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WILL1E
Member
# Posted: 22 Jan 2021 10:39 - Edited by: WILL1E
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I've been going back and forth with the building inspector for my area in WI regarding the piers for my elevated cabin floor. I told her it would be a 16' x 20 something foot long cabin with a loft. The only mention in the WI code is the following:

(b) Column or pier footing. 1. The minimum width and length
of column or pier footings shall measure at least 2 feet by 2 feet.
2. The minimum depth of column or pier footings shall measure at least 12 inches nominal.


I know our frost line is 4' in northern WI.

My question to the inspector was, can i go down to a smaller footprint pier, like a 12" sonotube and down to 4'. She said no unless load calcs were done.

So if i'm stuck with a 2'x2' pier footprint and i go down 1' below grade, am i going to need to be leveling the cabin all the time?

She also referenced a pad i suggested for a shed build as being acceptable for the cabin size i was proposing. I suspect this would be just as bad if i set those pads on grade.


Here is some additional details on soils from the WI code. I don't know if i'd consider mine loose or firm sand.

(3) SOIL−BEARING CAPACITY. No footing or foundation shall be
placed on soil with a bearing capacity of less than 2,000 pounds
per square foot unless the footing or foundation has been designed
through structural analysis. The soil−bearing values of common
soils may be determined through soil identification.
Note: The department will accept the soil−bearing values for the types of soil
listed in the following table:
Type of soil PSF
1. Wet, soft clay; very loose silt; silty clay . . . . . . . . . . . . . . . . . . . . . . 2,000
2. Loose, fine sand; medium clay; loose sandy clay soils . . . . . . . . . . 2,000
3. Stiff clay; firm inorganic silt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,000
4. Medium (firm) sand; loose sandy gravel; firm sandy clay soils;
hard dry clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4,000
5. Dense sand and gravel; very compact mixture of clay, sand and
gravel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6,000
6. Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12,000

Brettny
Member
# Posted: 22 Jan 2021 11:00
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What type of load calculations are needed would be something to ask. Going from 12in sono tube to 24in sono tube is a huge difference.

gcrank1
Member
# Posted: 22 Jan 2021 11:05
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Maybe it would be a good idea to have the BI make the determination of your soil type and have it a matter of record then go from there with planning?

WILL1E
Member
# Posted: 22 Jan 2021 12:34
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Quoting: Brettny
Going from 12in sono tube to 24in sono tube is a huge difference.
This is assuming round is even acceptable...given they gave a length and width dimension i just assumed it had to be a square pier as the surface area would be at it's greatest.

Brettny
Member
# Posted: 22 Jan 2021 12:45
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If it dosnt say it cant be round does that mean it has to be square?

Usualy building inspectors only inspect. They wont determine soil type. They may just tell you your foundation fails with 12in round tubes.

WILL1E
Member
# Posted: 22 Jan 2021 14:44
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Maybe our forums' IRC guru (member ICC) will stop by and bestow some IRC knowledge upon us that tells me how/what i should do for these piers

ICC
Member
# Posted: 22 Jan 2021 15:22
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Quoting: Brettny
What type of load calculations are needed would be something to ask.


From a building inspector that often means from an engineer

ICC
Member
# Posted: 22 Jan 2021 15:26
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Quoting: gcrank1
Maybe it would be a good idea to have the BI make the determination of your soil type and have it a matter of record then go from there with planning?


Inspectors inspect. Some are more helpful than others, but the job description and training is to inspect and compare to what code states.

Some inspectors are lax enforcers for assorted various reasons. Sometimes that is because the county or whomever they work for have decided to not enforce the rules as written.

ICC
Member
# Posted: 22 Jan 2021 15:30
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Quoting: Brettny
If it dosnt say it cant be round does that mean it has to be square?


The code often stipulates footing sizes in square sizes. However, the total square inches of the area is what counts so going round should be possible. That will necessitate an increase in diameter though. Do the math. For areas of a circle, there are apps that can make that easy.

ICC
Member
# Posted: 22 Jan 2021 15:40
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Quoting: WILL1E
.....what i should do for these piers


As previously mentioned someplace here, the IRC has no prescriptive solutions for pier foundations being used for a habitable building. The IRC has wording in many different sections that allow solutions that are not prescribed to be used, as long as an engineer signs off and stamps the plan.


I use the words prescribed or prescriptive. For example, with foundations that means if the perimeter footing and concrete wall method are used as described in the IRC then an engineer is not needed. Even those sizes of footings, concrete wall thickness, etc are dependant on the soil bearing strength and having the correct concrete mix. We have large areas where I am that have the same soil type so soil quality and load bearing is pretty much widely known. The building departments are also aware of some areas that have poor sandy soil; often a geotech is needed to test, or the builder assumes the worst, builds a wider footing and the permit department says good.

ICC
Member
# Posted: 22 Jan 2021 15:41
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Quoting: ICC
Quoting: WILL1E
.....what i should do for these piers



If the inspector states the footing size that must be used they probably mean what they say.

gcrank1
Member
# Posted: 22 Jan 2021 19:33 - Edited by: gcrank1
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Ok, so, if I got this right....
Your BI said what you had mentioned to use under a shed would be ok for your cabin 'of that size'; ie, 2x2' 1'deep below grade.
Why fight that? She's said she'd go with it.
Relatively cheap and easy to do compared to what else you have suggested. If you want to use more of them than the min, so much the better; she probably wouldnt object but you should ask.
Fwiw, my 12x24 c/w 12x12 loft built with 'substantial' lumber (heavy) and a lot of roof with that Swiss chalet style was on just silo blocks right on the ground (sand/gravel). I set it all up 'close' and after the deck was built I leveled it out with a simple laser level process (inexpensive laser level 3' long on a bracket on a tripod). I figured I could check it and shim it over time easy enough (done right you can get 3 corners from one setting of the tripod and do catch up on #4 with one re-set. In the 37ish years I only had to shim slightly 2 of the block 'piers'. I got the clue when the door started to drag a little on the threshold.
If you prep the ground after digging in 1' by good tamping yours might even do better than mine did.

ICC
Member
# Posted: 22 Jan 2021 20:18
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Quoting: WILL1E
(b) Column or pier footing. 1. The minimum width and length
of column or pier footings shall measure at least 2 feet by 2 feet.
2. The minimum depth of column or pier footings shall measure at least 12 inches nominal.



I don't understand that 12" minimum depth for the WI climate. That would be contradicted by the minimum depth required in the section that addresses frost depth, no?

In the IRC 12" deep is the absolute IRC minimum for any code approved footing anywhere the IRC is used, BUT that minimum will be deeper depending upon frost depth for the location. The 12" minimum depth applies to locations like the far southern latitudes where is is no listed frost depth.

gcrank1
Member
# Posted: 22 Jan 2021 22:01
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Oh my.....how does one tell a BI they dont know what they are doing?
Im thinking I would find what seems to be the appropriate section/reg and ask,"well, what about this here" rather than trying to convince by talking.

Brettny
Member
# Posted: 23 Jan 2021 05:49
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I would still start by asking what load calculations are needed. That could change the whole conversation here.

Nate R
Member
# Posted: 23 Jan 2021 10:00
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Quoting: ICC

Quoting: WILL1E
(b) Column or pier footing. 1. The minimum width and length
of column or pier footings shall measure at least 2 feet by 2 feet.
2. The minimum depth of column or pier footings shall measure at least 12 inches nominal.

I don't understand that 12" minimum depth for the WI climate. That would be contradicted by the minimum depth required in the section that addresses frost depth, no?


I think this is calling out the depth of the footing concrete itself, and not the depth in the ground. Navigating the code in WI can be fun, since we've written our own rules.

Willie, I know you want an elevated cabin. I think one option here that no one would bat an eye at would be using Bigfoot forms for the bottom, to spread out the soil load, and then 10-12" sonotubes on top. URL

No avoiding digging big holes for that, though.
Have you thought about how much concrete you'd be mixing on site? Seems like a lot of bags and water to haul, and then mix if you do any sort of piers to frost line.

Another thought is helical piles/piers. Not the cheapest, but someone else rolls in, and you have a foundation in a day, without digging.


We went through a lot of the same exercise for the foundation for our cabin. Looked at piers, looked at helical piles, thought about a crawlspace or even a basement. We settled on a thickened edge slab. No questioning from the inspector, they do fine in sandy soils, and no floor system to figure out, no pier calculations or lateral bracing. But I know concrete truck access for your site is more difficult.

If I were you, I'd look hard at helical piles and weigh those vs the time and labor to dig, haul, mix, pour, level, etc.

ICC
Member
# Posted: 23 Jan 2021 10:19
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Quoting: WILL1E
My question to the inspector was, can i go down to a smaller footprint pier, like a 12" sonotube and down to 4'. She said no unless load calcs were done.

So if i'm stuck with a 2'x2' pier footprint and i go down 1' below grade, am i going to need to be leveling the cabin all the time?


Thoughts.
We know the 48" is the frost depth for your area of Wisconsin as a fact. There is no changing that fact no matter what calculations are done.

If the BI is suggesting that your foundation plan would be approved if you used 24" x 24" footing placed at a 12" depth are you okay with what might happen? Sooner or later frost will cause a problem. We don't know when or how much movement. You might be lucky. You might not be. D you want to gamble?

The BI may be "throwing you a bone". Approval of the 12 " depth of footing will make construction easier but the approval does not guarantee you will have no problems.

Re: size of the footing. 24 x 24 = 576 sq inches. The area of a 12" diameter circle is 113 sq in. Divide 576 by 113 = 5.09. It would take Five - 12" diameter sonotubes to equal the support area of a single 24 x 24 inch footer.

ICC
Member
# Posted: 23 Jan 2021 10:37
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Quoting: Nate R
I think this is calling out the depth of the footing concrete itself, and not the depth in the ground.



The wording should have the thickness of the concrete pad specified and be referenced as so many inches thick, not deep (depth).. In common construction terms depth means distance from the nominal ground surface level to the bottom of the footing. Thickness is usually given as 8" minimum.

link of interest

Brettny
Member
# Posted: 23 Jan 2021 12:30
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I know I have said this before but if you start off with a bad foundation it dosnt matter how nice your cabin is. A foundation is nothing to skimp out on and possibly the hardest thing to fix later.

ICC
Member
# Posted: 23 Jan 2021 13:18 - Edited by: ICC
Reply 


Quoting: Brettny
I know I have said this before but if you start off with a bad foundation it dosnt matter how nice your cabin is. A foundation is nothing to skimp out on and possibly the hardest thing to fix later.



My thoughts exactly.

However, that has not stopped countless numbers of people to build their cabins on poor foundations. I see and hear the "it's only a cabin" refrain too often. There are a few members here who have built on full perimeter concrete or concrete block, proper frost depth foundations, but they do seem to be a minority.

another thought... Inspectors do have the authority to relax the inspection or enforcement of rules. That is not necessarily a good thing.

They can also misinterpret how one rule affects another and make poor judgment calls. They are people after all.

Nate R
Member
# Posted: 23 Jan 2021 14:34 - Edited by: Nate R
Reply 


Quoting: ICC
The wording should have the thickness of the concrete pad specified and be referenced as so many inches thick, not deep (depth).. In common construction terms depth means distance from the nominal ground surface level to the bottom of the footing. Thickness is usually given as 8" minimum.


I agree on what the wording SHOULD be.

(b)Column or pier footing.
1. The minimum width and length of column or pier footings shall measure at least 2 feet by 2 feet.
2. The minimum depth of column or pier footings shall measure at least 12 inches nominal.


I think this is referencing the footing itself. Farther down, (in the current code from 2020...URL ) they specify that the footing must be 48" below grade...
Again, this isn't written the best, but to me, it means 12" thick concrete, at least 2x2 if it's for a pier or column.

SPS 321.16 Frost protection.
(1) GENERAL.
(a) Footings and foundations, including those for landings and stoops, shall be placed below the frost penetration level or at least
48 inches below adjacent grade, whichever is deeper, except as allowed under sub. (2)


Sub 2 gets into frost protected foundation stuff.

Also, this stuff DOES matter, as others mentioned.
Check out this place for sale not too far away from where Willie's building: https://listings.northwoodsrealtors.org/listing/Price-WI/N7128-Dover-Rd-E/y5k4?u=1953 3

Serious rot in some of the joists and a...tilty pier.


Brettny
Member
# Posted: 23 Jan 2021 15:17 - Edited by: Brettny
Reply 


Wow that's a good one Nate. Sadly that cabin is prob a total teardown. You can see how crooked the siding even is on the front. Around here that cabin would "add" about 40k to the sale price...this is why I didnt want anything on the property we bought. Not even a driveway.

I should note too that a house on my home property once was "just a barn" we had to do major work to that too. It was built prior to 1930.

There was a member on here who had a failing cabin foundation and was asking questions on how to fix it. Last I knew they went back and the place was on the ground.

WILL1E
Member
# Posted: 25 Jan 2021 11:02
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Thanks everyone for your responses!

Quoting: Nate R
Have you thought about how much concrete you'd be mixing on site?
Yup...hence my question! A 24x24x48" column/footing would require (36) 60lb bags of concrete.

My measurements are going to have to be spot on for these 2'x2' columns. If it's a 3 layer built up beam, i'll have 9.75" of concrete on either side of the beam. And since the beam cannot be inset more than the depth of the joist, i'll have to use a minimum of a 2x10 joist. This will give me 1/4" between the outside face of the rim joist and edge of the concrete column.

Quoting: Nate R
Bigfoot forms for the bottom
Is that an offer to come dig holes?!

@Nate R....that place is a real gem. We should copy some of their foundation pictures and save them somewhere on this site of what not to do!!

If i use the forms Nate mentioned, each one would require (6) 60lb bags. I would then need a minimum 29" long 10" sonotube to reach the frost line which would be another 3 bags of concrete. So call it 10 bags of concrete to hit the frost line and stick out of the ground a bit. So i'm looking at $100 per column for materials.

Quoting: ICC
If the BI is suggesting that your foundation plan would be approved if you used 24" x 24" footing placed at a 12" depth are you okay with what might happen? Sooner or later frost will cause a problem. We don't know when or how much movement. You might be lucky. You might not be. D you want to gamble?
I'm guessing this is why alot of people just go and buy those roadside shabins and have them dropped off at their site on top of some precast pads.

Nate R
Member
# Posted: 25 Jan 2021 11:35
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Quoting: WILL1E
Is that an offer to come dig holes?!


Nope, I'll be way too busy with my own cabin build!

Still, 10 bags, and $100/hole is better than 36!

Wonder if it'd be worth it to rent a skid steer and auger attachment to get the main holes started/going, then widen with a shovel?

WILL1E
Member
# Posted: 25 Jan 2021 12:25
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Haha...i know

I'm thinking i'll just my hand power auger i bought 1-2 years ago when i built our wood fence at home. Auger 4 corners and then dig out the middle. Or for that size i might be able to do 5 holes in a X pattern and dig out the centers.

Peewee86
Member
# Posted: 25 Jan 2021 13:27
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A number of years ago I added a sunroom on the back of my home. The building inspector required a frost depth (42” in my case) 30 inch diameter footing on the two corners but then they allowed a 16 inch sonotube pier above the footing up to ground level. We rented a powered post hole digger for the 16” holes and then by hand created a bell at the bottom of the footing that measured 30 inches in diameter. This was in clay soil so I didn’t have too much trouble with the soil above collapsing. The inspector said code did not require rebar in the footings but that they highly recommended it. We dropped three 36” pieces of rebar into each footing as the concrete was setting. No movement at all in the seven years since we completed that project.

If this method is acceptable to the building inspector it would significantly reduce the amount of concrete used. I Purchased a 3.5 yard cement mixer from Harbor freight for under $200. I have kept mine but I’m sure a person could get turn around and sell it on craigslist for $.50-$.60 on the dollar once your project is completed.

WILL1E
Member
# Posted: 25 Jan 2021 14:07
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With the sand i have, i don't know that creating a bell bottom would be an option. I think i would just have to dig the full diameter hole and then use one of the forms like Nate R linked.

WILL1E
Member
# Posted: 26 Jan 2021 09:07
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Not saying this is the right way, but let's explore this option further. The building inspector says a precast concrete pad that's 14" x 4" and sitting on the surface would be acceptable. Then set 6x6" PT post on that which would then have the 3 layer built up on beams running across those with each pad and post properly spaced.

What things could be done to make this a viable solution?

gcrank1
Member
# Posted: 26 Jan 2021 10:57
Reply 


That is pretty much what my build sat on 37 yrs ago.
Worked fine. It lived thru some pretty big blows that took down tall jack pines around it (and sadly 3 on it! They kinda just layed over on the roof, minimal damage) in what they called a 'wind shear event'. Could never see that the structure had shifted.
If it had been a tornado I doubt bolted to poured piers 40+ inches below grade would have held it there.
Will the inspector let you put down silo blocks, precast concrete 10x30x2" thick as the pads? Easy enough to stack 2 for the 4" thick if that is important but the ground pressure loading of 10x30 (300 s.i.) would beat 14" square (196 s.i.) by a long shot.

WILL1E
Member
# Posted: 26 Jan 2021 12:00
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Quoting: gcrank1
That is pretty much what my build sat on 37 yrs ago
Where was that located? Any pictures of it?

Quoting: gcrank1
Will the inspector let you put down silo blocks, precast concrete 10x30x2" thick as the pads?
I don't think she would care. If you look at this link for Menards, they have tons of precast options. It would just be a matter of what i'm able to move around myself.

But you can see my delima...tells me one second i have to follow code and do 2'x2'x12" deep columns but then in the next breath says those precast pads are acceptable as well.

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