A carpenter is installing a new exterior window into a rough opening. The rough opening measures 920 mm x 1220 mm. The window unit has nominal dimensions of 900 mm x 1200 mm. What shimming strategy should be employed to properly plumb, level, and square the window, adhering to best practices?

Question: A carpenter is installing a new exterior window into a rough opening. The rough opening measures 920 mm x 1220 mm. The window unit has nominal dimensions of 900 mm x 1200 mm. What shimming strategy should be employed to properly plumb, level, and square the window, adhering to best practices?

Answer options:

• Shim only to lift the window off the sill and to plumb the sides. ✅ Shim at the bottom corners, middle of the sill, and along the jambs at fastener locations.
• Shim all four sides continuously to ensure a tight fit.
• Use shims only after the window is securely fastened with screws.

Correct answer: Shim at the bottom corners, middle of the sill, and along the jambs at fastener locations.

Explanation: Proper window installation requires shimming at specific points to ensure it is plumb, level, and square without distorting the frame. Shimming at the bottom corners, middle of the sill, and at the fastener locations along the jambs provides critical support and allows for precise adjustments. Continuous shimming or shimming after fastening are incorrect practices.