How to stabilize the earth under a pier foundation?

[California]

The first step should be to replace the concrete block that is being incorrectly used to hold up some weight. [ located in the top left of picture. ]

It's not quite that bad! That block only supports a plank (storage shelf) that has trivial weight on it.

 

[WayneB]

It's not quite that bad! That block only supports a plank (storage shelf) that has trivial weight on it.

What might be nice is to have some additional pictures showing the house itself and the wall structures. Building size would also be interesting.

Wayne

 

[metalsmith]

Start with the basics, like what are your long term plans are for this house. If your plans are for an authentic renovation then a wire mesh with toweled or gunite is going to look awful. Determine soil type and how deep you need to go to find firm load bearing conditions. A quick hole dug helps with this. Also determine the condition of the supporting beams as to not just current condition but that of the next several years. Decide if they can be used as is or need support or actual replacement. Think of jacking more of relieving foundation load, just enough to slide out old components and install new ones. Make absolutely sure your jacking locations are strong enough before starting any lift. As to pier placement, best would be to determine the buildings actual dead load and future live loads but can usually look at the old pier locations and use at least that many along with adding in additional ones as beam conditions dictate. If the beams are in less than seventy percent of their original condition then need to consider placing a continuous foundation for support but assess those beams for possible dry rot which will make them disappear in a few years regardless of the support. A continuous wall has the advantage of keeping the beams from contacting the ground and in keeping out varmints. This type of project is strictly about what the building means to you and your family. That will determine whether its worth the time (a lot of time) and money to do the work and the method of repair or if its time to let it go. I know first hand, having an old second house that has a hand laid stone wall foundation. But it can be very relaxing and rewarding to step back in time and rebuild something our ancestors built.

 

[California]

What might be nice is to have some additional pictures showing the house itself and the wall structures. Building size would also be interesting.

Here's the view from the SE, 2003. (The watertower isn't connected.)
And the view from the NW, 1951. I think that's me with Grandma in the attic.

Age is unknown. The parcel was deeded 1905. The outbuildings have equipment stalls but no horse stuff, so the house was built maybe 1910-15. It looked old when my grandparents bought it in 1950.

The first add-on (note the roof line in the first picture) added indoor plumbing. (before we owned it). Dad hired a carpenter and replaced the mudsill foundation (redwood timber in a trench) with the pier blocks about 1960.

Then Dad and I built the sunporch (next roofline, first photo) and added 6 ft to the bedroom (opposite end of the house) in 1962.

The additions made it 14 x 50, or 700 sq ft.
Sometimes I'm tempted to install a singlewide mobile home (same footprint!) to solve all the problems at once.

 

[California]

...what are your long term plans ... authentic renovation ...

It's not worth staying authentic. The original was cheap, probably a lumberyard kit, 14 x 30 or 32 ft; 450?? sq ft. No electricity. No indoor toilet or even space for a bathtub before that first remodel.

...how deep you need to go to find firm load bearing conditions.

Below the gophers. They're so bad Luther Burbank (horticulturist) abandoned this neighborhood and moved to Santa Rosa. Impermeable clay is 2 ft down. No frost here.

Also determine the condition of the supporting beams ... Decide if they can be used as is.

Thankfully the whole structure is heart redwood so the structural problems are limited to the earth bearing. (but all the other systems are failing from their own causes.)

Make absolutely sure your jacking locations are strong enough

I've worked with cribbing, long ago I was a Journeyman Carpenter for a few years following college. It's the tremendous work that a foundation replacement would entail, that I'm trying to patch around. Like Dad - once I'm sure it won't fall down in my lifetime, that's all this house deserves.

determine the buildings actual dead load and future live loads but can usually look at the old pier locations and use at least that many along with adding in additional ones as beam conditions dictate.

I think the present structural engineering is ok. I was amazed to cut through the shim on that pier beyond the new door, (see photo in first post) and find it was slack -not carrying any weight at all. It should have been loaded if the piers nearer the camera have settled into the gopher holes I found coming out from under them.

If the beams are in less than seventy percent ...assess those beams for possible dry rot

I'm lucky, I haven' found any bad wood, aside from that in direct earth contact which will be easy to replace. Heart redwood is great. What I'm most concerned about is the piers sliding down into that cavity.

A continuous wall has the advantage of keeping the beams from contacting the ground and in keeping out varmints.

Good point. When the racoons fight under there you would swear they are climbing up inside the walls.

This type of project is strictly about what the building means to you and your family. That will determine whether its worth the time (a lot of time) and money to do the work and the method of repair or if its time to let it go. I know first hand, having an old second house that has a hand laid stone wall foundation.

I wish this place was quality like that, worth preserving. I jokingly describe it as the sort of old simple house that everyone around here (who is still in farming) converted to labor housing years ago when they finally built a modern house for their family. The locals understand that metaphor instantly.

But it can be very relaxing and rewarding to step back in time and rebuild something our ancestors built.

I learned carpentry patching this place, and I'm still at it. I fear I'm becoming my Dad every time I get out the tools and hit the scrap lumber pile to repair something!


Back to my first question - how do I keep the piers from sliding into the basement cavity?
At the moment I'm thinking I should remove each pier one at a time (with safety cribbing), pour a pad under it, in a hole dug down another foot to the clay subsoil, and then reset it. This would double (at least) the bearing area under each pier, block the gophers, and reduce the risk of a pier turning over.

Out in the middle of the crawl space I could dig down and set piers much lower, (using longer posts), then eventually excavate down to that level in the future to make more basement space.

Everybody - I really appreciate the comments and suggestions. All of them are opening my eyes to possibilities I hadn't considered. Continuing comments would be greatly appreciated. The breadth of expertise here is amazing.

 

[Egon]

Back to my first question - how do I keep the piers from sliding into the basement cavity? 
At the moment I'm thinking I should remove each pier one at a time (with safety cribbing), pour a pad under it, in a hole dug down another foot to the clay subsoil, and then reset it. This would double (at least) the bearing area under each pier, block the gophers, and reduce the risk of a pier turning over.

It would sound like you have the solution in hand.

 

[California]

Back to my first question - how do I keep the piers from sliding into the basement cavity?
At the moment I'm thinking I should remove each pier one at a time (with safety cribbing), pour a pad under it, in a hole dug down another foot to the clay subsoil, and then reset it. This would double (at least) the bearing area under each pier, block the gophers, and reduce the risk of a pier turning over.

It would sound like you have the solution in hand.

Thanks Egon. That's the only solution I've thought of, so far.

 

[curly]

And the view from the NW, 1951. I think that's me with Grandma in the attic.

That pic alone may make it worth saving.

Go for it, shore that dude up good enough so that your grand kids will be vacationing there too. They will be looking at that prominately displayed pic of their granddad and great great grandma, and thanking granddaddy for the foresight.

 

[metalsmith]

Since firm soil is not far down find out what types of soil treatments are allowed in your area to deter those gophers and use that around the piers. Those little guys can tunnel down 20 feet or so if they choose. If foundation treatments are not allowed then will need to go down like harv said, 6ft or better for a fighting chance against em. Bottom of each pier foundation should be at least below any low area within the angle of repose, simply put the angle of which the soil stabilizes itself against erosion and or landslide. A rough rule of thumb angle would be 45 degrees down from the ground level of any given pier, most clays stabilize at a much less of an angle normally. We usually dig the hole not to worried about its upper width cause we use sonotube with a bell bottom, once poured can then compact the soil about the upper body of concrete column. I would also check the elevation of each existing pier along with the level of each beam and pick an average elevation for each new pier top. Any areas that are way off level adjust now with shims and slowly bring everything slowly to a common level elevation over a period of time to allow the building to adjust.

 

[rox]

California,
What does your wife think about this house? My aunt and uncle had a similar situation except the (I hope this next part will not hurt your feelings) "run down" house that they had rented 30 years previously and was "run down" then ended up to be thier primary residence. My aunt always had conflicted feelings she hated the house, even though she had good memories of life there 30 eyars previously. When my uncle died my aunt had the hosue torn down and built a new one. I'll tell you what, what a differnce that new home is on that property. Her property now is amazing, simply amazing.

For you it is not the same thing, since this is not your primary residence. However you are rpeating what your dad went through all those years and he never did turn a sows ear into a silk purse did he? If it were me, I'd tear it down and build something within my budget that really would last for the next generation, and the generation after that. My dad had a saying about spending good money after bad and from my detached vantage point, that appears to be what you are doing, and what your dad did. Again, what does your wife think? Could you use that heart redwood in the new construction? Although it is a bigger money commitment, youa re at least investing in a building that is going to appreciate in value. Honestly my aunts new house on that same property increased her oaverall property much more than the cost of the home. In other words a "run down" (and again I really hope I am not hurting your feelings using those words I could not come up with a nicer way of putting it) house brought the value of the over all property way way down. A nice home on the same property increaded the value of the property more than the cost of the new home.

Might you be happy with a painting of the photograph from the 1950's hanging inside your new comfortable cottage/home? That is what my aunt did, she took a great photo, had it blown up and framed and it hangs inside her new wonderful home. If you were to start a new construciton you would not need to build it all right away, instead of dribbling money year after year on repairs you could dribble money for a few years and build slow. Just something for you to think about, my armchair opinion formn a gret un-emotionally attached distance.