Sealing skylight windows prevents water leaks. You'll need the proper knowledge and materials, as well as enough courage to work on your roof!
Step 1 – Find the Leak
First search your skylight and roof area to find out exactly where leaks are located. Pinpoint whether the skylight itself is leaking or your roof is leaking moisture through the flashing.
If your skylight opens and closes, such as a ventilating skylight does, you will need to ensure that it was installed properly. With proper installation, the skylight itself should not leak. Poor installation may result in skylight windows that do not close securely and thus allow moisture inside. In this case, you should not use caulk or roofing cement. Instead give attention to proper installation.
Leaks often develop around the area where your skylight meets the roof. Roofs at a low pitch are especially prone to leaks because they do not drain water as efficiently as high-pitched roofs. Typically, the problem in these areas will be with the flashing. Shingles do not tend to leak unless they are old or damaged.
Skylight leaks become a little more complicated in regions where heavy snowfall occurs. Usually, the downward pattern of shingles prevents roof leaks, but if too much snow and ice collect on a roof, water can cause an ice dam and actually leak upward, resulting in problems. In this case, simply sealing skylight windows may not provide a sufficient answer to the leak problem. You may need to purchase special products that are designed to keep these ice dams from leaking through skylight windows.
Step 2 – Seal the Flashing Area
To seal these types of leaks in the flashing area, you will need to raise the shingles near the skylight window. Identify the areas where the flashing meets the roof and spread roofing cement around the entire window at these sections. You should spread the cement at a thickness of about 1/4 inch.
Step 3 – Secure the Shingles
Then apply roofing cement to the bottom side of the shingles that belong around the skylight window and secure the shingles again. Be sure to push the shingles down securely around the areas where they meet the flashing. Spread more roofing cement if needed.
Finally add roofing cement to the top areas and edges of the shingles, where other shingles meet and overlap. You may need to be especially careful of the areas above skylight windows, where water will flow down, though you should give plenty of attention to every shingle that surrounds skylight windows. Secure each of these areas with roofing cement until the entire area is sealed.