I get that some foundations do have sinking issues, but how does having a foundation help? If the foundation is poured and solidifies, what stops the weight of the house from immediately sinking/tilting the foundation?
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Basic principal of a foundation is pressure = load divided by area. The ground itself will have a maximum amount of pressure it can support. If the load of the house is constant, then a foundation pad with a larger area will cause a smaller pressure on the ground.
Foundation design of a slab tries to find the dimensions of the slab that will cause the pressure of the house to be less than the maximum capacity of the ground. If the soil is too weak and a foundation slab is not suitable for the area, then geotechnical designers look into using piles / piers instead.
I can answer this as I design foundations for a living!
The foundations transfer the load of the building to “stronger” more competent soil. Different types of foundations, piles/strips transfer that load in different ways to different soils at different depths.
It’s all about dissipating load over an area depending on hardness/strength
The foundation of most houses rests on what’s called a “footer”, which is concrete poured about 2 to 3 feet wide, around the rectangular area of a houses frame, which is then leveled, and allowed to dry, then bricklayers build the cement block foundation on that.
This “footer” goes unseen, because it’s about 2 to 12 feet underground, and you’ll usually never see it.
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Use to pour concrete basement walls. The trench for the footings has to be on clay and below the frost line. Clay supports the wall much better than top soil.
The foundation spreads the weight of the house over a wider area and transfers the load the the ground.
Depending on what the ground is made of (bedrock, shale, clay, sand, etc.) the design of the foundation is different.
For large buildings, geotechnical engineers do tests. They tell the structural engineers how good the ground is at supporting weight, and the engineers design the foundation to work with those ground conditions.
It does. Source: New Orleanian. On new builds they drive pilings deep into the muck. The rest of us just have crooked houses.
Others have given great responses but I’d like to add: the foundations usually sit on *undisturbed* soil. When you dig a hole and fill it back in, its usually a mound – it doesn’t fit like it did. There are tiny pockets of air where the bits of the soil don’t nestle into one another. This type of soil will eventually give way and sink if you build on it. Undisturbed soil is hard and packed, without voids, and will bear weight. Add footings to distribute the weight bearing on the foundation walls and it should be pretty solid.
I like to think of houses as ships sailing in the earth. the foundation is like the hull of a tanker In a way.
to explain it as simple as possible, theres 2 big reasons it works.
1. Poke your palm with one finger, now try it with your whole hand. One finger feels like a lot more pressure for the same push.
Houses sit on foundations for that reason, the foundation spreads out the weight of the house, where it would normally just sit on the walls. A bigger area is better than a smaller area to not sink into the ground.
2. Have you ever dug in sand at the beach? if you dig enough you get water/wet sand, yes? Much like that, if you dig into the dirt, or whatever the ground is made of where your house is, youll reach a depth where different things show up. A foundation lets you go below those areas to a layer where the weight of the house can be supported.
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