Foundation System Overview Ep.37

Summary

This video provides an in-depth explanation of a foundation system for a building, focusing on its key components like footings, stem walls, and concrete columns. The narrator highlights the importance of the footings' design to distribute weight effectively, while the taller stem walls help address potential settlement issues. Additional structural elements like strip footings are also discussed, with an honest admission of a small mistake in layout. Despite this, the builder reassures that it won’t affect the overall structural integrity. The video emphasizes the importance of careful planning and adjustments in ensuring long-term stability for the building.

Takeaways

• 😀 The foundation's footings act like snowshoes, floating on the soil and designed based on its bearing capacity.
• 😀 The stem wall, which functions like a beam, becomes stronger as its height increases, similar to the difference between a 2x4 and a 2x12.
• 😀 This foundation is taller than typical for Southern Oregon, specifically designed to address potential settlement issues.
• 😀 Initial settlement occurs when the soil is not compacted enough during the setup, but it’s a minimal and inevitable process.
• 😀 Differential settlement is handled by ensuring uniform soil compaction and increasing the footing size and stem wall depth to mitigate uneven settling.
• 😀 The stem wall design ensures that any localized settlement on the downhill side of the lot won't affect the overall structure.
• 😀 The four concrete columns in the front are tied to the house’s foundation to prevent them from rotating or misaligning due to settlement.
• 😀 Sonotubes are used to form concrete columns, providing a cost-effective and reliable method for pouring vertical structures.
• 😀 The foundation system is a coherent structure, designed to last long and provide stability, prior to backfilling and framing.
• 😀 Strip footings distribute load to the grade and help shorten the spans of the joists, preventing floor springiness and ensuring stability.
• 😀 A small misplacement of the strip footing is acknowledged, but it won’t affect the overall structural integrity as all joist spans remain within acceptable limits.

Q & A

What is the purpose of the footings in the foundation?

The footings function like snowshoes, floating on the soil and distributing the weight of the structure based on the soil's bearing capacity.

How does the stem wall in this foundation differ from typical stem walls?

The stem wall in this foundation is taller than usual, which increases its strength and helps address potential settlement issues.

Why is the height of the stem wall important for the foundation?

The height of the stem wall increases its strength, especially in resisting forces along its vertical direction. A taller wall is significantly stronger than a shorter one, much like the difference between a 2x4 and a 2x12 beam.

What is the difference between 'initial settlement' and 'differential settlement'?

Initial settlement refers to the minor settlement that occurs when the forms are being set up, typically negligible. Differential settlement occurs when different areas of the site settle unevenly, which could lead to structural issues if not properly addressed.

How does the design address potential differential settlement on the site?

The design addresses differential settlement by using a taller stem wall on the downhill side, which helps ensure the structure remains level even if there is some uneven settling in different areas.

Why were the concrete columns tied back to the house rather than placed on separate footings?

Tying the concrete columns back to the house ensures that if any settlement occurs around the columns, they remain aligned with the house and do not rotate or become misaligned.

What is the function of the strip footings in this foundation?

The strip footings are used to distribute the load and support the floor system, breaking up the span of the floor joists (TJIs) to prevent springiness and maintain floor rigidity.

What issue occurred with one of the strip footings during construction?

One of the strip footings was laid a few inches off from its intended location. However, this minor mistake does not affect the structural integrity of the foundation since the spans of the joists remain within allowable limits.

Why is the speaker not concerned about the minor error in the strip footing layout?

The speaker is not concerned because the misplacement does not affect the structural stability, and the spans of the floor joists are still within the acceptable range for the design.

What type of form was used for pouring the concrete columns, and why is it effective?

The speaker used 12-inch Sonotube forms to pour the concrete columns. Sonotubes are a cost-effective, reliable, and quick solution for forming concrete columns.