Flashing:  The flashing configuration will depend on
the surrounding construction.  You can install the
flashing before or after the new window (Method A or
B) is placed in the rough opening.  Either way, the
flashing must be installed in a manner to preclude
entry of water into the wall cavity and the rough
opening gap.  In some cases, the window may have
an integral flashing design. In other cases, flashing
materials can be used in conjunction with the 
application of the finish siding. (See section on
Penetration Flashing)  
Header Drip Cap:  At the head of the window, a drip
cap should be installed from under the sheathing
paper at the header, to beyond the exterior face of
the window.  It should also extend past the trim at
the sides of the window.  Install a continuous piece
of aluminum or galvanized flashing material onto 
the building sheathing, tucked under the sheathing
paper, with a 90 degree bend to extend over the new
window’s header.  A 1/4” return bend is applied
down the face of the window’s header.  To finish, the
siding veneer will overlap the header flashing. 
Penetration Flashing: Material for flashing shall be
barrier coated reinforced flashing material and shall
provide for 4-hour minimum protection from water
penetration when tested in accordance with current
ASTM specs.   
Drip Cap, Penetration Flashing Basics
WINDOW BRICK
MOULD TRIM
CAULK
GAP
BRICK
VENEER
Window Fitters Guide to Window Installation 
18           ©2022 AWDI, LLC Do not reproduce without permission
Sealant used with penetration flashing techniques
shall comply with current Federal Specifications.
Application: To flash against water penetration in a
wood frame and sheathing application, a strip of
approved flashing material, at least 9” wide, shall be
applied in overlapping, weatherboard fashion
(counter flashing), on all sides of the opening.  
The first strip is applied horizontally immediately
underneath the sill - before the window is installed.
It should be long enough to extend past each side of
the window, and beyond the jamb flashing when it is
applied.  Fasten the top edge of the sill flashing to 
the sill, but do not secure the middle or lower edge 
so that building paper, later applied, may be slipped
up and underneath the bottom of the applied sill
flashing.
Next cut and apply the two vertical jamb flashing seg-
ments, again making them 9 inches wide, and suffi-
ciently long enough to extend above the (to be
applied) header flashing, and to extend below the
(already applied) sill flashing.  The jamb flashings
should overlap the applied sill flashing.  Fasten only
the top portion of the jamb flashing so that the lower
section(s) will allow the to be applied building paper
to be slipped up and underneath the jamb flashing
ends as well as the sill flashing.
Header Flashing
Overlaps
Jamb Flashing
Window Installed
With Fin
Sill Flashing
Jamb Flashing
Building Paper
Applied Over
Sheathing
Window Frame
Jamb and Sill 
Flashing Overlaps
Building Paper
SAMPLE MANUAL

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