How to Shim a Window Properly: Do's and Dont's

If you're in the process of or have installed windows in the past, you may or may not know about the importance of shims in window installation. When you shim window edges, you ensure that it's properly leveled and positioned in the framing, providing easy operation for many years to come. But even though you may understand these parts of the process, you may still have questions, with "how do I shim windows properly?".

In this article, we'll cover the reasons for window shim installation, what type of materials provide the best, longest-lasting results, and what window shimming techniques you'll need to use to get the best performance. This will help you realize why shims are the perfect solution for window installation when you want a one-and-done solution. Let's get started with why it's important to use a window shim or more when you're installing your windows.

Let's start with the reasons why you need to shim window installations. Rough carpentry is just that - rough. Between the level being slightly off, a stud being slightly short, or another being a touch tall, your window framing may not be square or level. If you install your window directly into the framing, you may have issues with poor support for the frame on one area causing warping. Similarly, the window may end up out of level, out of plumb, or out of square, making it harder to open or close, depending on the type of window.
When you use a shim to help raise the lower part of your window and bring it to level, you're making it easier to open the window as designed while providing additional structural support to the window frame. This process helps reduce the risk of warping, which can make it impossible to open the window. Never force a window into place, but instead take a small amount off of the lower plate or side stud around the window to ensure it will fit in properly.

But what about the rest of the window? Once you've leveled the bottom of the window, you can center it using shims on the sides of the window, ensuring that it will remain centered so that the trim that will surround it will go on easily. This process helps prevent window breakage from falling out of position, keeping it safely locked into your home's framing until you can secure it in place properly.

For many years, window and door companies have used wood shims to install their products, and many companies continue to use these products today. However, as building technology has advanced, the call for plastic window shims has become a driving force in the industry. Here are a few of the many advantages of using plastic window shims instead of wood shims:

• Fire resistance. Wood is burnable, and though it's only a small proportion of the greater window structure, wood shims can help spread a fire in your home.
• Insect resistance. Wood is also subject to termites, mason bees, and similar insect pests. Plastic window shims provide a strong alternative.
• Rot resistance. If the area around your window casing gets wet, the wood can rot, swell, or shrink when dry, while plastic stays the same dimensions.
• Plastic is adaptable to more modern styles. When it's important to get the windows square in the case and square to each other, plastic works better.
• Strong. Available in a range of plastic types, plastic shims can better bear the weight of your windows without losing height due to compression.
• Long-Lasting. Plastics last a long time but are recyclable when needed. This ensures that plastic shims will last as long as your windows.

As you can see, there are many reasons why you should consider using plastic shims for your next window shim installation process. 

To start, let's talk a moment about how to use shims. You want to use them in pairs, one in each direction, so that the entire depth of the window is supported by the shims. If there are separate hinged areas, provide support at that location as well. Next, you'll want to place the window in the opening and add shims at the location where the vertical members meet the lower window plate. This provides an even distribution of the weight of the window down to the framing. As you work on these shims, check that the bottom of the window is level, adjusting as needed to get a good fit.  
Next, you'll place shims at the sides of the window, about six inches from the top and six inches from the bottom on each side. This ensures that the window is supported without binding up. Check whether the window is plumb across its depth and adjust your shims on an as-needed basis to properly position the window within the opening so that it will be parallel to the walls when complete. You'll also want to ensure that the window is approximately centered evenly between the framing members.  
Finally, you'll want to measure to check that the window is square. Though you could buy a square and hope that it is actually in square, the easiest way is to use a tape measure to measure from one corner to the diagonally opposite corner. Once you have one measurement, measure the diagonal the same way. If the measurements are equal, the window is square. If the measurement is off, you can gently and slowly shim the upper corner that is short towards the framing, which should lengthen the measurement and bring the window into square. 
Once you've completely squared, leveled, and plumbed your window in place, it's time to secure it in place. Take the time to ensure that it's well secured, then pass screws through the top of the window into the framing, being careful not to move the window itself out of place due to lifting with the screws. Once the window is secured, you can add window and door spray foam, caulking, and other sealants to prevent drafts, and then trim the window. 

Proper shim window installation can make a big difference in how well your new windows perform in your home or business. If you're ready to undertake a change in your windows or are installing windows in a new construction, the right window shimming techniques and plastic window shims can make a huge difference in how long the windows work well for your structure. If you're ready to make the switch to plastic shims, please feel free to reach out today for more details, with any questions, or for more information about our high-quality plastic window shims.