Design and make a house foundation
How to design and make a house foundation that is straight, strong and durable regardless of environment is not a complex process, but a very important start of the house construction project. There are major rules to follow and if you do those correctly, the project will go smooth afterward.
Make sure the foundation is:
1. Well below frost layer. The earth surface freezes only just so many inches deep in the ground depending on where you live. It's important to get the foundation footer beneath the frost layer to prevent frost heaves or dips. If frost gets under concrete, it can expand the ground upward lifting it, then when it relaxes you have a dip. This can make a house uneven over time.
2. Poured on undisturbed soil or compacted gravel. The ground needs to be compacted gravel or at the minimum, soil where you have dug down low enough and the ground is hard, like a rocky surface, not soft like clay or dirt.
3. In square. The forms you use need to be measured so that they are perfectly in square. Being "in square" means corners are at perfect 90 degree angles so that various building materials (plywood sheathing, sheetrock, cabinets, carpeting) fit into place.The forms will need to be braced so cement doesn't bow out the sides.
4. Is level. All houses and buildings are level. That's because the foundations are measured and formed with a level or transit so buildings are flat and straight up. They don't have a slope. Not even on mountain slopes.
5. Allowed to cure without freezing or dehydrating. Cement is delivered and poured with an exact amount of water as an industry standard. That moisture can freeze and damage the cement. On really hot days, the water in the cement can wick into the dry ground or evaporate before it has a chance to completely cure. It needs to slowly cure and dry to be strong.
Digging the foundation and making the footer
Deciding whether to dig by hand or hire an excavator is only a choice you can make. Digging with a shovel is hard work, especially if you live on a rock patch. If you have the energy to go that route, you can save a bunch of money that you otherwise would have paid the excavator. I dug my entire foundation out with a pick and shovel and it was hard work way back when I was younger.
I only talk about the option between digging by hand or hiring an excavator because the nature of this site is to save money by doing the labor without hiring contractors. If you have more time than money, you might want to consider it. You can always hire an excavator if the blisters on your hands get too sore. I had calloused farmer's hands so I was OK with a few blisters.
There are at least two ways to go if you decide to have a house foundation. The route I decided to go was to dig the entire area out so I could have a crawl space under my house for storage and better accessibility for working on plumbing if necessary. Cement is heavy and the weight can bow out the wooden forms if you don't brace them adequately. See how I have braced the forms. I also braced the lower parts of the forms that can't be seen in this photo. Please see here for a list of necessary tools needed for measuring, cutting and putting together cement forms.
Another thing to note to avoid confusion is that I opted to put a center footing up the middle where most contractors put reinforced beams on blocks to support the weight of the floor joists that run crossways over that span. I don't know why I decided that, I just did.
The other route is to dig trenches in the ground using the weight of the ground to reinforce the cement forms.
The weight of the ground can help support the cement forms so they don't pull apart. They still should be braced. It's really important to have accuracy when doing the foundation.
After the forms are made and braced, be sure to add rebar. I will discuss the rebar schedule and assembly a little later in. The rebar holds the concrete together when things get shaky. It also make the foundation much stronger.
There are several different ways of hanging the rebar so it is off the ground and sits about halfway to the top of the footer. The important thing is to tie it together so the footer seems like one piece.
Rebar basics
These images show two types of footer methods. The one on the left is easier. Some contractors make the footer slotted so the foundation wall is poured into an interlocking footer. I don't really see the need for this in smaller dwellings. It seems to add too much difficulty, but I'm not a professional.
You might be tempted to mix the cement yourself to save the cost of delivery, but I don't see any way that it would save money and it jeopardizes the strength and consistency of the cement. Plus mixing cement in a wheelbarrow or portable mixer is really hard and very uneconomical. It's best to trust the cement companies. They will ask what your project is and the exact dimensions. They will charge by the "yard" on cement.
This is the footer after it was poured. I made sure it was smooth and level. At this point it needs to cure for about a week.
This is what the first round of concrete will look like. It is the footer which will hold the foundation wall. In this photo, the rebar has protective covers on each end. This is so nobody will get impaled while the footer cement slowly dries and becomes concrete.
The footer is purposely wide to cover more ground because the weight of the house will rest on it. The wet cement needs to have rebar protruding out of it so when the wall foundation is poured, the foundation will adhere to the footer making it all one piece in purpose.
This is how to design and make a house foundation footing
After you have completed the footer, making sure that you installed the rebar in the forms so it goes throughout the footer, but every foot or so also has a piece bent upward so when you pour the foundation wall, it will hold the wall in place after drying making the footer and foundation wall essentially one piece.