What is a raised vs. slab foundation?
by Scott Robinson / Robinson Realty
As far as I can tell, there are only two types of foundation that rest on the ground raised and slab. I will try to get to what hangs off a cliff/cantilevered at a later time.
A raised foundation is accomplished mostly with a foundation around the perimeter of the house (sometimes stone or concrete block.), supporting the structure under the house. In real old houses say before the 1950′s they used “post and pier” foundation. There would be the foundation around the house and little posts holding up points inside between the cement exterior. Usually just wood stuck their on little cement blocks. No strapping or anchor in the ground! Now they have to be anchored with metal straps.
My step dad had some buildings like this when I was a kid. He had settling problems on a building once and we got under there with a car jack and leveled it. We then leveled other spots and left wood supports where we had used the jack. He said it lasted through the earthquakes?
A slab foundation is when they dig out the area you are going to build the house on, lay the plumbing and some electrical, steel supports to tie into, re-bar to support the cement and then pour the cement which becomes the foundation. As I understand four inches thick. A very solid structure held together with a network of long steel rods almost a half inch thick, called re bar.
Raised foundations are good because if you have a problem with plumbing or electrical you can crawl under the house and fix it, they aren’t encased in cement as above. If an earthquake or settling takes the level out of the house you can fairly simply level it. Much cheaper than re-pouring part of your slab.
The bad news is that over time a raised foundation is subject to dry rot, fungus, termites and rat infestation among other things I am sure. Nothing that can’t be dealt with. But in nature all things tend to have issues.
A slab foundation is what is mostly used to day. Cheap, easy and efficient, less edible and at the mercy of the elements.
In our area of Southern California we have mostly expansive. clay soil. When it gets wet it expands, when it dries is shrinks. In Southern California we go through about seven to ten years of a lot of rain and then is seems seven to ten years of none called drought. That’s when they make us conserve water.
If the water is getting under your house the clay expands when it rains and shrinks when it dries. This does not happen evenly and causes your house to be out of level and have cracks. At some point doors and windows won’t open or close properly. Slab foundations tend to crack and can have water come through. When the slab goes out of level it’s a major issue to fix.
Gutters that are properly set up and day lighted to the street, then kept clean will generally remedy the water problem. Unless you live by a hill or have other water issues(Some areas have ground water issues that may cause you to need to divert water. Like with an underground stream.) A hill or stream draining onto your property might need a French drain or even a culvert, which will divert water to the street or other system to get water away from the house.
Note: It’s not legal to divert water onto a neighbors property and you could be liable for any damage it causes.