How to Replace a Leaking Skylight

If left unaddressed, a leaky skylight can cause significant damage to your home’s interior. Fortunately, replacing a skylight is a manageable project for homeowners with moderate carpentry skills.

In this video and guide, This Old House general contractor Tom Silva demonstrates the process of replacing a leaky skylight step by step, ensuring a watertight seal to protect your home from water damage.

Preparing for Skylight Replacement

Before beginning the replacement process, it’s essential to gather the necessary tools and materials and take proper safety precautions.

Choosing the Right Skylight

Selecting the appropriate skylight for your home involves evaluating various factors:

1. Size and shape: Choose a skylight that fits the dimensions of your existing roof opening.
2. Glazing options: Consider double or triple glazing for better insulation.
3. Ventilation: Some skylights offer ventilation features to improve airflow in the house.

A Brief History of Skylight Leaks: Skylights have come a long way since Thomas Jefferson installed them at Monticello. As Sharon Park, a historical architect for the National Park Service, noted in This Old House Magazine: “They were notoriously leaky, and, due to their single glazing, often had problems with interior condensation.” Modern skylights benefit from double- or triple-pane insulating glass, heat-reflective low-e coatings, long-lived silicone or EPDM gaskets that seal the gap between sash and frame, and built-in condensation channels that stop interior drips before they dissolve drywall.

Tools and Materials Needed

To replace a leaky skylight, you’ll need the following:

• Flat pry bar
• Drill/driver
• Galvanized ring-shank nails
• Hammer
• New skylight unit
• Roofing shingles
• Self-sealing ice-and-water membrane
• Step flashing
• Counter flashing
• Head flashing
• Utility knife

Safety Precautions

Working on a roof can be dangerous, so it’s crucial to take proper safety measures. Use a sturdy ladder and secure it properly. Wear non-slip shoes with good traction, and use a safety harness if working on a steep roof. Work with a partner for added safety.

Removing the Old Skylight

The first step in replacing a leaky skylight is to carefully remove the old unit. This process involves removing shingles, flashing, and the skylight itself.

Remove Shingles and Flashing

Start by removing roof shingles around the skylight, beginning three to four courses above it. Here’s how:

1. Use a flat pry bar to carefully lift and remove shingles, exposing the step flashing.
2. Unscrew and remove the counter flashing from around the skylight.
3. Pry off the step flashing from the sides of the skylight.
4. Remove the head flashing from the top of the skylight.

Technique Detail: To remove shingles without damaging them, slide a flat pry bar under the shingle from below, work it up to grab the nail, then push down on the bar while gently pulling the shingle and the nail up at the same time. Once the nail is loosened, bang the shingle back down flat and pull the nail out cleanly.

Remove the Skylight Unit

Next, you’ll lift out the old skylight. Each step is important to avoid damaging the surrounding roofing material. Make sure to double-check that all fasteners are removed before attempting to lift the skylight out of the opening.

1. Use a utility knife to cut through the ice-and-water membrane around the skylight curb.
2. Peel back the membrane to expose the brackets holding the skylight to the roof deck.
3. Unscrew the brackets from the skylight curb.
4. Carefully lift the old skylight out of the opening.
5. Cut through the membrane along the bottom to completely free the skylight from the roof.

Installing the New Skylight

After removing the old skylight, you can prepare and install the new unit. This process involves several steps to ensure a proper fit and watertight seal. Before installation, take these preparatory steps:

1. Install any included accessories, such as a solar-powered window shade.
2. Attach the interior wooden trim package if provided.
3. Mark center lines on all sides of the skylight and the roof opening for proper alignment.

Ensuring the new skylight is properly prepared will make the installation process much smoother. Keep the instructions provided with your skylight handy for specific details related to your model.

Flashing the Sill First: Before placing the new skylight, apply a strip of self-adhesive membrane across the bottom edge of the roof opening, making sure it sits on top of the shingle below the opening and under the underlayment on the sides. Cut the ends diagonally and fold them into the opening. This critical step ensures any water that reaches the sill is directed safely onto the shingles below.

Position and Secure the Skylight

Proper alignment of the skylight is crucial. Take your time to make sure it is centered in the opening before securing it in place.

1. Place vinyl strips around the perimeter of the roof opening to cover exposed drywall edges.
2. Carefully lower the new skylight into the opening, aligning the center marks.
3. Secure the skylight by driving 2-inch galvanized ring-shank nails through the mounting brackets and into the roof deck.

Alignment Technique: On a This Old House project, Tommy marked center lines on each side, top, and bottom of both the roof opening and the skylight itself. By lining up these reference marks when positioning the unit, the skylight was perfectly centered in the opening without guesswork.

Waterproofing the Skylight

Proper waterproofing is crucial to prevent future leaks. Apply a self-sealing ice-and-water membrane along the bottom of the skylight. Cover both sides of the skylight and bottom flashing with continuous strips of membrane.

Then, install the proper flashing. Each type of flashing has a specific role in directing water away from the skylight. Make sure to follow the manufacturer’s instructions for installing the flashing components provided with your skylight.

1. Install the bottom flashing by lifting the rubber gasket at the lower end of the skylight and slipping the flashing into place.
2. Nail the bottom flashing to the sides of the skylight curb and down to the roof deck.
3. Along the sides of the skylight, install step flashing between each course of shingles. Nail the step flashing to the skylight curb, not the roof deck.
4. Install counter flashing around the perimeter of the skylight, starting at the bottom and working your way up and around.
5. Attach the head flashing across the top of the skylight, ensuring the upper edge is tucked beneath the roof shingles.

Finishing the Skylight Installation

The final steps involve replacing shingles and testing the new skylight to ensure proper function.

Reinstall roof shingles removed earlier, starting at the bottom and working up the roof. As you continue installing roof shingles, be careful not to nail through the step flashing. Finish with the shingles above the skylight.

Maintenance Tips for Your New Skylight

To keep your new skylight in top condition and prevent future leaks, inspect the skylight and surrounding area annually for signs of wear or damage. Clean the skylight regularly to prevent debris buildup, and check and reseal any visible gaps or cracks in the flashing or sealant. Promptly trim overhanging branches that could potentially damage the skylight.

Consider scheduling a professional inspection if you notice any issues with your skylight. Regular maintenance will extend the lifespan of your skylight and keep your home protected from water damage.

Additional Considerations When Replacing a Skylight

When replacing a skylight, there are a few additional factors to consider that can impact the success of your project. Check local building codes to ensure compliance with regulations.

Consider the orientation of your skylight to maximize natural light and minimize heat gain, and think about adding blinds or shades to control light and temperature inside your home.

Maximize Your Light: Architect Duo Dickinson wrote in This Old House Magazine that centering a skylight in the middle of a ceiling actually minimizes the light it brings in — light simply spills straight down to the floor. Instead, positioning the skylight so that a wall forms the back or side of the skylight well allows light to bounce off the wall and reach farther into the room. For the best results, set the skylight against the back wall of the room, opposite any windows, to even out illumination.

Our Conclusion

Replacing a leaky skylight is a manageable DIY project that can significantly improve your home’s comfort and energy efficiency. By following these steps and using quality materials, you can ensure a watertight installation that will protect your home for years to come. Remember to prioritize safety and consult a professional if you’re unsure about any aspect of the installation process.