A Guide to Window Rigid Head Flashing

Learn why rigid head flashing is important and how to install it correctly with these pro tips.

July 15, 2022

What is Window Flashing (Rigid Head Flashing)?

Rigid head flashing (RHF) works in conjunction with window flashing, weather resistant barrier (WRB) and the cladding to keep water from finding its way inside a building. RHF is made of steel, aluminum or PVC and is installed on the top, exterior side of a window. RHF is sometimes referred to as a window drip cap, drip edge, cap flashing or z-flashing.

One thing that distinguishes RHF from other flashing is that RHF protrudes past the plane of the window, which helps shed water out away from the face of the glass and window components. Rigid head flashing is available in many different colors at building supply stores or can be made on site with a brake from coil stock.

Read on for tips on how to install rigid head flashing along with some bonus pro tips you won’t find in typical installation manuals.
Illustration of the seal needed underneath flashing when intalled

Seal Underneath

Apply sealant between the wall and the back of a head flash. Use an exterior grade sealant that won’t shrink and stays flexible.

Pro tip: The horizontal part of the flashing should slope slightly down away from the wall to allow water to easily shed off it.
Illustration of tuck flashing

Tuck flashing under the WRB

A rigid head flash should be installed underneath the weather resistant barrier (WRB). Seal the rigid head flashing to the sheathing with a self-adhering flashing tape before folding the WRB down over the head flash.

Pro tip: Seal the corners of the WRB with tape, but don’t fasten the WRB to the whole length of the head flash. Instead, apply several small sections of tape, just enough to keep the WRB in place. This process of “skip taping” will create an outlet for any water that may have penetrated the building envelope above the window.
Illustration of how to fold flashing ends up or down

Fold the ends up or down

Pro tip: Instead of cutting a head flashing the same length as the top of the window, run it long and either bend it down over the edge of the window or bend it up and create an end dam. Folding the end of the RHF down will help prevent water from finding its way under the flashing. Folding the RHF up will help prevent water from getting behind the cladding where the flashing and cladding meet.

If neither the window nor siding manufacture suggests one of these methods, then just pick the method you’re most comfortable with. Folding an RHF up and creating an end dam will only work when the cladding is not installed tight onto the top of the window (see below).
Illustration of the gap you need to leave when installing flashing

Leave a gap

Most siding and window manufacturers require a gap of 1/4-in. to 3/8-in. between the head flashing and the bottom edge of the siding directly above it. This gap prevents wicking up into the cut edge of the siding and creates an outlet for water that may have found its way behind the cladding or WRB somewhere above the window.

Pro Tip: Install a self-adhering flashing tape over the RHF that is a similar color as the head flashing because it may be visible in the gap between the head flashing and the siding. Flashing tape colors are typically limited to black, white, gray and silver, but a white tape will stand out more than a black tape if the windows, trim and siding are all dark colors.
Illustration of instruction not to flash trim with head flashing

Don’t flash trim with head flashing

If the window is surrounded by trim, it’s not only important to install RHF between the top of the window and the trim, it’s important to flash the top of the horizontal head trim as well.

Pro tip: Head flashing designed for windows is often 1-1/4-in. wide. It will work fine if used on horizontal trim boards, its’ just wider than it needs to be. There’s no reason to have flashing protrude out farther than the face of the trim like head flashing protrudes out over a window; in fact, it looks better if it doesn’t. If your trim is ¾-in. thick, buy or make a z-flashing 3/4-in. wide.

Match the window color

Pro tip: Head flashing is less noticeable and looks better if it matches the color of the window instead of matching the color of the trim or siding.

Don’t skip it

Not all window manufacturer’s installation instructions will call for the addition of rigid head flashing but building codes in most municipalities require it. Even windows with a built-in flashing or an integral nailing fin benefit from RHF.

Pro tip: As always, when in doubt, ask your local building official.

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