Final answer:
The normal depth for a footing below grade can vary depending on factors such as soil capacity and structure size. An older guideline was 7-8 times the diameter, while newer work suggests 15 times the diameter. Consulting an engineer is recommended.
Step-by-step explanation:
The normal depth for a footing below grade can vary depending on several factors, such as the load-bearing capacity of the soil and the size of the structure being built. However, there are some general guidelines that can be followed.
An older rule of thumb suggests a depth of 7-8 times the diameter of the footing, while newer work suggests a depth of up to 15 diameters.
For example, if the diameter of the footing is 24 inches, the normal depth could be 24 x 7 = 168 inches (14 feet) or even 24 x 15 = 360 inches (30 feet).
It's important to note that these guidelines are not absolute and should be used as a starting point. Consulting with a professional engineer is recommended to ensure the footing depth meets the specific requirements of the project.