Thinking About Installing Replacement Windows Yourself? Not a Good Idea…

If you live in the twenty-first century (don’t we all) your house probably came with glass paned windows, but over the course of your tenure in your current residence, you might have to replace one or more of the windows.

can i install replacement windows myself

Whether an errant baseball broke one of the panes, or you’ve become aware that old windows are decreasing the energy efficiency of your home, you may consider installing the replacement window yourself, but hopefully, by the end of this article, you’ll see that’s not such a wise decision.

The Three Types of Replacement Windows

The sash replacement kit puts new movable parts into the window frame, without replacing the frame itself, for example, installing a new sash (that’s the framed glass pane you can slide up and down to open the window).

An insert replacement window is basically a fully assembled window and frame that you just slip into the existing frame, resulting in what seems like a slightly smaller window.

Full-frame replacement windows are essentially assembled units that replace the entire window, including the frame. In that way, they’re similar to inserts, but require you to remove the frame as well.

A Variety of Challenges

Each one of these replacement window types has its own set of challenges when it comes to installation, whether it’s the necessity of making the existing frame perfectly square and sized to fit a new sash, or stripping the window opening down to the insides to install a full-frame.

It can be tempting to do home improvement projects yourself since they can be fun activities with a satisfying result. However, there are certain home improvement projects that need to be turned over to a professional in order to be done well.

As we take a look at the process for installing replacement windows, hopefully, you’ll see that many parts of the process would be best suited by the performance from a professional with expertise, training, and finesse.

Our Example: Insert Replacement Windows

To illustrate the difficult process of installing replacement windows, we’ll take a look at installing an insert replacement window. If your home has decent window frames, or you appreciate their aesthetic contribution to the appearance of your home, this is probably the type of replacement you would go with, since it leaves the original frames intact.

However, it’s important to note that one of the most common reasons for replacing windows has to do with upgrading the energy efficiency of your home, and the window unit as whole (panes and fame) is often the culprit, which means you would have to also remove the frames, a process even more difficult than the one we’re about to describe.

You Don’t Have to Take Our Word for It

By the end of our description of this process, you’ll hopefully see that replacing windows isn’t just about popping a new unit into space, but that it actually involves a lot of peripheral work, which includes insulating and painting.

Moreover, because the window opening is probably not a perfect square, precise measurements and excruciatingly exact fitting and installment must be done. Otherwise, the window won’t be properly installed, resulting in potential structural damage and poor insulation.

As they used to say on a certain Public Television program promoting children’s literacy, “you don’t have to take my word for it.” Read on and see how difficult installing replacement windows can actually be.


Step one isn’t too difficult (although it only gets harder from there). You’d need to measure the width of the existing frame, from jamb to jamb, at the top, bottom, and middle of the window.

installing replacement windows yourself

Then you would need to get the height, obtaining another three set of numbers for the right, left, and middle. For the width and height, you’d need to retain the smallest number when it comes to ordering the new window.

Next, you need to check and see if the frame is square by measuring both diagonals and comparing them. If they’re off by more than a quarter of an inch, you wouldn’t be able to get an insert replacement window even if you wanted one, because the frame is too out of shape—and this scenario is more likely than you think, because houses settle over time, changing the dimensions and shapes of door and window openings ever so slightly, and even relatively new construction succumbs to this natural process fairly quickly.

Lastly, you need to measure the angle of the sill, which requires a specialized tool, because sill angle is another important dimension to consider when purchasing the replacement. After all these measurements, you could find out that your local hardware store doesn’t even carry a replacement window that matches the exact dimensions you need.

Removing the Sash and Jamb

Next, you would need to remove the sash by removing the stops, which can generally be done by unscrewing them or prying them off, but be careful if you’re planning on returning and reusing them because some of them can break easily.

You also need to remove the parting beads—the grooved strips of wood that hold the sash against the frame—and the jamb liners, which would need to be pried off with a flat bar. This may sound easy enough, but removing these elements without damaging the frame is extremely difficult.

Preparing the Frame

Next, you would need to patch holes and cracks with exterior-grade wood putty, sand the frame smooth, and then prime and paint the surface. You would also have to remove the sash weights (the pulley system that operates the sash) by unscrewing the access panel on each jamb.


Pulling out the sash weights and the pocket panel that houses them would necessitate re-insulating the inside of the frame. You would need to take out any old fiberglass insulation and then drill some small 3/8 inch holes near the ends and middle of the sill and the head jamb.

Follow that up with spraying polyurethane foam into the inside of the frame and waiting six hours. If the insulating process isn’t done correctly, the frame will buckle beyond use, requiring even more work to remove and replace it.

Putting in the New Window

Standing inside your house, you would then put the bottom of the insert replacement into the sill and then push it slowly into the opening, and then drill a 2-inch screw on the side of the upper jamb and into the frame to hold it in place.

Slipping some shims under the frame until the window was centered, you would then need to make sure the window was squarely positioned by measuring corner to corner. You’d then install it by putting screws through the pre-drilled holes.

Slipping a shim behind the frame at each screw and screwing through it would make sure the frame doesn’t bow, and once it was installed, you could trim the shims with a knife.

After all that, you’d finish up by determining if there were any gaps less than a quarter of an inch wide and caulk them. Any gaps larger than that would need to be insulated with foam rubber. Gaps on the inside would also need to be insulated with minimally expanding foam. After all of that, you would want to prime and paint the interior (and possibly the exterior).

Replacement Window Installation is Best Left to the Pros

After that description, you’ll see that installing replacement windows, even without removing the frame, requires a lot of peripheral work, and each component of that requires precision and exactitude.

Otherwise, the installation could have long-lasting negative repercussions resulting in poor insulation, structural damage, and poor appearance that degrades the look of your home—if you can even find a window that meets the exact dimensions you require. Therefore, your best bet is to seek out the services of a professional replacement window installer.

Feldco Professional Installation to Put Your Mind at Ease

If you’re thinking of self-installing replacement windows, think again. Feldco has certified installers with a lifetime warranty, putting your mind at ease. Get a free quote today.


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