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We are in the design phase of a home at the New Jersey seashore. We are having a hard time deciding between a grade beam over pile foundation or having the home built on a regular pile foundation.

The home is modest, 1500 sq.ft and is built about 8 feet off the ground (2 1/2 stories total)with a garage beneath. We’re told by the architect that the grade beam foundation will cause less lateral movement from the wind, etc. But, there will be a stud wall built on top of the 3’ block foundation wall.

How is this more rigid than having piling driven closer together, sticking out of the ground high enough to have the garage, with a beam connecting them and the main structure built on top? Wouldn’t the framed wall on top of the block wall cause lateral movement too? Is the extra cost of the grade beam worth it compared to the piling?

Thank you in advance for your expert advice.

Frank

Frank Pileiro
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In many cities including all beach communities in the state of California having a concrete grade beam tying the concrete piles together and forcing them to act as an integrated structure is actually required by the code. The reason is twofold:

  • A pile performs more effectively if restrained from rotation on top by a grade beam.
  • A foundation system connecting individual members by a grade beam ultimately can potentially compensate for a partial failure in an individual pile!
  • All building structures ought to be over designed with safety in mind.
Rhodie
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kamran
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For the proposed construction - stud wall on a 3' elevated block wall, a tie beam is absolutely necessary to support the weight above, as the block wall performs poorly as an elevated beam. Under load, it cracks easily and deflects more (block wall is weak in tension and shear even with reinforcing and grouted solid).

Note that the tie beams will force the piles to work in unison and distribute the horizontal force uniformly. Without tie beams, the piles can each move/deflect a different amount and cause very high stress locally, resulting in damages due to stress concentration and subsequent tearing/sheering.

Tie beam improves stability, but the ultimate stability is achieved by adding another important framing element - diagonal braces.

r13
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I'll be the devil's advocate here and say that I don't think the addition of a grade beam will reduce deflections by much in the grand scheme of things.

r13 is right in that the grade beam may be necessary to support the weight of the wall above. That being said, masonry shear walls are definitely a thing so the block wall could be designed to add stiffness to the building which will actually be far far better at reducing wind deflections than the grade beam. In fact, this may need to be done if the wind forces are large in your area - in which case, the grade beam will need to also be strong enough to resist the forces transferred to it from the wall.

So yes, you'll likely need the grade beam but not necessarily for the reasons the architect noted. Also, as others have noted- the grade beam may indeed be required by your local design code requirements.

You mentioned that you're working with an architect and a builder. What about a structural engineer ? You'll want to get a qualified PE's opinion on this as this is very much an engineering problem.

Andorrax
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