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Thread: New workshop, foundation considerations

  1. #1

    Question New workshop, foundation considerations

    I'm looking at starting a workshop for myself; probably 32' x 40' x 12'. (though technically, it's going to be a "Sugar Shack" with a boiling room and considered an Ag building because then I can skip the building permits)

    My issue is that the area I'm looking to build on is wet, with silty sand under the topsoil (it's along a creek). It's not officially in a flood zone, because the area has never been mapped by FEMA, but if it ever is mapped, I'm going to assume based upon the last really major flood I saw that it's about 2' under the 100-year flood line. What I'm going back and forth on now is what kind of foundation to use. My options as I see them are:


    1. Continuous concrete footer with a 2'-3' stem wall (basically creating a crawl space) and a wood platform floor.
    2. Continuous concrete footer with a bunch of fill to put in a concrete slab floor.
    3. Techno Metal Posts (helical piles) for a post and beam foundation with a wood platform floor.


    I've determined that even if I add fill to get high enough, a monoslab foundation isn't ideal for the size building I'm looking at on this kind of soil. Everything I've read seems to indicate that I'd be begging for shifting and cracks over time. But if you have enough experience to tell me I'm probably overthinking it, a monoslab would probably be the cheapest route for me since I could pour the slab around a pile of fill then backfill to get the footers deep enough to not freeze.

    My goal here is to build as much of this as I can myself, though I've accepted that for the foundation at least, that will probably only extend to site work. At this point, I'm strongly leaning towards the pile and beam foundation because issues like drainage basically go away except for access concerns. Plus, with a totally elevated building, I don't have to deal with keeping pests out of a crawl space. Though obviously, an elevated structure has fairly important requirements with regard to air sealing and insulating the floor.

    Anyone want to dump additional considerations on me here that might shift things one way or the other?
    Do you have experience with Techno Metal Posts that might be relevant?

    Any other suggestions for methods I just appear to be ignoring completely?

  2. #2
    Another option would be concrete pier and grade beam construction, but I think the helical piers would be the way to go. I've no first hand experience with them, but they go in fast and you are guaranteed to get the amount of bearing needed for the structure because the pier installer monitors the force required to turn the pier. They weld beam brackets on the piers all nice and lined up and level and you could take it from there.
    --Certainty is the refuge of a small mind--

  3. #3
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    This will be an interesting project. Your intention is to get the floor level above the 100 year flood level, right?

  4. #4
    Quote Originally Posted by Paul F Franklin View Post
    Another option would be concrete pier and grade beam construction, but I think the helical piers would be the way to go. I've no first hand experience with them, but they go in fast and you are guaranteed to get the amount of bearing needed for the structure because the pier installer monitors the force required to turn the pier. They weld beam brackets on the piers all nice and lined up and level and you could take it from there.
    I was originally considering concrete piers, but everything I've read makes it clear that with piers of that nature in sandy soil near water, you are constantly at risk of a pier being undermined and shifting out of position. Plus, while I don't want to deal with a building inspection now (primarily over the energy efficiency requirements), I may wish to in the future if I need to change the use of the building and getting a building with piers approved requires plans with an engineer's stamp, which would add a couple thousand dollars to the project I'm trying to keep cheap.

    Quote Originally Posted by Frank Pratt View Post
    This will be an interesting project. Your intention is to get the floor level above the 100 year flood level, right?
    As much as I can, yes. I don't actually know what the 100 year flood level is because there are no maps for my area, but I know from personal experience that this area was under a foot of water a few years ago during a record breaking rainfall, and it could go another 6"-8" higher before the water would begin spilling into the field across the creek. Plus, a lovely environmental group just went in 2 years ago and added baffles to the creek downstream in order to slow down the water draining downstream in flood situations.

  5. #5
    Iím neither a soils nor structural engineer, both of whom you need. From what I am reading about flood plain levels and what we are seeing in the States, I would add +ft to any water level estimate. In order to protect the investment value of the property, Iíve come to the conclusion that going the building permit route is the safest and therefore, best method. I have come to that conclusion the hard way, as I do with most things. Does a Permit alter your build method much? You reference a possible future change of use Of the structure. You may be tying your hands.

  6. #6
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    I also suggest you consult with the experts on the design that will be best for the location you intend to build and for the purpose that you intend to use it for. Even if you are the contractor, use the experts...even if it costs you a little money to do so.

    Personally, if it will actually work based on that consultation, I'd absolutely choose the crawl space with a wood floor above for comfort. But that's me.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
    Quote Originally Posted by Jack Frederick View Post
    I’m neither a soils nor structural engineer, both of whom you need. From what I am reading about flood plain levels and what we are seeing in the States, I would add +ft to any water level estimate. In order to protect the investment value of the property, I’ve come to the conclusion that going the building permit route is the safest and therefore, best method. I have come to that conclusion the hard way, as I do with most things. Does a Permit alter your build method much? You reference a possible future change of use Of the structure. You may be tying your hands.
    There are two big issues with a building permit.

    The first is the non-structural code requirements like energy efficiency. I'm being told that for any Residential Accessory building that will be occupied by people (workshops) you basically have to meet the EE requirements for a residential home. This will mean an R-value of 38 in the ceiling and 20 in the walls. And while I may well want to get there eventually, I don't want my C of O to be held up in the meantime since my plan is to acquire and install insulation materials as I can pick them up on the cheap. And if I get it classified as a "non-residential" structure, I end up needing to install a full bathroom which would require a new septic tank and drain field since the ones attached to my house don't meet the current codes as it is.

    The second issue is that my township's building inspector is well known for being a huge pain in the ass when dealing with anything that falls outside "normal construction and use". He is apparently very much the sort to simply red-tag anything that isn't "what he's used to seeing" without paying much attention to whether or not it actually meets the requirements. I've spoken with a number of people who've dealt with him and they all warned me to have an attorney ready before I try to start construction.

    As far as the foundation goes, I fully intend to get a permit for just the foundation either way since it's a huge pain to dig a footing up after the fact. And while a structural engineer might be nice, it's far cheaper to simply build using the worst possible assumptions than to pay an engineer to verify that a lower standard is sufficient. For example, if I use a continuous footer, the requirement is for a 6" thick wall if your load is below a certain level and an 8" thick wall above that point. But in that case, just paying 33% more for the actual concrete is WAY cheaper than having the load analysis done to prove that a 6" thick wall would work.

    Just as a note: I did speak with one engineer briefly who gave me quick ball-park range ($2000-$3000) to do a load check and certification on a building as I've described, but when I mentioned that it was in a flood zone he started in on the "Oh! Well, that does complicate things since none of my normal models will work...". Then he was unwilling to even speculate without a full soil study in his hands first which puts both analysis at somewhere upwards of $6000-$10,000.

    Honestly, that's a big part of the reason I'm leaning towards the helical piles. Since it's an engineered product, I won't need to deal with getting the inspector's approval.
    Last edited by Erik Litts; 09-28-2020 at 1:29 PM.

  8. #8
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    The more info you provide the more it looks like the helical piles is the way to go.
    I highly recommend you build the floor higher(feet higher) than you think you need even if this require a ramp up to the building.
    last thing you want to deal with is getting your shop flooded.
    Lived thru a 300 yr (1997) and a 500 yr(1998) flood
    good luck
    Ron

  9. #9
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    I'm guessing that if it's going to be for maple syrup then frost will need to be taken into account. Do you know how deep the sand/ silt layer is? Around here the sandy/ silty layer usually isn't too deep before getting into a gravel hard pan that's great for supporting a building. If you go with a wall you are going to have to put it on a footing of some sort. My guess is something 16" wide and 8" think or so. That would spread the load out. I assume that you don't have the means to install helical piles. If not I would find somebody who can drive them and ask their opinion. In the end I think you may need to dig a test hole or two so you can see what's down there to give you a better idea on which way to go.

  10. #10
    Quote Originally Posted by Ron Selzer View Post
    The more info you provide the more it looks like the helical piles is the way to go.
    I highly recommend you build the floor higher(feet higher) than you think you need even if this require a ramp up to the building.
    last thing you want to deal with is getting your shop flooded.
    Lived thru a 300 yr (1997) and a 500 yr(1998) flood
    good luck
    Ron
    During the last flood event the water pooled at about +18" and could have gone higher. But at about 22"-24" the water is high enough that the 20 acres of field on the other side of the creek. I figure If I start the floor joists at 3', that means the water would have to hit 46" before it gets inside the building and at that point, I'd have much bigger issues since my basement would be filled with a couple feet of water as well.


    And to everyone who has or does respond, I just want to say thank-you. I know sometimes I come off as argumentative or unwilling to accept input (even when I've asked for it). I promise I'm considering what everyone says, even if I try and explain why I think it won't work. Much to my ex-wife and son's frustration, I spent 6 years on a debate team in HS and college and I just can't seem to shake some of those habits, even 20+ years later.

  11. #11
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    Climate? You mention FEMA maps so i guess you live in the USA? Does it freeze there? any permafrost, if not depth to frost line? and how dry is it in summer? Will the clay soil dry and crack in summer
    Bil lD
    Last edited by Bill Dufour; 09-28-2020 at 6:21 PM.

  12. #12
    West Michigan. So yes it freezes. Footings need to be at least 42" deep. Summer isn't too dry, but the area is Ceresco Loam, which doesn't have much clay in it. It rarely gets dry enough to even get hard since it's fairly well shaded.

  13. #13
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    Hate to bring it up but a this a wetland? Might not be able to build there in any case.

    I like the techno piles and set the building high. Let the breeze blow under it.

    At some point you should put some things on paper.

    1. Plan and a couple of elevation views.

    2. Layout showing the building footprint on the property

    3. List of future equipment and approximate weights, including storage

    I know this is a really hard step for some but it will make a huge difference to your plans.

  14. #14
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    If you have to dig 42 inches down I would dig deeper or add a stem wall and get eight feet under the joists so you can throw junk underneath out of the weather. Will there be gravity drains for the foundation or pumps that will fail eventually.
    Bill D

  15. #15
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    Erik,

    First, I agree with everyone who says raise the floor elevation. IMO, you should be at least 12" higher than 'worst-case' water levels.
    Secondly, IMO you shouldn't drive/install any piles until your floor framing is designed, because, depending on floor joist spans, directions, etc., you may need the finish elevation of the various piles to be different. The attached pictures may help clarify that. I built my in-laws' home ~23 years ago in the TX Hill Country. It's on a raised foundation (concrete stem wall and piers). My FIL said he wanted a "stiff" floor. I went to one of the lumber companies that supplies home builders (NOT a big-box store), and asked them to design my flooring 'system' using their materials. They worked from a floor plan I gave them. You should show/locate any specific heavier-than-normal loads, so they can factor that into the design. The photos show they designed/used LVL girders that were to bear on interior piers and perimeter pilasters, and then the engineered I-joists terminated on them and my perimeter stem wall. So the interior piers were a lower finished elevation than the bearing ledge in the perimeter wall. Once I had their drawings, I built the foundation to their requirements, working to the elevations and location dictated by the various members (joists, girders) in their engineered design. You would have your piles installed/driven to the required elevations, in the required locations, based on the floor framing design.
    Then, buy the complete package (joists, LVL girders, and 1-1/8" T&G decking) from the supplier, have it delivered, and go to work. Install the LVL girders on the piles, and put the engineered I-joists on top of them. Put some temporary 2x4 'strapping' across the top of the joists to keep them straight and aligned prevent bowing. Then buy a trailer load of styrofoam, in whatever thickness you need to achieve whatever R value you're looking for in the floor (in my case it was 2" styrofoam). I had a sheetmetal shop produce several hundred clips I designed, in a sort of Z shape, that I used to support the styrofoam. Drag out your table saw, and rip the styrofoam to the width between your joists (maybe 10-1/2" or 14-1/2"?). Hang 3 or 4 of the clips over the top of each of two side-by-side joists, alternate some to the other side of every other joists, and put your styrofoam into the clips. The top of it will be flush with the top of the joists. Go across with a row of foam and alternating clips, then start glueing and screwing your decking down on top of the joists. The styrofoam will be fully supported, won't harbor pests or insects, and won't ever sag.
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