If the article in the last issue of MOTHER EARTH NEWS didn’t convince you that a skylight window is a great choice for a low-cost remodeling project (see MOTHER NO. 103, pages 38 to 40, January/February 1987), perhaps this follow-up will. Why? Because we’ll show you how to save up to half the cost of the job by doing the installation yourself. (See the skylight diagrams in the image gallery.)
Install Your Own Skylight Window
If you’ve never tackled anything like this before, it’ll offer a mildly challenging, but very rewarding, learning experience. And even if you’ve done a fair amount of home carpentry, installing a skylight window will present an opportunity to hone your skills on a fresh technique. Either way, you’ll have something worthwhile to show for your effort.
Plan Not, Pain Later
Let’s assume you have a pretty good idea of where you want to put your skylight window and you’re ready to price the model you have in mind. Don’t run out the door and plunk your money down. Instead, climb into the attic with a tape measure and find out exactly what will fit in the area that’s captured your imagination. Naturally, if your installation is to be in a cathedral ceiling-one in which the roof and interior ceiling sandwich the structural rafters-your job will be somewhat easier because you won’t need to build a well to penetrate an attic space.
Measure the depth of the roof rafters and the distance they’re spaced apart. Most likely, you’ll have either 2 by 4s placed 16 inches on center or 2 by 6s set at 24 inch intervals. Check the area for wiring, plumbing vents, and other fixtures, and be prepared to reroute or move them if you have to. Also, look for structural interference: horizontal collar ties or vertical posts that support rafters and joists, or in the case of trussed roofs, braces and struts that share the roof load. With the former, you can usually work around the components or reposition them. Trusses are less forgiving and will probably require the advice of a structural engineer or the building inspector.
Most skylights are designed to fit standard rafter spacings and come in lengths varying from 2 feet to 6 feet. It’s usually best to cut through no more than one rafter, so consider buying the narrowest skylight that will fit between three rafters and making up the area difference in length. When a rafter is cut, it’s standard procedure to support the loose ends with headers, or boards fastened between adjacent rafters. Doubling up headers is common practice, but with the largest skylights, you may have to double the rafters as well. If you can’t tie in to the ridge at the peak of the roof and the top plate of the wall below, merely “scabbing on” to the outside of the rafters with two-by’s twice the length of the skylight opening will help stiffen the structural members.