A carpenter is installing 20 mm thick subflooring panels. What is the recommended minimum gap to leave between the ends of the subfloor panels where they do not fall over a joist, but rather butt against each other?

Question: A carpenter is installing 20 mm thick subflooring panels. What is the recommended minimum gap to leave between the ends of the subfloor panels where they do not fall over a joist, but rather butt against each other?

Answer options:

• 1 mm ✅ 3 mm
• 6 mm
• 10 mm

Correct answer: 3 mm

Explanation: A 3 mm gap, approximately the thickness of a 8d nail, should be left between the ends and edges of subfloor panels that do not have tongue-and-groove connections to allow for expansion due to changes in humidity and temperature. This prevents buckling and warping of the subfloor. Tongue-and-groove edges typically do not require this gap, as the joint itself accommodates movement.