Another possibility is the foundations. If landfill was brought in to build the ground up which is often the case then there is the possibility the wall could have moved and collapsed due to subsidence movement. If landfill is not properly set and compacted there is plenty of potential for this to happen.
In a house I rented in Chiang Mai the ground around the house opened up in a number of places directly below the roof drip line during the rainy season. It had been backfilled on what was previously a rice field, probably with a whole lot of crap material and then not properly compacted.
Just a heads up for anyone planning to build.