How to Cut a Roof Opening for a Skylight
These instructions will walk you through the process of cutting a roof opening to install a skylight.
The first step in this remodeling project is to determine where your skylight should go. Making sketches of the room may help you figure out what you want to do and what you can do. There are also computer programs available that can create a 3D images of the space, which can give you a good sense of what the finished skylight will look like.
Keep in mind that you'll need power for the ventilation motor in the skylight, so the skylight needs to be located near an existing power source. Once you know where you want the skylight, check the attic for any possible wiring or plumbing issues, chimneys or rafter assemblies that might interfere with your installation. It may be easier to relocate the skylight than to move these obstacles.
Gather your tools and supplies, lay down plastic sheeting under the work area, especially where you are cutting drywall. Turn off the power at the breaker box.
This project takes place in a ranch-style home with a simple sloping roof. The complexity of the roof, the amount of attic space and other factors help determine the following steps.
Locate the ceiling rafters with a stud finder and mark the inside of their dimensions to indicate where the skylight will go.
Measure from the peak of the ceiling to the point where the wall and ceiling meet (the plate) to obtain an overall rafter length. You want to position the skylight hole in a place between the rafters that will maximize the dispersal of light while optimizing the ease of installation. Generally speaking, placing the top of the skylight a few feet down from the roof peak is ideal, but every roof is slightly different, so adjust as you need to.
Measure the rough-opening dimensions of the skylight and read the manufacturer's installation instructions carefully.
After measuring carefully, use a level to mark a line perpendicular to the rafters which marks the bottom of the installed skylight. Begin cutting the drywall with a keyhole saw (Image 1) until you hit the rafters. (Using a keyhole saw for this part of the process minimizes vibration and is less likely to crack the drywall).
Apply drywall tape onto the first horizontal line and then measure and mark a line for the top of the window; repeat this process on the other side. Use a level and draw vertical lines between the top and bottom to finish the outline of where the skylight will go (Image 2).
Put on a mask before you start cutting the drywall, as insulation may fall through the opening you are cutting.
Use a reciprocating saw or a circular saw to make the cuts along the rafters. Take care to cut as close to the rafters as possible.
Remove the drywall and insulation.
Transfer the four corners of the hole in the ceiling to the roof sheeting using a framing square. Make some marks on the roof sheeting where you will mark the hole in the roof.
Using a drill with a 1/4-inch bit, drill holes through the marks on the sheeting, making sure to drill all the way through the sheeting and the asphault shingles on the roof.
You're now ready to get up on the roof and complete the next step of the project.