How to Change a Rough Window Opening Size

New windows are a large investment and should always be installed carefully. Once you have removed the old window, the next step is inspecting the rough opening and gaining a proper measurement for the new window. Rough openings must be free of rotted wood and have good structural integrity. A DIY home builder can make a rough opening smaller if necessary, but it is not advisable for a nonprofessional to make the opening larger, as doing so could compromise the rough opening's structural integrity resulting in damage to the home and newly installed window. Building permits are required for any major modifications to your home's window size.

Things You'll Need

• Tape measure
• 2-by-8-inch boards
• Saw
• 3-inch wood screws
• Drill with screwdriver and countersink bits
• Caulking

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Instructions

1. • 1

     Measure the current window size and determine how much smaller you want to form the rough opening. In most cases, homeowners will have prebought a stock window, so this is the size you'll go with.

   • 2

     Inspect the existing rough opening wood for damage. If the wood has dry rot, then you must remove it before continuing.

   • 3

     Cut the 2-by-8 boards to size to fit the rough opening. You'll be stacking the new boards against the existing boards to make the opening smaller.

   • 4

     Screw the boards into position by placing wood screws every 6 inches along the entire board. Countersink all screw holes to be level with the wood.

   • 5

     Seal around each board's openings and the screw holes with caulking.