When erecting a scaffold with a 5' x 7' base using a 4:1 ratio, what is the maximum height for the first tie?

In construction and scaffolding practices, the 4:1 ratio is a critical guideline used to determine how tall a scaffold can go before adding ties for stabilization. This ratio means that for every 4 feet of height, there should be 1 foot of base width for the structure to remain stable and safe.

In this scenario, with a scaffold that has a base measuring 5 feet by 7 feet, the base width can be considered as 5 feet. To ensure stability, you can divide the base width by the ratio of 4:1, guiding how high you can build before the first tie needs to be added. By calculating, you take the base width (5 feet) multiplied by the ratio (4), leading to a maximum height of 20 feet (5 feet base × 4).

Thus, the maximum height for the first tie with a 5' x 7' base using the 4:1 ratio is 20 feet, making this the correct answer. The application of this ratio is essential in scaffold erection to prevent tipping and ensure worker safety.