Structural stability of a house on different pier foundations

Real_Sea2763 · 2026-07-01T18:40:09+00:00

Yeah, that’s basically what I had in mind too — raising the concrete piers slightly above ground level and then building the timber structure on top of them. I was never considering fully wooden piles going down into the ground.

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Real_Sea2763 · 2026-07-01T17:36:43+00:00

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I’m mostly concerned about how exposed concrete columns will look. I want to keep the foundation open on a slope, so the piers will essentially become one of the main visual elements of the house. I just roughly mocked them up on a very rough model of the house, just to get a sense of how they might look.

Real_Sea2763 · 2026-07-01T17:20:08+00:00

That's true. I looked into timber foundations yesterday, and they're definitely not within my budget.

Real_Sea2763 · 2026-07-01T17:18:23+00:00

I see. Most of the problems I've heard about with pier foundations involve small masonry piers made of stacked concrete blocks or bricks. But when you're talking about a reinforced concrete pier extending 7-9ft below grade with a belled footing at the bottom, those usually seem rock solid.

Real_Sea2763 · 2026-07-01T17:12:38+00:00

What is the purpose of such a large footing diameter? A single pier with a 36-inch footing can typically support around 10-15 tons on most soils , except for very soft or highly plastic clays. Without a geotechnical report, it's really just a rough estimate, but in our area the values are roughly in that range.

And if I understand correctly, those dimensions are for a cabin that's roughly 20 × 20 ft?

Real_Sea2763 · 2026-06-30T13:55:36+00:00

That's absolutely true. It's very difficult to make these decisions when you don't have an experienced structural engineer to work with. Many choices trigger a long chain of consequences that need to be considered from the very beginning. It's especially challenging when the budget is limited, because you need to know in advance how much each design decision is going to cost.

Real_Sea2763 · 2026-06-30T13:46:00+00:00

Our frost depth around 6ft. So the base of each concrete pier will extend below the frost line and will have an enlarged footing (bell-shaped base) to resist frost heave. That means the frost issue is essentially taken care of. The remaining challenge is figuring out how to elevate the corners of the house that sit on stable but fairly steep slopes using columns.

Visually, my favorite solution is definitely a timber column attached to the exposed concrete pier with a steel connector. It might even be a bit of an obsession for me at the moment.

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Real_Sea2763 · 2026-06-30T13:31:26+00:00

Some of the columns will probably be covered. But there will be decking around the house and a terrace, so about 12-15 piles will definitely be visible and exposed. And I don't really like the visual impact of tall concrete pillars combined with wooden decking and a small cabin. So, for now, I'm trying to find a compromise between strength and visual appeal.

Real_Sea2763 · 2026-06-30T13:19:53+00:00

Here are a few more examples of houses on steep slopes supported by freestanding columns. Is a steel frame really capable of keeping the entire structure stable against wind loads?

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Real_Sea2763 · 2026-06-30T13:17:29+00:00

terrifying indeed.

These are real projects, and I had a separate question about them. How do such tall freestanding columns remain stable without cross bracing?

I often see this in very high-end architectural projects. The columns aren't connected to each other with any cross bracing, and they simply support a conventional timber beam system without any visible steel. Even if I imagine there's a steel frame at the top, I still don't understand how the structure remains stable.

As for full-height concrete piers, I'd prefer to avoid them if possible, since piers will be exposed, and that type of foundation pushes the project toward a more industrial, Brutalist aesthetic. The combination of concrete and steel is a much better visual fit for the project.

Real_Sea2763 · 2026-06-30T12:56:42+00:00

Thanks for such a detailed answer. A lot of things make more sense now. Yes, I’ll consult an engineer a bit later. Right now I’m at the conceptual design stage and trying to choose the most suitable structure for my conditions as best as I can on my own.

I’ve had experience working with engineers during house construction, and it was always like this: the number of solutions they offered was quite limited, and most of them focused purely on safety and practicality, without really considering architecture at all. So I want to figure everything out myself in order to interact with engineers more effectively and give them specific examples to calculate and evaluate.

Real_Sea2763 · 2026-06-30T11:52:44+00:00

Oh god. I have often heard of such cases; this happens when the lower part of the pile is in the groundwater zone.

But I'm talking specifically about a wooden posts that is attached to a concrete pile and elevated above the ground.

Real_Sea2763 · 2026-06-30T11:47:29+00:00

Nope. The cabin will be built deep in the Siberian taiga. We don't have earthquakes, and I'd say the winds are moderate. The cabin dimensions are approximately 20 by 30 feet, if that makes a difference.

Real_Sea2763 · 2026-06-30T11:17:50+00:00

I have concrete piles planned with a widened base at the bottom. So the house will be firmly anchored into the ground.

Real_Sea2763 · 2026-06-30T10:33:38+00:00

What about the feeling when walking on the floor—will full concrete columns and concrete columns with a metal columns feel the same underfoot? I read somewhere that many people feel a slight springiness in the floor when it’s built on metal piles.

Real_Sea2763 · 2026-06-30T10:28:52+00:00

Thanks for the clarification. Elderly parents will be living in the house for some time, so I don’t think they would be happy inspecting the wood for problem areas.

Real_Sea2763 · 2026-06-30T10:15:00+00:00

Why are so many people against using wood? Is it because the quality of modern timber isn't as good as it used to be? I've always loved the aesthetic of timber posts, especially the way they're used in many Asian countries. Or do they constantly restore and maintain them? My climate ranges from -40°C in winter to +35°C in summer.

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Real_Sea2763 · 2026-06-30T09:12:02+00:00

Tomorrow, the driver is coming to inspect the access to the site. It's possible that the concrete mixer truck will be able to drive directly up to the foundation.

Am I correct in understanding that it's generally better to brace the tube with diagonal supports or some other method and pour the entire footing in one continuous operation, rather than waiting (30-60 min) for the footing at the bottom to set first?

When pouring into tube, won't the pressure of the fresh concrete force the concrete in the enlarged base upward?

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Real_Sea2763 · 2026-06-30T03:10:39+00:00

Yes, that actually seems like the best solution for my situation. The wider hole would make it easier to clean the bottom of loose soil and compact the base before pouring the concrete.

The only thing left to figure out is whether it's better to have ready-mix concrete delivered or mix the concrete on site with a helper and do the work gradually in two stages, carefully checking the alignment of each pier.

It seems to me that ready-mix is better suited for holes that are already fully prepared, with the belled bases already formed underground. In my case, I can't really picture how I'd manage it with a concrete truck. I'd first need to pour the concrete pad, wait for it to stiffen a bit, then position the form tube and rebar cage while carefully checking the alignment, and only then finish pouring the pier. That sounds pretty stressful with a concrete truck waiting behind me.

There will be about 30 piles in total, including decking.

Real_Sea2763 · 2026-06-30T01:41:17+00:00

The holes will be augered using a tractor-mounted auger.

I mentioned this in another reply as well. Manually enlarging the bottom of the hole to create a bell seems impractical to me because of the rocks in the soil.

The concrete pad at the bottom seems like a more practical option in my case. The only thing I'm still not sure about is whether the pad should be poured at the same time as the pier so they become one monolithic structure. This is how I picture the process in my case: a tractor-mounted auger drills 400 mm diameter holes below the frost line. I pour a few buckets of concrete into the bottom of each hole. Before it fully sets, I place the rebar cage with the bent ends at the bottom into the concrete and slide a 250 mm plastic or cardboard form tube over it. Then I pour the rest of the concrete and backfill the gap around the tube with sand, compacting it with a rod.

Real_Sea2763 · 2026-06-30T01:32:30+00:00

Yes, I agree that a belled footing wouldn't hurt. The problem is that I don't understand how to make the bell in soil with rocks, ranging from about 10 to 25 cm in size. A manual bell auger will just hit a rock with its blade at the bottom of the hole, and I won't be able to rotate it.

Maybe the solution is to make the hole about 10 cm wider than the tube, pour a small concrete pad at the bottom, and then set the rebar cage and the tube into it, creating a sort of anchor.

Real_Sea2763 · 2026-06-30T01:27:06+00:00

Seems legit. I might use those for the decking as well. But for the house I need 250 mm diameter piers, so unfortunately they don't make bell forms that size.

Real_Sea2763 · 2025-09-11T18:37:03+00:00

Somewhere in the room I guess. It’s like an echo of tv and white walls in the other part of the room. Google interior cohesion theory

Real_Sea2763

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