How Do You Stop Condensation In A Solar Tube?

Do you have a solar tube in your home that is accumulating condensation, and do you want to know how to stop it? You’ve come to the right place, for we have researched this question, and we have the answer for you.

Silicon caulk is effective in preventing warm air from reaching the cooler metal surfaces and creating condensation. Insulation like fiberglass batt and expanding foam can prevent a temperature difference inside the tube.

Let’s talk more about the different techniques of how to prevent condensation inside your solar tube in the sections below.

Read on!

Dome shaped solar tube skylight on asphalt shingle roof, How Do You Stop Condensation In A Solar Tube?

What is a solar tube?

Solar tubes—also known as tubular skylights, light pipes, or light tubes—are small channels through your roof and ceiling that bring the light of the sun into the dark areas of your house.

The name can be misleading since there are solar-powered tubes that heat water, but this is not that.

A solar tube has a pipe with a reflective inner layer that connects to a translucent panel on your roof that provides an entry path for the light of the sun that hits your roof. The pipe connects to a light diffuser inside your house where it can radiate the light from the sun throughout a room or hallway.

Solar tubes are more compact than traditional skylights and cost less to install. Because of their smaller size, they are less likely to leak, unlike skylights.

The design of solar tubes makes them look like sleek domes on your roof instead of large bulky constructs. This can be important in preserving the aesthetics of your roof.

How do solar tubes work?

Dome shaped solar tube skylight on asphalt shingle roof

The part of solar tubes that are on your roof can be anywhere from 10 inches to 24 inches in diameter. This panel redirects as much light from the sun as possible into the reflective tunnel. A weather-resistant acrylic dome protects this topmost layer.

The reflective tunnel redirects the light into your home. You can install your solar tubes at an angle, but you need to follow the manufacturer’s instructions when it comes to the length and total angle of the tube. keep in mind that longer tubes will diminish the light that reaches your home.

The part of the tube that connects to your roof is normally perpendicular to the outer surface of the roof, while the part of the tube that goes to your house is perpendicular to the ceiling. The meeting point of these two tubes creates an angle.

The reflective tube can be extended to any length to match the space between your ceiling and roof. The reflectiveness of the tunnel produces a continuous mirror for capturing as much sunlight as it can.

Some solar tube manufacturers add an aluminum mirror on half the perimeter of the dome on your roof. This aluminum mirror faces the sun and reflects additional light from the sun into the tube. This helps increase the amount of light that gets into your home.

Some solar tube models include solar LEDs. These LEDs charge during the day and automatically light up once the sun sets. The solar LEDs allow the solar tube to provide light for an entire day.

Natural Light Energy Systems 10-Inch Tubular Skylight is available on Amazon through this link.

How does condensation happen on a glass?

Solar light tube on tiled roof.

Let’s talk about what condensation is so that we can understand better the solutions that are needed to stop condensation inside your solar tube.

If evaporation is the process where liquid matter turns into gas, condensation is the opposite process. Condensation allows the transformation of gaseous matter into liquid.

First, a gaseous matter must lose energy to turn into liquid.

Water vapor in the air is in a gaseous state.

When water molecules lose some of their heat energy, their movement slows down. The distance between the molecules becomes smaller as their movement slows down. As water vapor molecules lose more heat, their movement becomes slower, and the distance between molecules becomes less until the molecules become close enough to each other to turn into liquid.

Warm air from outside your house has a lot of water content.

The heat causes the molecules of water to move very fast and turn into gas. When the warm and water-vapor-rich outside air gets into the tunnel of your solar tube, the cold temperature of the metal tube will cause the water molecules to lose their heat energy and turn into water. Thus, forming condensation in your solar tubes.

Dangers Of Condensation In Solar Tube

Condensation inside the tube can lead to mold growth. Moreover, it can also rust the screws and the clips that hold the tube and joints together. To make it worse, it can also rust the reflective tube if it is made of steel.

Rust on the screws and clips will compromise the structural strength of the solar tube. Rust on the reflective surface reduces the effectiveness of the tube to relay light into your house. Molds bring with them a health risk for you and your family.

How to prevent the formation of condensation in your solar tube?

Dome shaped solar tube skylight on asphalt shingle roof

Condensation forms when warm air gets into the tube and the cold metal of the tube removes the heat energy from the air molecules.

The solutions below will revolve around this concept to prevent the formation of condensation inside your solar tube.

Sealing The Tube

Solar light tube on a tiled roof.

Most solar tube designs do not have a perfect seal on their protective dome. The protective dome can either be acrylic or polycarbonate. These two materials expand when heated and contract when cooled.

What this means is that the dome will not have a perfect fit with the tube that goes into your house because it needs to have space to contract during winter. Without that gap, the protective dome can crack once it contracts because there is not enough space for contraction.

An expanding protective dome doesn’t have the same problem when it comes to space. The protective dome can expand as much as it needs. However, this means that the gap between the protective dome and the tube gets bigger when it expands on warm days.

This means that there is more warm air (that is full of water vapor) getting into your solar tube whenever it is hot outside. The cold air inside your house cools this air and produces condensation.

Sealing the protective dome with silicone caulk will prevent warm air from entering your solar tunnel.

Gorilla Silicone Caulk & Seal is available on Amazon through this link.

Insulating The Tube

Condensation happens because the cold metal surface cools the warm air that is heavy with water vapor.

The air around your house can easily cool the surface of the tube because it is made of metal. Moreover, cold air coming from inside your house can fill the reflective tube. The temperature difference will produce condensation.

Moreover, the uninsulated solar tube will be a route to lose heating during winter.

If it is not possible to seal the protective dome, another option is to insulate the reflective tube.

This route is more effective if you also seal the light diffusing panel. Use a white self-adhesive sealing strip that has an adhesive only on one side.

Apply the weatherstripping on the part of the reflective tube that makes contact with the diffusing panel. Make a circular seal when you apply the weatherstripping, making sure that there is no opening between the two ends of the weatherstripping when you make a circle with it.

Self-Adhesive Seal Strip Weatherstrip is available on Amazon through this link.

Insulating With Fiberglass Batt

One effective insulation that you can use is fiberglass batt. Wrap the outer surface of the tube with a fiberglass batt. Use polyethylene tape to connect the edges together.

Make a diagonal slice on one edge of the batt so that it will be flush with the other side after it wraps around your solar tube. Alternatively, use smaller parts of fiberglass batt that you attach to each other with polyethylene tape.

Once you’ve covered the entire outside surface of the solar tube, you can connect the top and bottom of the solar tube insulation to the attic and roof insulation. You can use expanding foam to connect the insulation. Alternatively, you can install the fiberglass batt until it gets under the attic or roof insulation.

Finish the insulation by sealing any gap with caulk or sealant.

Blue Summit Supplies Polyethylene Tape is available on Amazon through this link.

Insulating With Expanding Foam

Another way to insulate the metal tube is with expanding foam.

Spray insulating foam on the surface of the metal tube. Quickly spread the foam after applying a few square feet. Keep applying and spreading until you cover the entire surface with expanding foam.

This method allows you to easily connect the top and bottom solar tube insulation to the attic and roof insulation.


Knowing how condensation forms is important to understanding how to prevent it from forming inside your solar tube. Keeping your solar tube condensation free is important in preventing possible health hazards inside your home and in preserving the structural integrity and effectiveness of your solar tube.

If you enjoyed reading this article, you might find the articles below equally enjoyable to read:

How To Insulate A Roof From The Inside?

How To Install Radiant Barrier Roof Sheathing?

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