Home & Garden Columns
Skylights are great. Nearly everyone agrees. They lighten up dark spaces and do so without any energy expense but like so many things, what seems like a good thing at first glance is a bit more complex and not right for every situation. Moreover, as most people know, they come with the possibility of leaks. So let’s take a look at some of the issues associated with putting in a skylight, living with one that you have now and just for fun, some of the newer things happening in this corner of construction.
First, from a design stance, I’d like to say that skylights don’t belong everywhere. If you have a 1910 craftsman house, they may not be suitable. Now, every old house doesn’t have to be a restoration showplace, so before you go down this particular road, take a look at what your skylights will look like and where it will be placed. If it’s installed in the fashion of the time (skylight go way back) with suitable trim around the edges, a fitting vault between ceiling and roof and, perhaps, a window or stained glass at the ceiling line, it might be just the right upgrade. Every room isn’t right for a skylight and a gorgeous old room can be ruined by the wrong upgrade. Window light increases as we climb the wall and a placement of one or more high windows near the ceiling (especially those old 10’ beauties in older homes) can provide a great deal of light and approximate the gains that a skylight can provide, especially if they’re placed in a south facing wall (or east for morning … or west for afternoon).
I’ve seen rooms with some high narrow windows on a south and western faces that were nearly as light as those with skylights and in some cases I think it’s a better choice since a skylight can really flood a room with light (more on that later).
Light for more than one direction is best since it helps to shape and color objects and spaces. People will tend to gravitate toward rooms that feature windows in two walls and, of course, any well-lit space.
In an older house, skylights might be a better choice in upstairs rooms or a developed attic. The integrity of style becomes less of an issue in these spaces, but design is still important.
If you’re thinking about installing a skylight, here are a few tips:
First, involve a first-rate roofer. This is where these folks earn their money. A skylight is, ultimately, a hole in your roof, so it’s best to be very careful about how you do that since leakage is quite likely to result if everything isn’t done just right. Also, a carpenter must be sure that the wooden members to be cut through are properly supported as the hole is created. If a rafter or joist is cut through to accommodate a skylight of more than about 2’ in width, the member must be joined to the neighboring members by use of a “trimmer.” These are generally installed in pairs (doubled up) and the neighboring members (joists or rafters) must sometimes be doubled up or “sistered” if the resulting load is going to be too great. A skilled contractor should be consulted and lumber sizing tables may need to be consulted. For a skylight of about 16” square this isn’t an issue. For a 2’ skylight, the ceiling joist may need some strengthening. A 4’ skylight is where things get more critical. A skylight that is narrow and long, running down between the joists, can provide a lot of light with a minimum of framing. This also has less leak potential per lumen (unit of light) since the leakage tends to be associated with the top edge.
For more modern spaces a skylight can also be placed on a diamond or an odd angle for fun. This isn’t that hard for a skilled carpenter and the cost won’t be much more so don’t miss out on cool details because you’re afraid of cost. The real cost will result in hiring the wrong folks and dealing with years of leakage.
When I got started, skylights were mostly single-layered (or “glazed”) but today, the double-layered bubble or double-glazed type is much more common and thank goodness. Skylights are, after all, placed where the heat gathers and the cold wind wants to “convect” the heat away. There is no window in your house more important to double insulate than your skylight.
Skylights need to be “flashed” to the roof. In other words, a series of roofing pieces, which continue to overlap and carry the water away down the roof, must be installed around the shape of the “curb” or lip that gets built onto the roof surface. This set of flashings must be installed exactly right so that water doesn’t ever get the chance to drop into that “hole” you’ve just cut in your roof. This is by no means impossible but it’s not for the inexperienced and, again, leave it to a really good roofer. The curb, hole and skylight mounting is less important. Good roof safety is critical. No job is worth the cost of falling off a roof.
As I mentioned, the skylight is where the heat goes and it’s cold just above. This heat differential can and often does cause condensation to form in the skylight and to weep down the well between roof and ceiling. This is often mistaken for leakage and often a cause of consternation. A vented skylight is less apt to do this, as is a double insulated one but this is no guarantee.
If you have excess moisture entering your dwelling from the crawlspace or from gas appliances (like stoves, teapots, water heaters and dryers), they can contribute. This may be your chance to find out why the basement is moldy and to finally address the elevated humidity in your house (but that’s definitely another article). So, don’t be surprised if you have weeping skylight syndrome.
Lastly, let’s take a minute to look at some old and new choices. For slanted roofs, a Velux roof window is a really nice choice. Be sure to buy the correct flashing kit. For a flatter roof, a well built and roofed curb is critical. These babies really beg to leak if not done right. For big light on a small budget, check out one of the new types of tube skylights, such as a Solatube or Sun-Dome. Velux makes one too and I’m very fond of their products because they seem very intent on making sure that the contractor has what they need to do the job right. These tube types are very inexpensive, fairly easy to install and more leak proof since they are modular and require almost no framing modification. They are essentially self-flashing, which is not a guarantee but they are a bit more fool proof (although, as we all know, there is no limit to the wreckage a true fool can manifest). Tube skylights are very modern, so think about what they’ll look like. Nonetheless, I see them as a real asset.
Here’s an exciting notion that you might take a look at. Solar-Tube type skylights can be quite long and can easily run from a roof, all the way down to a basement if a 1-2’ square space can be found for the trip. The corner of a closet or an abandoned chimney shaft (you’ve been meaning to take that crumbly old thing out anyway) can be enough room for one of these and when you punch through into that dank basement room, you’ll be astounded at the volume of light these silvery tubes can retain and deliver. This is a project that I consider well worth the effort because the result can be so fulfilling.
Think of skylights as an alternative energy source since they substitute for electric light and, during the day and well into dusk, keep the use of lights at a minimum. This of course applies to all fenestration but most prominently to skylights. When you price this job, consider the electric savings you’ll have over the years, as well as the decreased carbon you’ll be adding to the air and water.
Remember that skylights are extremely effective and sometimes TOO effective. A small skylight can deliver more light than a wall of windows simply because that’s where the light is. So don’t overdo it. When you paint in this medium, a little goes a long, long way.
Got a question about home repairs and inspections? Send them to Matt Cantor at email@example.com.