I happen to be a firm believer that (for many reasons) a house in Thailand belongs on stilts. (Rural Thai Style). I seem to be getting a lot of differing views as far as how deep the foundation (stilts) would have to go down to assure that the building would not start "to move" over time.

A major factor would be: Building on rock-bottom or on an ex-rice-patty! Any rule of thumb on this subject ?

Thanks & cheers.

A major factor would be: Building on rock-bottom or on an ex-rice-patty! Any rule of thumb on this subject ?

Load bearing capacity of the supporting soil is only one major factor. The other is the load on the soil. Type of structural material - timber, concrete, steel, etc. No. of floors. Spans of the stilts.

Thus, there is no rule of thumb.

Not an answer to your question, but a neigbour in my wife's home village thought to save money and not put the stilts in the ground, only on it. Soon there was a little storm and he woke up with his house resting on his car.

He now has he new car and house, this time the stilts are deep in the ground.

The rule of thumb is "Every structure & site are different." The geotechnical conditions below grade are a hidden condition, even as local pile drivers may have a good estimate of required depth for a typical, local house, based on directly-localized experience. Still, as the saying goes, your results may vary, and just within one structure you can observe huge differences in the driven depth of piers.

The driven, i-beam-shaped concrete 'piers' of typical Thai houses on filled swamp/rice paddie sites are driven until firm resistance is met by the rig operators, not exactly a science , and they string piers together as needed as they drive them down. The bearing capacity of piers in deep soil is based on surface friction between the pier and the soil - not end bearing on rock strata below. Think about it: with straws driven into yoghurt without reaching the bottom of the bowl, one can build a multi-story toothpick house. Scale it up, and with enough piers, high-rises are built on piers that do not rest on rock.

It's all about the weight of your total system - wood, concrete, # of stories, tin roof or concrete tile, wind/seismic zone, even occupancy type - and the number of posts/piers carrying the load. If you're building an all-wood traditional Thai house [typical geometry, materials & stories] the local pier driver guys may have you covered. But why bother? Structural engineers are really cheap insurance compared to the cost of a failed foundation, especially after you've build your dream home on it!

Lets be careful out there!

oh yeah, Rule of Thumb: hire the most completely deaf pier driver you can find - he's the most experienced

We built our house in Roi-et last year , and the construction crew dug down 1.5 metres and made 1 metre square concrete pads and then built up from these bases with upright concrete stanchions to support a two story house , and to date all is in fine fettle !

oh yeah, Rule of Thumb: hire the most completely deaf pier driver you can find - he's the most experienced

I will probably go with this. Thanks for all the reply's. Cheers.