Installing Bay or Bow Windows
As with any replacement, accurate measurement is
the key to a simple and successful installation. Refer
to the measurement and specifying section to famil-
iarize yourself with the parts and pieces that have to
be removed. You must be able to measure the exist-
ing window and be able to add the proper inches to
the height and width to accommodate the frame that
must be removed, but is hidden beneath the trim. 
If you’re not sure of the dimensions, don’t be afraid to
remove any trim when you measure. It is more pru-
dent to be concerned with a properly installed and
sealed new window, rather than with tampering with
the old window.
Removing the Old Window
There are two types of old windows that are usually
replaced with a new Bay or Bow Window- a picture
window/double hung or slider combination, or an old
Bay or Bow Window. If the window to be replaced is a
combination window, then it is best to remove the
entire window, frame and all.  
If the window to be replaced is an old Bay or Bow
Window, it might be easier to just remove the window
parts and leave the old head and seat board.  If the
old head and seat boards are structurally sound, the
new window might able to be installed to fit within
these boards and limit the amount of disturbance
you must make to the trim and siding around the old
Bay or Bow Window. 
If the total old Bay or Bow Window needs to be
removed, the old roof and outer lower support may
also need to be replaced regardless of their condition.
New, custom made Bay or Bow Windows may have a
different angle or curve than the old bay or bow, and
the roof and lower support would have to be rebuilt
or replaced to match the shape of the new window
and avoid leaks or an unsightly installation. Minor
variances can be accommodated by quality capping
and trim. Remember, the finished looks are as impor-
tant as the structural support.
Whenever possible, work with the factory and try to
be able to make a custom window and save the work.
If the home owner wants new trim outside, at the
most offer it as an extra, because if the window fits
the opening, new outside trim may not be necessary. 
Follow the drawings and remove all parts of the old
windows until you are down to the head and seat
board. The existing header, sill, roof and support are
all held fast to the wall. Removing the old window
shouldn’t interfere with any of these. 
The only item you may want to check would be the
support since the new window might be heavier
because of the insulated glass in the window units.
Carefully removing the covering of the support struc-
ture will probably allow you to add additional sup-
port if necessary. The old covering can be re-applied
and trimmed new to blend the new window to the
existing siding.
Removing an existing combination window should
clear the opening down to the header, sill, and jack
studs, as shown. 
Custom Wall Depth
Most bay, Bow, or Garden Windows have 6"
standard side board depths. For most applications
these are the correct dimensions.
For some applications, however, the opening is
extra deep requiring a custom side board depth.
Using the diagrams for Siding and Brick, 
measure the opening depth.
Inside Trim
King
Stud
Sill 
Plate
Jack
Stud
Cripple
Stud
Head
SIDING
BRICK
HEIGHT
WIDTH
Measure Here
Measure Here
Window Fitters Guide to Window Installation 
61               ©2022 AWDI, LLC Do not reproduce without permission
SAMPLE MANUAL

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