Skylights can be designed to suit different applications and to take into account different climate zones.
We can consider clear tempered glass skylights to respond to the needs of sunrooms and to let plant-friendly light to enter them. Or consider skylights with special laminated glass to withstand the extreme winds of hurricane-prone regions... And also skylights able to respond to your climate requirements.
Some skylight manufacturers have special lines, for specific climates: Velux, the world leader in skylights, has a line of skylights for heavy cold northern areas – Snowload glass skylights -, and a line of skylights designed for hot climates, the Miami-dade glass skylights; Wasco has the EcoSky Satin skylight line, specially designed for hot climates... That's just two examples.
That's after all what happens with windows. Windows – especially the glazing – should be selected according to the climate zone and the sides of the house where they are going to be installed (see: Windows & Climate).
Also do not forget that even the best skylights, designed to respond to specific climate conditions, can be a source of problems.
The 0,30/030 approach
Skylights are subject to harder constraints, pressures and temperatures than windows; especially they have to respond both to very high and very low temperatures, whatever the climate zone.
Hence the old 0,30/0,30 approach recommended by the National Fenestration Rating Council to meet tax credit criteria: skylights should have both an high resistance to heat loss (through a U-factor lower than 0.3) and to solar heat gains (through a Solar Heat Gains Coefficient lower than 0.3).
Anyway, that's not enough. It’s important to consider the skylight features that are especially important for each climate.
Skylights for cold climates
In cold northen climates - where skylights are a common cause of water problems and ice dams- the flashing and the underlayment are critical. It's up to them to provide water-tightness. Make sure that the flashing and the underlayment are the ideal. Consider "ice and water shield underlayment"; that's very important for water-tightness.
But thermal insulation is also very important, to minimize heat transfer. And to get it, the glazing is crucial. You must ensure that the skylight has a proper glazing (with very low U-factor, lower than 0.3, and as close to 0.2 as possible), to reduce heat loss to lower levels.
And you should ensure a proper insulation (and sealing) of the shaft light and the rough opening area.
Cold Climate skylights and snow Accumulation
Whatever the glass and the type and effectiveness of the flassing and the underlayment, protecting the skylights from extreme winds or snow is also critical, in cold climates.
To prevent snow accumulation near the skylight, it should be positioned far enough from the walls, chimneys, and other roof protrusions. A saddle (a small roof-built to divert runoff water) above the skylight, on the upper part of the roof, can also help solve snow accumulation problems - though it may also create other problems.
Skylights in hot climates
In hot climates, the most important feature of skylights is the glazing, which should have the lowest SHGC coefficient possible: lower than 0.3. That's important to minimize solar heat gain and help prevent overheating.
High levels insulation around the skylight and in the light shaft, and architectural features to protect the skylight from the sun are only critical to avoid overheating.
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