(This is Part 1 of a two-part series. See Part 2: Small-scale model helps see the skylight.)

Adding a skylight is among the most popular do-it-yourself projects around. Too often, though, people decide where to put in their skylight by gosh and by golly, and then just hope for the best. For shame: like any other remodeling project, a skylight installation demands a little planning to avoid an expensive disappointment.

A few simple rules can help ensure that your skylight not only goes in easily and looks good when it’s finished, but also brings in light where and when you want it.

Rule one: don’t expect a skylight to do a window’s job. A well-placed window is inherently better at daylighting than a skylight, since it automatically admits more low-angle winter sun when it’s welcome, and blocks the high-angle summer sun when it’s not needed. A typical skylight does just the opposite: Being much closer to horizontal, it tends to block the winter sun, yet lets the hot summer sun pour in just when you don’t want it. Therefore, if your goal is efficient daylighting, consider adding a new window or enlarging an existing one before you resort to a skylight. It may cost a bit more, but it’ll usually do a better job.

On the other hand, if a lack of wall space, a bad view, or some other constraint rules out a bigger window, a skylight is probably your best option – but you’ll still want to consider its location, shape, and size very carefully before you reach for the Sawzall.

Your first step is to decide where not to put the skylight. Rule out any spot that’s beneath a roof ridge, valley, hip, or some other roof intersection, as it’s generally not possible to cut roof openings there. Also avoid locations that’ll interfere with existing pipes, wiring or ducts, as they’ll have to be re-routed at extra expense. Lastly, unless your house is in a modernist style, avoid locating the skylight where it’ll be visible from the street. Why? Skylights – especially the common “bubble” variety – aren’t part of the grammar of traditional architecture, and will stick out like a sore thumb if placed on a conspicuous roof surface.

As for shape, it’s common to use narrower skylights that’ll fit between the existing roof rafters, but don’t hesitate to use a different shape if it suits the room better. However, if your house has prefabricated roof trusses or if you’re not sure whether your roof can accommodate the size and shape of skylight you have in mind, talk to an architect or engineer first. It’s a lot cheaper than having your roof collapse.

Lastly, don’t make the common mistake of making your skylight too small. The cost of adding a skylight is mostly in labor, not in material. And since it takes just about the same effort to install a small skylight as a large one, there’s little to be gained by wimping out on the dimensions. For the same reason, one large skylight is usually cheaper to install than a group of smaller ones. Use generous sizes, and make your installation worth all the trouble.

Once you’ve figured out your skylight’s size and location, it’s time to fine-tune your design and then test it out – without making a hole in your roof. We’ll find out how next time.


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