Common Causes of a Leaking Skylight
Skylights are a fantastic way to bring natural light into your home, but when they start leaking, they can cause significant damage to your ceiling, insulation, and even your walls. Understanding the root cause is the first step toward a permanent fix. Most leaks are not due to the glass itself but rather the installation or aging components surrounding it.
- Failed Flashing: The metal flashing that seals the gap between the skylight and your roof is the most common culprit. Over time, it can corrode, crack, or simply pull away from the roof due to thermal expansion.
- Cracked or Missing Sealant: The rubber gaskets or silicone caulk around the perimeter of the skylight can dry out and shrink, creating gaps for water to seep through.
- Improper Installation: If the skylight was not installed with the correct pitch or was set too low against the roofing material, water can pool around the frame instead of running off.
- Damaged Shingles: The shingles directly above the skylight may be broken, curled, or missing, allowing water to run underneath the flashing.
- Condensation Issues: While not a true "leak," excessive condensation inside the glass can mimic a leak. This often points to a broken seal on a double-pane unit or poor bathroom ventilation.
Step-by-Step Guide to Resealing Your Skylight
Before you climb onto the roof, inspect the leak from inside your attic during a rainstorm. Mark the exact entry point with a piece of chalk. Once the roof is dry, follow these steps to reseal the skylight effectively.
Tools and Materials You Will Need:
- Ladder (stable and tall enough to reach the roof safely)
- Utility knife and putty knife
- Wire brush (for cleaning metal)
- High-quality exterior-grade silicone caulk or butyl tape
- New flashing (if old is severely rusted)
- Roofing nails and hammer
- Safety harness (highly recommended)
| Step | Action | Key Tip |
|---|---|---|
| 1 | Remove old sealant and flashing | Use a utility knife to cut away old caulk. Pull flashing nails carefully to avoid damaging surrounding shingles. |
| 2 | Clean the surface thoroughly | Scrub the area with a wire brush to remove rust, dirt, and old adhesive. Wipe down with rubbing alcohol for a clean bond. |
| 3 | Install new flashing (if needed) | Slide the new flashing under the shingles above the skylight. Secure with roofing nails but do not overdrive them. |
| 4 | Apply fresh sealant | Run a continuous bead of silicone caulk along the top and sides of the flashing. Use a putty knife to smooth it out. |
| 5 | Test the repair | Wait 24 hours for the sealant to cure. Then, spray the area with a garden hose for 10 minutes. Check inside for any moisture. |
When to Replace Instead of Repair
While resealing can solve many leaks, some situations demand a full replacement. If your skylight is over 15 years old and the glass is foggy or the frame is warped, a new unit is a better investment. Modern skylights come with integrated flashing systems and low-E glass that significantly reduce heat loss and condensation. Additionally, if the wood curb (the raised frame on the roof) is rotting, no amount of caulk will fix the structural failure.
Pro tip: If you notice daylight around the edges of the frame from inside your attic, the seal has completely failed. In this case, a full replacement is often more cost-effective than chasing leaks with sealant.
Preventive Maintenance for Long-Term Results
Once you have resealed your skylight, regular maintenance can prevent future leaks. Every spring and fall, perform a quick visual inspection from the ground using binoculars. Look for lifted shingles, cracked caulk, or debris buildup around the skylight. Keep the gutters directly below the skylight clear to prevent ice dams in winter, which can push water up under the flashing.
Finally, remember that roof work is dangerous. If your roof has a steep pitch, is more than two stories high, or if you are uncomfortable working at heights, hire a licensed roofing contractor. A professional will have the liability insurance and experience to handle complex flashing details, especially on tile or slate roofs.