Leak Free Skylight Installation

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Plastic 'bubble' skylights, commonly installed in the 1970s, helped create the leaky, unreliable image that homeowners still hold. Installed properly, glass skylights won't leak.

September 06, 2000

It’s difficult to overcome a negative first impression, and that’s just what remodelers have to do when installing skylights. Plastic "bubble" skylights, commonly installed in the 1970s, helped create the leaky, unreliable image that homeowners still hold. Installed properly, glass skylights won’t leak. Velux-America, now launching a sales program geared towards remodelers who use skylights, offers the following installation guidelines:

1. Choose the measurement type to work with. Rough openings allow for more flexibility when installing skylights, but using the frame dimensions provides a straighter fit. Cut the opening as desired.

2. Frame the light shaft. Consider flaring the shaft at the top and bottom. Not only is it more pleasing, architecturally, it also lets more light into the room and provides better air circulation and ventilation.


Step 5: Mount the brackets.


Step 6: Screw Skylight over the rough opening.


Step 7: Position the skylight on the roof.


Step 10: Flash the skylight.


3. Ventilate the framing. In vaulted ceilings, skylight headers block airflow between soffits and ridge vents. To compensate, drill holes through the rafters above and below the headers, after checking size and placement codebooks for guidelines.

4. Remove the cladding. Do this on a level surface to prevent damage.

5. Mount the brackets. Thickness and profile of roofing material will determine the skylight’s ideal mounting bracket position.

6. Screw skylight over the rough opening. Thin roofing requires no bracket adjustment. Thicker roofs, such as those made of tile, will necessitate a bracket adjustment. Drop the bracket down by as much as 3/4 inch.

7. Position the skylight on the roof. Line the edge of the skylight frame up to the edges of the rough opening.

8. Secure the mounting brackets. Standard fasteners can be used on shingles. The mounting bracket attaches to the roof sheathing. In other applications, you may need to raise the skylight to the proper height by lowering the brackets and wrapping the skylight with underlayment.

9. Install underlayment. All skylight installations should include underlayment. Felt paper works for many applications, but for extremely cold or wet climates, use rubberized self-adhesive underlayment. Install the underlayment before flashing, and make sure the underlayment covers 4 inches up the skylight and at least 5 inches along the roof deck.

10. Flash the skylight. Reinstall cladding before flashing. Be sure to place the sill flashing between the under-glass rubber gasket and the bottom frame. Cover any exposed flanges with "dummy" shingles. Be sure to place one piece of step flashing with each course of roofing material.

11. Replace the cladding. Reinstall the bottom frame cover before the side covers. Next, replace the screws before securing the top cladding into place. Then the interior light shaft can be insulated and finished.

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