The importance of first establishing a firm foundation is a commonly used phrase. The “foundation” might refer to a mission statement that governs an organization. It might refer to the base coat of finish on a new painting. Or it might be the masonry footings and walls that support a building. Like many metaphors, this one is often put to use without much thought to its origins or its most literal meaning. So let’s take a moment to determine if the “good foundation” cliché is as solid as it appears to be.
The foundation of a building is the stationary structural element that supports other major structural elements such as floors, walls, roofs, chimneys, porches, and decks. The foundation supports and anchors these to the ground and protects certain materials like wood and metal from ground contact that can cause moisture damage such as rot and rust.
Dead Foundation Loads
Foundation-designing structural engineers divide the “loads” that weigh on a foundation, into the “dead” load and the “live” load.
The dead load is the weight of the building itself. The building’s structural systems and all the materials used to build them qualify as “dead” load -stuff like plywood, floor joists, studs, ceiling joists, nails, rafters, roof sheathing, shingles, insulation, and gypsum board.
The “dead” load that bears on a foundation doesn’t change, but the “live” load does.
Live Foundation Load retaining wall shotcrete
The “live” load is the combined weight of the people who occupy the building and all the furniture, appliances, clothing and other items. The live load can also refer to the weight of snow or ice that accumulates on a building’s roof and sidewalls.
Other Foundation Forces
Although dead and live loads are the main forces that weigh on a typical foundation, there are other foundation “stressors” worth mentioning. For example, hydrostatic pressure is the pressure of water in the soil. In worst-case scenarios, hydrostatic pressure can cause a foundation wall to crack and leak; it can also push a foundation up out of the ground.
Expansive soil can also cause foundation damage. Certain types of soil with high clay content can expand with tremendous force when they become saturated with water. When this happens, the foundation experiences loading from the side, which is more likely to cause damage such as cracking and shifting.