Scenario: You’ve been hired to reroof a home and find that the existing skylights are old enough to warrant replacement. How should you measure the skylights to ensure you select the correct size replacement model?

The following are best practices for measuring different types of skylights you may encounter.

Identifying the skylight brand

First, try to identify what brand the old skylight is. Tags that include the brand name are often found on the inside frame, exterior sash or even etched into the glass.

On VELUX skylights the ID tag, which includes the logo, model, size, variant and product information, will be in one of these locations, depending on when it was manufactured.

• Deck-Mounted VELUX Skylights – Look on the inside frame.
• Curb-Mounted VELUX Skylights – Find it stamped on one of the four exterior sides.
• VELUX Roof Windows – Look inside the ventilation flap.

If you can’t find an ID tag, a VELTERM number printed on the spacer bar separating the glass panes identifies it as VELUX.

Measuring to replace an old VELUX deck-mounted skylight

Having the product ID tag information in hand when you call VELUX customer service, will help the customer service agent find the right replacement skylight. Even with the ID tag information, it’s still important to measure the old VELUX skylight to ensure you order the replacement size that fits best. For deck-mounted models, measure the exterior glass pane length and width from the inside edge of the cladding.

The newest VELUX models have a slightly different drywall groove, so the drywall panel at the top of the skylight may need to be trimmed down for the new skylight to fit. If there’s a gap between the drywall and the skylight, use door casing molding or crown molding to cover it. For small gaps, use painter’s caulk to fill in the gap.

Measuring to replace a non-VELUX deck-mounted skylight

For non-VELUX deck-mounted skylights, measure the drywall opening length and width on the inside of the house, the length and width of the exterior glass inside the cladding and the overall size of the skylight (inclusive of cladding).

Measuring to replace VELUX or non-VELUX curb-mounted skylights

For curb-mounted models that are VELUX or other brands, measure:

• the length and width of the outside curb, including the curb and any roofing membrane material, and
• the outside glass and width from the inside edge of the skylight cladding.

This short video shows how to measure curb-mounted skylights for a skylight replacement job.

Choosing the right skylight size

With measurements and product information in hand, contact VELUX customer service for assistance in selecting the right skylight size for the replacement.

Replacing the flashing

Make sure you protect the newly installed roof and skylight by installing new VELUX flashing on the new skylight. Doing so will ensure that your customer is covered by the VELUX 10-year No Leak warranty on product and installation.