Window Flashing Installation: Step-by-Step Guide [Video]
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How To Install Window Flashing (Video Guide)

Posted by Northface Construction

Window flashing is critical to ensuring your new window will be safe from any leaks. Flashing needs to be done properly to do its job, so we’re going to walk you through the steps to install window flashing the right way.

What Does Window Flashing Do?

In general, flashing seals any joint or angle that is cut into your siding or roof. This means chimneys, vents, windows, skylights, and other additions to your home require flashing to be installed to seal that joint.

Window flashing is a continuous piece of material that lines the inside of the window or other apparatus that ensures a tight seal all the way around. It prevents any intrusion of water and moisture. If that moisture infiltrates your window frame, you will deal with water damage to your walls and window frames.

That damage can spread and cause mold and mildew growth, which makes for a messy repair. Always install window flashing to protect yourself and your home from having to make such repairs.

When to Replace Your Window Flashing.

If you notice signs that your window flashing is failing, you want to get that replaced immediately. Signs include water spots or discoloration around the edges of your window (either on the interior or exterior). It can also be visibly damaged or rusted.

Strong storms can tear away flashing on your roof very easily. Window flashing is on the inside and would be less likely to be damaged in a storm, but if your window sustained damage, it’s a good idea to check your flashing.

And of course, anytime you are replacing a window, you will probably want to replace the flashing as well. The window removal can damage its integrity, and why not start fresh with brand new everything?

How Do I Remove Old Flashing?

To remove old window flashing, you need to have a hammer and a putty knife. Once your window frame is removed, you will start by pulling up the nails holding the flashing in. Then, remove any sealants and caulk with your putty knife. It should come off relatively easily and ensure you have an immaculately smooth surface free of any caulk before installing your new flashing.

How to Install New Window Flashing.

Here is a step-by-step process on how to install a new construction window with flashing.

  1. Frame your window in the desired location of the wall. Support any exposed studs.
  2. Install a weather-resistant barrier (WRB) to the wall around the rough opening. Staple it using a grid pattern to ensure it is secure.
  3. Cut the excess WRB around your window opening in an “I” shape. Fold those back and cut diagonal slits at each corner so that flap can be easily folded down and secured with some tape.
  4. Install flashing on the bottom window sill. Your rubber flashing tape will go over the WRB on the sill and must be long enough (6-7 inches) to be able to fold up the sides of your trim studs after the siding is installed. For extra security, use the same cap staples you used for the WRB to secure it.
  5. When all of your seals are flush and trimmed inside your window opening, it’s time to install the window. Follow the manufacturer’s instructions for install and gently set the window in the opening, ensuring its level and flush against the sides and secure it with the appropriate fasteners, caulk, and other materials.
  6. Install the side and top flashing. Make sure the flashing tape you get is a little wider than your window trim. This is so any fasteners that attach your trim will also go through your flashing trim and secure it. Install the side flashing first, followed by the top.
  7. Install your window trim.
  8. Install metal z-flashing over the top trim, secured with the appropriate type of fastener for that z-flashing.
  9. Fold down that extra weather-resistant barrier you had taped up in step-3. These will go over the corner of that newly installed z-flashing.
  10. Lastly, install the siding and trim on the outside!
  11. When all is said and done, do any trim painting on the interior and exterior walls to touch up your newly installed window.

These are basic instructions for installing your new construction window plus flashing. We have more information you can find here on how to replace a window. We are happy to help you with any window replacements, or siding installs around your new windows. Give us a call at 763-710-2933 to get started on your FREE quote!

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