The right skylight - installing roof windows

Sunset, May, 1999 by Lisa Stockwell

How to get the model that fits your needs

Do you find yourself avoiding the darkest rooms in your home because they feel cramped and closed in? You can transform your living space to make it appear larger and more appealing by installing skylights or roof windows that bathe a room in natural light. And there are skylight solutions to fit a wide range of budgets.

First considerations

Adding a skylight is not as simple as filling a hole in your ceiling with a window or some other form of glazing. Many variables affect your use of a skylight.

* The shape and size of the room: A small ceiling area will limit your choices.

* The house structure: For example, beams, ductwork, or other service lines may be in the way. Choosing another location or a smaller skylight is easier and far less costly than rerouting ducts or making major structural changes.

* The height and configuration of the attic: If there is one, it can affect the shape and character of the skylight well.

Maximizing the light

To achieve the best solutions, follow three rules.

Rule 1. A skylight is not just like a light fixture; plan its shape and placement so natural light spreads evenly through the room. According to Berkeley architect Gary Earl Parsons, the goal is to avoid harsh, high-contrast light. "Whenever possible, place the skylight so that a wall aligns with one or more sides of the skylight opening," he suggests. "The side of the skylight well and the wall should be one continuous plane so that light can wash down the surface uninterrupted." Long, narrow skylights spread light across a greater portion of the wall than square ones do.

Rule 2. Design the light well to maximize the light. A deep well provides less light than a shallow one. A flared well distributes more light than one with straight sides. Smooth white walls on a well give up to 80 percent reflectance, while a natural wood finish gives only 40 percent.

Rule 3. The glazed area should be at least 10 to 15 percent of a room's total square footage. For very large rooms you can now purchase skylights up to 26 square feet. Beyond that you will need to use a multipane unit or gang smaller single units together.

Choices

Once you've established your skylighting plan, you'll be faced with a number of other questions. Should the skylight be glass or acrylic? Fixed or ventilating? Do you need accessories such as built-in miniblinds, roller shades, or motorized openers? The cost of an installed skylight can be $500 to $1,700 - or more if the light well is extremely complex. Accessories will increase the cost significantly. Establish a budget before you start shopping.

As you consider functional options, try to select a skylight that suits the style of your home's exterior and is compatible with the character of the room. Skylights come in a wide range of shapes - from square and rectangular to pyramid-shaped, double-pitched, and round.

The glass skylight is now the most popular choice for residential use, preferred by many for its low-profile design and high-quality appearance. While more expensive than other choices, glass skylights provide superior energy efficiency and the option of built-in miniblinds or roller shades for sunscreening. However, to hold a glass skylight, your roof must have at least a 3-inch rise for every 12 horizontal inches. (If your roof is too flat, you may be able to create the necessary rise by building up one side of the wood curb that holds the skylight.)

Glazing options vary from the simple - two panes of glass separated by a layer of argon gas for insulation - to the complex: combining argon-filled glass with low-emissivity coating (low-E) that provides superior thermal performance and filters out most of the sun's ultraviolet radiation.

The lower-cost alternative is the acrylic dome. Quality domes now feature watertight aluminum frames and two layers of an acrylic that is much stronger than the plastic used decades ago. The main advantage of acrylic glazing is that it is less vulnerable to breaking on impact than glass. Pyramid-shaped and hipped units are available.

Both glass and acrylic skylights come in fixed and ventilating (openable) models. Some manufacturers, such as Velux, offer a fixed model with a ventilation flap that allows fresh air to circulate. Openable skylights (for use in spaces where heat buildup can be a problem) average $250 more than fixed ones but can be opened and closed with a manual or motorized control rod or can be wired to an electric motor controlled by a wall switch. Some models come with sensors that automatically close the unit when it rains. Others offer a remote-control hand unit to operate the window from anywhere in the room.

If your main concern is bringing natural light into a room as inexpensively as possible, consider the tubular skylight. Tubular skylights are relatively small (10 to 22 inches in diameter); installing them requires no structural alterations. The tube skylight is a single unit that collects light through a small clear acrylic dome mounted on the roof, reflects it down a flexible transfer tube (which can bend around obstacles), and spreads it through a flat interior light diffuser built into a room's ceiling. While the tubular skylight provides little architectural interest (the light diffuser resembles a recessed light fixture), it is an efficient way to brighten any room.