Waterproofing is a critical step in the window installation process. The key to window flashing is to start from the bottom of the window and work your way to the top of the window, making sure the whole system is shingle flashed — so that when water hits the wall, it will drain downhill and have a seamless escape from the wall assembly. Follow this step-by-step guide to learn how to flash windows with traditional housewrap.
Always check your window manufacturer's warranty information and weather-resistant barrier (WRB) details to make sure you are following installation practices that uphold the product warranties. In this guide, our window pros follow standard practices for flashing windows, using a Marvin Elevate Double-Hung Window with Dupont Weathermate Plus Housewrap as an example.
Step #1: Seal the Corners
“L” shape flashing tape to be applied to the window corners
To bridge the gap between the nailing fins and properly seal the corners, cut a 2” by 4” strip of flashing material and place it on all four corners — spanning each corner to keep water from getting in. Another option is to cut an “L” shape (pictured above) out of the flashing tape and place it on each corner.
Marvin previously directed installers to use their foam corner gaskets. However, as of 2022 the installation guidelines from Marvin simplify the process by allowing the use of flashing tape to seal the corners. Learn more in our quick video on Marvin’s Corner Gasket Update.
Step #2: Add a Rain Skirt
Apply a 12” rain skirt underneath the window for additional protection against rain
A “rain skirt” is a piece of housewrap (12”) with seaming tape that applies to the bottom of the nail fin underneath the window. Marvin doesn’t require installers to apply a rain skirt, but they do recommend it to help prevent any wind-driven rain from getting into the building. This step is particularly helpful for waterproofing buildings in extreme weather climates.
When applying the rain skirt, it's important to take the seam tape and run it at least a quarter inch up onto the actual window frame itself to ensure you get the appropriate seal.
In the demonstration pictured above, the window sill pan was flashed with Zip System stretch tape. Learn about sill pan flashing in our step-by-step guide on How to Prepare a Window Rough Opening.
Step #3: Flash the Window Jamb
Apply window jamb flashing tape past the top flange and onto the frame
Next, flash the window legs, applying flashing tape a minimum of 2” past the top nailing flange and a minimum of ¼” inch up onto the window frame. One reason our team likes working with 3M All-Weather Flashing Tape is because the split release makes it easy to get that quarter inch onto the window flange.
The window flange makes a great reference point for where to place the tape.
Step #4: Flash the Header
Flash the header, making sure that the head flash piece is above the leg flashing
Apply flashing tape to the header. The head flash piece should extend above and past the leg tape edges and wrap ¼” onto the window.
Untuck the housewrap over the head flashing tape for proper shingle flashing
Finally, untuck the housewrap down over the head flashing tape and tape the corners with seam tape. This will ensure proper shingle flashing so everything will flow downhill and not get caught on leading or uphill laps.
Step-By-Step Video Tutorials for Installing Marvin Windows
Watch our video tutorials on how to install a Marvin Elevate Double-Hung Window according to the manufacturer’s instructions — from prepping the window opening to flashing the exterior window to prevent water penetration. Our team covers best practices for installing new windows with a variety of weather-resistant barriers:
- Huber Engineered Woods ZIP System Sheathing [VIDEO]
- Dupont Weathermate Plus Housewrap [VIDEO]
- Henry Blueskin VP100 [VIDEO]
If you have any questions about working with these housewrap systems or how to install new construction or replacement windows from Marvin, let us know! The Ring’s End window team will be happy to help.
Marvin-Approved Sealants and Flashing Tape
To maintain the window’s warranty, it’s crucial to only use manufacturer-approved products during installation. Here are the flashing and sealant guidelines provided by Marvin, along with our team’s product recommendations.
Sealants
Marvin requires the caulk to be compliant with ASTM C920, Grade NS, Class 25. Our window team recommends these products:
Flashing Tape
Marvin requires non-rubberized asphalt flashing (minimum 4”) on their PVC flanged windows. We recommend at least using butyl flashing, or better yet — acrylic adhesive flashing such as 3M All-Weather Flashing Tape. An acrylic adhesive is going to allow you to get good adhesion in a lot of different temperatures and a lot of different environments.
To make sure all warranties are upheld, the flashing tape should also complement the housewrap system you are using.
Ring’s End is a Trusted Resource for Window Installers
As an experienced window supplier and installer in the Northeast, we know how important it is to create weathertight window systems that ensure homeowners enjoy optimal window performance and energy efficiency year-round.
The window pros here at Ring’s End have been working with the Marvin brand for over 50 years, and we’re proud to be an authorized Marvin dealer due to the quality performance and design versatility of Marvin products. If you want to experience Marvin windows for yourself or talk with our window specialists in person, visit one of our eight showrooms across the Northeast. We offer a variety of complimentary services for window contractors and would love to be a resource for your business.