For an area measuring 18" X 36", how many floor joists are required at 6" on center?

• A. 5
• B. 7
• C. 10
• D. 12

Answer: (B)

To determine the number of floor joists required for an area measuring 18 inches by 36 inches with joists spaced 6 inches on center, start by calculating the total length of the area where the joists will be positioned.

First, note that "on center" means the distance from the center of one joist to the center of the next. With joists spaced every 6 inches, consider the entire length of the area where the joists will be laid. The shorter side of the area is 18 inches.

When spacing joists 6 inches apart, you can find the number of joists needed by using the formula:

• Total length in inches divided by spacing (6 inches) plus one joist at the start.

For the 18-inch side:

1. Divide 18 inches by 6 inches, which gives you 3.

2. Add 1 for the starting joist, resulting in 3 + 1 = 4 joists needed along this dimension.

Now, examine the 36-inch side:

1. Divide 36 inches by 6 inches, which equals 6.

2. Add 1 for the starting joist, resulting in 6 + 1 =