Skylights
A skylight can provide your home with daylighting
and warmth. When properly selected and installed, an
energy-efficient skylight can help minimize your
heating, cooling, and lighting costs.
Maximizing a skylight's performance in your home
involves three steps:
• Design
Consider your home's design and climate in relation
to the energy performance of a skylight.
Skylight Design Considerations
Before selecting a skylight for your home, you need
to determine what type of skylight will work best
and where to improve your home's energy efficiency.
Energy Performance
First, it's a good idea to understand the energy
performance ratings of skylights if you don't
already. You can then determine what energy
performance ratings you need for your skylight based
on your climate and home's design.
For labeling energy-efficient skylights, ENERGY
STAR® has established minimum energy performance
rating criteria by climate. However, this criteria
doesn't account for a home's design. Therefore, if
you're constructing a new home or doing some major
remodeling, you should also take advantage of the
opportunity to incorporate your skylight design and
selection as an integral part of your whole-house
design—an approach for building an energy-efficient
home.
Size and Position
The physical size of the skylight greatly affects
the illumination level and temperature of the space
below. As a rule of thumb, the skylight size should
never be more than 5% of the floor area in rooms
with many windows and no more than 15% of the room's
total floor area for spaces with few windows.
You should also consider a skylight's position if
you want to maximize daylighting and/or passive
solar heating potential. Skylights on roofs that
face north provide fairly constant but cool
illumination. Those on east-facing roofs provide
maximum light and solar heat gain in the morning.
West-facing skylights provide afternoon sunlight and
heat gain. South-facing skylights provide the
greatest potential for desirable winter passive
solar heat gain than any other location, but often
allow unwanted heat gain in the summer. You can
prevent unwanted solar heat gain by installing the
skylight in the shade of deciduous (leaf-shedding)
trees or adding a movable window covering on the
inside or outside of the skylight. Some units have
special glazing that can help control solar heat
gain.
• Selection
Find a skylight that meets your energy performance
requirements.
Skylight Selection
You'll find that you have several options to
consider when selecting the type of skylight to use
in your home.
When selecting a skylight for energy efficiency,
it's important to first consider its energy
performance ratings in relation to your climate and
home's design. This will help narrow your selection.
A skylight's energy efficiency is dependent upon
all of its components:
• Glazing
• Operation and Use
• Shape.
• Installation
Ensure proper installation of skylights to maximize
their energy efficiency.
Skylight Installation
Even the most energy-efficient skylight must be
properly installed to ensure that its energy
performance is achieved. Therefore, it's best to
have a professional install your skylight.
In addition to following the manufacturer's
guidelines when installing a skylight, it's also
important to consider slope and moisture control.
Slope
The slope or tilt of the skylight affects solar heat
gain. A low-slope will admit relatively more solar
heat in the summer and less in the winter, exactly
the opposite of what is desirable.
As a general rule of thumb, you want to achieve a
slope equal to your geographical latitude plus 5 to
15 degrees. For example, the optimum slope for a
south-facing skylight in Columbus, Ohio, at 40º
North latitude, is 45º to 55º. At least one skylight
manufacturer makes a prefabricated, tilted base that
increases the angle of a skylight above the roof.
Moisture Control
Water leaks are a common problem with skylights.
Take the following steps to avoid water leaks:
• Mount the skylight above the roof surface
• Install a curb (a raised, watertight lip that
helps to deflect water away from the skylight) and
flashing
• Thoroughly seal joints
• Follow the manufacturer's guidelines.
It is also prudent to apply a layer of sheet
waterproofing over the flanges/flashing of the
skylight. This is generally installed under the
finish roofing material as an aid in protecting
against ice dams. Avoid water diversion devices such
as roof crickets or diverter strips, as they often
create more problems than they solve.
