Installing a New Window on Your Own? Here's How to Do It

There are plenty of DIY tasks you can do to improve your home's looks and functionality and window installations is one of them. If you want to try your hand at installing your own windows, read on! This step-by-step guide assumes that you've already removed your existing window or that you're working on a new home that hasn't had its windows installed yet. 

Check the Rough Opening First

The last thing you want is to attempt to install your window, only to discover that it doesn't fit because the measurements of the rough opening are off. For this reason, you'll want to measure the opening prior to getting started on the installation.

To accomplish this, use your measuring tape to check the width at the top, middle and bottom of the opening. Also, check the height at both sides and at the middle of the opening. If the measurements are off by more than an inch, you'll have to cut filler strips and nail those to the areas that aren't level or plumb.

Keep in mind that the outside dimensions of the window itself should be slightly narrower and shorter than the width and height dimensions for the rough opening.

Waterproof the Opening

Next, you'll have to seal the window opening against water and moisture intrusion. You should use self-adhering waterproof membrane to line the window opening. The material should be at least 6 inches wide and18 to 24 inches longer than the width of the rough opening.

You'll need to layer several strips of waterproof membrane underneath and alongside the rough opening, with each strip layered so that the top layer always overlaps the bottom-most layer. This should be done before applying the bottom sill flashing to the rough opening.

Gibson also warns that the seams for waterproofing material should never face up. If they do, water can get in between the seams, defeating the whole purpose for the material being in place.

Mount the Window

After the waterproofing is finished, you can finally move the window into place. You'll always want to mount the window from the outside of your home. You can also have an assistant remain indoors and make sure the window is being mounted level.

Start mounting the window by resting it on the bottom of the opening, then tilt the window towards the interior of the home until it fits into place. Drive a nail partially through the trim at one of the upper corners of the window to hold it in position.

Use a bubble level to make sure that the window sits level and plumb within the opening. Use shims, if necessary, to correct the window level and plumb. As you adjust the window to make it level and plumb, you should also tack nails into the remaining corners of the window trim to preserve the adjustments.

Once the window is level and plumb, you can fully drive the nails into the corner of the window and secure the window to the opening with more nails. Keep in mind that the window manufacturer may have specific instructions on how to secure the window to the opening, so there may be other specific steps involved.

After installing the window, use caulk to seal the space between the window and siding or brick on your home. This space will be covered with decorative molding or trim.

If All Else Fails, Don't Hesitate to Turn to a Pro

Installing a window can be a rather lengthy and intensive process, so there's no shame in having a professional step in if the going gets rough. Remember that this may add to your current window installation costs, since the professional will not only finish up the job, but also correct any mistakes you may have made along the way. For more information, consult resources like