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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

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  • $\begingroup$ sun-sentinel.com/news/weather/hurricane/… Your piles might survive, but what about the rest of the house $\endgroup$
    – Tony Stewart EE75
    Commented Aug 8, 2022 at 16:45
  • $\begingroup$ Then nothing could stop it. They are hurricane codes here, but Mother Nature is stronger than anything we can build. My current house is up on wooden pile and survived Super Storm Sandy. We had 4 feet of flooding in inundation and the house was fine. All the water went right under it. $\endgroup$
    – Frank Pileiro
    Commented Aug 12, 2022 at 21:06

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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.

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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.
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  • $\begingroup$ Kamran, thank you for the answer and explanation. I can see the advantages of a grade beam for pile failure. What I’m dealing with is a difference of opinion between the builder and architect in terms of the strength of the pile foundation when it comes to lateral forces such as wind and flooding. The architect said the house will move less when wind hits it. We are a barrier island and sometimes get flooding. Is there much of a difference between the grade beam and pile in terms of that? Is there a concern with soil erosion with a grade beam flooding? Cost vs. Benefit $\endgroup$
    – Frank Pileiro
    Commented Aug 8, 2022 at 11:46
  • $\begingroup$ The same pile if restrained with a grad beam will be a lot stronger than the one without. I have designed a few homes on the beach. All were subject to wind and also crashing surf erosion. After checking the weather pattern and the neighborhood foundations' performance, we concluded soldier piles tied with grade beams were the optimal alternative. And after 24 years we are satisfied with the choice. $\endgroup$
    – kamran
    Commented Aug 9, 2022 at 2:25
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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.

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  • $\begingroup$ Andorrax thank you for the info. The architect is also an engineer. I live in a house on piling and it’s pretty solid and Super Storm Sandy did not effect it. So, I’m really torn if the grade beam is with the extra cost. $\endgroup$
    – Frank Pileiro
    Commented Aug 9, 2022 at 12:52
  • $\begingroup$ I see. Are they a licensed PE for structures though ? I ask because if the code actually requires the grade beam, then doing away with it will make your house non-compliant. In my neck of the woods, one can get away with non-compliance on very specific items by submitting documents noting justifications to the building authorities. These documents usually include detailed calculations and require a licensed PE to take on the risks associated with non-compliance of said code (i.e, on their insurance). If your architect is not a PE/ are not willing to certify the design, then the risk is on you $\endgroup$
    – Andorrax
    Commented Aug 10, 2022 at 0:01
  • $\begingroup$ Also, how much of an extra cost is the grade beam ? Perhaps there are some design optimisations that could reduce the size of the beam (and therefore the cost) ? $\endgroup$
    – Andorrax
    Commented Aug 10, 2022 at 0:03
  • $\begingroup$ Lastly, it may be worth posting your query to this forum as well: eng-tips.com/threadminder.cfm?pid=507 It's a forum exclusively for structural engineers. You'll be able to get more detailed responses from engineers close to your region too. Do put up as many images/drawings as you can when making your post though - they always help $\endgroup$
    – Andorrax
    Commented Aug 10, 2022 at 0:05
  • $\begingroup$ Thank you! I will check it out. I appreciate all the feedback $\endgroup$
    – Frank Pileiro
    Commented Aug 12, 2022 at 21:00

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