Western Washington winters are dark, and a skylight in a north-facing room or a hallway with no windows makes a real difference to how a house feels. That benefit is genuine and worth weighing against the risk.
The risk is the penetration
A skylight is a hole in the roof. Everything about whether it succeeds comes down to how that hole is detailed.
Most skylight leaks are not the unit failing. They are the flashing failing, or having been installed incorrectly in the first place. That means the choice of installer matters considerably more than the choice of product.
Ask specifically how they flash a skylight and whether they use the manufacturer’s flashing kit designed for your roof type. A contractor who answers that clearly is a different proposition from one who does not.
Install with a roof replacement
The best time to add or replace skylights is during a roof replacement. The flashing integrates with the new roofing as a system rather than being worked into an existing one.
The converse is also true: if you are replacing a roof and have skylights older than a decade or so, replacing them at the same time frequently makes sense. Fitting new roofing around old skylights means you will be disturbing the new roof when the skylight eventually fails.
Condensation, not leaking
A common confusion in Washington. Water appearing around a skylight is not always a leak.
A skylight is a cold surface high in a room where warm moist air collects. In a marine climate with elevated indoor humidity, condensation on and around a skylight is common — particularly above a bathroom or kitchen.
The distinction matters because the remedies differ entirely. Leaks relate to flashing; condensation relates to indoor humidity and ventilation. Before assuming a leak, consider whether the water appears in relation to weather or in relation to household activity.
Solar tubes
A useful alternative worth knowing about. A tubular skylight carries daylight down through a reflective tube from a small roof-mounted dome.
Smaller penetration, simpler flashing, less heat loss and gain, and no ceiling opening large enough to require structural alteration. Considerably less dramatic than a full skylight, and considerably lower risk.
For a hallway, bathroom or interior room where the goal is daylight rather than a view, they often make more sense.
Heat gain and loss
A skylight is glazing in the plane most exposed to sun, so summer heat gain is a real consideration — increasingly so in Washington, and especially in the Tri-Cities and Yakima.
Glazing specification, orientation and shading options all matter. In winter, glazing loses heat, so a poorly specified skylight is a cold spot in the ceiling.
Existing skylights
If you have older skylights, check them. Staining on the surrounding ceiling, particularly recurring after painting. Fogging between the panes, which indicates a failed seal. Visible deterioration of the flashing or sealant from outside.
Skylights have a service life, and one that is original to an older house has probably reached it.