How to Form a House Foundation
A house foundation needs to go through three separate stages to form. The first is the footing stage and it requires a trench in the bottom of the excavated hole right beneath the location of the proposed basement or foundation walls. The next stage, the wall portion, takes place after the concrete in the footings is set. The final stage of a house foundation is the basement floor. If your home has a crawl space or low foundation walls, you will skip this step. Read on to learn the whole process.
- Dimensional lumber
- Concrete forms (wood, steel or Styrofoam)
- Chalk box and line
- Rebar bender
- Rebar cutter
- Concrete ties
- Concrete drill and bolts
1 Prepare to form the footings
Prepare to form the footings. In soils with a clay base, you may pour directly into the trenches, depending upon your local code. In other areas, you will use 2-inch by 4-inch dimensional lumber to frame the edges.
2 Measure your footing width correctly
Measure your footing width correctly. The traditional width of a footing is 8 inches wide on each side of a finished concrete wall. For a traditional 8-inch thick concrete wall, that means your footing is 24 inches wide. Use dimensional lumber to form the edges and insert rebar stays according to your local code. Pour the footings and allow the concrete to cure for at least 48 hours before forming the walls.
Form the basement walls by installing 2-inch by 4-inch dimensional lumber on the finished footing, where the form will go. On an 8-inch thick concrete wall, this will be 4 inches out from the center of your footing. Make sure to include additional space to accommodate the thickens of your form. For instance, add an additional ¾ inch if you are using wooden forms, which are traditionally ¾-inch wide.
Pop a chalk line where the inside edge of your dimensional lumber will go. Double check both ends, then use the concrete drill and bolt the boards securely to the footings. Repeat this procedure all the way around the foundation, making sure your measurements are accurate.
5 Begin setting your outside forms
Begin setting your outside forms along the inside edge of the boards you bolted down. The easiest way is to set a corner form first and work your way around the rest of the foundation. When you near another corner, set another corner form. Most of the time, your forms will not fit exactly and you will have to cut and fit filler forms for the gaps after the other forms are set.
6 Install steel reinforcement on the inside of the form
Install steel reinforcement on the inside of the form before setting your interior forms. Call your building inspector and ask how much steel you must put in the wall. He will give you a minimum allowable amount in your area. Install the steel rebar, bending and cutting it to fit the dimensions of the walls.
7 Place your form ties in the wall
Place your form ties in the wall, with the help of an assistant. You will stick the end of a tie through the exterior form holes and the assistant will use long braces or rebar to secure the ties on the outside. On the inside, they will hang loosely until the interior forms are set.
8 Set your interior forms
Set your interior forms once the steel is complete. You will bolt down another row of dimensional lumber on the inside of your footing. Follow the earlier method, measuring from the inside of the exterior form to the wall's width and allowing for the width of your form. Once again, pop a chalk line and bolt the boards down.
9 Your interior forms
Ready your interior forms by placing against the inside of the dimensional support boards and installing the ties from the bottom to the top. Secure the loop on the outside of the ties with braces or rebar.
10 Add walers
Add walers to the top of your forms for support. Walers are boards or metal straps, often cut from 2-inch by 4-inch dimensional lumber and attached to the top of the forms for stability. Now you’re ready for concrete.
- Don’t skip support steps, like the steel ties or the whalers. When the concrete truck begins to dump the wet concrete, the forms will strain and groan against the immense pressure. Forms that are not properly secured may suffer a blowout which will effectively shut down your pour and add force you to re-form the walls.
- Check with your local building inspector before pouring. In some areas, an inspector must come out and make sure you installed enough reinforcement before you pour a foundation wall.