The Ultimate Guide To Skylights

A skylight can be a wonderful way to add natural light to a home. Whether you’re a roofer who needs to replace a skylight, a contractor installing new skylights, or a do-it-yourselfer, you need to know what options are available. You should consider skylight size and shape, frame and glazing materials, opening or fixed style, cost, location on the roof, type of roofing, roof construction, and even mounting techniques. Measurement and skylight size selection is critical. You may need to measure the finished opening, the rough opening, or the outside of the curb. By carefully considering the options available, you can choose a skylight that you will enjoy every day for the life of your home. 

Skylight Placement

Your first major consideration should be placement of the skylight, which will also help you decide on size and possibly glazing type. From what direction will the sun be shining? How will the skylight look in the room? Is the location on the roof in an area that will not be likely to trap debris? What is the view outside? Depending on placement, you may see that beautiful oak tree or even a mountaintop! Higher on the roof is generally better, both to allow debris and dirt to wash off and to let in maximum light. When you decide generally where the skylight will be located, check for rafters, wiring, and duct work in the space above the ceiling where you will be cutting the holes and making the light shaft from the ceiling to the roof. Consider the various ways you can construct the light shaft itself to direct and/or maximize the light entering the room. You can install larger skylights (think 4 feet by 10 feet) with proper reinforcement of the rafters you need to cut; however, installing a skylight between rafters is simplest. Consider specially shaped or multiple skylights if you want an interesting architectural effect, a grander view, and more light.

Types of Mounting

There are two main types of skylights, described by how they are mounted on the roof – curb mounting skylights and deck mounting skylights, also called flush mounted skylights.

Square glass skylight mounted on a wooden curb sits atop a raised part of a home solarium roof
Glass curb mounted skylight

Curb Mount Skylight

A curb mounting skylight is mounted over a frame, called a curb – usually wooden – which is built up from the roof. Curb mounted skylights are ideal for very low-pitched roofs and those with metal roofing or shakes, and especially for replacing curb mounted fiberglass, acrylic, or plastic skylights. Commercial skylights for flat roofs are nearly always curb mounted. 

To install an SIG Curb Mounting (CM) Skylight on a roof with no existing skylight, we recommend using a knowledgeable contractor. They’ll need to build a curb and use proper flashing techniques. Replacing an existing curb mounted skylight is fairly easy and can be done by a DIY-er. Just remove the old skylight, being careful not to damage the curb or disturb the flashing. Seal the new skylight to the top of the curb with glazing tape or a quality sealant, and then fasten the new skylight to the curb with screws. 

Correct measurement is critical when ordering your skylight. Talk to the skylight vendor about which measurements to take. For the SIG Curb Mounting Skylight, measure the outside of the curb. You will also need to choose from two frame heights depending on the height of your curb. 

glass deck mounted skylights
Glass deck mounted skylights

Deck Mount Skylight

A deck mounting skylight attaches directly to the roof. This type of skylight has a lower profile and higher energy efficiency than curb mounts. You also have the benefit of not having to construct and provide flashing for a separate curb. Some deck mounted skylights, like SIG’s, are made with built-in flashing. Self flashing skylights have a metal, plastic, or rubber “flange” (the part that seals directly to the roof), and these flanges range from about 2” to 5” wide. 

SIG Skylights’ Deck Mounted Self Flashing Skylight (FM) is made with one piece of solid, welded aluminum, so there is no degradation over time and no possibility of leaks through the skylight frame. It has the widest flange available, at 4 5/8” wide. Installation of this SIG FM style skylight is straightforward, so it is ideal for the competent DIY-er. Many other deck (flush) mounted skylights require a complicated flashing kit, which costs more and requires specific knowledge to install properly. 

Deck mounted skylights come in many standard sizes. Many SIG deck mounting (FM) skylights are perfectly sized to replace common sizes of deck mounted skylights including fiberglass, acrylic, or plastic dome skylights with no or very low curbs.

SIG recommends deck mounted skylights for sloped, shingled roofs with a pitch of 3:12 or greater.

tubular skylight in hallway
Tubular skylight in hallway

Tubular Skylight

Tubular skylights can be a cheaper option for small areas like a closet or hall.  A small, often bubble-shaped plastic lens is installed on the roof deck. A flexible metal tube runs from the lens to the ceiling fixture, allowing light to travel through the tube into the room. This type of skylight can light a small area,  but provides none of the outside view and architectural aesthetics of a larger glass skylight.

Fixed Skylights or Operable/Vented Skylights

Skylights can be either fixed, or not opening – like a picture window – or operable, or opening, also called venting skylights. 

Fixed skylights are by far the most common and most recommended because of cost and reliability. Fixed skylights are simple – install and enjoy. 

Vented skylights can provide ventilation, which can remove some hot air at the ceiling. Typical vented skylights are hinged at the top and open a short distance with a manual crank and extension pole. If you are willing to spend significantly more, many other options are available, including electric, solar powered, remote opening, and blinds. All these options add cost and a much higher potential for breaking down. Most importantly, opening skylights are inherently more prone to leak than fixed skylights.

skylight in bedroom attic
Operable, opening or vented skylight

Types of Material

Skylights are made with glass, acrylic, fiberglass, or other plastic glazing. While acrylic skylights are economically priced and weigh less than glass,  a glass skylight is the better long-term investment.  Glass makes for a more energy efficient skylight, as well as more durable and MUCH more beautiful.

Glass skylights are generally made with double paned,  tempered,  insulated glass, which will remain clear forever. The insulated glass is more energy efficient because of the airspace between panes and thickness of the glass. Thicker glass is strong and less likely to break. If it does break, which can happen with a strike from a very heavy or sharp object, the tempered glass breaks into tiny pieces instead of larger sharp shards. Laminated glass is also an option.

Plastic dome skylights can scratch and break easily, and do not age well. Many plastic  skylights are not clear  even when new. All plastic will eventually turn hazy and yellow, and becomes increasingly brittle in sunlight. When this happens, your view is very diminished, less light enters the building, and the plastic cracks easily from a branch or tool falling on it, resulting in leaks and interior damage. Brittle plastic skylights also create a safety hazard in the case of falls from the roof through the skylights. 

If you already have a plastic curb mounted skylight, and you just want to inexpensively replace it to repair a leak or allow light into a garage or working area, and budget is very limited, go with another plastic bubble skylight. Otherwise, choose glass. Glass is more expensive, but well worth the initial investment in a home or business, especially when you consider that installation is usually the most expensive part. 

Consider the benefits of glass versus plastic. You certainly do not want to replace skylights frequently! 

Skylight Frames – Like windows, skylights come in a variety of materials and quality of construction, which can affect the operation and the life of a skylight. Many are made with a combination of materials; wood bodies with metal or plastic cladding is one popular type. Depending on the design, this type of skylight can allow water to seep into the wood and cause it to rot and eventually leak. Vinyl cladding cracks in the harsh climate on a roof, with constant attack from damaging UV rays. SIG Skylights frames are made from heavy, one piece welded aluminum, so they never degrade in the sun and will literally last a lifetime. 

Types of Glass Glazing

Skylight glazing (the see-through part) is either plastic or glass. We discussed the preference for glass above. Let’s discuss different types of glass glazing. 

While you can use clear glass glazing for skylights, we generally don’t recommend it. There are a variety of glass glazing colors and coatings you can use to reduce glare, reflect solar light, and reduce UV rays.

skylight Glazing Comparison

SIG Skylights’ standard skylights have a light bronze tint, shown in the left panel above. The tint blocks significant glare, UV rays, and solar heat gain while retaining great transparency. You can also choose a cooler gray color, shown on the far right. 

If your skylight will be exposed to full sun or if you have large or multiple skylights, you should consider SIG Skylights’ Solar Reflective Full Sun™ Skylights, shown in the center two panels. These have additional heat, glare, and UV blocking properties. When you look at the skylight from the outside, there is some reflection. You can still choose bronze or gray. 

You can also get a low-e, or low-emissivity, coating, which is applied to an inner pane and is nearly clear. We recommend low-e skylights where you want to have some heat and UV reduction compared with clear glass and still receive maximum light with little to no added color, for example, in an art studio. Please note that although low–e glass windows are known for their improved U or R (insulating) values, when installing low-e glass in a horizontal position like a skylight, the benefit is largely negated, so other glazing choices often provide better overall performance, sometimes at a lower cost.

An additional glazing offering is a “hurricane glass” skylight. Designed for areas where hurricanes are common, this type of skylight meets the Miami-Dade County, Florida standards for impact resistant skylights. It has a plastic layer laminated between thick  glass panes. Thinner laminated glass is also available at a lower cost.

Skylight Shape and Size

The most common skylights are square or rectangular. SIG’s standard sizes range from 13½ X 13½ inches to 49 ½ X 49 ½ inches, with many different sizes between.

If a standard size doesn’t meet your needs, you can order skylights in almost any size and geometric shape with straight lines, even skylights with multiple panes.

custom multiple skylights
Custom multi-paned skylight by SIG Skylights

Custom skylights take more time, since they will need to be designed specifically for you. You will need to provide exact measurements or, for some special shapes, have someone draw the design. You can see more custom shaped skylights here.

octagon skylight deck
Octagon skylight

Skylight Installers

A skylight is part of your roof, and if installed properly, can be a beautiful, functional, trouble-free feature. Installed improperly, however, they can cause leaks. With either deck mounted or curb mounted skylights, you need to take steps to ensure the installation is watertight with good quality self-sealing underlayment and proper flashing technique. Unless you are a serious DIYer,  it is safest to have a well qualified contractor install your skylights. A skylight specialist may be the most expensive option. Sometimes they are affiliated with and install skylights from just one major skylight supplier. Another fine option is a builder or remodeling contractor. Roofers are also commonly installers of skylights, as a good time to replace a skylight is when the roof is being replaced. This is discussed in another blog. For skylight replacements or installations on an existing roof, it is best to use an experienced roofer. Either way, we recommend you review the manufacturer’s installation instructions with the contractor to be sure they agree to follow the skylight manufacturer’s guidelines. Regardless of who you choose, make sure they are experienced in installing skylights, and particularly the type of skylights you plan to use. Also, insist on an installation warranty against leaks in addition to the skylight warranty provided by the manufacturer. References are a good idea, and – as always – make sure the contractor is bonded and insured. SIG Skylights is happy to give you the names of skylight installation contractors who have installed our skylights in your area. 

Cost of a Skylight

When considering new skylights,  you need to consider both the cost of the skylight and the cost of installation labor and materials.  Many people do not realize that the actual cost of the skylight itself is often much less than the installation cost.

A skylight alone can cost from $150 for a small basic plastic dome skylight to $5000 or more for a remote operated venting  glass skylight with blinds. Costs vary greatly depending on the skylight size, mounting type, materials and options. Custom  size skylights and custom shaped skylights cost more than standard sized ones. Curb mounted skylights are cheaper than deck mounted skylights, but you must also add $150 to $300 for the cost of building  a curb and flashing it. Quality insulated glass skylights cost  more than acrylic or fiberglass skylights, but pay back their value in the long run in efficiency and longevity.

A Typical Skylight Cost

 A common size skylight  is 22 ½” x 46 ½”, which fits between 24” spaced rafters.  A fixed glass, deck mounted  skylight this size is typically $300-350, plus about $100 if the particular skylight requires a  flashing kit. The same size in a curb mounted glass skylight costs only about $200-$250.

Skylight Installation Cost

Of course, installation, which can range from $200 to $3000, is not included in the cost of the skylight. Skylight installation costs depend on your contractor and the actual work to be done. If you install the skylight when building a new home or installing a new roof, costs are often less. You’ll pay more if your contractor needs to remove existing shingles,  cut through rafters or trusses and alter the framing, install on a tile or metal roof, or build a chase, or light tunnel, due to the additional planning and labor. Building the chase can add $1000 to $2000, including finishing and repainting the ceiling. Simply replacing a skylight on an existing asphalt shingle roof may cost $200 to $400,  and more for tile or metal roofs.  The cost will be lowest when the roof is already being replaced, and higher if they have to remove some existing shingles to replace it. 

Remember, the costs quoted are averages. Your skylight retailer and contractor can give you a detailed quote so you know exactly what you’re paying for.

Caring For Your Skylight

When you’re planning for your new skylights, you should think about how to keep them clean and working properly. Avoid debris and ice build-up, as it can cause problems because of the expansion of the water when it freezes. Plan to clean your skylights yearly – both inside and outside. If you have operable skylights, check and lubricate hinges and other moving hardware. 

Check skylights for damage periodically, especially after major storms. While standard skylights can withstand normal weather, they can be damaged, and it is always better to find any issues as soon as possible so that you can fix them before they become major problems. 

Planning for your skylights may take some time and research, and careful thought while you decide on the options. Taking the time to plan now, however, will help you to enjoy them fully and lead to a longer life for your new skylights.


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