What Is the Size of a Pella Window Rough Opening?

One of the first steps to installing your new Pella windows is to make sure the rough opening is the correct size.

Rough Opening

When framing a building, it is necessary to take into account the locations of the windows that will be installed. A rough opening in a wall is slightly larger all the way around than the window that will be installed. This allows enough room to install the flashing materials to waterproof the opening, as well as makes installation of the window into the opening easier. The normal on-center spacing of the wall studs is not disturbed when a rough opening is framed, but a header may need to be built into the top of the opening on load-bearing walls to make the wall above the opening stronger.

Pella Rough Opening

According to Pella, the size of the rough opening to accommodate one of its windows should be 3/4 inch bigger than the window in both height and width. Since some framing lumber may have a tendency to warp or bow, the height and width of the rough opening should be checked in several places along the opening to ensure it is the required 3/4 inch larger in both directions.

Plumb and Level

If the window is not installed correctly, its operation may suffer. It may be difficult or almost impossible to operate the sash of a window that is off-square. This is why it is important to check the rough opening for plumb and levelness. Place a 2- or 3-foot level along the top, sides and bottom of the window opening. Ensure the level bubble is between the two marks. If the plumb of the vertical sides of the opening is off slightly, this may not affect the window installation. However, the levelness of the bottom horizontal surface — or sill — of the opening cannot be compromised. If the sill is off, it must be corrected before the window can be installed. This may involve removing the sill and adjusting the height of the short studs below to correct the problem.

Window Installation Tips

Some Pella windows may require the installation of spacers on the sill of the rough opening before the window is installed. This ensures the window is centered in the opening and has equal spacing all around its perimeter in the rough opening. Improper use of spacers may cause the bottom of the window to bow down, so ensure you follow the directions that came with your particular window when installing spacers. The levelness and plumb of the window should also be checked and adjusted with wood shims where appropriate. Use 2-inch galvanized roofing nails to secure the window into the opening, as use of standard nails may cause corrosion.