Sealed simply means that the skylight cannot be opened like some other skylights. The benefits of this type of skylight include very little maintenance and reduced cost both to buy and install.

Sealed skylights are perfect for those spaces that do not require additional airflow, including hallways, stairways, living rooms and other areas of the house. They are also a good choice for hard-to-access roof areas since they require less maintenance than opening skylights.

No skylight of any kind that has been installed by an experienced, qualified professional should ever leak. Leaks typically occur because the skylight was installed by a homeowner or some other unqualified person in an effort to save money.

They should. Anywhere you install a sealed skylight, it will flood the space below with natural light, making it possible to turn off your electric lights during the day. This will likely result in a noticeable reduction in your home's energy bill and carbon footprint. 

They should. Sealed skylights should be just at home on seriously sloped roofs as they are on low-pitch roofs or even flat roofs.

Planning permission is typically required if the highest point on the skylight will rise above the highest established point of the existing roof. In addition, if your home is a Listed structure, it will almost certainly require planning permission. The same is true if your home is located in a conservation area.

Many types of sealed skylights are compatible with manual or solar-powered blinds. This allows you to control light levels during peak sun periods to protect furniture from the UV rays of the sun.

If it is professionally installed and properly maintained, it is likely that a sealed skylight will last 20 or 25 years. Maybe more.

If you believe it's in your best interest and the best interest of your home to replace a skylight that opens with one that doesn't, then replacement can be handled quickly and easily by a qualified and experienced professional.