This Old House - All About Fiberglass Windows

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ALL
ABOUT

Fiberglass
Windows

Stronger than vinyl, more affordable than
clad wood, they stand out for their strength,
low upkeep, and good looks BY THOMAS BAKER

WE ASK A LOT OF OUR WINDOWS. We expect them to
usher in light and fresh air when open, and to keep out the
wet, the cold, and the heat when closed. And we expect them
to function well for decades. Wood has been doing the job
for centuries, but even with a low-maintenance exterior
cladding, it swells and shrinks with temperature swings,
undermining longevity. Vinyl windows do away with upkeep
issues, but the floppy material must be made into chunky
profiles that reduce the amount of glass, and it loses
resiliency as it gets older, not a hallmark of durability.

Fiberglass doesn’t have these shortcomings. It’s stiffer and
lighter than wood, as low-maintenance as vinyl, and
unaffected by water or temperature fluctuations. While early
fiberglass models had some limitations, improvements in
manufacturing have resolved the issues of the past.

“Fifteen years ago, fiberglass windows were available only
in limited sizes, turned chalky from sun exposure, and came in
just one color—white,” says Matt Risinger, a builder based in
Austin, Texas, with more than 20 years’ experience. Today
you get custom sizes, durable UV-blocking coatings, a wider
color selection, and even the option of a wood interior. “With
all these windows have to offer, at such a reasonable price,
they’re hard to beat,” Risinger says.

Read on for a look at how fiberglass windows are made
and the ways they can light up a house, inside and out.

These traditional-looking fiberglass windows feature wood interiors
that have been painted to match the rest of this white kitchen.
Shown: Integrity Wood-Ultrex Double Hungs; marvin.com/integrity

84 THISOLDHOUSE.COM SEPTEMBER 2017

VITALS

HOW MUCH DO THEY COST? On average,

fiberglass windows run about 25 percent more than vinyl
and about half the price of aluminum-clad wood. Expect to
pay about $300 for a basic 3-by-5-foot fiberglass unit.

DIY OR HIRE A PRO? They’re available for new

construction as well as replacements. Some manufacturers
sell only through approved installers. Others will sell directly
to homeowners or through big-box stores. Hiring a pro is
recommended to ensure long-term, leak-free performance.

HOW LONG DO THEY LAST? Warranties against

construction defects range from 10 years to “lifetime”­or
for as long as you own your house. Insulating glass
typically carries a 20-year warranty against seal failure.

HOW MUCH CARE? Not much, other than cleaning

the glass and replacing the weatherstripping every decade
or so. If the factory-applied coating gets scratched, you
can touch it up with a 100 percent acrylic paint.

ILLUSTRATION: IAN WORPOLE roving strand mat HOW THEY’RE MADE

resin surfacing veil Most parts for a fiberglass window are fabricated
pullers heated die by pultrusion. In this automated process, lengths
lineal cut-off saw of fiberglass roving and strand mat are bathed in a
resin, covered with a fiberglass veil, and pulled
into a heated die that hardens the resin. (Separate
dies are used for each window part.) The smooth,
rigid lineal that emerges from the die is then
typically cut to length, coated, and fitted with
hidden nylon-reinforced corner blocks. When
screwed and glued together, lineals and blocks
form tight, clean, nearly indestructible joints.

ALL FIBERGLASS WINDOWS
ABOUT

These insert windows are FIBERGLASS THREE WAYS
installed from the inside,
so the existing wood Choose the look that works best with
trim can remain in place. your decor and budget

Are fiberglass windows ALL FIBERGLASS
right for you?
They resemble painted
The answer is yes, if you’re looking for a wood inside and out. For
window that offers high performance and about 10 percent more,
exceptional durability at an affordable price Pella can apply different
colors on the interior and
PROS CONS the exterior. Marvin’s
optional Everwood
Not bothered by water Fewer options interior finish (shown)
Because fiberglass is inert to Compared with wood, which looks like wood
moisture, there’s no concern fiberglass is more difficult when stained, adds 15 to
about rot, corrosion, mold, or to customize into unique 20 percent to the price.
shrinking and swelling. shapes and profiles, and has
fewer color and hardware WOOD INTERIOR
Temperature stable options to choose from.
Neither heat nor cold will The sills, sashes, and
induce fiberglass to flex, sag, Harder to find frames are fiberglass, but
or change dimension. That Only a handful of companies the interior surfaces are
reduces the chance of leaks make these windows, covered with either wood
around window perimeters. and not all of them veneer or solid wood
distribute nationwide. (shown). Compared with
More glass, less frame all-fiberglass models, the
The stiffness and strength Sensitive to UV ones with solid-wood
of fiber-reinforced resins Fiberglass resin becomes interiors command about
means that window frames chalky when exposed to UV a 15 percent premium.
and sashes can be narrower rays. A long-lasting, factory-
and less bulky without applied coating on the HYBRID
compromising their ability exterior is a must; the
to resist high winds. thicker, the better. Only the sash of the
Andersen A-series
window (shown) is
fiberglass, which moves
as little as glass. The
interior parts are wood,
while the exterior frame
is a composite of ground
wood and vinyl. Its price
is comparable to that
of a wood window clad
in aluminum.

ASSESS THEIR EFFICIENCY
Learn how to compare the energy
performance of all types of windows at
thisoldhouse.com/save-energy

86 THISOLDHOUSE.COM SEPTEMBER 2017

Improving the view

No longer plain-Jane vinyl look-alikes, fiberglass
windows have undergone big changes in key areas

COATINGS Factory-applied finishes are much tougher and more UV-
resistant than before, whether as a thick acrylic layer applied during
the pultrusion process or as a spray-on paint or powder coating
added before window assembly.

COLORS Once available only in white, fiberglass windows
now come in a range of colors, both on the interior and the
exterior (right). And if you want a different hue later on,
fiberglass can be painted as easily as wood.

CURVES The pultrusion process makes only straight wood aluminum
pieces, but manufacturers can nboerwglassmold fibevinrylglass
into classic arch-tops (left) and curves.

COMBINATIONS Windows no longer have to be
grouped together on-site to put together bays,
bows, and other combined sets; they can now be
delivered as integrated, reacode yci-enttoof-install units.

expansion

ENERGY PERFORMANCE By itself, f0iberg5lass1d0 oes15 20 25 30
a fairly good job of keeping out the cold. Filling the(x10-8)
frame with foam and adding triple-pane glazing
improves performance even more.

The competition DO THE NUMBERSthermal

When compared with other window materials, conductivity
fiberglass comes up strong berglass vinyl wood aluminum

0.H0 igh-0p.1erfor0m.2 ing f1ib00ergla1s10s is 120
rigid, stable, and slows heat flow

fiberglass vinyl aluminum wood

coe cient of RIGIDITY
expansion

modulus 0 5 10 15 20 25 30

(x10-8)

Moduliun smi(llpiosnsi 106)
HEAT TRANSFER

VINYL CLAD WOOD ALUMINUM thermal vinyl wood aluminum
conductivityberglass
This extruded plastic makes These high-end wood
the least expensive and most windows have an exterior This lightweight, extruded 0.0 0.1 0.2 100 110 120
commonly installed windows, layer of vinyl or metal—
but it turns brittle with age and usually aluminum—that metal is about as rigid and (Btu/Hr.-Ft.-oF)
exposure to cold. The frames reduces maintenance
and sashes have thin, flexible and improves longevity. low-maintenance as THERMAL EXPANSION
walls, can’t be repaired, and They are a close match to fiberglass. But it’s a terrible
don’t take paint well. Joints are fiberglass in performance,
heat-welded together, leaving but have a much higher insulator, readily carrying
obvious bumps at corners. price point.
heat to the outside in winctoee rcient of
and to the inside in summexepran.sion

That’s why this type of modulus 0 5 10 15 20 25 30
window is suited only for Coefficient of exp(xa1n0-8s) ion (In.-In. oF 10 -8)
mild climates.

in millions

FOR MORE INFORMATION, SEE DIRECTORY, PAGE 90

ALL FIBERGLASS WINDOWS
ABOUT

Pick your style

In addition to their structural virtues, fiberglass windows
hold their own in terms of aesthetics and versatility

WIDE OPEN These wood-lined SEEING GREEN Gray, black, forest WALL OF GLASS Big windows open up
casements and transoms demonstrate green—colored windows are more popular big views, but then they have to resist big
how narrow frames and sashes can be than ever, but dark colors are especially wind loads, too. These flanking casements
when they’re made of fiberglass. One more vulnerable to fading. The powder-coat finish are strong enough to defy winds up to 142
benefit: The sashes can’t warp, as wood on these custom casements and double- mph, while the picture windows and
ones are prone to do. Shown: Essence hung windows is virtually immune to UV transoms can withstand 190-mph gusts.
Series; milgard.com rays. Shown: Essence Series; milgard.com Shown: 300 Series; fibertec.com

BATHING BEAUTY These solid- THROW A CURVE Bow windows add HISTORIC LOOK Three double-hungs fit
fiberglass picture windows and transom are space to a room and funnel in lots of natural perfectly into the original gable openings of
immune to the humid air and occasional light. These five fiberglass casements are this 1897 Queen Anne. The center arch-top
splashes that come with a bathroom assembled into a single faceted curve to was custom-made using a proprietary
environment. They nicely frame a tub-side form a traditional bow unit. Shown: Infinity molding process. Shown: Integrity Wood-
view, too. Shown: Impervia; pella.com All Ultrex; marvin.com Ultrex; marvin.com

88 THISOLDHOUSE.COM SEPTEMBER 2017