@vickie007,
In coastal areas with high water tables, houses are built on low pylons with crawl spaces under them. If you watch it being built, it looks like it is up on blocks. If the house was built with a basement, there would be sever water problems. In beach front towns, houses are often built on very high pylons so that flood waters can go under them.
"Up on blocks" can also be a slang term as mentioned above, but that is not what the writer is referring to.