Q: What is the difference between skylights, sky windows, and roof windows?
—Edith, Ashland, Ore.
A: Tom Silva replies: Not a whole lot. Any glazed assembly that admits natural light through a roof can be called a skylight. Some manufacturers use the term "roof window" to describe a relatively large skylight placed low enough that you can see out to the landscape. So I guess if you can see only sky, it's a skylight, but if you can see sky and land, you call it a roof window. Also, roof windows are generally big enough to qualify as means of egress in case of a fire. That's seldom if ever the case with a skylight. The term "sky window" is not as common as the others. At least one manufacturer uses it to describe huge glazed areas in a flat roof. Most skylights are meant for roofs with a slope of at least 15 degrees.