How big should a rough opening for a window be?

For standard wood framed construction the rough openings for doors and windows is typically the actual unit size plus 2-1/2 inches in height and width.

How much does it cost to add a window to an existing wall?

Insulation installation costs $450 to $3,000. Trim repair costs range from $300 to $1,000. Siding repair pricing runs $300 to $1,100. Drywall installation costs $1.50 per square foot.