How to Measure a Skylight for Replacement

To upgrade to new skylights, it’s important to have accurate measurements of your existing skylights. Knowing the size of your current skylights will help you determine what size your new skylights need to be in order to minimize the amount of additional cutting or reframing required for installation.

Check For Model Information

The easiest way to determine the size of a replacement skylight is to check the model number on your existing skylights. Velux is the largest manufacturer of skylights so chances are pretty good that you have a Velux skylight installed in your home.

Locate the Product ID Tag

  1. Locate the product ID tag on your skylights. For deck mounted skylights the tag will be on the interior of the skylight. For curb mounted models the tag will be found on the exterior.
  2. The first set of letters is your model, the next set of identifiers in the sequence contain your model size.
  3. Once you’ve identified all models and model sizes needed, place your order!

Interior and Exterior Measurements

Both external and internal measurements are required for a perfect fit. For the external measurements, start on the roof and measure along the side of the skylight where the shingles meet the flashing, noting the width and length. Then, measure the height of your skylight or curb. For the internal measurements, measure the width and length of the drywall around the skylight’s opening. Record all of these measurements to ensure that your new skylights will fit perfectly. If you’re not hiring a contractor or roofer to do the installation, you can use these measurements to order your replacement skylights.

Measure to Replace Deck Mounted Skylights

To begin, measure the exterior length of the glass and then the width of the glass from the interior of the cladding. Accuracy is crucial because new skylight models come with various drywall grooves.

These variations may necessitate trimming the drywall panel or filling any gaps with molding or painter’s caulk.

Additionally, for non-VELUX deck-mounted skylights, you must measure the length and width of the drywall opening inside the house and the entire skylight, including the cladding.

Velux Deck Mount Skylight Measurement Detail

How to Measure Curb Mount Skylights

Similar to skylights that are mounted on the deck, when measuring the width of the exterior glass from the inside of the cladding, it’s important to also measure the outside length of the glass. However, in this case, it’s crucial to make sure that your outside length measurements of the glass include the flashing.

Watch one of our skylight pros demonstrate the way to measure curb mounted skylight for replacement in this brief informative video.

Pro Tips

When replacing your skylight with a Velux brand skylight, it’s required to install a Velux Flashing Kit to get a 10 year no leak warranty. When installing a solar powered unit you also qualify for a solar tax credit.