When the opening is properly flashed, moisture will make
its way down the sides of the new window towards the sill,
where the sill configuration should allow this moisture to
exit.
The Sequence is Important.
The process is called shingling, and it describes the 
overlapping of each flashing layer when creating a 
water-tight window and door installation.
Method A: It is advisable to staple building paper
over the edges of the rough opening as shown. Put
the bottom strip on first, and the sides next. The top
strip is mounted after the window is installed and
overlaps the top nailing flange.  This will direct water
away from the window opening.
Once the bottom and side strips of WRB  are mount-
ed, apply bedding sealant around the inside of the
nailing fin.
Place the window in the opening with the flanges
tight against the opening.  Position the window 1/8”
from the top, and 3/8” from the bottom, and center
the window side to side.  This will allow the interior
trim to be installed without impeding the operation of
the window.
Nail across the top first (in every other slot), making
sure the window-top is level.  This procedure will in
effect “hang the window” and assure that it is both
level and plumb.  Re-check the level and plumb, and
nail the sides (in every other slot) from the top down.  
Do not nail the flange tight. Like siding, nailing
should be just tight enough to hold the window, 
but not impede movement of the structure under-
neath during environmentally caused expansion 
and contraction. 
Staple the top strip of building paper in place if 
needed.
When siding and/or trim is installed, it should be 
fitted over the nailing flange using the proper drip-
caps, J-channels, or other flashing materials.
Interior Trim
Though there are many ways to trim-out the interior
of the new Vinyl Window, the two most popular ways
are Wood Jamb/Trim, & Casing;  and Full Sheetrock
Return on all 4 sides. Even with the sheetrock
return, a wood stool is recommended to facilitate
cleaning, and minimize marks.
Figure 3 details typical, conventional wood trim -
including wood jambs, wood stool, and clamshell or
colonial casing and apron. Using standard 3/4” or
5/4” wood stock, butt the stool and jamb to the win-
dow, and then the sheetrock can be butted to the
jamb and stool and covered as shown.
Figure 4 details a typical sheetrock return. Be careful
to trim the sheetrock square as it will butt against
the window. If possible use the outside, wrapped,
edges of the sheet to keep the joint neat. Using metal
corner bead, cover the wall and jamb/sill joints and
spackle as necessary.
It is also desirable to install a 3/4” wood stool over
the sheetrock sill and use casing for an apron below.
WRB
Sheathing
Window Fitters Guide to Window Installation 
97               ©2022 AWDI, LLC Do not reproduce without permission
EXTERIOR
SEAL
INTERIOR
SEAL
DRIP CAP
INSULATION
FASTENING
SHIMS
PLUMB/
LEVEL
FIG 3 WOOD TRIM
FIG 4 SHEETROCK TRIM
SAMPLE MANUAL

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