Skylights may be both aesthetically pleasing and functional additions to any home. Whether you're considering pitched roof skylights or flat roof skylights, they are an excellent source of natural light and can be an ideal alternative for conserving energy and lowering your utility expenses.

Skylights are a great way to bring in more natural light into your home, but did you know there are different types of skylights? Learn about the differences between skylights, rooflights, and roof windows. However, in order to get the most out of these windows, you must ensure that they are adequately insulated.

Skylights with proper insulation will not only improve energy efficiency and lower your bills but will also minimize noise pollution and make your home more comfortable to live in.

In this article, we will walk you through the ins and outs of skylight insulation, giving you helpful insights and practical ideas for tackling this home improvement project. Whether you already have a skylight or plan to install one, our guide will give you the information and ideas you need to efficiently insulate your skylight windows.

We will look at the various methods of insulating skylights, from rigid foam to batt insulation and window film, so you can find the best solution for your needs. And keep in mind that if you wish to receive the best advice and recommendations based on your specific situation, it's best to consult with a professional skylight installer.

The importance of proper skylight insulation

Having properly insulated skylights is important for several reasons, including:

  • Energy efficiency. Insulation plays a crucial role in ensuring the effectiveness and energy performance of the skylights. The better insulation, the more energy efficient the window is. The insulation of the skylights acts as a thermal barrier, reducing heat transfer and minimizing the impact on indoor temperature. As a result, you won't need to use a heating or cooling system too much, saving you money on electricity.
  • Noise abatement. Not properly insulated windows may let some external noise inside your home. This can be particularly annoying when living near busy boulevards. You can easily deal with this problem by investing in good insulation for your skylight.
  • Comfortable indoor environment. By insulating your skylights you can make your home much more comfortable to live in. Insulation can minimize heat loss and heat gain through the window, providing steady and pleasant indoor temperatures all year.
  • Protection from UV rays. Glare from the skylights might be bothersome at times, especially if you work in that room. In addition, this consistent streaming sunlight may cause fading of your furniture or artwork. Insulation with built-in UV protection or the use of appropriate window treatments can be particularly beneficial in such situations. Attaching window film, for example, can reduce UV ray penetration.

When considering skylight installation or replacing existing skylights, investing in quality insulation is critical for long-term advantages and a more sustainable home.

How to insulate a skylight window: Best practices

Here are some of the most popular methods of insulating skylights.

1. Installing rigid foam insulation panels

One highly efficient way to insulate your skylights is by installing a rigid foam insulation panel such as a hinged foam insulation board, rigid plastic sheets or closed cell foam insulation sheets. These panels are usually made of materials such as expanded polystyrene (EPS) or extruded polystyrene (XPS) foam which are highly resistant to air infiltration. Rigid foam insulation panels come in a variety of shapes and sizes, providing for insulation depth flexibility and customisation to accommodate varied skylight sizes and forms. They can be modified to meet certain architectural or design specifications.

Rigid foam insulation panels can be installed on various kinds of skylights including fixed skylights, operable skylights, and tubular skylights (light tunnel). You can also use them for skylight shafts. To insulate the area and enhance energy efficiency, the panels can be put along the skylight shaft walls. All rigid foams need to be additionally sealed with canned spray foam or caulk to effectively address air pressure dynamics. In some cases, high-quality tape may also work well.

2. Applying spray foam insulation

It is another popular option for insulating skylights. Spray foam is a material that is usually applied as a liquid which then expands to several times its original volume, adhering to the surface and forming a solid, cellular foam. The foam quickly cures and hardens, creating an insulating layer that seals air leaks, prevents heat transfer and provides thermal insulation.

Spray foams can be a good choice if you want to fill all the gaps and cracks around the windows. These products can be applied to the skylight frame, around wooden framing elements or the area around the skylight shaft to provide proper air sealing and stop the warm air inside from passing into the framing cavity.

3. Fitting fibreglass batts

Fitting fibreglass batts is a less expensive solution for insulating skylights. This is a kind of air-permeable insulation composed of tiny glass fibres that are densely packed together. These fibres trap air pockets within the material, which helps to reduce heat transfer through conduction.

Fibreglass batts are normally fitted between the framing members of a skylight, such as the studs and joists. They are positioned tightly within the space, ensuring full coverage and reducing gaps or holes. One of the sides of the batt is commonly made of paper or foil which acts as a vapor barrier.

While fibreglass insulation is a popular and cost-effective solution, it may have some limitations. The fibreglass batts may not give a proper fit around irregular shapes or angles associated with skylight frames or shafts because of their flexibility. This may result in indoor air leaks which is the main culprit of winter condensation.

4. Attaching insulating window films

Insulating window films are made of thin, transparent material, typically polyester. When applied to the surface of the glass, this coverage can prevent UV rays from streaming inside as well as minimize heat transfer.

These films are typically placed on the interior surface of the glass. There are several types of films available, some of which are self-adhesive and just need to be peeled and affixed, while others require a wet installation strategy that involves applying and positioning the film with a solution.

If you choose this skylight insulation technique it is best to invest in high-quality films and hire a professional to attach them. This is because not all window films are equal and some of them might be not as effective as you expected.

5. Selecting skylights with low-emissivity (Low-E) coatings and gas-filled glazing

In case you are planning to install new skylights or replace old ones, then you may want to consider having windows with low-emissivity (Low-E) coatings and gas-filled glazing. The Low-E coating is a thin metallic or metal layer placed on the glass. Choosing windows with such coatings will help you reduce glare caused by sunlight as well as achieve better insulation performance.

Also, when looking for new skylights think about investing in double or triple-glazed windows. Although they are typically more expensive, such skylights incorporate gas-filled glazing between the glass panes which significantly enhances their insulating properties.

6. Choosing skylights with a high R-value

Another important factor to consider when choosing new skylights is their R-value or insulation value. The higher the R-value, the greater the material's resistance to heat transfer and the better its insulation performance. This means that skylights with higher R-value will contribute to energy savings, hence lower utility bills too.

However, keep in mind that the R-value is impacted not just by the glass itself but also by the overall design of the skylight such as the frame and any other insulation or sealing measures. The proper installation has a key role in maximizing the insulation properties of the window and achieving great insulation value. Always work with a reliable skylight supplier and installer.

It's important to note that the R-value is a measure of resistance to heat flow, which is different from U-value that quantifies the rate of heat transfer; if you're interested in learning more about U-value, be sure to check out our dedicated guide on the topic.

How to choose the right insulation for you?

When considering insulation, the type of glazing in your skylights can make a significant difference. Check out our article on Double Glazing vs Triple Glazing for more details.

To determine which skylight insulation method is right for you, it is best to consult with insulation professionals or skylight manufacturers. The specialists can give you specific recommendations based on your needs and the characteristics of your skylight.

There are some factors that should be taken into account when determining the most suitable insulation option including the characteristics of the existing construction, the desired level of insulation, compatibility with skylight design and so on.

Rigid foams and rigid plastic sheets are usually very popular choices for skylight insulation. They can be used for insulating fixed and operable skylights as well as for skylight shaft insulation. Installed properly, they can effectively minimize thermal bridging and provide good insulation.

Spray foams are also very efficient in preventing moisture leaks and enhancing the energy efficiency of skylights. They can be a good choice if you want to prevent warm indoor air from escaping outside. Spray foams can also be an ideal solution for insulating skylight shafts. In such instances, they function as both an insulation layer and an air barrier. However, due to the specialized equipment and techniques involved, their application should be done by professionals.

Fibreglass batt insulation is a less expensive and easier-to-install option. However, you should be aware of the fact that fibreglass batts may not be as effective in insulating irregular or difficult-to-reach places. They can provide thermal resistance but may not achieve R-values as high as other solutions.

Insulating window films is another alternative that you may want to consider, especially if you want to reduce the glare that passes through your skylights. But while they can enhance energy efficiency to some extent by reducing heat transfer, their insulating properties are generally lower compared to other options.

When considering insulating a skylight do not forget to also pay attention to the roof sheathing surrounding the window. To create a seamless and continuous thermal barrier, the insulation should be precisely aligned and incorporated with the roof sheathing. This guarantees that there are no gaps or spaces, eliminating any potential air movement and air leakage that could undermine the insulation's effectiveness.

Ultimately, the best method for insulating your skylights will depend on your specific requirements and priorities. As stated earlier, make sure to work with a reliable supplier and installer to ensure your skylights are properly installed. Also, be aware of the building regulations for skylights to ensure compliance.

What costs are involved in insulation?

The cost of insulating a skylight can vary in a very large range starting as low as £80-100 and rising to £500. It is really difficult to provide you with a more accurate estimate because there are many factors that can influence the overall price. Here are some costs that are normally involved in the project.

  • The type of insulation you choose. Polystyrene foam insulation, spray foam insulation, fibreglass batts, and insulating window films all have different price ranges. Research the prices of various insulation options to get an idea of the cost per square foot or per unit.
  • The number and size of skylights you want to insulate. Obviously, larger skylights or multiple skylights will require more insulation material, potentially increasing the cost.
  • The cost of installation. It will vary depending on the extent of work required and the contractor you chose. Obtaining quotes from insulation contractors can give you a better understanding of the installation cost.

If you are planning to install new skylight windows, then you can expect to pay anywhere between £500 and £2000. The final installation cost will mainly depend on the existing roof construction, the type of skylight you choose, its size, etc. Insulation accounts for just a small percentage of the total installation cost. Tubular skylights tend to be less costly than regular fixed and operable windows. Double glazing is also usually a cheaper option compared to triple glazing. However, triple-glazed windows provide greater thermal performance, resulting in lower energy bills in the long run. 

If your existing skylights are old and less efficient, you might consider a skylight window replacement to improve insulation and reduce energy costs.

Frequently asked questions

Can you apply spray foam yourself?

Yes, you can do so, by using spray-it-yourself foam kits. You can normally find them in many home improvement stores. Such kits typically come with all the accessories needed such as pressurized tanks, applicator guns, nozzles and others. However, when working with such products remember to take safety precautions and follow the manufacturer's directions. Always wear a respirator mask and eye protection.

Are tubular skylights energy efficient?

Yes, in general, they are considered to be energy efficient. These types of skylights are designed to capture natural sunlight and distribute it into interior spaces. They consist of a dome or lens on the roof that collects sunlight, a highly reflective tube that channels the light, and a diffuser that disperses the light into the room. Despite being smaller than regular skylights, tubular skylights can still bring a good amount of natural sunlight, reducing the need for artificial light during daylight hours.

Is it expensive to insulate tubular skylights?

The cost of insulating a tubular skylight ranges from £30 to £60 depending on the specific insulating method, the materials used and the complexity of the job. Installing an insulation cover or sleeve around the tube inside the attic space is one common method of insulating a tubular skylight. These coverings are intended to minimize heat loss in the winter and heat gain in the summer, thereby enhancing energy efficiency.

If you are looking for a more comprehensive solution, you may consider installing an attic-side air barrier. Rigid foam panels are usually great for this purpose. Keep in mind, though, that such a project will usually cost you extra money.

Should you insulate skylight wells?

Insulating skylight wells or shafts is an effective approach to improve energy performance. It contributes to the formation of a thermal barrier surrounding the skylight, minimizing heat or cold transfer between the inside and exterior of the building. It is recommended that the walls of skylight shafts be insulated to the same level as other exterior walls if the attic through which they pass is not insulated.