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How to Replace a Window

Nov 06, 2019

When it comes time to replace a window, popping in the replacement yourself is a tempting thought. How hard can it be, right? Moreover, some will tell you replacing a broken or cracked pane of glass is considered easier than replacing the entire unit. That may be true of an older single-pane window, but single pane glass is a rarity today. Many homeowners choose to upgrade their old windows because new windows increase the energy efficiency of your home. The added benefits of hurricane resistance, UV protection, and noise reduction make the inconvenience of taking a cracked pain in for repair or having someone come to the house much less of an inconvenience.

Before you jump in and tackle replacing the window yourself, we’ll go over the process. Once you get a clear view of what the job entails, you can see how things look from there.

Some things to think about

First of all, if you’ll be using a ladder, be careful! Replacing windows can be a dangerous job and adding a ladder to the mix makes it more so. The Bureau of Labor Statistics reported that 50% of all ladder-related accidents involved carrying something up or down the ladder.

Also, some DIY “how-to’s” suggest using a standard stock replacement window for convenience’s sake even if you need to make some frame adjustments. While it’s true that a custom-built window is more expensive and there’s going to be a wait, installing a window built specifically to fill the opening is your best defense against moisture.

Moisture moseys along

The think about moisture is that once it gains access to your home’s interior, it travels. Granted, it’s a slow process and it can take years for major damage to occur, but it can happen.

The problem is it can be hard to detect before the real damage is done.

Moisture issues lead to mold, mildew, and wood rot. Mold is a known health hazard. Wood rot is caused by fungi that live on the wood causing it to rot to pieces. Left unchecked, mold and wood rot spread throughout the wood framing of your home. They can get started when moisture gains access to your home’s interior, even through cracks in the caulk around your windows.

When you replace your window with a standard replacement unit, you run the risk of an improper measurement or an ill fit allowing rain or snow to gain entry to your home.

They’re not just terms

Theoretically, the new window should fit perfectly into the old opening, however, you need to be certain that it goes in level, plumb, and square. Failing to make sure of that is going to cause problems.


When something is “level,” it creates a perfectly straight horizontal line. If your window isn’t level, it allows airflow. You risk losing your EnergyStar rating because the sash won’t seat up with the weather-strip seals correctly. It’s also going to open you up to possible moisture issues down the road.


Assuring your window is “plumb” means that it forms a perfect vertical line. If a window isn’t plumb, the window will fail to operate properly. By the way, all may seem well at first, but eventually, you’re going to have mechanical issues.


Next, you want to assure that your window is sitting “square.” That means that it makes a 90-degree corner at all four points. To be perfectly square, the window must be set level and plumb at the same time.


Lastly, you’ll want to ensure that your window is “true.” The term refers to your window being level, plumb, and square at the same time on all four sides of the new unit.

The process can be tricky—even frustrating—but it’s essential that you make sure to complete it correctly.


We can explain the replacement process in five steps, so it’s going to be a quick read. However, we’ll let you know that it takes roughly four to six hours to install a full-frame replacement window—longer, of course, if it’s a large window or if you run into any issues getting the old window out.

Out with the old

Use a crowbar to remove the entire window casing, including the trim and sill plate.

Carefully, lift the old window out of the opening.

Install the new unit

First, apply window wrap to the exterior framing of the window. Start at the bottom and work your way up thoroughly insulating the window.

Install your window into the opening from the outside of your home. Push it into place and then hold the window up until it’s flush to the frame. Anchor the unit in place with screws firmly attached to wood.

You’re now ready to make sure the window is level, plumb, square, and true. Use wood shims to help you hold the window in position as you measure and adjust.

When you have the unit where it needs to be, screw or nail the window into place from the exterior of your home.

Wrap it up

After securing your window in place, add another layer of window wrap around the window fins. Overlap the wrap to completely cover the surface and guard against letting the wrap crinkle or fold over on itself. The wrap is a key component to keeping moisture out. Keeping it straight and flush is the key to success.


Expanding-foam sealant is commonly used to fill the gap between the window casing and the window. Cover the edges of your new window with painter’s tape to protect it. The process can get messy so if some gets on the window, you’ll need to scrape it off after it dries. Be careful not to use too much foam or the window will bow and not open or close.

Replace your trim and casing

After the foam dries, cut away the excess before trying to install your new window casing. Lastly, replace your exterior trim if necessary and then step back and enjoy the satisfaction of a job done.

If you decide to hire a professional to replace the window unit rather than handling the job yourself, no harm, no foul. Having your window professionally installed is the best way to ensure moisture—and all that comes with it—is kept at bay.

Furthermore, a professional should guarantee their workmanship. If you encounter problems down the road attributed to the installation, you’re covered.


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By submitting, you authorize Reece Windows to reach out to you with questions about your project, via phone, email, or text. Message/data rates apply. Consent is not a condition of purchase. You may unsubscribe at any time. Terms & Conditions | Privacy Policy