How to Install a Skylight: A Step-by-Step Guide

2 man skylight installation_how to install a skylight

Skylight installation

Everyone loves the idea of having a skylight in their home. However, most people don’t know how to install a skylight.  

In fact, many people are deterred from buying one simply because they think the installation process will be too complicated. In reality, however, it’s not that difficult. If you’ve got the right tools, a few hours and at least some experience in building things (please don’t get on the roof with a circular saw if you’ve never even picked up a hammer), you’ll find that installing a skylight is a manageable task. 

First Things First: Plan Your Installation 

The first, and most important step is to determine the correct skylight style for your installation. This will be based on the roof pitch and roofing materials installed.

Roof pitch refers to the amount of rise per ft of slope.  Examples are 3:12, 5;12, 7:12, 10:12, 12:12.

3:12 = 3” rise for every 12” of slope.

Examples of roofing material are: asphalt shingle, standing seam metal roof and high profile Spanish tile or slate, etc.

  • Flat roof = curb mounted domed skylight
  • Low pitch roof typically = curb mount skylight  < 3:12 pitch
  • Fair to steep pitch roof typically = deck mount skylight > 3:12 pitch.
  • However, if you have a metal roof or high profile roofing material such as Spanish tile then you will need a curb mounted skylight to exceed the thickness of the roofing material.

Another key (but, unfortunately, tedious) step in the process is to obtain any necessary building permits. If your town or neighborhood requires you to have a building permit (which is typically needed for skylight installation), make sure to obtain them beforehand. We don’t want anyone receiving fines or having their project shut down before it’s complete.   

Once you’ve gotten the approval from the local authorities, it’s time to gather your tools and materials. 

Heres What Youll Need 

Gather the following materials: 

  • A skylight that fits the size and slope of your roof 
  • 2×4’s to support the frame  
  • Roofing nails 
  • Nails (16D hot-galvanized steel ones work best) 
  • Continuous flashing 
  • Step flashing 
  • Circular saw 
  • Hammer 
  • Tin snips 
  • Pry bar 
  • Carpenter’s knife with hook blade 
  • Chalk line
  • Adhesive underlayment
  • Power drill 
  • Screws 
  • Tape measure 
  • Pencil 

Remember, skylights come in a variety of different styles and each has its own nuances when it comes to skylight installation. A VELUX Sun Tunnel, for example, may require a bit more construction than a traditional curb mounted skylight. Each model will come with directions that outline the specific requirements for installation. This guide is intended to provide basic instructions on how to install a skylight and to give you an idea of what the process is like.   

Step 1: Cut Your Opening 

Start by cutting an opening that aligns with the size of your skylight. The manufacturer’s instructions will list the exact size of your light. This will tell you how big the opening needs to be.  

It’s important to note that different styles of skylights require a different sized hole. For example, a curb-mounted light is intended to dip below the surface of your roof, resting on the wood as a support. A deck mounted skylight, on the other hand, will sit above the surface of your roof. The size of your opening will depend on the size of the skylight’s frame.  

You should choose the placement of your opening from inside the house. Drill a screw through the roof where you want the corners of your frame to be. Move to the roof and make a perfect square by snapping the chalk line from screw to screw. Then you can use your circular saw to cut out the opening.  

Step 2: Build Your Frame  

The frame is the wood structure that supports the skylight. Essentially, you’ll make it by cutting 2x4s and mounting them to the preexisting support beams in your roof. Make sure that your roof beams are supported if you are cutting through them. Your frame should be mounted to the roof beams at the edges of the skylight’s opening.  

Note: If you dont have a carpentry background, this is the step where youll want help from someone who does. Its crucial that your light is properly supported by a sturdy frame.  

Step 3: Peel Back the Roofing and Install Your Skylight 

Once your opening is cut and supported, use your carpenter’s knife with hook blade to slice the roof shingles around it. Cut back 2.5-3 inches around the entire perimeter.   

Set your skylight into the opening. You might want to have someone else help you insert the light into place. After it’s in there, you can mount it using screws or nails.  

Step 4: Lay Down Your Adhesive Underlayment and Tiles  

Adhesive underlayment keeps the wood on your roof from becoming saturated. Cut 8” pieces and lay them down underneath the existing shingles. Start with the bottom pieces (the ones closest to the ground) and work upward on your roof. This will allow the rain to run down over the underlayment without letting any seep in between the cracks.   

The toughest part about this step is getting the underlayment underneath the shingles. Use your pry bar to pull up any nails that prevent you from getting the paper completely under each shingle.  

Step 5: Attach Your Step Flashing and Bottom Flashing 

Flashing is incredibly important as it prevents water from leaking through the edges of your skylight.  Whenever we get a call from someone who thinks they have a leaky skylight, it’s usually because the flashing was never installed with the skylight!    

Your flashing kit will come with a specifically-labeled piece of bottom flashing. This piece should be placed along the bottom edge of the skylight. This piece should sit directly on the roof shingles. Gently nail the piece of bottom flashing into the skylight. 

Once you’ve done that, slide single pieces of step flashing underneath your shingles. Use your tin snips to cut each piece as necessary. Allow each piece of flashing to overlap the others by 3.5-4 inches. Start from the bottom and work your way upwards. Nail each piece into the sides of the skylight.  

Step 6: Attach Your Solid Flashing 

The solid flashing usually comes in three parts: the bottom, sides, and top. When installed correctly, they should fit snugly against your skylight. Start with the bottom piece and follow it with the sides. After those have been attached, you can put the top piece (also known as “head flashing) on. Slide the edges under the roof, attach it to the top and you’re good to go.   

Still Wondering How to Install a Skylight? 

There are a number of great video tutorials available on VELUX’s Installation Help page. Make sure to check that out if you’re looking for additional tips.   

And remember, there’s nothing wrong with asking someone for a hand. If the whole installation process feels daunting to you, you may want to reach out to a professional.  This is an important investment, you are cutting a hole in your roof, after all, so you want to make sure it’s done right the first time.  This will save you a lot of headache and extra cost if work has to be redone by a professional.

It may take some additional time to coordinate, but you’ll be reaping the benefits of your new skylight before you know it.  







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