Last month, I wrote an entry about the Benefits of Skylights. Now, with summer rolling towards the final months before the cool autumn weather comes, it’s the perfect time to install skylights. This blog will give you a basic idea of how to install skylights.

Before we start

Before we go ahead and start putting holes in your roof, you should pick out which kind of skylights you want to install. There are two types of skylights available: curb-mounted and frame-in-place.

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An example of the curb-mounted skylight about to be glazed with a
transparent dome made from plastic. A glass dome can also be used to glaze
over the skylight. This kind of skylight sits on an elevated frame.
An example of a frame-in-place
skylight. This kind of skylight can only be glazed over with glass

The main difference between these two types of skylights lies in the flashing system.

  • In a curb-mounted skylight, we will want to use a solid head flashing at the top, a sill flashing at the bottom, and the middle sections are sealed off with solid side flashing.
  • In a frame-in-place skylight, the solid side flashing is replaced with incremental step shingles that are woven into the roof itself.

In both skylight installations, we want to put the head flashing underneath the shingles and have the sill flashing running underneath both layers to allow for proper drainage of water. This will prevent water accumulation underneath your shingles—increasing the longevity of your shingles and staving off damage to your skylight. At Biondo Contracting, we offer both heavy gauge aluminum and copper flashings.

Making and Framing the Opening

This is probably the scariest part for any homeowner: watching the roofing contractors breach a hole in your beloved roof. I’m going to walk you through the steps so that you know exactly what we’ll be doing. Now, the skylight framing is made up of three separate parts:

  • Roof opening—this is framed with the headers and run across the newly cut hole on the rafters in a horizontal fashion. We measure the rafters beforehand to properly cut the lumber for the headers so that they’re equal in size
  • Light shaft—this is built in your roof by us and will connect the two openings in the roof and your ceiling. In most cases, we use 2x4s and insulate it with drywall. There are two types: vertical or flared (wider at the base). The flared light shafts let in more light while the vertical light shaft is generally easier to install.
  • Ceiling opening—this will be cut from your ceiling joists separating your ceiling from your attic space. We put down a piece of plywood on the joists prior to entering to avoid accidentally stepping through the drywall while we work.

When we start the process of actually cutting into your roof, we begin by drilling into your ceiling where you want the ceiling opening to be and inserting something to help us see where the location will be.

After that, we use a plumb bob to find the spots on the underside of the roof that are right over the bottom corners of the ceiling opening. After we’ve done that, we will put four nails all the way through the roof so that we know exactly where to cut the roof opening.

Once we’re on the roof, we remove the shingles and cut away the roofing felt with a knife. After that, we can cut through the roof sheathing itself.

Now, this is the part where things can get slightly tricky. When we install the headers in those cases, we will put temporary supports in the nearby rafters to ensure roof integrity and prevent sagging.

Most skylights will fit the rafters in modern houses. Thus, after we’ve placed in the supports, we can add in the header very easily. However, if your roof is older or if the skylight you want doesn’t quite fit in the rafters, then we will have to cut the rafters. In those cases, we will put a double header and fill the openings with trimmer rafters to maintain the strength of your roof.

Installing the skylight

Finally, the moment of truth! Skylight installation starts by assembling the exterior skylight first before moving downward.

Preparing the skylight

  • For Curb-Mounted skylights, we first build the curb by assembling four 2×6 in a box and then nailing them together in a square. Once that’s done, we toenail it over the roof opening with galvanized nails, put the skylight in, and then re-shingle the area around it while leaving enough room for us to install the flashing underneath the shingles.
  • For framed-in-place skylights, the brackets on the side of the skylight is mounted in first, then the entire thing is set into the roof opening and fastened into place. We never twist it into the hole but rather lay it in to ensure that it’s a snug fit.

Installing the flashing

  • The sill flashing is installed first. Generally, this is nailed into the curb or cemented to the roof with plastic roof cement. We never nail this to the roof because that can present a weak point as well as area for moisture to penetrate the roof.
  • The side flashing comes next. For both the solid side flashing and the step shingles, we will fasten them into place with the step shingles being slipped under each row of shingles from the bottom up.
  • After that, we will remove any and all temporary supports we may have put into the ceiling.
  • We’re now ready to move onto building the ceiling opening and the light shaft.

Installing the Ceiling Opening and Light Shaft

We’re almost there. This is the last step before we finish up your skylight installation. This is a relatively simple process.

We first go into the attic and find where we’ve marked the ceiling opening to be. Once we’ve made sure that it’s a square or rectangle, we will cut through the ceiling drywall.

Like with the rafters, if ceiling joists are cut, we will put supports across the opening to prevent sagging. In the cases of flared joists, we will cut the joists at the angle of the flare. Otherwise, the joists will be cut perpendicularly.

Headers will be installed on the joists. Just like rafters, if the joists are cut, a double header will be placed to provide additionally support. After that, we will place studs along the opening to nail the backing for the drywall to.

Once we’ve completed that, we will nail rigid foam insulation on the attic side of the light shaft and cover the inside of the light shaft (the part that you see) with a layer of drywall.

And there you have it! A perfectly installed skylight that you can use immediately. As per our clean-up policy, we will promptly remove any garbage we generated so that you don’t have to spend all your time cleaning up after us.

Questions? Concerns?

Installing skylights is a huge undertaking, made even more so because the contractor are making a hole in your roof and ceiling. It’s understandable to be somewhat nervous about the whole process. That’s why here at Biondo Contracting, one of the premier NJ roofing contractors, I am more than happy to answer any questions you may have regarding skylight installations. Just give us a call at (732) 257-2926 or send us an email at