How Skylights Can Impact Solar Gain

yurt skylight

February 3, 2018

Skylights are much more than design elements. They can provide natural light, and when strategically placed, these roof-top windows can help heat and cool a building using the principles of ventilation and solar gain. As a result, skylights can assist in reducing energy costs on both lighting and climate control.

There are some important considerations to be aware of if you intend to install skylights. Placement, quality of the windows, glazing, and other variables can help homeowners maximize energy savings.

Because of the potential for future issues, it is not a good idea to choose cheaply made windows or discounted installation. Luckily, because of their energy saving potential, skylights often qualify for property assessed clean energy financing (PACE financing). PACE programs help homeowners handle the upfront costs of installing energy efficiency features such as skylights. This means that you can schedule the upgrade and installation now, and then pay for the improvement over time as a line item on your property tax bill.

Why is Investing in Good Skylights Important?

Skylights can help lower heating costs during the wintertime because of something called solar gain – an occurrence that takes place when heat from the sunlight passes inside a home. Obviously, a skylight is one of the most effective means of giving the heat-providing rays a path to the interior of the building.

In the summer, however, this benefit could become a significant disadvantage. The solar gain will work against air conditioners, fans, or other cooling appliances. If the skylight does not include features which allow it to negate the summertime solar gain, then the air conditioner in an average home could spend as much as 240 kWh (kilowatt hours) more energy than if the skylight was not installed at all.

Another drawback to consider: the loss of heat through the skylight in colder months could be greater than the heat provided by solar gain. Anyone who remembers elementary school science class knows that “hot air rises.” Since the skylight is at (or at least near) the highest point in the house, it is an ideal target for hot air trying to escape.

These drawbacks are not necessarily deal-breakers. However, they highlight the need for high-quality skylights that can capture solar gain when it is needed, keep heat inside, and block out the sun when solar gain will hurt energy consumption.

Finding the Right Specifications

Size, quality, and glazing are three important variables for selecting the right skylight. Energy Star has established an efficiency performance rating system specifically for skylights. This makes it easier to choose a properly insulated window that won’t release heat or cool air.

Correct sizing is also crucial. The Department of Energy says that a skylight should not be more than five percent of the floor surface area in a room with multiple windows. In a room with few windows, the skylight’s surface area can be up to 15 percent of the floor area.

The other specification to consider is glazing, which can help control solar gain. There are two options here: plastic and glass. Plastic glazing is cheaper than glass glazing. It is also more durable in terms of breakage. However, plastic is prone to scratching and discoloration.

Glass glazing is more effective at blocking UV rays, and it does not scratch as easily. Unfortunately, this type of glazing is more expensive than plastic alternatives. Glass-glazed windows may also have a special laminate layer on their interior side to protect against shattering.

Placement Matters

When it comes to solar gain, the location and slope of the skylight are significant. The first step is to make certain that there is nothing between the sun and the skylight. Trees, a chimney, an adjacent home, or other impediments may not fully block natural light, but they could still cast a shadow that will lower the effect of solar gain.

Also, in winter, the sun is lower in the sky than it is during the summer. Homeowners can take advantage of this natural phenomena by placing skylights on a south-facing section of the roof near an overhang. The skylight will allow the winter sun to enter and provide additional heat, but the overhang will block the direct sun in the summertime so that solar gain does not work against cooling appliances.

Fixed or Vented Skylights?

Would a home be better served by fixed or vented skylights? As the name suggests, fixed skylights cannot be opened. Vented skylights, on the other hand, can be opened. It might seem better to always have the option to open the skylight, but this flexibility is not superior in every situation.

Though quality installation can make both types of skylights virtually leak-proof, fixed windows better protect against leaks. Furthermore, since the window does not open, moisture will not seep in – even if the skylight is incorrectly closed. Vented skylights can, however, improve air circulation and also help reduce moisture. At the same time, improperly sealed or closed vented windows could allow heat or cool air to escape.

The skylight itself, either fixed or vented, is not much more expensive than a standard window. However, the cost of installation could be substantially more. If you opt for a vented skylight, a quality window and a skilled installer are even more critical than with a fixed skylight.

If a vented skylight is correctly installed and always properly closed, the aforementioned drawbacks will not be a problem.

Go Tubular

One alternative to a typical window-like skylight is a tubular skylight. These installations – also called solar tubes, light tubes, or sun tubes – consist of a weatherproof plastic dome and a tube of reflective material that runs below the roof. While they may not be as “attractive” as standard skylights from a design standpoint, these skylights provide many of the benefits of traditional models at a much lower cost.

Since they come with a tube, there is no need to cut a large opening for the light to reach the living space. The tube design is especially handy for homes with unfinished attics because installation only requires cutting two small holes: one in the roof and one in the ceiling of the living space. Also, the tube may be bendable so that it can twist around any pipes or other obstructions.

These tubes are effective at catching and amplifying natural light. For people who spend a lot of time at home during daylight hours, these installations can cut back on artificial light usage, especially if they are connected to interior rooms that do not have exterior windows.

The tubes do not allow as much solar gain as skylights – but this is a positive aspect for homeowners in warmer climates. However, if the goal of your skylight installation is to improve solar gain to reduce the amount of energy that you use for heat, going for a traditional skylight might prove a better option.

Making the Right Choices

Making the correct choices is very important when it comes to installing skylights. You will want to choose the type of window and other details that fit your specific needs, and make certain that everything is done with the highest quality products and greatest level of skill possible. That way you can get the many benefits of skylights – without having to deal with the potential drawbacks.

PACE can help you increase your home's comfort and energy efficiency. Call Ygrene at (855) 901-3999 to learn more, or check your eligibility online.