Skylight Leaks & Repairs on Flat Roofs- Watch Video

Rubber Gaskets on Skylights that Hardens and Crack

We typically find that leaks from skylights, that have been installed on rubber roofs, develop because of the degradation of the rubber gasket in between the window and window frame or the flashing around the curb that connects the skylight to the roof system. We install and repair all skylight leaks on flat roofs in Pittsburgh, Monroeville, New Stanton, Stamford, Greenwich and White Plains.

Installing new skylights is easy, however, repairing them can be a little more costly if there is degradation beyond the rubber gasket or curb flashing. If the extent of the leak involves any degradation to any portion of the rubber roof, we will gladly include the installation of a 2-ply Modified Bitumen membrane in that area, in addition to the replacement of a rubber gasket or curb flashing.

Skylights in place of Windows

When a room does not have windows, the best way to get natural light into that room is to install skylights. They can set the tone by enhancing the look and feel of a room. There are many types of skylights available in both glass and plexiglass.

Installing a Skylight

To install a skylight, determine the size of the opening and carefully cut through the roof. A skylight consist of 2 parts; the curb and glass or plexiglass, sections. The curb is the base that sits over the cut hole in the roof and is installed separately from the glass section, but both are secured. Metal flashing is placed around the curb and the Modified Bitumen 2-ply membrane is fused to it for a leak proof seal.

Repair leaky skylights on a flat roof

Skylights are notorious for leaks. When we are called to repair a leak around a skylight, the first thing we check is the condition of the roof; the type of roofing material that was used and the age of it. Each roofing material has its own technique for installation. Often, we find that skylight leaks can stem from the roofing material that has separated from the flashing due to age; single-ply rubber roofing often degrades due to shrinkage and ultraviolet degradation.

Another common leaking problem can be caused by the brittleness of the rubber gasket. Skylights have a metal frame whereby a rubber gasket is used to seal the window to the frame.

Skylight with metal frame

This is a skylight with a metal frame holding the glass in place. In between is a gasket that seals the glass and the metal. Part of the curb and flashing is exposed.

The gasket will get hard over time and crack causing a leak.

Why Does a Skylight Leak?

  • improper installation of the flashing
  • the gasket becomes old and shrinks compromises the seal of the window frame
  • a poorly designed skylight or placed at an improper angle
  • the plexiglass will degrade and crack from years of exposure to ultraviolet sunlight

The plexiglass on this skylight below is secured by a metal frame. The rubber gasket between the metal frame and plexiglass will deteriorate over time and need to be replaced.

Domed Plexiglass skylights

There are many type of skylights that takes on all kinds of shapes. The important fact to remember is when you install a glass skylight, the curb should be angled so water will not collect inside the frame that holds the glass. Most commonly a plexiglass skylights that are domed are the best choices for a flat roof.

Plexiglass Skylights

The plexiglass skylight is ideal for flat roofs, but they will need maintenance or replacement over the years due to ultraviolet damage to the plexiglass itself.

When stripping a flat roof, it is sometimes necessary to reinstall the curbs for height. Stamford

The curb on this skylight was removed when a new roof was installed. After the roof was done the skylight was re-installed.

Installing a Skylight on a Curb

The proper way to install a skylight is to have it sit on a curb as seen in the image to the right. The curb helps to make a transition to the roof and also keep the the skylight above the water and snow levels when a roof floods.

These are the best type of skylights for a flat roof. They stay clean and water and snow does not collect on top because the window is bubbled.

Plexi Dome skylights are very common and can last up to ten years without any maintenance.

Leaky Concerns with Skylights

It often happens that water will pool on a flat roof. Pooling water can eventually penetrate through the roof’s rubber membrane and metal flashing of a skylight resulting in a leak. The best solution, in this case, is to slope or build the roof up so water will not pool. The curb can also be raised, but that is not the best remedy because water will continue to pool there and penetrate the membrane again and again.

Skylight Manufacturers


Velux  is known for quality skylights, sun tunnels or roof windows. They also market solar, electric and manually powered skylights. No matter what the application is, they have the proper product for you. We have installed this brand many times without incident. As in the many repair calls we have answered, the issue of leaking is not the fault of the skylight itself, rather, it is the installation technique. It is very important that the flashing be installed properly. A pitch roof has a different kind of flashing requirement than a flat roof. Sometimes, a carpenter or roofing contractor will not know the difference and install the wrong flashing on a flat roof.


Wasco is another manufacturer of skylights. Wasco has all shapes and sizes and specialize in the acrylic type of skylight. If you want a circular or extended vault type of design, they are known for those kinds of specialty designs, as well.

Structure for all skylights are basically the same

There are many types of skylights, but they all have the same basic type of structure. A skylight has two parts; the glass section and the frame section called a curb. Some manufacturers will sell a curb with a skylight and some don’t. A carpenter can make a curb; it’s basically a wood frame. Regardless of the type of curb, some kind of metal flashing has to cover

Skylights on a Shingle Flat Roof.

When a roof is relatively flat, as in the picture below, shingles are not the best roof system to consider for installation. Shingles on a flat roof with any number of skylights is cause for concern. It will not matter how well the skylights are installed, many leaks will occur within a relatively short amount of time.

Two things went wrong on this roof:

The person who installed the roof did not know that the pitch was too low for the installation of shingles. Secondly, the skylights now had step flashing, and the curb was too low to the roof itself.

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Skylight Issues and Answers on Different Types of Roofs

Weakened Plexiglass: All skylights need maintenance. Depending on where a skylight is located on a roof, a plexiglass skylight may deteriorate and crack over time. If it is located in direct sunlight throughout the daylight hours, it will have a shorter life span id there is not protection from the ultraviolet sunlight. The glass in skylights will last almost indefinitely but the seal between the glass and the frame is will need maintenance over time.

Skylight Issues and Answers on Different Types of Roofs

Weakened Plexiglass: All skylights need maintenance. Depending on where a skylight is located on a roof, a plexiglass skylight may deteriorate and crack over time. If it is located in direct sunlight throughout the daylight hours, it will have a shorter life span id there is not protection from the ultraviolet sunlight. The glass in skylights will last almost indefinitely but the seal between the glass and the frame is will need maintenance over time.

Atrium Skylights:

As with all skylights, the frame that secures the glass has a gasket secured in between them. Theses gaskets dry out, shrink and causes leaks.

It is not easy to replace a gasket on steep shingled roofs, but on a flat roofs, regular maintenance is much easier.  Most of the time people use caulking to reseal a skylight glass to the frame, but if the appearance is an issue, it is best to replace the entire gasket.

This atrium style skylight on a flat roof can be maintained regularly to ensure the gasket between the glass and the metal frame remains strong and leakproof.

Level Skylights:

 Skylights are a very nice feature to add to a home or commercial building, but many things should be considered before installation. One such consideration is the angle for which it will best appear, be accessible for regular maintenance, and have little need for continuous repair. If completely level, these things will collect debris that should have washed away during rainstorms.

When installing a skylight on a flat roof, installing one without an angle will need more maintenance around the curb (notice the smeared tar).

Angled Curb Skylight:

 Skylights installed on a curb that is angled will prevent water and debris collection. For instance, care should be taken to install a skylight at a slight angle so that water and debris do not collect on the glass or around the curb. One can purchase skylights for a flat roof with angled curbs that can be professional placed for water flow toward a drainage system.

Its best to install a glass type of skylight with an angled curb. That way water will not collect on the glass and debris will wash off.

One Solid Piece of Flashing:

 It is important that a skylight be installed on a flat roof with curb flashing that is in one piece. The corners where the flashing meets the curb must be welded for a proper seal. Just as crucial for a water tight seal, the flashing must also be clean from debris or tar. In the case of EPDM rubber, the flashing on the right will not work. To create the best transition from metal to roof, we use the Modified Bitumen Torch Down membrane to fuse the materials together.

Preparing the Flashing for a New Rubber Roof:

 It is labor intensive work to clean and prepare the flashing of existing skylights, however, it is a very important process that must be done properly because the new rubber membrane must be attached to the metal.

Bubble, Domed, and Tunnel Skylights for a Flat Roof:

These Bubble skylights are made by Wasco Manufacturer. They are very popular on industrial commercial roofs because they allow ample light through. It is difficult for debris to collect on top of them. They also come in two parts; the curb and glass sections. Despite their effectiveness and low maintenance needs, they do not last as long as a glass skylight because the plexiglass dome becomes brittle and will crack over time.

This is called a bubble skylight. They are very popular on commercial roofs.

Domed Plexiglass Skylights are the best for flat roofs

The best choice for a flat roof skylight is a domed plexiglass skylight. Debris and dirt will not collect on top.

Fancy Skylights that can have an aesthetic value

Skylights add a certain effect to a room. Some skylight windows are tinted. Some have a atrium look. Still others have a tunnel look which all give a room more natural light. There should never be a problem with any skylight leaking. If the installation of the flashing is properly done, and regular roof maintenance becomes part of a homeowner or business owner’s routine, then damage from leaks will not be an costly issue.

Skylights on Metal roofs

As in the picture to the right, pouring and smearing tar to seal the flashing of a skylight onto the metal roof is an improper procedure. In a rather short time, the tar will dry out, crack, and leak water to the interior of the structure.

We have seen smeared tar used as a common fix for leaking flashing of a skylight.

Removing the old tar around a skylight on a metal roof is laborious and becomes an added expense to the building owner.

Rubber Membramne installed around Flashing

This what it looks like after the rubber membrane has been installed. This membrane will last for many years to come and will not crack with the expansion and contraction of the metal during heating and cooling conditions.

Torch Down Roofing Explained

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  1. Arline Van Gessel

    Great information! Wish you guys were in the SF Bay Area!

    • Naas Ferreira

      Thanks Arline
      We try to help where we can. I hope this article on skylights was helpful. We are busy putting an article together that is all about better drain systems.

  2. John

    Thanks for the 3d video on skylights. I have a better idea where to look for the leak. The 3 D video was well-made showing where the skylights could leak. I hope I can just find a product to seal the frame and Plexi Glass instead of replacing the entire unit.

  3. Mona

    Naas, I think you have done a great job showing people how to care for the skylights on their roofs. Will you please provide an estimate for replacing three skylights on my roof?


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