How far down do they dig, on average, when building a house without a basement?

I assume there might be differences in different parts of the country, but how far down do they dig when building a house without a basement?

When my parents built our house in northwestern Louisiana, they only dug down a enough to lay the foundation. That was only several inches. Of course, the building site was composed of compacted red clay so I don’t really see why you would need to dig much.

I am not sure that I am following. Most of the houses without basements that I have seen built didn’t require much digging at all. The site is leveled and then a shallow impression is cut to lay the foundation. There are some trenches that need to be dug such as to lay the main water line to the house etc.

I assume you mean no basement, but still a foundation, right? If this is the case, then it probably does vary across the country. But, generally, the foundation is a large concrete slab the dimensions of the house. Since the whole house can be attached, not just the outside walls, it doesn’t need to go as deep. I’m not by any means a foundation dude, but I would think 12" would be enough. From what I have seen, about 4-8" are above ground, leaving maybe another 4-8" below the ground.
Now, if the house has no basement AND no foundation, then they don’t dig down at all, aside from enough to provide a level surface.

Again, I’m not in any way some guy who knows about foundations, I’m just using what little knowlegdge and expereince I do have in construction to come up with a logical answer. Someone more experienced will be with you shortly.

Not far enough in many cases. This site gives considerable information on what should be considered inbuilding site selection and preparation.

In many cases a search into the history of construction in the area will answer many of the questions as to soil stability, drainage, etc. Usually, though, the contractor will merely clear the site of brush, grass, etc., level it and compact any fill by driving a bulldozer and maybe sheeps-foot roller around and then pour the slab.

In general, you want your foundation to extend below the frost line, so that if the ground freezes, the resultant expansion does not heave and crack the foundation. In areas where the ground freezing is not a concern, the foundation can be a slab just thick enough to support the house, or only a few inches.

In parts of the country where ground freezing is an issue, the foundation may have to extend as much as 4-5 feet below grade. Rather than pour a 4-5 foot thick solid slab of concrete, builders usually simply pour a slab at the required depth below grade, and surround the slab with concrete walls, resulting in a basement.

You always want to build your foundation on a subgrade made up of suitable material that is sufficiently compacted.

I didn’t mention it in the OP, but this question was triggered by watching the movie “Poletergeist” yesterday.

[spoiler]It occured to me that there was a big flaw in the flick, in that if the developers had kept the bodies in the ground but only moved the headstones, the builders would have come across the bodies when digging the foundations of the house, and the cat would have been out of the bag (unless the contruction guys can keep a secret).

Sounds like the foundations wouldn’t have gone deep enough to hit the bodies, assuming no basements. Thanks for the info guys.

Of course, the guys digging out the pool still should have hit a coffin or two… or one of the other houses in the area that had a pool put in. Not to mention the trenches for pipes and other utilites.[/spoiler]

My very limited understanding of this is that there are 2 options, the standard slab which should go below the frost line, and something called the Alaskian slab which is a thinner, and curved (concave or convex) and designed to be handle the stress of being above the frost line somehow.

This site explains Frost Protected Shallow Foundations which were developed in Scandinavia. The edges of the slab consist of footings that go down from 12 to 16 inches and are insulated from the ground.

From the site: “FPSFs use rigid polystyrene slab-edge insulation to reduce slab edge heat loss and to hold heat from the house in the ground under the footing. This prevents ground temperature under the footings from freezing, essentially protecting the building from frost heave by raising the frost line around the foundation. In cold climates, builders place horizontal ground insulation around the foundation and extra insulation at the corners, which tend to have higher heat loss.”

Here in North Texas, we have a problem with clay soils that have a tendency to expand during the wet season and contract during the dry season. This can result in a shifting foundation for a house built with a slab (as opposed to pier and beam construction.)

When our house was built four years ago, the builder dug trenches about six feet deep layed out in a ten-foot by ten-foot grid pattern. Concrete was poured into the trenches to create “walls” about eight inches wide, which served as a type of pier I guess. The space between the “walls” was left filled with soil, and the concrete slab for the house was poured on top of the soil and piers.

This is a relatively new way to pour slab foundations around here. Most older houses have slabs that only extend a few inches into the ground. These are the ones that typically have foundation shifting over time. The remedy is to dig under the slab about eight to ten feet, then install concrete pylons to jack up the house and level it off.