the projection fits under the header. Maneuver the
window unit outward until it is about halfway out-
side. The sill will now be holding the weight of the
unit. Have one or two of your helpers go outside to
help steady the window as you continue to push it
through the opening.
If there is no existing exterior support, use 2 x 4
studs as shown,  Pre-cut to the anticipated length to
support the outer edge of the projection as it is eased
outside. Work the unit outside until the edges of the
side boards, head board, and seat board are flush
with the interior wall surface.
Secure the outer edge of the projection with adequate
support from the temporary braces. Using a level, be
sure that the window sits plumb and square in the
opening. Using 3” wood screws, countersunk in the
sides, head, and seat, gently anchor the window unit
in the opening using shims under each screw. Check
the plumb, square, and level again and adjust as
necessary. Then you can tighten the screws.
Any Bay, Bow, or Garden Window with a projection
over 8” outside the exterior siding of the house needs
support brackets. If none are supplied with the unit,
a pair can be cut from 2x12, or 2x10 pressure treat-
ed lumber. They can then be covered with pre-fin-
ished aluminum capping stock or form the base for
an enclosed support, as shown.
Making a Support for Bay, 
Bow, or Garden Windows
Outside the house, set a knee brace or angled sup-
port under each mullion of the window. Place the
long leg of the brace against the house,and drill pilot
holes through the brace into cripple studs in the
wall. You can identify the location of the cripple
studs after you have removed the old window. 
Nails in the rough sill will show where they are.  If
there is no cripple stud in a proper position, move
the brace left or right (within reason) until it lines up
correctly.
The idea is to support the window, under the mul-
lions, as close as possible, yet maintain a balanced,
symmetrical look to the braces.  If they are to be cov-
ered, the symmetry is less important.
Fasten the support bracket using a 3/8” lag bolt that
is long enough to penetrate into the stud at least 2".
Fasten the brace to the underside of the Bay or Bow
unit with a wood screw of sufficient length to anchor
into the seat board, but not puncture through.
Using a Cable Support System
Most manufacturers can supply a cable support sys-
tem for Bay and Bow Windows to eliminate the need
for knee brackets. Garden Windows, with glass roofs
that cannot use a cable system, will still require knee
brackets. If a cable support system is not available
from the manufacturer, lumber and building materi-
als dealers can usually supply a kit.
The typical cable kit consists of two threaded pins,
washers and nuts, cables, and cable anchor brack-
ets. Cable support systems work easiest where there
is an overhang (soffit or cantilevered floor) above the
installed window. Follow the instructions supplied
with the cable system.
Temporary 
Support
Shims
Shims
Stud
Stud
Window Fitters Guide to Window Installation 
63              ©2022 AWDI, LLC Do not reproduce without permission
SAMPLE MANUAL

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