Do You Have to Shim New Construction Windows?

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We previously discussed the importance of installing new construction windows yourself and whether they come with sills and screens,and mentioned that you may have to shim your windows. Shims are an important part of window installation since they help installers make the necessary adjustments as and when needed.

But do you really need to shim every new window? Can you install new construction windows without shims as well? And what are shims? In this article, we’ll shed light on some of the more important elements regarding window shims to help you install windows properly. But first; some clarification.

Not every new construction window requires shimming. The purpose of shims is to make adjustments to home elements, including new construction windows and doors, sothat they are level and don’t wear out due to improper installation. Now, let’s get into the details.

What Are Shims?

Shims are basically tapered wedges made out of wood (or more recently, out of PVC) that can be inserted around new construction windows or door frames to make necessary adjustments. The goal with these shims is to make sure the windows and doors are level when they open or close, thus not straining the joints.

DO you have to shim new construction windows?

They are also used to ensure that they seal the room when closed. If there are any seams or gaps when the window or door is closed, it could let cold (or hot) air in, not to mention give a place to insects to slither inside.

As mentioned above, shims are made out of wood or PVC. Wood shims are preferred for indoor use, while plastic shims are used outside more often. Wooden shims are made out of cedar or pine woods to ensure cost-effectiveness and adjustability. When installing a shim, remember that wooden shims are more prone to rot, or can expand because of the weather.

This is why they’re more widely used indoors compared to plastic shims, which are rot and weather resistant.

When you buy a new construction window, don’t expect a bag of these shims along with the purchase. You’re going to have to purchase them separately. Experienced DIY-ers often make their own wooden shims. We’ll explain how you can do that as well in a later section.

These wedges seem like scrap, but they are an important tool for DIY-ers, especially if you’re looking for a professional or near-professional finish.

Remember, there is nothing wrong with using a shim to make adjustments. Even professionals do that.

What Is Window Shimming?

Even the most meticulous among us who make sure everything is accurate right down to a millimeter are bound to find open spaces and gaps when we install a new door or a new construction window. Of course, the more carefully you install it, the smaller this gap will be, but you’ll find some, nonetheless.

This is because it is highly unlikely that the structure you build (or is already built) around the window will be a perfect square. Instead of having to tear the whole thing down and try again (and therefore cutting or buying a new frame),you can use shims for your window.

Hammering the wedge we mentioned above (shims) around the frame is known as window shimming. You wedge shims between the frames and studs slowly, checking again and again to first ensure that the window is level and then to ensure that it is plumb.

Do New Construction Windows Need Shimming?

The answer to this question depends on where you are and whether you’re replacing it with your old window or are just moving into a new home.

If you’re upgrading your window, you’re going to have to shim your window for it to be level. In fact, manufacturers themselves recommend that you shim your new construction windows in at least two to four places. This is particularly the case if the sill is rough or one that didn’t come with the purchase.

When you move in to a new house, all windows will already be shimmed. If not, check whether your house is still in the builder’s guarantee or if you have a home warranty. If you don’t have either, you will have to shim it yourself.

In the US, builders aren’t required to shim a window; just seal it. They can either do so with a shim or some other way. You will have to ask specifically for shimming if you are moving into a new home.

UK builders, however, are required not just to seal windows, but to do so by shimming before homeowners move in. This is because of the relatively bad weather UK faces. If there is any reveal in your windows despite being shimmed, it is recommended that you call the builder and have them fix it, instead of doing it yourself else you risk voiding the warranty.

How to Shim a Window

To shim a window, you will need the following:

  1. A spirit level (also known as bubble level)
  2. A few shims or wedges. Choose wooden shims for indoor installation since these are more cost-effective, or plastic shims for outdoor applications
  3. A chisel (or crowbar, if you’re really adventurous). If you have an air wedge, it can be a particularly helpful tool to help you put your shims in place
  4. A mallet
  5. A new construction window that you just installed

Before you start shimming your new window, place the spirit level on the base of your window and see which side is elevated. Check under it with a flashlight (or your phone’s light – this is the 21st century, after all) for any debris under the window. Do the same across all four sides. If you find anything, try to remove it WITHOUT TEARING THE WHOLE WINDOW DOWN.

When you’re ready to start shimming:

  • Place your spirit level on the window’s base
  • Insert the chisel or air wedge under the window and insert two shims underneath the window, two on one side, and two on the other. Place each shim 4-6 inches from the corner.
  • Shim all contact points. Contact points include:
    • Center
    • Check rails
    • Meeting stiles
    • Lock points
    • Hinge points
  • Once all the shims are in place, look at your level. If it’s not level, you then have two options.
    • You can either start pushing shims further in with your mallet. Do it softly. You’ll see that the deeper you drive shims, the higher your window gets. Continue driving the shim until your window is level. If needed, you can push another shim in as well.
    • You can also pull shims out from the raised side of your window. Continue pulling it slowly until the window is level. Cut the excess off.

And that’s it. You now have a shimmed window!

To enhance privacy you may include blinds to the construction windows.

How Much Does It Cost?

Wooden window shims may be found lying around in your woodworking den, or you can use a scrap piece of pine wood to make your own. If you don’t have spare wood, you can buy shims from any hardware shop. Wooden shims cost $5 a pack and there are 12 shims in each packet. These shims are roughly 12 inches long, so you can always turn the pack of 12 into a pack of 24!

Plastic shims cost the same, with each packet including 24 shims.

The labor costs involved in a shimming job are roughly $60 to $80 per window, although if multiple windows are being done then this per-window price will likely drop.

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About Charlie D Paige

Charlie is a massive DIY fan, with dozens of DIY projects under his belt - ranging from tiling to electrics, and concrete pads to walls. Charlie loves tinkering, seeing how things works, the outdoors and playing with power tools... so is it any wonder that he's completed so many DIY jobs over the years?

Charlie loves spreading his hard-won DIY experience with the world via this blog.