Foundations are one of the most important parts of any building. Fortunately, as framers, we almost always build our floors over top an already set foundation. Despite this, there are still a lot of things to consider when setting up a floor system
There are 3 main types of foundations. You have hard slab, crawlspace, and basement. Obviously, if you are dealing with a hard slab foundation a floor system is not necessary, but for the other two you will need to install a floor system over the top.
 Floor systems are always going to consist of either floor joists or floor trusses. When figuring out where to lay them out, always look at the shape of your foundation. If you have a foundation in a rectangular shape, it is best to run the floor joists perpendicular to the longest side of your foundation.