Digging Deep: Adventures in Foundation Follies (Part 2)

Perhaps you’ve returned because Part 1 of this two-part series tickled your curiosity. Or perhaps you’ve wandered here in a digital stupor, doom scrolling through the infinite expanse of the internet. If the latter is true, consider this your cue to step away from the screen. You’ve landed on a page talking about foundation walls, and it must have been a wild ride to get here. But for all remaining interested parties, we’re going to discuss two common failure modes involving tall crawlspace walls. The first mode of failure probably won’t knock your hair back: it’s fairly obvious. The second mode of failure might just surprise you and make you that much more interesting at a cocktail party should you be cornered by an engineer or overzealous builder.

Wall Failure Modes

Solid Connections

You can have the most robust footing design in the world, but if it’s not actually connected to the wall that it’s supporting, it effectively does half of its intended purpose. See, I told you the first failure mode was obvious.

But how we connect the wall to its counterpart is massively important, and this part is not so obvious. This connection is typically done with rebar. Two things should be considered here: ‘embedment depth’ (how far the rebar in the footing is submerged in concrete) and ‘developmental length’ (how long two pieces of steel must overlap each other). Embedment depth is like trying to stake a beach umbrella in place with a toothpick. A gust of wind and your sunny day at the beach turns into a chase down the shore. But plant a sturdy beach umbrella anchor deep into the sand, and it will stand firm against the strongest winds.

Developmental length for rebar is like the overlap in a Velcro strip. If the hooks and loops only engage over a short distance, they easily detach with minimal force. But when they interlock over a long stretch, the bond is strong, resisting separation even under significant stress. Similarly, in construction, a longer developmental length for rebar ensures a robust connection that can withstand the forces acting on the structure over time.

Lateral Restraint

Another critical aspect of foundation walls is their top bracing, which involves how the walls are supported by the house’s floor system. Proper top bracing helps the walls resist lateral forces, like soil pressure, that can push against them.

Important Considerations:

• Floor Joists: Ideally, the floor joists (the horizontal beams that support the floor) should run perpendicular to the foundation wall. This alignment provides better support and bracing for the wall.

• Rebar Placement: When the flooring system braces the wall, the rebar should be placed on the side opposite the soil fill. This helps the wall withstand the pressure from the soil. Why on the opposite side of the fill? Because the wall wants to elongate or bow at this location, and to properly counteract the elongating forces (tension), one must bias the material suited for the job toward these areas of stress.

What If Joists Aren’t Perpendicular?

If the floor joists aren’t perpendicular to the foundation wall, it might not be adequately braced. This can cause the tension side of the wall to reverse, meaning the rebar should be placed toward the side with the soil to provide proper support.

Why It Matters for You:

• Preventing Cracks and Failures: Proper bracing helps prevent cracks and structural failures. If the wall isn’t adequately supported at the top, it may develop issues over time.

• Structural Stability: Ensuring the top of the wall is well-braced contributes to the overall stability of your home’s foundation.

Conclusion

When considering a new construction home, understanding these foundation wall issues can help you make a more informed decision. Ask your builder or inspector about how the foundation walls are connected to the footing and how they are braced at the top. Ask if the tension side of the wall has been considered where joists run parallel to walls in high-fill situations. This knowledge can give you peace of mind and ensure your new home has a strong, stable foundation. Remember, while walls may not be the life of the party, they certainly keep the party standing upright.