Why Skylights Are Not Just Windows For the Roof

Installing a Skylight in a Roof 173640605
Installing a Skylight in a Roof. Getty / KristianSeptimiusKrogh

Skylights as luxury items?  Many homeowners consider them the window equivalent hot tubs, heated bathroom tile, or outdoor kitchens.  But they are far more than just a “luxury”; they are almost a necessity for homes located in northern areas that receive limited natural light.

It's a Window, But a Window For Your Roof

Think of a skylight as just another a glazed window, like all of your home's other vertically-positioned windows.

 After that comparison, the two diverge.

Skylights can be flat or domed, fixed or vented. The vented ones are like casement windows for your roof.  Some vented skylights operated by an electric motor, while others open and close manually.  Because skylights get so much sunlight, they are usually more tinted than regular windows equipped with Low-E coating.  Because roofs have things fall on them, skylights are made to withstand impact.  

Why a Window Company Is NOT Your Best Bet

Skylight installation can be performed by you, a window company, or a contractor.  In ascending order, here are your options (and why a GC is best):

  1. You – If your skylight is small enough to fit between two trusses, your installation job will be vastly easier if you need to cut trusses.  If you feel comfortable with basic carpentry, shingling, basic window installation, drywall work, and painting, you can put in your own skylight.  For motor-driven skylights, you’ll need electrical experience, too. DIY skylight installation is not a project that lends itself to impulsiveness.  Honestly, consider your strengths and weaknesses before tackling a job that rips open your house envelope.
  1. Window Company – Search for replacement windows, and you’ll find a qualified professional who can install skylights. Pella, Marvin, and Andersen are among the big names in windows who can not only supply you with a skylight but the qualified professionals to install it. The big downside is that most window-only companies will do just that:  the window only.  They will require a fully framed out area in advance so that all they need to do is put in the skylight.  Everything else--including the skylight shaft--is up to you.
  1. General Contractor or Carpenter – Any general contractor, general carpenter, or even some handymen should be able to install your skylight. This option will be vastly cheaper than going with the window contractor. With this option, the GC wears two hats:  framing the area and installing the skylight itself.  A GC will outsource activities to sub-contractors (notably, drywall work for the shaft).  A carpenter/handyman/fix it guy may do everything with just himself and a partner.

4 Basic Types

Conventional Windows vs. Skylights

Most homeowners, given the choice, will choose a window over a skylight. But logistical considerations may not allow for this.  Almost everything about conventional windows--from the material to labor--will be cheaper.  Keep in mind:

  • Windows are often required by building code because they provide egress (escape) in the event of emergencies.  So, a skylight cannot always be used as a replacement for windows.
  • Most skylights are fixed in place; most windows are some type of opening capability. It should be noted that skylights with the ability to open are available.
  • Most skylights don't come with any kind of blind or method of blocking out the sun.  This is an option that will usually cost you more.  If you have extreme sunlight in your area, it's almost unthinkable not to have a blind.

Fixed vs. Vented Skylights

A fixed skylight borrows window terminology again. “Fixed,” in window parlance, means that it cannot be opened. Never, ever. Think of your typical office building window, and that is a fixed window.

A vented skylight is openable. While it may seem like these are better than fixed skylights, that is not necessarily so. A few of the pros and cons of fixed vs. vented skylight:

  • A fixed skylight is theoretically considered leak-proof. Because it is sealed in the factory, a fixed skylight should not leak. Most leaks, then, would occur due to improperly fixed skylight installation.
  • A vented skylight provides opportunities for leakage, though it should be noted that window manufacturers in recent years have been producing virtually leak-proof vented skylights.
  • Vented skylights can accidentally be left open, allowing rain to enter the house. However, automatically closing vented skylights are available which close at the first drop of rain.
  • Vented skylights allow excess moisture in kitchens and bathrooms to escape—a good thing. Also, you can vent out heat build-up. Fixed skylights do not have this option.
  • Don't be afraid of skylights due to potential moisture. Effective skylight moisture control is possible for either vented or fixed skylights.


Skylights are not all that expensive. In fact, in the 6 years since I first wrote this article, the cost of the Velux 22.5" fixed skylight has not risen:

  • Fixed:  Velux Skylight, 22 1/2" X 22 1/2": About $258.
  • Manually Venting:  Velux Skylight, 30 1/16" x  37 7/8".  About $450.

But that's only the cost of the skylight itself.  You also have lumber, drywall, paint, and related materials for the skylight well or “tunnel.” Also roofing materials for the top side.

Skilled labor is what will cost you.  Triple the materials cost to get a sense of what the overall cost will be, labor included.

Q:  Do You Have To Wait Until Summer To Install?

A: No. While it is always preferable to install during dry/warm months, contractors and window companies who claim to be able to install skylights should be able to do this is a day or two.  But if you intend to install the skylight yourself, find the driest month of the year in your area and do it then. 

Q:  Does Positioning Affect the Skylight Shaft?

Yes.  Barring any obstructions in the attic and roof, skylights can be positioned anywhere in the ceiling. But consider roof slope.  The closer to the center of the house that you position the skylight, the more vertical space in the attic you need to traverse with a skylight shaft. Conversely, the closer to an exterior wall that you position the skylight, the shorter the skylight shaft you need to build.

Q:  How About Positioning For Maximum Light?

The skylight's position on the roof can dramatically affect your interior light.  Trees, chimneys, and tall structures can wipe out much of the great sunlight you're trying to get. You'll want to have a nice, clear opening around your intended skylight position in order to pull in as much light as possible.

Q:  How Are Tubular Skylights vs. Fixed Skylights?

A tubular skylight is a quick fix for many of the problems that plague conventional skylights. For one, you'll find that it's not so much the installation that's the problem—it's building the shaft.

The shaft is the structure made of lumber and drywall that connects the skylight on the roof with the opening in the ceiling.  One great advantage of a tubular skylight is that comes with its own shaft—the tube. The tube is typically the same type of foil-wrapped coil that you would use for dryer vents, except in a super-sized version.

Another advantage of tubular skylights is that this tube is bendable. Attics often have obstructions that make it difficult, if not impossible, to construct a conventional skylight shaft. The tube section of the tubular skylight lets you snake around these obstructions.

Q:  Any Reason To Paint the Shaft Anything Other Than White?

No.  Typically, skylight shafts are painted semi-gloss, eggshell, or flat white.  Think of these shafts are light-reflection devices:  you want to gain every possible advantage to keep pushing that light downward and into your home.  Darker colors may look interesting, but light reflection will be hampered.

Q: Are They Strong Enough To Withstand Impact?

A: Yes, to some degree.  Skylights are made either with tempered glass or laminated glass. Tempered glass is like your automotive glass: when struck, it shatters into thousands of smooth pebbles. Laminated glass is plastic attached to the glass. So, when laminated glass breaks, it stays together.  But no type of fenestration will ever be as strong as the trusses and shingles found in roofs.

Q: Do You Need To Cut Out Roof Trusses?

A: Not always.  The 22.5" Velux mentioned above will fit between two 24" on center trusses; the 30 1/16" Velux will not.  As a rule of thumb, you can remove up to one rafter to accommodate the roof opening and shaft.  Adjoining rafters should be sistered to carry the weight. Additional horizontal bracing helps this cripple rafter (that is, the cut rafter) hold its own.

Do you need to remove two rafters to install an extra-sized skylight? Then, you may want to consult a contractor or a good carpenter for this job.