As the name implies, "Skylight" brings daylight into your home, especially helpful in windowless spaces. But first you must make a hole in your roof. The hole is the tricky part; you want the light, but not the leaks that so often occur with skylight installations. In this article, we will talk about the two primary types of modern skylights and proper installation methods.
The most common type of skylight is a framed rectangular or square of double-pane thermal glass that is slightly elevated relative to your roof surface. A close variance is the curbed skylight with a higher profile. Both typically rest on the same plane as your roof pitch.
The other type consists of a cylindrical tube (usually rigid or flexible metal) with a roof-top light gathering component and a termination point in the space targeted to receive natural light. These are frequently referred to as "solar tubes" but are also known as sun tunnels. The (usually) domed top allows light to enter and travel down the tube to a diffuser lens which is mounted in the ceiling of the target room. During daylight hours, it can bring natural light to an otherwise gloomy space in your home. It is important to try to install solar tubes with as much sun exposure as possible; to realize their potential to bring light into a gloomy room.
The main differences between conventional skylights and solar tubes are:
- Size of the roof opening – solar tubes usually require a circular hole that is generally a smaller opening than a conventional skylight. As a result, you will often get more light from a skylight installation.
- A skylight most often sits at the top of an enclosed "well". This well transits the space between the roof-top and the ceiling below (the attic space). It is usually open at the bottom with the walls of the well composed as a framed enclosure finished in drywall or wood. The solar tube, however, is closed at both ends. The skylight well is exposed to the interior air of the room, while the solar tube typically experiences little air movement, being closed at both ends. This becomes important as discussed later.
- Skylights can be fixed or operable (opening or non-opening). Solar tubes are closed at both ends with dead air between the roof and the ceiling. On a hot day, operable skylights can be opened to allow warm air to exit the room.
Flashing
The most critical aspect of any skylight or solar tube installation is the flashing at the roof opening where the skylight or solar tube is installed. Failed or improper flashing is the leading cause of leaks at skylights. Most prefabricated skylights and solar tubes come with available flashing kits, or the flashing is already present as part of the assembled unit. In addition to the usual flashing, ice and water shield can be used to provide a waterproof membrane around the roof opening. An experienced roofing contractor will be able to install skylights and solar tubes properly to reduce the likelihood of leaks at the roof opening. Unattended leaks can cause significant damage to roof sheathing, attic framing, and interior components.
Condensation
There is also a moisture hazard related to condensation in the skylight well, more so than solar tubes. The skylight well is open to the home's interior air, and depending on the type of room, there is a possibility that the moisture in the air will condense on the cool walls of the well, as that framed well enclosure is directly adjacent to the cooler attic space through which it passes. In bathrooms and kitchens, where moist air occurs more frequently, this can present a serious problem, especially during cooler weather. There are two ways to prevent such condensation, and one or both methods can be used:
- The best way to prevent condensation in skylight wells is to insulate the walls of the well enclosure where it passes through the attic space. Ideally, a vapour barrier will be installed on the attic side of the enclosure before you install the insulation. Fiberglass batts are the best material to use as they will retain their shape. Twelve inches of depth, with the batts secured to prevent them from falling out of position will be effective.
- In addition to the insulation, an exhaust fan can be installed to remove moist air from the room to the exterior. This is a standard installation in bathrooms and some kitchens.
Skylights may also be more prone to condensation if the thermal seal fails in the glass, allowing the interior pane to be cooler. The only fix in that situation is to replace the failed glass.
With correctly installed solar tubes, the air inside the tube will not be subject to movement and less likely to acquire interior air, and therefore less likely to experience condensation. However, if condensation does become a problem, it can be mitigated by insulating the tube where it passes through the attic.
Identifying Problems
At the interior of a skylight, it is easy to identify a leak or condensation problem. In most cases, there will be visible water damage or staining. With solar tubes, there is no interior view of the roof-top component, so defect detection may be more difficult.If leakage is suspected, but there are no visible indications, a professional home inspector, trained in the use of infrared imaging may be able to confirm or refute the presence of unwanted moisture.
At the exterior, up on the roof, visible problems may include damaged or poorly installed flashing, a failed thermal seal, or cracked glass. The flashing issue can best be dealt with by a roofing professional. A failed thermal seal or cracked glass will require replacement of the affected component.
The service life of skylights and solar tubes is often consistent with the usual service life of a typical roof covering such as asphalt shingles. So, when you engage a contractor to replace your present roof covering, it is always a good idea to determine if the solar tube or skylight should be replaced at the same time. A CAHPI qualified home inspector can help you determine the condition of the roof covering and related components as part of a general home maintenance inspection because they look for installations that may have been done by non-professionals, especially where structural roof framing has been modified.