Skylights can bring natural light and ventilation into a commercial or residential building, but they can also become a source of water intrusion when the roofing system around them begins to fail. A skylight leak is not always caused by the skylight itself. Problems with flashing, roofing materials, seals, fasteners, drainage, or even condensation can allow moisture to enter the building. Understanding the common causes and how professionals diagnose them is essential for preventing more extensive roof damage.
What Causes Skylight Leaks?
One of the most common causes of skylight leaks is failed or improperly installed flashing. Flashing creates a watertight transition between the skylight and the surrounding roof. If the flashing is damaged, corroded, poorly sealed, or incorrectly installed, rainwater can work its way beneath the roofing system.
Deteriorated seals and gaskets are another frequent cause. Over time, exposure to ultraviolet radiation, temperature changes, wind, and moisture can cause sealants and gaskets to crack, shrink, or lose their flexibility. Once these components deteriorate, water may enter around the skylight frame.
Roofing material around a skylight can also contribute to leaks. Cracked membranes, damaged shingles, punctures, loose seams, and deteriorated coatings can create pathways for water. In some cases, the skylight appears to be leaking when the actual source is several feet away and water is traveling beneath the roofing material before entering the building.
Loose or deteriorated fasteners can create additional entry points. Metal components may expand and contract with temperature changes, gradually weakening fastener holes and seals. On commercial roofs, aged membrane systems around skylights can be particularly vulnerable if maintenance has been neglected.
Another potential issue is poor drainage. Debris, leaves, dirt, or improperly designed roof slopes can cause water to collect around a skylight. Standing water increases the amount of time the roof assembly is exposed to moisture and can eventually lead to leakage.
Finally, not every moisture problem around a skylight is a roof leak. Condensation can form when warm, humid interior air contacts a cold skylight surface. Proper diagnosis is therefore important before assuming the skylight needs to be repaired or replaced.
How Are Skylight Leaks Diagnosed?
Professional skylight leak diagnosis usually begins with a visual inspection. A roofing professional examines the skylight dome or glazing, frame, flashing, sealants, fasteners, surrounding membrane, roof penetrations, and nearby drainage areas. Interior inspection is also important because water stains, damaged insulation, peeling paint, or wet decking can help identify where moisture is entering.
The inspection then moves beyond the visible leak. Roofing professionals look for cracks, punctures, open seams, deteriorated flashing, ponding water, and other defects that could allow water to travel beneath the surface.
When the source is difficult to identify, controlled water testing may be performed. Specific areas around the skylight are tested systematically while the interior is monitored for moisture. Moisture meters, infrared technology, and other diagnostic tools may also help identify wet insulation or hidden moisture within the roof assembly.
When Should a Skylight Be Repaired or Replaced?
The appropriate solution depends on the condition and age of the skylight and surrounding roofing system. Minor flashing or sealant problems may be repairable, while severely damaged glazing, frames, curbs, or surrounding roofing materials may require replacement.
The key is to diagnose the actual source of water intrusion rather than simply applying sealant over the visible symptom. A professional roofing inspection can determine whether the problem is the skylight, its flashing, the surrounding roof system, or condensation.
For persistent skylight leaks, early professional diagnosis can help prevent water damage, deterioration of insulation and decking, interior damage, and more expensive roof repairs.
Related Questions
- What is the difference between a unit skylight and a structural skylight?
- What are the most common causes of roof hatch leaks?
- What is the difference between a curb-mounted and deck-mounted skylight?
- What causes coping joint leaks and how are they prevented?
- How should skylights and smoke vents be flashed and maintained?
- What warranty covers skylights versus the roof membrane?
- How do you inspect a skylight without walking on or near it?
- How do you diagnose a leak from a clogged condensate drain pan?
Commercial Skylights & Roof Access
