Another concern is that the skylight be properly installed. Many 'do-it-yourselfers' today prefer the flush-mount self-flashing models. You simply remove the appropriate amount of roofing, cut the hole to the correct size, and mount the skylight right on top. The flashing, used to keep out water, comes with the unit and you replace the roofing material right on top. The less expensive edge- or curb-mounted models require that a curb be built onto the roof to accommodate the skylight and that flashing be manufactured on the site. Professional installation is required. Here is an excellent article on the history of skylights.
If the skylight is not properly installed, it will indeed leak. For that reason, professional installation is recommended. However, a 'do-it-yourselfer' who purchases a flush-mount self- flashing unit and follows the instructions carefully should not have problems. Beware of installing skylights on tile roofs. The roofs themselves are fragile and simply walking on them incorrectly can result in breaking the tiles.
Some buildings do not have an attic. Instead, the roof is attached to the top of the rafters. And, insulation is installed between the ceiling and the rafters. A skylight can be installed in this case in an attractive manner without compromising the roofs structural integrity. In this case, the rafters will be left in their existing position. The skylight will be installed on top of the roof by the removal of both the ceiling and the insulation that is installed between the rafters. The space between the rafters is framed in a manner that enables the skylight to be completely secured to the roof. The exposed rafters provide a contemporary design to the room below the skylight. Be sure to utilize a skylight that sealed and cannot be opened. A skylight that can be opened will expose the rafters to too much weathering from the elements including sunshine.
There are important considerations when setting the framing of a large skylight. It is important that the integrity of the roof not to be weakened if the rafters are cut. If the roof has been constructed according to snow-load building requirements this concern becomes even more important. In the event that the space between the rafters is too narrow to install the skylight that has been selected, one rafter will be cut after the remaining rafters are reinforced before the frame for the skylight box is constructed. For a particularly large project, it is recommended that a structural engineer be consulted with to determine the best method to frame out the box that will support the skylight so that all rafters are properly supported.
A skylight installation concern that should never be overlooked is the weather forcast for the day that the skylight is scheduled to be installed. Needless to say, the skylight should be installed on a day when the weather forecast does predict precipitation. Having a hole in the roof when it starts to rain is not a pleasant thought. What is odd though is the fact that many professional roofing installers do not pay attention to the weather forecast. Roofing contractors frequently feel that they can install a skylight quickly before the weather begins to threaten precipitation. After all, a roofer does not get paid unless he is working. Under no circumstances should you let a roofer install a skylight on the roof of your home unless the sun is shining.