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Steve_S
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# Posted: 29 Dec 2025 08:29am - Edited by: Steve_S
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An Observation with a bit of surprise.
The Elephant in the Room no one wants to talk about.
Any foundation, be it piers, concrete or rubble or even just a "simple slab" and others ALL depend on the Soil type "Under your feet" not a 1/2 mile or more away. It also depends if you can reach Stable Bedrock or not and last but not least, what the site drainage & flows are like with regards to the soil and if it will be affected by heavy saturation.
Simple things that get missed (because some won't consider it, for whatever reason) is WHY are piers Round and not Square and what effect that can have on piers... Just a bit of structural engineering stuff, feel free to ignore that.
While I haven't "read all responses" even piers need footings, most especially if you are not reaching stable bedrock. Footings like "Big Foots" or concrete base pads. See image attached. REF: https://www.bigfootsystems.com/index.htm
Forget building on top of "Sandy Loam" because it is injherently unstable but if you excavate and solidify the base several feet deep you can.
SIMPLY PUT: You will have to dig yourself a hole at least 8-10' deep to really know what's under your feet and then plan accordingly. Sometimes the best option is a Floating Foundation (different type of slab) because it can work very well on softer / more permiable soils.
RE: A floating foundation is a type of foundation that consists of a rigid structure, often made of reinforced concrete, which is set at a depth where the weight of the soil removed equals the weight of the building. This design allows the building to "float" on the soil, similar to how a boat floats on water, making it suitable for areas with soft soil or seismic activity.
Build it ONCE and do it right the 1st time... Just some things to consider.
Big Foot form with Tube
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Floating Slab Foundation
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DRP
Member
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# Posted: 29 Dec 2025 11:57am
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A couple I built for in NC was originally from MN. They inherited some family land and were talked into a Frost Protected Shallow Foundation for a vacation cabin. They then had to rebuild the foundation after it heaved. Here's the reason:
R403.3 Frost-protected shallow foundations.
For buildings where the monthly mean temperature of the building is maintained at not less than 64°F (18°C), footings are not required to extend below the frost line where protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).
The prescriptive soil bearing table is at R401.4.1
We typically use 2,000 psf for good soil and a geotech when someone wants to build where one should not build. Keep in mind that point loaded piers generally have higher loads than uniformly supporting strip footings. Pier loads also vary considerably in relation to one another.
Without design the bottom of the turned down edge is the portion of a monolithic pour used for bearing calculations.
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gcrank1
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# Posted: 29 Dec 2025 12:07pm
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Excellence is often the victim of (perceived) good enough.
The quality of the actual build begins with the foundation.
All the time, work, money and love that builds upon a poor foundation may be a waste.
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Steve_S
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# Posted: 29 Dec 2025 04:13pm
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FYI: The Floating Slab image & talk was NOT for a Frost Protected Slab Foundation liek I have, they are similar in basic design but an FPSF Foundation is also sitting on top of a minimum if 2" think High Density sheet foam (I used 4" for R20). Insulation also runs up along side to teh surface level and has a minimum of 24" "wings" out from teh foundation to prevent frost creep from going underneath. Remember I am a hell of a LOT further North than most of you up here near the Algonquin Park, North Eastern Ontario where -30C is just a typical winter day when it's not snowing... Although, it is seriously messed up this year, bouncing (flip flopping fast) from deep Negatives to low Positive temps...
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