The most basic part of the designing your home plan is the foundation. The foundation wall is actually attached to the footings or footer. You will put the footings in first and the size of the footings and how deep they are to be dug really depends on the frost level and the type of soil.
The footings need to be deeper in the ground than the frost layer or the frost can expand under the foundation and push it up in places and make it uneven. That causes a host of new problems. At all cost, get below the frost line with the footer.
The dimension of the footings will be determined by the building inspector. The foundation wall will be attached to the footings by either pouring them together, or by pouring them separately, but joined together with rebar. See the pic:
The hardest part of the house design plan is the foundation and the hardest part of that is the excavation. I did all mine with a pick and shovel.
I’ll never do that again. I dug it all out and laid the forms for the footings. Then we checked it for squareness. This is totally important! Then we called the cement truck.
That’s not me in the dorky hat, I’m the dork in blue. The hat guy is my brother. His arms are bigger than my legs and he’s twice as strong as I am, so having him around to help with the cement work was handy. My brother is built like a gorilla, but he has a heart of gold so I don’t mind if he drags his knuckles a little.
As you can see, the footings has the foundation wall on it and this pic even has the sill plate and the rim joist started.
I put a cement column down the middle of our foundation. A girder in this case is almost always used. I don’t know what I was thinking.