Flashing Replacement Windows: How It Is Done?

Window flashing is a thin, frequently flexible material that is put around a window frame to block the entry of water, moisture, or wind between the window and the building’s outside wall.

Flashing assists in directing water downward and away from the house’s exterior and keeps it from leaking around the window, where it may cause structural damage, the formation of mold, and wood rot.

Water damage is frequently the result of defective flashing. It is necessary to temporarily remove portions of the external siding, except brick, in order to fix broken flashing.

It is possible for the flashing to lose its original integrity when a window is replaced. So you must inspect the condition of your flashing regularly.

In this article, I will show you how you can get done with flashing replacement windows in just 6 easy steps.

6 Steps To Flashing Replacement Windows

StepsEstimated Required Time
Cut Your Flashing Material15 – 30 minutes
Ensure The Sill Pan Flashing10 – 15 minutes
Seal The Window Unit15 – 30 minutes
Install The Replacement Window Unit15 – 30 minutes
Attach Drip Cap15 – 30 minutes
Final Touch10 – 15 minutes

Step 1: Cut Your Flashing Material

Required Tools

  • WRB flashing material.
  • Blade.
  • Sticky tape.


  • The WRB (Weather Resistive Barrier) material should enclose the window’s rough opening. You will need to remove the barrier before you can begin the project.
  • Especially at the window opening, trim the material vertically.
  • Make horizontal cuts at the top and bottom, then drag the flaps out of the opening.
  • After that, secure the flaps in place with a little piece of window flashing tape.
  • Cut at a 45-degree angle from the top edge of the rough opening while maintaining control of the blade.
  • And then, fold or tape the flap at the top of the gap.

Step 2: Ensure The Sill Pan Flashing

Required Tools

  • WRB flashing material.
  • Measuring tape.
  • Sticky tape.


  • Both the sill pan flashing with a sticky surface and the version that stops water from entering your property are options.
  • If you prefer peel-and-stick waterproofing, make sure the flashing extends at least 6 inches past the window jamb and covers the whole sill.
  • Wrap the side WRB panels around the inner portion of the rough opening and hold it down when the sill pan flashing is finished.

Step 3: Seal The Window Unit

Required Tools

  • Sealant.
  • Measuring tape.


  • After the barrier is in place and the waterproofing is fixed, add a little sealant to prepare for the window unit.
  • Avoid putting this sealing on the window opening’s lower portion or sill.
  • Leave the bottom of the window unit open to avoid standing water.
  • Add additional sealant to the top and edge of the gap.
  • Start on both sides, 3/4 of 1 inch from the edge.
  • Stop adding the sealant when you have gone three-quarters of the way through.
  • Be aware that if you seal up all of the gaps in the window, standing water can cause mold and wood damage.

Step 4: Install The Replacement Window Unit

Required Tools


  • The replacement window unit may now be brought in and installed.
  • Use the product’s instruction manual or follow the instructions of a reliable window flashing tutorial video.
  • Before adding a window flashing, check that the window is in the proper place using a square or a plumb.
  • Now, use fiberglass insulation or spray foam to insulate the window on all sides.
  • Attach some adhesive flashing to the replacement window’s vertical sides. This flashing should extend beyond the sill and be 4 to 5 inches above the opening.

Step 5: Attach Drip Cap


  • The majority of replacement windows have drip caps to prevent water damage to the head jamb. If your window unit has one, set it up according to the manufacturer’s instructions.

Step 6: Final Touch

Required Tools

  • WRB flashing material.
  • Measuring tape.
  • Blade.
  • Sticky tape.


  • Installing the flashing for the jamb head is the last step in flashing replacement windows.
  • The flashing should be positioned horizontally and toward the top of the window.
  • The flashing needs to extend at least 6 inches beyond the window jamb.
  • The upper flap of the flashing should then be folded, rounded up, and taped.

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When Do You Need To Fix Your Window Flashing?

You should check your window flashing if you notice water leaking into your house or evidence of water damage, mold, or mildew.

Whether or not water will enter your home is determined by the efficiency of the sealing system.

To guarantee that your window unit is waterproof without replacing the entire window, replacing damaged or missing flashing is a recommended first step.

If your window is broken in any manner, the window flashing might also be harmed. The window flashing will also need to be replaced when you are replacing your windows.

5 Things To Remember While Flashing Replacement Windows

  • Drip caps, flashing tape, and molded vinyl are the three primary types of window flashing, and each one is intended for a different window area.
  • Although aluminum is a widely accessible and adaptable metal for window flashing, not all homes and locations are best suited for it. Aluminum can pit and oxidize in coastal places due to the presence of salty air, and it can corrode due to the harsh conditions of urban air pollution.
  • Check your local building codes before performing window flashing repairs or replacements. To effectively install flashing, many may demand that you adhere to the manufacturer’s directions for the window or flashing.
  • Even though flashing a window is a simple procedure, leaks might happen if you don’t install the flashing tape in the right position or follow the manufacturer’s instructions.
  • If you notice a thin strip of sheet metal coming loose from above the window, It’s possible that the drip cap was improperly installed or that the wood sheathing anchoring the nails in place has decayed, causing the drip cap to fall out.

Final Verdict

Water entering your home through a window can damage the building’s structure in a number of ways. However, you can avoid such incidents if your window has strong flashing.

If the window is weak in this area, you can install window flashing yourself.

A window that is flashed with vinyl siding or an aluminum sliding window provides better protection against water damage. To take advantage of this benefit, you must correctly install the flashing.

That’s it! I hope my article on flashing replacement windows will simplify things. If your unit doesn’t come with a drip cap, make sure to purchase one. Fortunately, you can get this at any window hardware shop.


How much does it cost to reflash a window?

The price ranges from $300 to $575 or more because replacing broken or damaged window flashing requires taking out the entire window.

The typical cost for this procedure is around $430, but your cost may be higher if there is related water damage.