A carpenter is framing a wall opening for a window that measures 900 mm wide by 1200 mm high. The rough opening dimensions specified are 920 mm wide by 1220 mm high. If using 38 mm thick lumber, what length should the header be cut to account for two jack studs and the rough opening width?

Question: A carpenter is framing a wall opening for a window that measures 900 mm wide by 1200 mm high. The rough opening dimensions specified are 920 mm wide by 1220 mm high. If using 38 mm thick lumber, what length should the header be cut to account for two jack studs and the rough opening width?

Answer options:

• 958 mm
• 996 mm
• 1034 mm ✅ 1072 mm

Correct answer: 1072 mm

Explanation: The rough opening width is 920 mm. A jack stud (or trimmer) is typically 38 mm thick. With two jack studs, the additional width required for the header is 2 * 38 mm = 76 mm. Therefore, the header length should be 920 mm (rough opening) + 76 mm (two jack studs) = 996 mm. Re-evaluating based on common practice for header length being the rough opening plus two king stud thicknesses (or two jack stud thicknesses) + 38mm for the cripples. This question assumes a header is supported by king studs and jack studs. The length of the header spans the rough opening plus the thickness of two jack studs (trimmers), which is 920 mm + (2 * 38 mm) = 996 mm. This ensures the header rests on the jack studs. The distractor 1072 mm could be derived if one also considered the thickness of two additional cripples on top of everything else.