Aluminum Window Frames
Aluminum window frames are strong, but lightweight. They are ideal
for openings that require customized frames. They can hold large,
heavy, or odd-sized panes of glass. Frames made exclusively from
aluminum, however, are not as energy-efficient as other frames.
Aluminum frames often account for large amounts of heat loss, and
contribute to condensation around the edge of the pane and on the
frame. New aluminum frames usually have thermal breaks, which are
insulating plastic strips between the inside and the outside of the
frame and sash. Thermal breaks improve the R-value of aluminum
windows, although the most basic aluminum window with thermal
breaks still may not be the best choice for cold climates.
In some of the more advanced aluminum windows, the thermal break is
combined with foam insulation to create a super energy-efficient
frame. One window manufacturer produces an aluminum frame with foam
insulation that has a frame R-value of about R-5.6. When combined
with high-efficiency glazing, the window has an overall R-value of
Because they corrode easily, aluminum window frames may be a poor
choice for those who live near the seashore or in heavily polluted
areas. You can paint aluminum frames, although they need special
coatings to ensure an attractive, long-lasting finish.
Wooden Window Frames
Wood window frames are still the choice of most homeowners and most
major window manufacturers. Wooden window frames have a higher
R-value than aluminum and may have a more traditional look.
Temperature extremes do not effect them, and condensation is less
common because the inside of the frame stays relatively warm. Since
they are easy to paint, wooden window frames also allow the
consumer to change the color of the window. Wooden window frames,
however, require considerable maintenance, including periodic
painting. If they are not protected from moisture, they can stick,
crack, and warp. As the cost of wood increases, manufacturers have
begun using veneers over lower grade wood or strandboard cores.
While these are not solid wood, the wood fiber determines the
performance of the frames if the percentage of resin is less than
Aluminum-clad and Vinyl-clad Wooden Frames
Vinyl-clad and aluminum-clad wood frames are wood frames covered on
the exterior with either vinyl or aluminum. This allows the
homeowner to have the higher R-value and traditional look of the
wood frame indoors, while avoiding periodic painting outdoors.
These window frames, however, may rot if the cladding leaks and
moisture reaches the wooden frame.
Several companies produce window frames made from wood scraps,
vinyl waste, polyethylene, and other recycled products. They may
contain as little as 50% wood fiber. The advantages of composite
frames are strength and resistance to moisture. Although made from
recycled products themselves, the mixture of materials used to make
composites makes them difficult to recycle.
Vinyl Window Frames
Vinyl window frames have become a popular option, especially for
consumers who want to replace old window frames or install windows
in unconventional openings. Vinyl window frames are primarily made
from polyvinyl chloride (PVC), a relatively flexible material that
allows them to be easily customized to fit almost any opening.
Vinyl window frames are available in a wide range of styles and
Vinyl window frames offer many advantages because they require
little maintenance and mold easily into almost any shape. The
thermal performance of vinyl windows depends on the type and
quality of the window. At least one manufacturer produces frames
filled with foam insulation. Computer calculations and at least one
laboratory test suggest that the R-value difference between
foam-filled and hollow vinyl windows adds little to the overall
window energy performance.
Vinyl frames do not need to be painted because the color is uniform
throughout. They do not swell, shrink, peel, or corrode, which make
them ideal for homes and businesses near the ocean or in heavy
industrial areas. Vinyl window frames are one of the best options
for remodeling projects, because the manufacturer fabricates the
frames to the specified dimension of the opening. This ensures that
the windows will fit tightly in the opening, reducing heat loss and
condensation. Dealers can usually install replacement windows in
one or two days. Vinyl window frames are also competitively priced.
Because of the nature of the material used, vinyl window frames
also have disadvantages. For example, they are not inherently
strong or rigid. The flexible qualities of PVC also limit the size
of the frame and the weight of the glass used in it. Some vinyl
frames are reinforced with metal to compensate for these
limitations, but this lowers their R-value. Vinyl window frames can
soften, warp, twist, and bow if heat builds up within the frame.
Moreover, the color of the window frames may fade over time. One
manufacturer offers a new type of vinyl frame that is more
resistant to distortion and discoloration from the sun and heat. In
hot climates, ordinary vinyl windows are only sold with white
frames, to limit solar heat absorption. Because this new material
tolerates higher temperatures, this will allow it to be available
in more colors for hot climates.
When purchasing vinyl windows, you may also want to consider
certain other qualities of window frames. For example, window
frames with corners that are welded together with heat (often
referred to as fusion- or heat-welded) are usually more durable
than frames with plastic corner gussets or corner keys, or those
that are glued together (solvent-welded). You can paint vinyl
window frames with special paints, but you should make sure that
painting the vinyl does not violate the frame manufacturer's
warranty. You should also beware of dealers who claim that they
have windows in stock and can alter the opening to accommodate the
new window. The window frame may not fit properly, and the added
cost for labor may exceed the cost of a customized window frame.
Fiberglass Window Frames
Fiberglass window frames are a relatively new type of frame made of
fiberglass composite material. Some of these window frames are
hollow; others are filled with fiberglass insulation. Most are
prefinished with a white or brown polyurethane coating. These
window frames are manufactured using a process called "pultrusion."
Glass matting and continuous glass strands are pulled through a tub
filled with resin. The window frames are then formed in a preformer
and pulled into a heated die. A chemical reaction hardens the
Fiberglass is an excellent insulating material. In addition,
fiberglass window frames do not warp, shrink, swell, rot, or
corrode. They do not soften and degrade under the thermal
conditions that most windows are exposed to, and they require
virtually no maintenance. Fiberglass window frames are also
relatively strong and durable, and can hold a large expanse of
glass. You can specify almost any color you desire. You can also
Although fiberglass may be the window frame of the future, there
are a few disadvantages. They may not be widely available.
Currently, only a few companies manufacture them, and the long-term
performance is still unknown. Fiberglass window frames also cost
more than the other types of window frames. Dark-colored fiberglass
frames can also fade. Consumers should not use harsh or abrasive
cleaning agents on the sash and frame, as they can fade, discolor,
or physically weaken the material. Also, insulated window
coverings, shutters, and other shading devices, as well as direct
applications of certain films to the surface of the glazing, may
cause thermal stress and adversely effect the thermal performance
of the window.
Traditional windows are divided into smaller sections (or "lights")
by muntins. These are small framelike dividers or grilles. When
they truly divide the window, there is a considerable energy
penalty caused by the increased edge area. Most manufacturers use
removable plastic or wood grilles that clip onto the inside of the
sash. Some manufacturers obtain a traditional look, without losing
energy, by gluing muntins to both sides of the window.
The insulation value of a double-pane or triple-pane window is
primarily a product of the still air space between the panes of
glass. Spacers separate the panes at the edges. Until recently,
most edge spacers were made of square metal tubing, usually
aluminum. Metal edge spacers are easy to manufacture and easily
formed to various window shapes. Unfortunately, metal conducts heat
extremely well. In a window with metal edge spacers, this means
that the edge of the window has little or no insulating value. The
temperature of the inside pane of glass in this area will be very
close to the temperature of the outside pane. The colder edges can
cause heat to escape and condensation to occur along the window
Recently, several manufacturers have introduced edge spacers with
increased insulation values. The alternative edge spacers come in a
variety of forms. By using reduced metal thickness, a less
conductive metal (such as steel), and by changing the geometry of
the spacer from a "D" shaped tube to a "U" shaped channel, some
manufacturers have been able to get increased energy efficiency
from edge spacers without having to retool their production
machinery. Other alternatives include using two layers of rubber
with a thin piece of metal sandwiched in between for structural
rigidity, or using other materials such as foam or fiberglass with
no metal at all. One of the most effective new edge spacers uses
both approaches. A thin layer (1/8 inch or 0.3175 cm.) of rigid
polyurethane foam separates two steel spacers. This type of spacer
boosts the overall energy performance of a typical window by 20%
over one using a standard aluminum spacer.
Although welded corners provide the most durable, watertight seal,
windows with plastic or urethane thermal breaks cannot be welded.
They use a mechanical fastener or bracket in conjunction with
gaskets and/or sealant Argon gas-filled windows use a dual seal
method. Polybutylene is the most common primary seal and prevents
gas leakage from between the panes. A secondary seal of silicon
holds the spacer in place and protects the primary seal from
moisture degradation. Seals can be damaged during transport or
installation. They can also degrade from exposure to sunlight,
pooled water, or chemicals. Window units are rated A, B, or C
according to their performance in an ASTM "aging" test that
involves exposure to Ultraviolet (UV) light, moisture, and extreme
temperatures. "A" rated windows are the best performers.
Energy efficiency is an important factor when purchasing windows
for your home, or when replacing old windows. Windows with
energy-efficient frames can enhance the thermal performance of the
opening, and the entire home as well. You should carefully consider
the needs for your home, the climate in your area, your budget, the
availability of the windows, required maintenance, and the
qualities of the window frame. You should also check for
durability, quality, warranties, and cost-effectiveness. The
purchase of the right window can turn your drafty home into a warm,
cozy, energy-efficient one. The installation of windows should be
done after careful research and planning.