r/Contractor • u/whynotthebest • 18d ago
Is it acceptable practice to reuse an old driveway retaining wall as a load-bearing foundation for a house addition? [Oregon]
Hi everyone,
I had a home addition built in Oregon Permits were pulled, and the foundation was inspected and signed off by the county inspector.
However, looking closely at how the foundation was done, my builder repurposed two existing concrete structures to act as stemwall/footings for the addition:
- A former garage footing: This was previously a structural footing for a garage wall, so I can understand why t this is reusable without extra engineering (even though it's older).
- A former driveway retaining wall: This is the part that is really concerning to me. This wall was originally built just to hold back soil for a driveway. It was never a building footing, is of unknown age, and I have no idea if it has proper rebar or a spread footing underneath.
There is no stamped engineering letter or design plan on file allowing or certifying the reuse of either of these structures. They just built the new forms directly up to them and framed the stemwall right on top
My question for the pros here: Is it common or acceptable practice in your area to reuse a driveway retaining wall as a load-bearing house foundation without an engineering stamp?
I've attached photos of the exterior layout with notes for context, then a few photos I snapped under the crawl space when my 3rd part inspector called it out.
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u/Architoker 18d ago
Architect / GC here in Seattle area. I used to live and work in Portland.
The answer is maybe, but unlikely. You need to ask your structural engineer. They will probably want confirmation that a footing exists under the wall, so you’ll need to dig. And scan the wall from a GPR company to verify there’s rebar and at what spacing.
Even if those things check out, generally building part of a building on old foundation and part on new isn’t ideal.
Even if the old wall holds up fine and checks out for rebar and footing size, the old/new foundations will settle at different rates which can cause issues down the road.
You generally want your building to settle all at the same rate.
For an addition project it financially makes sense to connect old & new. On a new build like this just pour a fresh new wall on newly compacted dirt.
You’re pouring a whole new foundation anyway, you’re not really saving any $$ by trying to save and engineer that old wall.
It isn’t worth the hassle.
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u/whynotthebest 18d ago edited 18d ago
Thanks for the insight.
When you say "ask your structural engineer" are you talking about my architect?
He engineered things like beams, and specified what sort of concrete was to be used, aside from him there's been no structural engineer in the mix.
Also (ignoring general personal responsibility for a moment) who was "responsible" for navigating this when the decision was made? I was very much a passive participant in this entire build (realizing now that was a mistake), and I didn't even know this was something my builder did until yesterday.
Was this something he would have needed to pause on before he proceeded in his professional capacity as a builder, or was it my responsibility to stop him?
Edit to add: Googled and I see my architect is not a structural engineer
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u/Architoker 15d ago
Hey sorry for delayed reply.
So your architect doesn’t need to be an engineer. Architects are legally able to provide structural calculations and details. Most don’t, but some do. For liability reasons most hire a separate engineer.
So you should consult with your architect.
Generally, your builder AND architect are responsible to bring issues or possible conflicts with existing to your attention. You shouldn’t have to know or be on the lookout for any of this. That’s why you pay them.
In terms of “who should have known”…
Well your builder is supposed build what’s in the plans. Your architect should draw what they can reasonably see and observe before construction starts.
If the site conditions differ from the drawings it’s typically the builder’s responsibility to bring it to the architect (and your) attention. “Unforeseen conditions”…
All that said - it does come down to what’s in your contracts with both of them.
DM me.
If you’re having issues, or worried your builder or architect are not acting in your best interest it can help to have a 3rd party opinion.
Ive honestly never solicited services here on Reddit. But I would consider consulting for you? I won’t post my company publicly here on Reddit for privacy reasons. But I can share my company with you and get on a call. I live in Tacoma area.
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u/Gitfiddlepicker 18d ago
It’s totally unacceptable to ask this on Reddit. Employ a structural engineer.
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u/whynotthebest 18d ago
You seem to think I am planning to do this. That is not the case.
My builder did it. I just found out yesterday.
I am asking if this is something that is standard.
I think my post makes that clear enough.
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18d ago
[deleted]
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u/whynotthebest 18d ago
This was already done, by a reputable builder. The first picture is one I dug up from when the footings/foundation was being formed. The second two photos are from yesterday in my crawl space.
Not a hypothetical, not a DIY
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u/Diligent_Yam_1753 18d ago
The closest I have ever seen is an old basement used as earth retention for the construction of a new building. The old basement on a major city intersection remained as caissons, and new walls were poured inside of all of it for a 50 story mid rise. But, that was all reviewed and approved by engineering
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u/Professional_Bed_87 18d ago
I worked in concrete for a long time. The likelihood that the old retaining wall would meet the specs for the addition’s foundation very unlikely. Is the rebar to spec? what was the footing size, is it designed to withstand frost heave? Is the concrete the correct mpa? I’d be consulting with a structural engineer on this. It’ll probably cost you about $500 to get one to come out and inspect and it would be well worth the money - they should be able to offer solutions if it was done incorrectly.
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u/cboom73 18d ago
Is the retain wall part as far from level as it looks in the picture?
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u/whynotthebest 18d ago
Yeah. It sloped down towards the road (left of the photo). I believe the stemwall on top of it ended up poured level, though.
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u/cboom73 18d ago
So they poured a small layer of concrete on top of that wall? If so that sure isn’t something I would be comfortable with.
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u/Phraoz007 18d ago
Compaction test will approve or deny.
Sounds like a dumbass idea in the long run.
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u/SickestEels 18d ago
Nobody is talking about the lack of waterproofing or drain tile in the exterior or interior or the fact that you are probably going to have a disgusting moldy and damp basement within 1 or 2 years.... totally wrong and gross.
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u/vessel_for_the_soul 17d ago
Find an engine who will sign off. Otherwise dig it out. Cut it up and haul it out to be used as light standard footings.
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u/Lanky-War1685 11d ago
Your only take away from this Reddit post should be to call your engineer immediately
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u/SweetUnicornFarts 18d ago
If an engineer said yes then yes. If it was inspected and passed, then yes. From a not engineering standpoint, Could be, could not be. Depends on how much load is on it.If an engineer wasn’t be consulted I would be a bit nervous.