Rough Opening Window Replacement

When considering window replacement options for an older home – there are is not shortage of approaches: tilt-pack replacement, complete window replacement, storm windows, or historical restoration work. Far too many things to cover in one article.
This post is about complete window replacement: removing the old window, frame and all, including the interior and exterior trim, down to the rough opening. This often includes altering the size of the rough opening to maximize the glass for a window opening and welcome in the most light. Depending on your choice of window style, the opening could get bigger, stay the same, or sometimes even shrink.
What’s the Right Way to Do It?
Installation Masters’ – a program helping to standardize window replacement methods – produces best practice methods to accommodate for energy efficiency and long-term durability. I want to save you the trouble of sifting through all 89 ways to install a window and focus on a few common considerations.
Once-in-a-Generation Opportunity (aka – Let’s Get This Right)

If the window retro-fit is part of a siding replacement, it is wise to add a layer of exterior insulation to cut down on air leaks and to provide continuous thermal coverage to complete the exterior envelope of your home. Insulation is a relatively cheap upgrade to an expensive siding project that happens only once every 50 years. And it is one chance to make a big difference in a home’s energy performance.
An additional layer of foam can complicate the window install, however, because it adds thickness to the wall and covers the nailing base that most “new construction” contractors would fasten a standard size window. The good part is that newer replacement window options – especially those from Andersen Windows – come with pre-drilled fastening options directly into the stud through the jamb.
Modifying the Opening
If you’re not replacing the siding and the rough opening size is changing, you’ll likely need to trim the siding back. By doing so,  be very careful not to damage the exterior barrier existing beneath the siding. A thin house wrap is an integral part that will become the continuous watershed to tie-in to on the exterior of the house when installing a window.

Nothing But Pressure
A couple of ways to protect the underlying weather barrier come to mind. Softly peel it back and tack it to the siding. Once the window frame is removed, complete the weather protective opening using a pliable sealant strip like Grace ice and water shield.
For working behind brick, there is always the struggle with mortar squeeze. Mortar droppings could pose a challenge to navigation if the pieces are too large. Stucco can also be very challenging. Typically stucco has two layers of water barrier: one as a bond break and the other as a drainage plane.

Detailing the R.O.
The rough opening will be prepped down with a weather resistant membrane. Membranes, gravity, and drainage beat water (nearly) every time. Install a backdam could also work, but make sure that slope is incorporated in the sill installation. Gravity is the friend you don’t want to leave behind.

Sloping the sill means that the taller opening will be figured in to the ordering of the window to accommodate the slope of the R.O. With the window is hand, we will install a pan flashing – likely a peel-and-stick flashing tape. The ice and water shield is installed around the perimeter of the entire opening to create a water resistant barrier.

A Clean Finish

We’ve covered the guts of window replacement because like almost every home improvement project, the work is in the preparation. Once the window opening is prepared, it is simply a matter of installing a plumb and level window that is air-sealed and properly fastened. We’ll finish the rough opening with new window trim and jamb extensions on the interior and custom fabricated (on-site) aluminum cladding on the exterior. The great part about working with Andersen is that windows we install come ready to accept the materials we use in finishing the opening.

Worry-Free Remodeling

If you’re like most people, you like to sleep. Same with us at Wisconsin Home Remodeling. We do things right the first time so we don’t have to chase our tails and lose sleep over “could’ve dones”. Please consider us – and all of our expertise – including two NARI certified remodelers on staff! We have the knowledge and experience to complete your project the right way!


About the Author

Ben Lindberg is a NARI Certified Remodeler in Madison, WI. He is an avid blogger at Wisconsin Home Remodeling and focuses his time on Window Replacement and Entry Door Replacement with Wisconsin Home Remodeling. Ben and his team of remodeling contractor professionals are in a constant state of pursuing remodeling knowledge. You can find out more about his firm at


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