bottom swings outward.
strip, crud collecting in tracks can impede opera-
Pros: A single large pane of glass maximizes
tion, and only half of a window’s area offers
solar gain, and you can leave the window open
ventilation.
for ventilation even when it’s raining—the window Fixed windows don’t open.
acts as an awning. It has a tight compression seal
Pros: A fixed window can’t be beat for being
like a casement.
airtight, and it’s less expensive than an operable
Cons: A sash that swings onto a deck or walk-
window of the same design. With acoustic glaz-
way is hazardous, and the screen is on the inside. ing, it’s the best choice to reduce outside noise.
Hopper windows, which tilt from the bottom,
Cons: It offers no ventilation and no egress.
are like upside-down awning windows.
You can’t wash the outside from the inside.
Pros: It has the same energy profile and com-
FRAMe MAteRIAlS
pression seal as casement and awning windows.
Cons: It’s hazardous if it swings down at head
In the last few decades, there have been so many
height, and it’s a poor choice for egress.
improvements in insulated glass that the R-value
Tilt-and-turn windows are hybrids that swing
of the glazing generally exceeds that of the frames.
like a casement or bottom-tilt like a hopper.
In other words, windows with a larger percent-
134 Chapter 6
Window Words
Many of the terms used to describe doors are also used for windows. Window frames
consist of jambs—side jambs and a head jamb—and a sloped sill. Window frames
also have stops to guide sash movement and provide a seal. Window sashes, like
doors, have horizontal rails and vertical stiles. And casing is applied, inside and out,
to limit air infiltration and impart a trim, finished look to the perimeter of windows.
lastly, many styles have terms that describe particulars of construction, such as the
muntins and meeting rails of double-hung windows.
Muntins
zzzzzz Double-Hung Window elements
Upper sash
Side jamb
Parting
bead
Pulley
Meeting
rail
Sash weight
Interior
stop
Sash cord
or chain
Lower
sash
Pocket cover
(not always
present)
Stool
Apron
age of glass (and a smaller percentage of frame)
late the energy performance your window must
are better energy performers. In response, win-
deliver (hence, the type of glazing, etc.), and then
dow makers are hustling to make window frames talk to builders and building-supply staffers
less conductive (of heat and cold), more airtight,
about which manufacturers they favor. Try out
and more durable. To do so, they have developed
windows as well, opening and shutting display
frames with a wide range of core materials, clad-
models to see how tightly they fit, how smoothly
ding, finishes, and in some cases insulation.
they operate, and how sturdy they feel. Look
The chart on p. 136 will give you an overview
especially closely at frame corners, glazing seals,
of how different frame materials perform, but to
and weatherstripping gaskets, for that’s where
be honest, the best way to select a window is to
windows fail first. And when scrutinizing win-
choose a frame style that fits your house, calcu-
dow cross sections, try to envision cold air
Doors, Windows, and Skylights
135
Window Frame Materials
FrAme
mATeriAL
dUrABiLiTy
insULATing LeVeL
mAinTenAnce
cosT
coLors
commenTs
Most conductive of cold,
Aluminum
good
Poor
low
$
limited
but Ok in mild climates
Needs painting every 10 years,
Wood
Fair
good
High
$$ to $$$
Paintable
cleaning
Custom colors
As attractive as wood but easy
clad
good
Best
low
$$$$
cost extra
to maintain; choice of claddings
Degrades if overheated;
Vinyl
Fair
Fair to good
Fair
$
limited
otherwise, it’s durable
least conductive, can also be
Fiberglass*
good
good
low
$$$
Paintable
insulated with foam
*Fiberglass’s rate of expansion and contraction is virtually the same as that of glass, which helps glazing seals last longer.
encountering that frame: Is there a thermal break make economic sense for your region, have a
that will slow or prevent cold air from chilling
look at the calculator at www.efficientwindows.
the frame and causing conductive heat loss?
org/selection.cfm.
Lastly, “you get what you pay for” is especially
Well, that will get you started. And of course
true when buying windows. Even frames fabri-
there’s a wealth of professionals, from architects
cated from less expensive materials, such as
to energy consultants, who can help you balance
vinyl, offer options such as chambers filled with
the competing claims of cost, performance, and a
foam insulation that raise performance—and cost. plethora of features that there’s no room for
here—including impact-resistant glazing that’s
ReAD tHe lABel: UNDeRStANDINg
required in storm-prone areas, acoustic windows
WINDOW eFFICIeNCy
whose ability to reduce noise is rated with a
sound transmission coefficient (STC), and even
R-value, the ability of a material to resist heat
“self-cleaning” coatings that claim to slow the
flow through it, became a household word in the
buildup of dirt on glass.
1970s, when soaring energy costs led to a boom
in home insulation. The higher the R-value, the
CHOOSINg A RePlACeMeNt WINDOW
better, we learned. Given the push to make hous-
es ever more energy-efficient, the next frontier
If you need to replace windows, whether because
was windows because single-pane glass is a terri-
they are drafty and waste energy or because they
ble insulator. Shortly, there was a blizzard of
show signs of deterioration, you have three basic
energy-saving technologies applied to windows,
choices.
doors, and skylights—and a flurry of new terms
1. replacement
sashes. If the frame and sill are
to describe them.
in decent shape, you can install jamb liners along
Chief among this thicket of terms is the
the inside of the frame and insert new sashes into
U-factor, an aggregate measure of how well non-
the liners. In general, this option is the most eco-
solar heat flows through a window’s glazing and
nomical way to make windows tighter and more
frame. Simply put, U-factor is the inverse of
energy-efficient. This is such a popular option
R-value (1 divided by the R-value), so the lower
that many window makers offer replacement-
the U-factor, the better. The U-factor is a rough
sash kits that fit easily into old frames. Detractors
measure of conductive heat loss and gain. But
of this option tend to dislike plastic jamb liners
the more elaborate window science became, the
and doubt that they provide much of an air
more crowded labels grew—as you can see in the seal. That aside, it’s tough to knock the value for
drawing on the facing page. This information is
the money.
all good, but to figure out which window features
136 Chapter 6
2. Window insert. This option features a rigid
to make the window weathertight—and thus
P R O T I P
frame and sash assembly that sits inside an exist-
replace the exterior casing. But real life doesn’t
ing frame and generally seats against an interior
always go by the book, as you’ll see on p. 143.
Retrofitting cap flashing takes
or exterior window stop. The existing windowsill
Sometimes disturbing the existing casing is both
dexterity. Cut back the siding
stays put. Inserts offer a better air seal and great-
inordinately expensive and disruptive and not
nails 2 in. to 4 in. above the
er energy efficiency than a replacement sash, yet
warranted when a less-disruptive method will be
opening, and pry up the siding so
the space between the insert frame and existing
sufficiently effective.
you can slide the top leg of the
jambs must be caulked or insulated in some
cap flashing under the building
manner. Inserts cost slightly more than a new-
INStAllINg RePlACeMeNt SASHeS
paper and siding, while simulta-
construction window but less to install because
neously holding up the window
The Marvin Tilt Pac® shown in the photo sequence
you leave the casing in place. The downside of
unit. you can nail the top leg of
is but one of many sash replacement and liner kits.
inserts is that a frame within a frame reduces the
the flashing through the siding,
For best results, consult the manufacturer’s
amount of light that can enter and cuts the view.
but that’s not imperative.
instructions that come with your unit. Each win-
Wedged into place, the cap flash-
3. new-construction window. When there’s
dow maker also will have specific instructions for
ing won’t go anywhere.
water damage and rot present, you must remove
measuring the rough opening. In the sequence
the existing window entirely, including its sill. A
shown, the installer measured width and height at
new-construction unit thus sits inside the rough
the frame’s centerpoint—the point at which the
opening and has a full-dimension sloping sill. To
upper and lower sashes meet.
install this unit “by the book,” you’ll need to
The installation sequence shown is pretty
replace old head and pan flashings, and use self-
straightforward, but a few things are worth
adhesive flashing tape and compatible sealants
emphasizing: Be sure to remove any impediment
Double glazing: Today’s standard insulated glass unit, consisting of two
Gas filling: clear, inert, nontoxic gas that
glass panes separated by spacers, with a sealed, airtight space between
insulates between panes. Argon and krypton,
them. Triple glazing is often specified for cold climates. Glazing, by the
for example, are less conductive than air and
way, is the fancy name for glass panes, the space between them, their
hence better insulators.
airtight seals, and the putty or caulk that seats them in the frame.
Low-emissivity (low-e) coatings: Thin,
nearly invisible window coatings that
selectively reflect heat back into a
U-factor: The sum of a
room (to conserve energy) or block
window’s insulating values,
sunlight to reduce solar gain. Low-e
drawn from all its parts
coatings also filter damaging UV rays.
(glazing, frame, sashes).
measuring nonsolar heat flow,
the smaller a U-factor
Solar heat gain coefficient (SHGC):
number, the better.
The percentage of solar heat that
passes through the glazing. higher
shgc numbers indicate greater
Visible transmittance (VT):
passive solar gain—desirable in
The amount of visible light
cold regions. conversely, lower
that enters. Values range from
shgc numbers mean lower air-
0 to 1; higher is better. Wide
conditioning bills in hot climates.
sashes and frames block
light, lowering VT numbers.
Air leakage (AL): The movement
of air through a window system,
Condensation resistance (CR):
measured in cu. ft./sq. ft. Lower
higher ratings (from 0 to
is better; <0.03 is optimal.
100) predict less
condensation.
Reading the NFRC label on a window is an education in itself. NFRC, for starters, is the National
Fenestration Rating Council, a nonprofit organization that independently rates the energy
efficiency of windows, doors, and skylights. Here’s what the label is telling you.
Doors, Windows, and Skylights
137
Sizing Windows
Window catalogs have several ways of
denoting window dimensions, including a
zzzzzz Measure Windows in three Directions
callout size, which usually indicates the size
of rough opening required, or a unit size,
which denotes the outer dimensions (width
and height) of the window frame. Window
dimensions are stated as pairs of numbers;
the first number is always width.
So, a window with a callout size of 4030
denotes an RO 4 ft. 0 in. by 3 ft. in. 0 in.
typically, the unit size of a window (frame) is
1⁄2 in. less in height and width than the call-
out size, but always check the manufacturer’s
Measure
specs to be sure. Window sashes are usually
horizontally
and vertically,
13⁄8 in. thick unless otherwise noted.
and use the
When ordering window units, measure the
smallest
width of t
he ROs in three places from top to
measurement in
each direction
bottom and the height in three places from
so replacement
side to side. Window manufacturers usually
jambs will be
sure to fit the
prefer the smallest reading in each direction,
opening.
but, again, follow the manufacturer’s order-
ing instructions to the letter. Also measure
the thickness of the walls, from interior fin-
ish surfaces to exterior sheathing; you may
need jamb extensions as well.
Measure openings and order windows well
in advance. If your window units are in odd
Measure diagonally to see if the old window is square.
sizes or otherwise unusual, they may require
a special order, which takes longer.
exterior trim: let It Be
If you need to upgrade windows, try to choose an option that avoids
disturbing casing—especially exterior casing. House exteriors consist
of interconnected elements that must remain intact to be weather-
tight. Window cap flashing is especially difficult to retrofit because,
ideally, its top leg goes under building paper and siding and is caulked
as well. yes, you can slide a metal-cutting recip saw blade under the
siding to cut nail shanks and slide a piece of metal head flashing up
underneath. But it’s rarely as simple as that.
Here, the lower roof leaked because the corner of the
window was too close and a lazy roofer didn’t bother to
install step-flashing (see p. 88). Also, the window lacked cap
flashing. As you can see, retrofitting flashing is no simple
matter.
138 Chapter 6
with the frame that would prevent the jamb lin-
ers from lying flat. Jamb liners are backed with
compressible foam, which will bridge minor
irregularities. But to ensure that sashes slide
freely and the unit is as airtight as possible, all
jambs must be straight, plumb (sides) or level
(head), and the frame must be square. The jamb
and head channels can accommodate minor dis-
crepancies but not large ones. In the sequence
shown, the installer packs cotton insulation
around the frame; loose fiberglass also would
work. Low-expanding foam is another option,
but one I don’t recommend.
Another reason for the Tilt Pac’s popularity:
1. Remove the interior stops from the side jambs,
2. Remove parting stops from side and
After installation, you can pivot sashes to wash
disconnect sash weights or other balancing devices, and
head jambs, lift out the top sash, then
the outside of the window.
Renovation 4th Edition Page 32