Rough Openings for Windows Explained

Rough Openings for Windows Explained

If you’re interested in installing a window, or at least trying your hand at getting one started, the process begins with a rough opening. You need to know about the basics of rough openings for windows and how to properly measure and build one. You may also need to understand how to adjust an existing rough opening for efficient and accurate installation.

What Is a Rough Opening for a Window?

A rough opening refers to a framed opening for your planned window. It has a header across the top, a sill plate across the bottom, and vertical trimmers on either side.

Naturally, these elements take up space, so the final measurements of the installed window will be slightly smaller than the measurements of the rough frame. The variance will depend ultimately on the manufacturer of the window you install.

Rough Opening for a Window: The Basic Steps

There are several fundamental steps needed to either create a new rough opening or to adjust an existing one.

Measure the Opening

Mark on the wall where the planned opening will go, or if you’re assessing or adjusting an opening that’s already there, measure what’s in place. The measurements you’ll need are:

  • Width of the top and bottom of the opening between the inside faces of the frame
  • Height of the opening from the bottom of the header to the top of the sill at the left, center, and right

You’ll also need to account for paper flashing on each side of the opening. This generally means deducting half an inch from the measured width and 5/8 in. from the measured height.

Cut and Frame the Opening

If you’re starting with a blank wall, you’ll need to cut and frame your new opening. This itself is really a multi-step process too involved to detail here, but you can seek out guides online to help you through the process if you want to try it yourself.

Check for Plumb and Level

It’s important to double-check that all four sides of your rough opening are plumb and level and whether the wall it’s being installed in is plumb, before ordering windows.

In an existing rough opening, it’s perfectly possible that studs might be out of alignment or that the sill and header are out of level. Walls of sufficient age may lean slightly in or out. It’s possible to compensate for these problems but only if you know about them first.

Adjusting a Rough Opening

There are several ways to adjust a rough opening if needed:

  • Sloping the sill. A sill should slope slightly outward for drainage purposes. Shaving down the outer edge of a sill or installing a sill wedge can provide the needed slope.
  • Expanding the opening. If the existing opening isn’t large enough for your planned window, shaving from the sill can gain you the space you need. It’s always best to shave from the bottom, as shaving from the header weakens the frame.
  • Making the opening smaller. An opening too large won’t be able to properly seat the final installation. You can add lumber or boards to the inside of the frame to make up the difference.

Talk to a Professional

Overall, hiring a professional is the best way to ensure your windows are measured, ordered, and installed properly. Contact the experts at Thompson Creek Windows today to learn more.