Concrete 
Block
Wood 
Window
Stone
Sill
FLASHING BETWEEN
ROUGH OPENING
AND EXTRUDED
JAMB LINER
CREATING DRIP CAP
SIMILAR ON JAMBS
FLASHING BETWEEN
ROUGH AND SILL
CREATING SILL PAN
FIN
OPENING
EXTERIOR
SHEATHING
ROUGH OPENING
Window Fitters Guide to Window Installation 
73                ©2022 AWDI, LLC Do not reproduce without permission
Installing Vinyl Windows in Masonry
In most masonry applications, the old frame will
remain and installation will be as described previously
for wood or metal.  In those instances where the win-
dows to be replaced were installed in a block opening
(block, brick or stone), the opening depth will be 6” to
9” and require a wood frame (wood buck) for installa-
tion.  Also you must allow an additional 
1 1/2” in the width and 3/4” in height when you 
measure.  Order the smaller replacement window size
to allow for the use of the wood frame to attach to the
masonry opening.
If the old window is a metal window “cemented in,” 
it will need to be “cut out” as you would do with a steel
window.  The installed wood buck will butt up against
the remaining metal frame on the sides and top.
If the old window is wood, it usually can be totally
removed.
Once the old window is removed, clean opening and
remove old caulk.  Using 3/4” plywood or 1” x 6” or 
1” x 4” pine, install a wood frame across the top and
on both sides using cut nails to anchor wood into 
the masonry.
If desired, cover the wood buck with coil stock 
before placing in opening.  Also, the exposed outside
areas can be covered with wood trim or capping as
necessary. 
Using Aluminum angle or wood molding 
(1” x 1”) create outside “blindstop” along outside of
wood frame leaving enough space (3 1/4”) for 
replacement window.
Install the window against the “blindstop” and trim
outside and inside as necessary for completed job.
Pre-extruded shapes or available “Snap-Trim” can
make the job easier.  Mount the angle of the snap trim
with “pop rivet” to the top of window.  After placed in
opening, mount angle to other sides.
The chief method of installation of new windows in 
a concrete block wall system is with a tapered wood
buck.  The windows and doors are of a "flange" 
design, screwed to the wood buck usually with a
sheetrock interior return and a stucco wash finish 
on the outside.  Where the upper stories are allowed 
to be frame, fin design windows are used.
A. Flange
Application: A “flange”
allows the unit to be
applied against a wood
buck fastened to the
rough opening.  Flange
mount is used most often
with concrete block, such
as CBS construction.  The
window is mounted with
screws applied through
the frame, into the buck.
B. Fin Application: 
A nailing “fin” on a vinyl
window is integrally
affixed to the frame
between the outer and the
interior edge.  Fin mount-
ing is used in wood frame
construction by nailing
through the fin into the
wood framing and sheath-
ing.
C. Flush Application:
When the unit does not
contain a flange or a fin,
it can be mounted flush
in the opening by using
mounting screws through
the jambs into the rough
opening frame.
FLANGE
WOOD BUCK
Flashing
between
window
and 
buck
Flashing
under 
window is
sill pan
SAMPLE MANUAL

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