How to Mount Flat Roof Skylights

living room with large couch, fireplace, coffee table, and skylight
What You'll Need
Roof paper
Water membrane
2 x 6 boards
Tin shears
Caulking/caulking gun
Chalk line
Reciprocating saw
Skill saw
Measuring tape
Aluminum flashing

Many homeowners are looking to dress up their home with flat roof skylights. These flat roof skylights might seem like they would not be very functional, but they do allow a great deal of natural light into your home. With some knowledge of roofing techniques, proper tools, and the use of a special frame, installing a skylight is a moderately-difficult project that can be done by most do it yourselfers. Here are the steps to take in mounting flat roof skylights for tons of natural light and great views of the night sky.

Step 1 - Determine Location for Skylight

It is important to know the exact location of where the skylight will go on your flat roof. You will want a location that is not directly under any type of branches or adjacent to a valley of a second level to the home. Also, choose a skylight for your flat roof that has a pre-soldered lip for eliminating any type of leak.

Step 2 - Measure Roof for Skylight

skylight in a roof

Once you have the location determined, and a skylight in your possession, measure the roof according to the dimensions of the skylight. Mark these dimensions with a chalk line so they are clearly visible for cutting.

Step 3 - Cut the Roof

With the marks for the skylight set onto the roof you can get ready to cut the hole. Begin the cut under the position of the skylight. This will ensure that you do not cut into any wiring, lights, or other obstacles. Cut away the ceiling under the skylight position, remove wiring, and insulation. Remove the roofing shingles from the section where the skylight will be installed and cut the hole with the reciprocating saw.

Step 4 - Build Frame for Skylight

The skylight will need to have a mounting frame in order to keep the skylight at a 15-degree angle. Use 2 x 6 lumber to build this frame for the skylight around the existing hole. Set 2 x 6 lumber adjacent to any joists to add support for the skylight. Before each piece of lumber is screwed into the joists around the hole, place a bead of caulking on the backside.

Step 5 - Install Skylight

large kitchen with wood cabinets and flooring and a skylight

After the frame is installed, you can then mount the flat roof skylight into the hole. Cut out some of the water membrane and set it along the edges of the hole. The edge of the membrane should be tucked under the shingles. Run a bead of caulking around the membrane and set the skylight into position. Using the fasteners included with the skylight, hammer or drill them into place along the edge of the skylight.

Step 6 - Caulk Edges of Flat Roof Skylight

Making sure that flat roof skylights are water tight is important as the water has a tendency to puddle up. Install a 6-inch wide strip of aluminum flashing along the edge of the skylight lip and secure it with roofing tar. Lay a bead of caulking along the edge of the flashing to create a watertight seal.