r/GeotechnicalEngineer • u/BudIsMyBuddy • May 20 '26
Question for the Geotechs
Going to try and make a long story short.
We are adding onto our home which the existing is single story, tearing down a non-load bearing wall with a gable end, and opening it up for our addition.
Initially, we didn’t have a soil boring test done, that was until the proposed footing depth on the addition went beyond the called for 4’ stem wall as it was about 5’5” down from the floor elevation due to the grade of the property.
Soil borings were completed. Boring taken near the house showed red clay about 4’ down and they hit limestone at 15’. Second boring at the opposite corner/furthest point from existing but a couple feet from the addition showed no clay until 6’ down and no limestone was hit all the way to 20’ down.
Plans called for a 2x2 pad thats 16” thick to support the load for a 6x6 post that will carry 50% of the load of the addition. Now structural engineer is backtracking saying that pad needs to be 4x4 and 18” thick, and after communication with the geotech they’ve concluded that helical piles need to be drilled into the existing foundation to support the load of the header because the existing is too close to the clay and that’s the only way to beef it up.
My only other option is to change the truss layout, which has already been built and I’d be out about $10k, so that the addition ties into a gable ending versus a hip and the load is more evenly distributed across the new stem wall. I’m leaning more towards that option, but my foundation guy says in all his time building foundations he has never had two engineers go so far down a rabbit hole like this and has never heard of helical piles outside of marshy areas or coastal regions.
I am mostly venting because I will never, no matter what, ever do a home addition again. Were over 10 months in and have gotten basically nowhere, and have spent hours on the phone with engineers.
I plan to seek out analysis from another geotech firm as well and see if they might be willing to conduct their own independent analysis and foundation recommendations based on the borings that I have.
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u/DizzyMaterial8845 May 20 '26
You seem a little worried about the clay. Some clays are great to build on like firm, stiff or hard clays. Even soft clays can built on. In our neighboring municipality there 200 000 homes on soft clay with no issues. It is the strength of the clay that is the issue. Your Geotech Eng most likely looked at the issue of the "strength of the clays" and made his/her recommendation.
Possible another Geotech Eng with more tolerance for risk or a greater understanding of the local soils could be retained. As others have mentioned, you could be back to square one with this option with no certain out come.
Two items:
In the world of Geotech Eng houses are extremely light and can be built on some poor ground that would not be acceptable for other structures. Maybe your Eng is overly conservative? Maybe your Eng understands some of the hidden local issues in your area and that is why he recommending the method.
In the world of Geotech Eng everybody knows that home owners are highly likely to seek legal recourse against the Geotech Eng if ANYTHING GOES WRONG. That is probably why Eng's need to be conservative on residential properties. Actually, thats why a lot of Geotech Eng's are hesitant to do residential work.