: 35 cm high · roof opening = daylight size + 30 cm

Sloping curb range

The curb code

Read it like this:

The curb code shows the height and the roof opening.

  • 20/00: 20 cm high, roof opening = daylight size.
  • 16/00: 16 cm high, roof opening = daylight size. Only for skylights.
  • 16/20: 16 cm high, roof opening = daylight size + 20 cm.

E.g. with a daylight size of 40 × 40 cm, the roof opening with 20/00 or 16/00 is also 40 × 40 cm. With 16/20, it becomes 60 × 60 cm.

Read more about our curbs

Find your size

View the range and order straight away by daylight size - skylight or flat roof window.