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What is a Windows Rough Opening?

10/7/2014 8:42:00 AM

If you’re planning a DIY window installation project, you’ve probably read that you need to know the window’s rough opening, but what exactly does this mean? 

A rough opening refers to the framed opening of a window. A window frame, however, has a header across the top, a sill plate across the bottom, and vertical trimmers on either side. Because these elements take up space, a window that measures, for example, 3 feet wide and 4 feet tall is listed as 3/0 – 4/0, but the actual window measurements will be slightly less than this to accommodate the installation system. The difference between rough opening and actual window size will vary by manufacturer.

How to Measure for Windows for Your Rough Opening

When measuring for windows that will fit in your rough opening, follow these simple steps:

  • Measure the width across the window top of your opening between the inside faces of the framing on each side. 
  • Measure the width across the bottom of your window opening between the inside faces of the framing on each side. 
  • Measure the height of the opening between the bottom of the header and the top of the sill on the left, right, and center of the opening. 
  • Measure the thickness of the flashing needed. 
Deduct ½ inch from the measured width and 5/8 inch from the measured height to allow room for paper flashing on each side of the rough opening. 

Once you have the openings based on these measurements, you are ready to order the window.

Professional Window Installation

Professional window measurement and installation are the best way to ensure that your windows are installed properly. Additionally, it removes the burden of risk from you to the window installer. If you measure your windows incorrectly and order the wrong size, you are ultimately responsible for the added time and expense of making the windows fit.

With a professional window installation contractor, you are more likely to have snugly fitting windows. Should the contractor measure wrong, they will ultimately be responsible for making the windows fit into your home or ordering new windows that meet your home’s specifications.


Find a Window Contractor in Your Area

If you’d prefer to have your window replacement project completed by a professional, check out our dealer locator. Weather Shield dealers are highly trained, certified, and experienced in window replacement projects. We provide them with ongoing education and training opportunities to ensure that they are well equipped to provide the highest quality service available.

To get started, visit our dealer locator today!

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