I pass this one house on my way to work this morning – a '50s era single-story ranch. They are in the process of building a new foundation – a full story’s worth – underneath it, In other words, they’re turning it from a one-story house into a two-story house, but doing it by lifting the whole thing up, not by building a second story onto the existing building.
Why would you do it this way?
Just as a guess, possibly the supporting walls of the existing structure are not sturdy enough to hold a second story.
Building a heftier story underneath the existing dwelling would avoid that.
Is it in a flood plain?
There’s several houses around here that were flooded out during Isabel, and FEMA/Fed Flood insurance required the houses be raised above the 200 year flood level to receive damage money.
Guessing that it would also be much easier to separate the building from the foundation than it would be to separate the roof from the walls.
Also, the internal walls on the first floor wouldn’t be built necessarily as load bearing walls in the correct locations.
Maybe the foundation was bad anyways and had to be fixed. I would imagine the additional cost to make it a full story would be comparatively low.
Hm, good theories.
There’s a creek running through the front yard – just a trickle most of the time, but it can fill up during storms. There are other houses along that stretch – I’ll look more carefully at them tomorrow, see how high off the ground they are. What SmackFu says makes sense – once they’ve jacked that puppy up, you might as well make it a full extra story.
As far as load-bearing walls are concerned, Toykyo Player, that makes sense – but I read a lot of house and home type mags (Met Home, BH&G), and I’ve never seen a second story added from below, so I’m not sure that’s it. You could probably reinforce interior walls or add support beams more easily from above rather than lift the whole thing up.
Just as an aside…
There was a two story house down the road from me…the took the second story off…as a unit.
Never saw that before.
I live on the side of a hill in Hollywood. We have a huge unused space under our house, which is already 2 stories. The foundation area is basically 25 feet high, due to the sloped ground it is on.
If we ever wanted to add another floor, and we tried building on top of the existing house, we’d have to re-do the foundation and then there’s huge neighborhood building codes we’d have to deal with.
But if we turned the foundation into another room, the neighborhood council can’t do anything about it as it’s technically inside existing walls. And we’d already have to redo the foundation, so it’d be cheaper to keep building under the house as the crew would already be working there.
Doesn’t sound like it applies exactly to that situation, but the building codes in the area may permit one and not the other.
Oh yeah… another possible reason would be that it’s much harder for your kidnapped victims to attract attention while chained in a windowless basement, as opposed to in plain view on your second floor with the big french windows.
Now we’re getting somewhere! 
Looked at the house more carefully this morning as I went by this morning – filmyak’s theory is starting to look better and better. There’s going to be a door on the ground level, and a couple of high windows – but it definitely looks like this was more about adding a basement/improving the foundation than it was about adding living space.
Just in case it wasn’t clear when I looked at the house again, that was this morning. :smack:
All the house-raisings I’ve ever seen were first and foremost to remedy a failing foundation. Once you’ve disconnected all the plumbing that comes into the house from below and separated the house from its foundation, there’s comparatively little extra effort to raise it one foot or ten. If you like the house enough to mess with jacking it up, you might as well give serious thought to adding a level.
As for doing this from below, rather than above, if you only want to add space, a roof is much more fragile and difficult to separate and move than an intact house. Also, as **DrFidelius ** said, the existing structure was engineered and built to carry its own weight. It’s simpler to lift it and put something designed for holding up another level underneath than it is to retrofit.
My ex’s sister jacked up her house to replace the foundation - it had crumbled enough that the pieces were settling into the bog it was built on. Except for moving the lifting beams and pouring the concrete she did it all herself - excavation, placing the jacks, lifting, building the forms for the new foundation, and lowering everything into place. The rest of the house was still crap, but it was a great foundation.
so many houses have flooded around here (S. Louisiana) that FEMA got fed up. Three homes were just torn down. The lot across from my house is now a pocket park. One house went from one story to two. But the ground floor can’t be permanent living space. It is a garage and a play room. Kind of like an upsidedown basement. 
Want to watch some real fun? Watch what happens when the geographers finish redrawing the FEMA flood maps using accurate data. Relief is so small down here that a 1 foot adjustment can take in many acres-and many homes. LOTS of people are going to be upset.
I’ve thought it would be nice to raise my house a couple of feet. I live on the crest of a hill (the house came with a little sign that says ‘Hillcrest’), so flooding isn’t a problem. But raising the house a couple of feet would make it look better from the street (which is higher than the house) and also make more room for any maintenance that needs to be done underneath. (It’s a post-and-block foundation, and they had to excavate a bit to bring the under-house room up to code. They also had to jack it up to fix a support beam.)
But I wonder how much it would cost to just tear it down and build something more efficient? This house is 71 years old and not well insulated. Since it’s had three additions over the years, the floorplan is a little funky. My mom’s 3-BR house in Arizona cost $145,000 when she bought it. Now, there are economies of scale since it was built with a lot of other houses; but it seems to me that it mightn’t be too expensive to build a new, better home. (Incidentally, I only paid $96,000 for this place 21 months ago. My realtor told me it’s currently valued at between $169,000 and $179,000.)
Update on the house in the OP: When I went by this morning, I saw they’d trucked in a few loads of dirt and were grading it up against the basement walls they’d just put in. IOW, they are now building a new little knoll under (um, around) the house they just raised.
Curiouser and curiouser.
Once on an episode of This Old House or some similar show, they had to raise the house and build underneath it in order to comply with some building code, i.e., they had to maintain the old structure lest it be considered new contruction. There was some compelling reason that they wanted to avoid “new construction.”
Maybe he’s practicing to be a shoplifter? :dubious:
There’s a house around the corner from mine that had this exact thing done for that exact reason. It was a much, much older house, though. Probably built in the late 1800s.