Building a basement under an existing house is, according to general contractor Carl Heldmann, "one of life's more challenging tasks," but it could be worth it if you need the extra space. Avoid shortcuts, as you risk damaging your house or foundation. Building a basement may shift your house, no matter how it's done. Use proper tools for the job, too. Hiring general contractors may minimise damage to your house. They come equipped with both knowledge and professional tools.
- Skill level:
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Things you need
- House jack
- Front loader and Bobcat
- Shovel and bucket
- Steel beams and supports
- Concrete mix
- Pressure-treated wood framing
Test the soil under your house. Soil conditions and make-up will affect digging. Clay soil may slow digging and rocky soil may make the project impossible.
Jack up the house with a professional-grade jack and install stilts, or cribs, under the house. It's also helpful, and sometimes even necessary, to install additional supports to avoid damage to your house.
Remove the dirt under the house. Creating an entry into the basement cuts digging time. Use a front loader if it'll fit into your access point; otherwise use buckets and shovels.
Frame the new basement with pressure-treated wood framing. The floor should be flat, level and parallel with the house floor.
Pour the concrete for the floor and walls. Call for the concrete only when you are ready to use it and be prepared to pour it quickly.
Return the house to its location. Use proper equipment to avoid damage to the house or foundation. Rest the house level on the ground to avoid cracking the foundation.
Tips and warnings
- It's possible to hire house movers to jack up the house and move it while the basement is constructed, but you risk shifting the foundation when the house is replaced.
- Most tools can be rented at a local hardware store. Save money, especially on larger tools, by renting instead of buying.
- Test your soil for pests before starting, and treat the soil if needed. Termites can cause problems if left untreated.
- Leave a wide base under your house so the building doesn't resettle. This can cause wall cracks and jammed doors, as well as damage to the utilities.
- Purchase all necessary permits before beginning work.
- If your house is built on a slab, consider having a professional do the work, as the slab foundation won't support the walls during excavation.
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