Cost of post & pier foundation retrofit in California

[StructuresDesign]

A potential client want to replace the existing post & pier foundation for their 500-600 sf 1930s cabin with a typical stem wall foundation due to uneven settlement. The piers are 12"x12"x12" precast concrete blocks on grade. Since the existing piers are only located along the exterior walls, this should be doable. However, there is only a couple of inches of clear space below the floor joists, so access is not going to be easy. There is also a small addition that has a stem wall around all 4 sides of a small addition (about 70sf), which will make it more difficult to raise up the cabin.

Additional info: the local permitting will be easier if the earthwork is kept at a minimum, and the local frost depth is 24".

I am concerned about the cost and think that a hybrid system will probably be cheaper. However, I am not sure what would be optimal cost wise. So this is where I would greatly appreciate some input: what would the following systems cost (SWAG):
1. Stem walls exclusively.
2. New post & pier system (concrete) with hardware providing lateral capacity.
3. New post & pier system (helical)with hardware providing lateral capacity.
4. Hybrid stem wall & pier system with hardware providing lateral capacity.
5. Something else?

Thanks,
Cecilia

 

[MiketheEngineer]

As crazy as it may seem -

How about getting some house movers in and lift it up about 5', do the work right - quickly and easily and set the house back down??

 

[StructuresDesign]

I appreciate the suggestion, but I am not particularly concerned with the means & methods of how the contractor accomplishes the job (as long as it is done correctly). Some lift the building, others do not. My question was about the cost.

 

[cvg]

regardless of which way you go, seismic restraint will be necessary. Stemwall might be the better option. How will you provide that with post and pier?

 

[StructuresDesign]

Using a post and pier system with straps or earth anchors is typical for permanent foundations for mobile homes in this area. Since this is a cabin of comparable materials, weight, and size to a mobile home, it does not seem unreasonable to assume that a similar system can be engineered for this situation.

Stem walls are definitely the ideal solution, but I am trying to value-engineer this and come up with the most cost-effective solution (that meets local code requirements, of course).

 

[cvg]

a cabin is a permanent structure, not mobile. you might want to check with the permitting agency to see what the seismic requirements are

 

[StructuresDesign]

In order for a mobile home to be considered real estate, it has to be placed on a permanent foundation. By doing so, local jurisdictions, the federal government, and lenders consider it "immobile", thus qualifying for being taxed as real property, rather than personal property, and a mortgage.

Even though a mobile home typically only meet federal regulations and not local building codes, the foundation must meet local codes since it is constructed on site.

But that is not the question that I have. I am curious about what prices other engineers have encoutered for this type of work. The quote ($40k) that I have gotten from a local contractor just seems a bit high considering the size and value of the cabin.

 

[MiketheEngineer]

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