I’ve been asked to think about how to level a sinking house just in case it should prove to be worth it and haven’t a clue about how to go about it. Does anybody have any ideas?
Here’s the situation: This house is newish, less than ten years old and is a two-storey built on a poured concrete frost wall. There is no crawl space. The first floor is a slab poured within the foundation walls and is nearly at the grade level. The second floor is conventional wood framing with a subfloor of diagonal laid board.
The whole house is built on fill on a steep slope. The fill was large boulders, 6″ crushed stone, some kind of sand or inorganic soil and a lot of 1″ clear stone. The foundation was designed and supervised by a soil engineer.
The house has tipped a little over 7″ from the high point at a back corner to the low point at a front corner. That’s a span of a little over 40′ It could have subsided as well, but we have no way to know that. Both the wood main floor and the concrete basement slab have tipped and are still pretty much parallel to each other.
The house has moved as a unit with very little interior damage. There have been three or four small drywall cracks and two or three doors that needed attention. All the windows still work properly. There are five small cracks showing on the whole perimeter of the foundation. They could be bigger underground though I’ve been thinking the foundation top edge is the tension edge.
The present plan is to dig to the footing at the lowest corner and see if we can figure out what’s going on. What I can’t figure is: if it is possible to stop this house from sinking then how do we get it back level? The basement slab is floating free of the foundation walls and would have to be raised independently.
My own feeling is that it would take a hell of a lot more house than this one to make this job worthwhile, but I’ve only been asked to think about it.
Ron
Replies
It might be possible to raise it with helicial (did I spell that right?) piers. I think FHB may have done an article on them. Anyway, they are galvanized steel piers that are screwed into the ground to a depth determined by the resistance to the screwing which has a relationship to the soil's load bearing capacity. They are large, and screwed in with a backhoe. There are attachment mechanisms that are bolted to the footings, and are used to jack the house up before the footings are bolted to the piers.
Anything can be done for the right price.
You need a pro to evaluate it_______________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Yes, you need a pro to evaluate it. Specifically, you need a house mover. What a mover can do for this is build up cribbing in the downstairs rooms on the existing slab, cut the wood frame loose from the footing, and lift the whole shebang on steel on top of the cribbing to get it out of the way. Then with the foundation fixes done, the house mover will put it back down for you. What you'd have to do is the corrected foundation, patching up the holes where the steel went thru, re-connecting all the electrical and plumbing stuff, etc. Given that it's a slab, that plumbing and electrical stuff could turn out to be a lot of unpleasant little jobs. BTW, you'd be renting the mover's cribbing and steel for the duration, which can add up.
-- J.S.
In theory, Steve has the right idea with piers BUT
how would anyone go about engineering it? An engineer already supervised the original work and he knows more about what is there than anyone else.
And he already screwed up! The very idea of building over fill on a steep slope scares me to death.
Before I got to that point in the description, I was alreadyu muttering to myself, "I'll bet they built this one over fill."
Steep slopes are their own kind of problem. Combine the two problems and the potential for failure increases exponentially.
I think the only way I would consider this one is to take readings for three years and see if it and the soil around have stopped moving for three years and then, in three years, I would over-engineer.
Better to sell tickets to the "leaning tower of [wherever you are]"
Excellence is its own reward!
Again one for an engineer, or a lawyer. Was the fill designed by a engineer or just the foundation. My guess the fill was not set in lifts and compacted correctly or under it all is something like expanable clay
Helical piers sound interesting. I'l have to check for that issue. Thanks Steve. If that turns out to be the solution, I won't be doing it.
I had been thinking along the lines of a concrete slurry injection, but that wouldn't do anything to stabilize the foundation and prevent the same problem from recurring.
Excavation, fill and foundation were done under the supervision of a PE. I've already mentioned the word "lawyer" to the homeowner. To tell you the truth, I think my connection with this job is done. There's not much I can do there. I just find it interesting.
The only other time I've seen a house shift as a unit like this one with no interior damage was a job I was on in Yellowknife NWT in the 70's. This house had been built using normal southern techniques - on permafrost. So it started melting its way out of sight. I was working with a crew mining shafts under this house to bedrock with jackhammer and dynamite. 40 feet. We then formed and poured reinforced concrete columns up to the footings so that it would sink down on them level. And that wasn't the worst job I ever had, either.
We've got a similar situation here in Seattle. Three (I think) houses were built about 10 years ago on a steep slope above Interstate 5 overlooking Lake Union. Despite overlooking the freeway as well as the lake, these are very expensive houses because of the view.
About 6 years ago, we had a very rainy winter, and at least one of the houses began to tilt. I don't think there's any question of fill, just the steep slope (the same one the freeway's built on!) All three (I think) were initially declared unihabitable, but only the one remains unihabited. A couple of hundred thousand people a day pass by, and the sight of this house would stop traffic, if it weren't already going 60 mph.
The homeowner has long since bought another home, but continues to pay a mortgage on this one and I believe has lawsuits pending against the builder and the city (for issuing a building permit). Every year or two, one of our two (soon to be one) daily papers writes an article about the situation.
The thing is, about half the people who read the articles think the city is to blame and should reimburse the homeowner. The other half complain that since this house slipped, the city has made it harder to get a permit to build on a steep slope—they say such a restriction on building amounts to an "illegal taking" of private property. So the city can't win!
Anyone else have thoughts on the matter?
I was told never build in the foothills in Boise unless you know what you are doing. What am I up to building my first home for my family in the foothills. Who am I to sue my self.I also Know of the house you talk of it has been boarded up if I am right. Its Been like that a while I think?
What the heck is this thread? Did my wife put you up to beginning it?
The best thing you can do here is walk away. Unless you're able to buy the whole thing for 20 to 25 % of replacement cost.
Been there, done that. Only I didn't walk away.
A number of excellent points have already been made. Piffin is right in that you never build in those locations. Steve is right about the piers - although I would think the use of those boulders you mention wouldn't allow the drilling blades to pass. John has a great point about the house movers, but instead of repositioning the house on a repaired foundation, it should be moved elsewhere cause this settling issue is not over.
But if one had to fix it (because he's too bullheaded to walk away), another approach would involve digging 3' x 3' square holes every 7 to 8 feet along the entire footing - including any interior footings holding up posts or load bearing walls (oops - too bad about the hardwood floors, they have to be torn up and replaced). These holes go down about 18 inches below and underneath the footing (darn fancy landscape bushes are in the way as well as the sidewalks and driveway - and garage floor - and shoot, the darn utilities have to be repositioned). Good square holes are important for the subsequent steps.
Jack stands are custom fabricated for each hole (32 in my case). Out of 1/2" steel plate and 3/8" wall 3" steel tube. The top portion will be fashioned like a big "L", a piece of 3 1/2" steel tube welded to the vertical and supported with gussets. Both sides of the "L" need to be about 15" long and wide. The bottom portion will be the base. Also out of 1/2" plate steel, 24" square, and a corresponding 3 1/2" steel tube in the middle similarly reinforced.
The sides and bottom of the footing at each hole where these jacks will be located needs to be cleaned up with a electric chipping hammer so it is as flat and perpendicular as possible.
The jacks are then assembled. Between the top L bracket and bottom plate, a 20 ton hydrualic house jack is placed. At each location. These are specially plumbed jacks which are pressurized from a remote location and each jack is hosed up to the pump's manifold. The manifold has individual valves for each line, so's the operator can slowly and evenly raise the house by the footings until it's level. The leveling is done through water levels.
At this point, holes are drilled through the two intertwined tubes on the top L bracket and lags inserted or some will have holes predrilled into the vertical outside tube with nuts welded in place and bolts are torqued in to keep the jack from slipping. The hydraulic jacks are removed, leaving the house totally supported on the fabricated jack stands.
Then, the diggers come back in and connect each hole. They clean out the void under the raised footings and build forms in place to receive a new pour - which is carefully pumped under the footings to be sure that gap is filled. The fabricated jacks stay in place and get covered by the new concrete. Enough concrete is put in place to totally cover the jacks and any exposed steel, thereby also creating a bit of outside pour to the footing (it becomes wider). After setting, the forms are pulled and the holes filled in. The inside holes are filled to just barely above the bottom of the slab.
However, on the inside, your slab has fallen into the shape of a large bowl. Here, you'll have to core out a number of holes and have grout pumped in to mudjack up the slab until even. Then the rest of the inside holes are finished. And then the wonderful job of replacing the entire flooring on the first floor. Dirty bums that ripped out the floor, they took the base with it. And one of the guys accidently put a jack pipe through the wallpapered wall. No cracks before? Now you'll have them!!
And then comes the replacement of the garage slab and outside hardscape. As well as bushes. But you might want to wait on those items because the entire process will, somewhere, somehow cause other consequences not previously considered or noticed.
Such as your comment about a bit of tilt. The vertical vectors of the house load need to be carried vertically down to the footings. Where a deviation of these vectors occur, horizontal forces are created. These are most likely to be found at the top of the foundation wall. You may need to pull back the siding to see, but where the bottom plate meets the foundation wall, frequently diagonal cracks will occur from the knuckling over of the load. These need to be repaired after releveling. (You thought the problem of raising the house was difficult, how in the heck will you fix that? And so it can carry the load?) OOPS, Darn siding was in the way. Oh, you have real stucco like me? Oh, man, the wife now claims the insdie doors won't close. And she can't open the windows. What's this about the toilet not properly flushing? Water leak? Gas leak? Why in the world did I ever start this job?
These projects never seem to end. Cost? Just a wag, but based on experience, you're talking over 6 figures. By the time I got done, it was 500K and 4 years.
And no one has any idea that the slide has stopped. Why would anyone want to repair this until that happened? It's better to move the house elsewhere.
But from the way you describe, that PE's insurance company needs to become involved.
Walk away. And know that you made a very good decision.
Stoney! Man!
Did you invent this technique? Are you sorry you did?
I'll take your word for it and I'm gone.
And Busta, you make it seem like a piece of cake.I understand what you're saying and It sounds like something I could handle for a small lift but this job might have to go 20 feet to find good reliable bearing from the existing footing through the engineered fill to something reasonably solid. It probably won't happen because, like Stonefever said, they would have to spend a great deal of money and destroy the lower half of the house to maybe save the upper half.
A friend suggested that the proper solution was for the engineering company to buy the house for their CEO to live in.
Ron
No, I subbed it out.
The guy had a decent business going. Little competition and lots of prospects in California. He used his profits to buy those houses no one would buy and then send his crews in to rebuild, remodel and resell.
Like anything, if you focus on a sector little served, yet feared by willing customers...
I'ved raised (leveled) lots of houses here in New Orleans. The way we do it is you dig out under the exterior and interior foundation grade beams 2'-6" wide by 3'-0" deep. The we install 8"x 8" concrete blocks that are made with holes in the center to incert 1/2" steel pins in them. Every 5' under the existing beams we push these concrete blocks one on top the other conecting them with steel pins into the ground using jacks until we start to lift the foundation. After all the blocks are installed like concrete pilings we then install re-bar and pour concrete to make a new grade beam footing 2'-6" wide by 1'-0" deep over newly installed block pilings. We let the new grade beam set for 21 days. Then jack the existing foundation off of the new grade beam and block the foundation up with concrete blocks and back fill voids with sand. All the years we've been doing this we haven't had one call back because of the foundation moving again. The cost of a 3000 SF home would run you about $35,000 to $45,000 to do this excluding repairs to the house after leveling it.
busta :0)