A skylight is a special type of window built into the roof of a house in order to allow natural light to come into the house directly. A skylight may be installed for aesthetic purposes, or as part of a general passive-heating strategy. There are many different types of skylight, with differing designs, materials, and added components.
Many people end up choosing a skylight that is far too large for their house in order to try to add as much light as possible. Unfortunately, even the best skylights have much poorer insulation than a comparable space of roof, so a large skylight allows large amounts of heat to escape during cold weather, and too much heat to enter the house during warm weather. For this reason, it is recommended to consider how much direct sun the roof receives, and how great the temperature shift is from season to season, before choosing a skylight. In general, a skylight allows approximately eight times as much light to enter the house as a comparably sized wall window.
There are three main classes of skylight widely in use. A ventilating skylight may be opened to allow air to pass through. These skylights are ideal for bathrooms and kitchens, where they help to relieve excess moisture and keep the flow of air steady. Ventilating skylights may be controlled by a remote, by a hand crank, or by an automatic sensor which tracks inside temperature.
A fixed skylight is any type of skylight which doesn't open. This type of skylight is intended solely to allow light to pass into the house. Lastly, the tubular skylight is essentially a very small skylight, intended mainly for hallways and small rooms where a traditional skylight wouldn't easily fit.
There are nine main skylight styles in use, which may be used for both ventilating and fixed skylights. Five of these are relatively common in small to mid-sized houses, with the cost and difficulty of installation depending greatly on the style chosen.
A flat skylight is probably the most common, consisting of a square or rectangular piece of flat glass or acrylic, which may be fixed or ventilating. A round skylight emerges from the roof as a half-sphere bubble. A polygon skylight peaks up out of the roof with a number of glass or acrylic polygons -- these skylights are considerably more expensive than simpler models, but are also very aesthetically impressive. A pyramid skylight is a simple four-triangle pyramid which juts out of the roof. Finally, a dome skylight is similar to a flat skylight, except that the glass rounds up past the surface of the roof.
In addition to these primary residential styles, there are four styles of skylight more often associated with large buildings. The hip ridge skylight is a long rectangular skylight which peaks up above the roof surface to a central ridge, with a sloping triangular piece of glass on either short end. The ridge skylight is a simpler version, with two long triangles sloping in towards one another, and straight triangles closing off either end. The lean-to skylight is a simple slope which rises from the roof of one story and ends by leaning against an upper wall of the next story. The barrel vault skylight is a more complex form of the lean-to, which consists of a half-sphere against an upper wall, often seen in large arboretums.
The two main materials used to construct a skylight are glass and acrylic. Both have their strengths and weaknesses, and often it comes down to a simple matter of preference. Both have different glazings available, different insulation factors, and a slightly different look to the trained eye. Some other synthetic materials are also occasionally used, particularly Lexan, which has the added benefit of high durability, and is recommended for regions which experience powerful storms.
The glazing, insulation factor, and durability of a skylight are all additional factors to take into consideration when purchasing a skylight. Glass skylights may be purchased with multiple panes, with the area between the panes serving as a region of insulation. All skylights can be glazed to shield against UV radiation, to reduce the amount of light allowed to pass, or to increase the amount of heat that is retained. Purchasing and installing a basic skylight costs approximately US$1000-US$2000, with more durable and more technologically advanced models increasing in price rapidly. Ornate shapes and peaks also add significantly to the cost, while the installation of multiple modules will usually reduce the per-unit cost noticeably.