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ketchgould
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# Posted: 8 Jun 2022 11:58am
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I am going to start my foundation in Sawyer County (AFI 3000) this August.
From what I have researched and priced, the frost protected shallow foundation (fpsf) for an unheated space seems the simplest and also the least expensive foundation.
Every contractor, plumber, neighbor, soil test septic guy has said just do an ICF frost footing. This would be three concrete pours as opposed to one.
What do you all think are the pros and cons of icf frost wall compared to a monolithic, thickened frost slab?
Do the contractors prefer the icfs because they are not familiar with the fpsf?
Any thoughts would be great, thanks.
Christian
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jhp
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# Posted: 8 Jun 2022 12:09pm
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Since you asked for thoughts:
What reason would you have to doubt those contractors who have seen what works and what doesn't work in your area?
If I was building something big enough to necessitate a "real" foundation I wouldn't heavily weight low cost against building something that will not cause problems down the road.
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gcrank1
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# Posted: 8 Jun 2022 12:25pm
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Ive lived most of my 69 in sc WI. So many older poured slab buildings Ive been in have cracked somewhere. Those with perimeter stub walls on footings also often have cracked walls where settling/subsidence has taken a toll.
Granted, these were older buildings, maybe not done the best.....but there are countless houses with foundation/basement 'issues', places built to code. We have a company that specializes in such repairs advertising regularly in our area.
So, that said, if your build needs a foundation that is the wrong place to save a buck.
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MJH
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# Posted: 8 Jun 2022 04:55pm
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Quoting: ketchgould From what I have researched and priced, the frost protected shallow foundation (fpsf) for an unheated space seems the simplest and also the least expensive foundation.
I went through this last summer. I had the concrete guy over to talk about piers. He suggested an insulated slab. I had him put four courses of blocks on top to give me a "crawlspace."
I can't speak to the ICF frost wall, but the area we're in has literally everything and the majority of it has been done by the same guy.
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Nate R
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# Posted: 9 Jun 2022 08:35am
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"Do the contractors prefer the icfs because they are not familiar with the fpsf?"
I bet that's some of it.
Monolithic slab....I think it depends on your soil type and how susceptible to frost heave and/or expansion (like clay) it is. Where my place is in NE WI, I did the slab, but I'm on sand/sandy gravel. No real risk of frost heave, soil drains well/quickly. I've got a relative with a cabin on an uninsulated slab that was poured 15 years ago now...no cracking, etc.
In theory the slab should be fine everywhere as you should be putting gravel under it, right? I just feel like at least with garages, etc....that part is often skipped.
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gcrank1
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# Posted: 9 Jun 2022 10:32am
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Then there are those pesky groundhogs..... 
They tunneled under my home sgl car garage, I believe it is rather extensive.
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Nate R
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# Posted: 9 Jun 2022 12:15pm
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I've seen that on smaller slabs...I'd be impressed to see that on a 1' thick slab edge w/ insulation around it, too...
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NorthRick
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# Posted: 9 Jun 2022 05:37pm - Edited by: NorthRick
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I have to ask the question since this is the Small Cabin forum - is the structure going to be heated all the time in the winter? If yes, go with the FPSF. If no, I'd go with what has been traditionally done in your area.
A FPSF relies on the heat from the house/cabin to prevent the soil beneath the structure's slab from freezing. The insulation installed during construction (around the perimeter) keeps the cold side and warm side separated. If this is going to go long periods of time unheated, the insulation doesn't matter as the ground beneath the slab will start to freeze from the building being below freezing. And, that's when you can expect problems.
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Nate R
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# Posted: 10 Jun 2022 07:59am
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FPSF can be set up for heated or unheated buildings. OP talks about doing FPSF for unheated... Non-frost-susceptible fill is called for under an unheated slab... So even if what you point out happens, there shouldn't be any problems.
Again, I think the local soil type/conditions will dictate what makes the most sense here, but if one follows the conservative FPSF guidelines, I think you'll be fine.
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ketchgould
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# Posted: 12 Jun 2022 10:27am
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My spills are Sandy loam and seem like they would drain well. The alluring part of the slab is the reduced excavation and equipment needs.
I think the locals like what they were taught to do thirty years ago. Kind of like advanced framing or thermal breaks, why bother is what they might think
Ask an architect and they say one thing, ask a guy with a pickup and some tools in his truck you certainly get another idea.
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gedna002
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# Posted: 4 Jul 2022 10:29am - Edited by: gedna002
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@ketchgould
What size is your cabin and can I ask how much you were quoted for the work? I'm building about 30 minutes north of you. Just got a quote for a 20x28 with a 6' porch FPSF for $11k.
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ketchgould
Member
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# Posted: 4 Jul 2022 11:25am
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I’ve decided to use ICFS for 2-3 courses on top of a 10x20 footing. I’m doing the work with some friends!
The wing insulation and design/digging required for the FPSF when the slab is unheated made me decide on the ICFs.
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