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Standalone 20x24 workshop foundation questions

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  • #16

    Re: Standalone 20x24 workshop foundation questions

    Originally posted by Egon View Post
    build above grade with concrete piles set below the frost level.
    I am done with piles, sorry. I need stable and flat floor that will withstand 1.5 ton milling machine and non-wobbling surface grinder. Some of my lighter stuff is on casters, so I will be able to roll it away

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    • #17

      Re: Standalone 20x24 workshop foundation questions

      Originally posted by geshka View Post

      I am done with piles, sorry. I need stable and flat floor that will withstand 1.5 ton milling machine and non-wobbling surface grinder. Some of my lighter stuff is on casters, so I will be able to roll it away
      May I suggest screw piles, with a poured concrete floor supported on the piles? If you place the screw piles well below the frost line and form the floor to be poured off the ground, you should have a complete solution? Alternatively, pre-cast floor sections, set onto the piles? A friend built his house like this near Dunrobin. It worked very well.

      Just a thought ....

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      • #18

        Re: Standalone 20x24 workshop foundation questions

        Precast floor sections are a good idea.
        Egon
        from
        The South Shore, Nova Scotia

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        • #19

          Re: Standalone 20x24 workshop foundation questions

          Hm, having read about the issues more in-depth with your latest post, I'm not sure what the best approach for you is! The good thing about a monolithic slab is that you can design it to be big, heavy and solid, which means when it moves it's moving together... but the problems you describe with the existing shop suggest your clay is very expansive, and i'm not sure that any kind of pile system would get you a different result... if it's an expansive clay problem then it doesn't matter if it's below the frost line - you need your piles to go down below the clay (which may not even be possible.) Even precast floor sections will be prone to lifting and shifting out of plane and I don't know if they give you any benefit over poured-in-place if you go with an at-grade approach. To be honest I would contact Legalett, explain your situation and give them your geotechnical report if you have one, and see what they say. Even if you don't use them, they may give you advise which you can carry through to your eventual project.

          When I was working in ottawa I knew someone who worked on a house on along the ottawa river, and the hydrostatic uplift pressure was so high in the basement that their floor slab was about a meter thick. Most people would forget about the basement but where there's a will there's a way I guess!

          You never did mention - what was the advice you have received so far? You said it was conflicting but what was recommended?

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          • #20

            Re: Standalone 20x24 workshop foundation questions

            Any chance to excavate deep enough with a drain to a low point to remove the water at least from under the shop area? If you can do that and refill with clear stone and weeper pipes then you should be able to get rid of the freeze/thaw movement?

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            • #21

              Re: Standalone 20x24 workshop foundation questions

              @guitarchitect Basically it was two recommendations that was already outlined here - 1. Concrete slab on grade (different thickness and some variations of perimeter depth) 2. Concrete floor on concrete piles.
              I am more inclined to go for concrete monolithic slab with thickened edges. Just need to figure out dimensions - how thick is the main part, how thick is section under walls.

              @John Bartley It is a bedrock somewhere 8 feet down - I don't believe i need to excavate that deep? Also, if i will form a channel around foundation with weeping pipe - it is not clear to were pump excess of water, I will accept any ideas
              Last edited by geshka; 05-17-2019, 08:17 PM.

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              • #22

                Re: Standalone 20x24 workshop foundation questions

                [QUOTE=geshka;n1237385]WOW, thanks for the responses, folks.

                @Egon . I do want to meet local building code, though I don't have to. I am in rural area with no neighbors close to me or other constructions, so I am a bit relaxed in this


                even if if you are in a rural area, if your building is more than 108 sq feet, most if not all jurisdictions require that you obtain a building permit from your local municipality and they do require that you comply with the building code.

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                • #23

                  Re: Standalone 20x24 workshop foundation questions

                  Thanks Les. Can you point me, please, to the building code that normal person is able to read ? LOL . Everything I saw so far is lowers cryptic, WW2 Enigma generated gibberish.

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                  • #24

                    Re: Standalone 20x24 workshop foundation questions

                    Home depot carriers a homeowners version of the code... i used something similar when I wired my garage - the homeowner's version of the electrical code. true to my username i can read the Ontario Building Code pretty well but the electrical code was new to me! for anyone else reading along there's another good detail-related resource that is put out by the Toronto Area Chief Building Officials Committee (TACBOC), which is their go-to set of details for homeowner projects in the GTA. Cheaper than buying a book from home depot and it shows tried-and-true ways of doing everything. This is the link - Ottawa-area is different for insulation values, footing depths (1.8m vs 1.2m) and things but much of the detailing strategies are the same - it's all based on OBC requirements.

                    With the amount of heaving you're talking about I'd be wary of doing it yourself - I think you want an engineer. I'm an architect and if I was in your shoes I would still work with a geotechnical and a structural engineer if i didn't want the thing to ever move. My garage was only 12' wide so I was comfortable with 5" and a thick perimeter, but with a big 20x24 slab you might need a beam down the middle in both directions. Who knows!

                    in terms of the options you were given - the thing with your situation is that there isn't a clearcut approach. A structural engineer might take you beyond a monolithic slab and recommend a waffle slab or even thicker perimeter beams (which would make it even more resistant to uplift), or you might do caissons (piles) since your bedrock is only 8' down. piers concentrate the load more and are therefore more resistant to uplift so they could still be an option with the right design, if the soil is as bad as you make it sound. so who knows the right approach!

                    I will always recommend talking to your neighbours - if you know anyone nearby who did a similar project, figure out who they used and how happy they were. Similarly it doesn't hurt to call up local builders and ask who they use for engineering services. What you really want is the advice of someone who has seen your conditions before and knows the area, or who has seen similar situations before. I sound like a broken record but I was very impressed with the Legalett guys and i didn't even use their system - very informative and they have their own engineers, and they work with all sorts of soils conditions. I only recommend them because I got a huge amount of information for free out of them (but not intentionally - i had fully intended to use their system)

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                    • #25

                      Re: Standalone 20x24 workshop foundation questions

                      Originally posted by geshka View Post
                      Thanks Les. Can you point me, please, to the building code that normal person is able to read ? LOL . Everything I saw so far is lowers cryptic, WW2 Enigma generated gibberish.
                      The building code can be a very complex document for someone (like me) who doesn’t work with it on a regular basis. When I was planning my shop build , I received differing suggestions from people I asked as you have here. What I did was call the municipal office and made an appointment with the building inspector. I outlined what I wanted to build and he then told me what was required under the code and what I needed to present to him to obtain my building permit and subsequently build my shop. Great advice and I followed his advice and everything passed inspection.

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                      • #26

                        Re: Standalone 20x24 workshop foundation questions

                        It’s a 20x24 Shop that requires a floor that must remain even.
                        If piles are out pour a thick monolithic slab. A slab designed to remain as a block without cracking even with vertical movement. Have it professionally designed.
                        Egon
                        from
                        The South Shore, Nova Scotia

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                        • #27

                          Re: Standalone 20x24 workshop foundation questions

                          Egon's suggestion of piles is a perfect solution to your issue. You most likely will not accept it because it's different construction than you are used to but it will work and has been proven for years. You need to research concrete grade beams. That's what Egon is describing and most of the garages in Edmonton are supported on grade beams and we park 2, 3 and 4 cars in our garages without failures like sinkage or heaving. Pay particular attention to void form construction under the grade beam!
                          "Do it Right!"

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                          • #28

                            Re: Standalone 20x24 workshop foundation questions

                            Couple of thoughts:

                            Water wicks quite well through concrete, and can generate significant hydrostatic pressure. I think usual practice now is to put a vapour barrier in the mix somewhere.

                            If you insulate the slab, doesn't frost come in under the edges. If you don't insulate the slab, the building is hard to heat.

                            Frost free shallow foundations: Does this idea work for a building that is unheated, or intermittently heated?

                            If water is a problem would there be merit in making a mound and building on that? E.g. build your 20 x24 foot shop on a 28 x 32 mound 18" high. That would be about 100 cubic meters of road crush. Pack in 4" layers.

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                            • #29

                              Re: Standalone 20x24 workshop foundation questions

                              Originally posted by geshka View Post

                              I am done with piles, sorry. I need stable and flat floor that will withstand 1.5 ton milling machine and non-wobbling surface grinder. Some of my lighter stuff is on casters, so I will be able to roll it away
                              That changes things. Woodworking tools are one thing but with heavy loads like this I would't use a simple floating slab like I described. I'd be talking to an engineer. The slab itself would be fine under a 1.5 ton load but it's the ability for the soil beneath it to carry the load year in year out that would bother me. One solution may be piles or cassions and a reinforced thickened section (band beam) under the load .... it's really up to the engineer.

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                              • #30

                                Re: Standalone 20x24 workshop foundation questions

                                Originally posted by geshka View Post
                                Thanks Les. Can you point me, please, to the building code that normal person is able to read ? LOL . Everything I saw so far is lowers cryptic, WW2 Enigma generated gibberish.
                                There really isn't much out there for what you want to do. The problem is there is a simple prescriptive code for single occupancy buildings under 6000 SF (part 9) and the really dense part for buildings designed by architects and engineers (all the other parts).

                                Unfortunately floating slab foundations are not dealt with under the prescriptive code. They have to be designed by an engineer under part 4 and part 2 of the OBC. Unless you are a p.eng. you can't design these foundations.

                                Under part 9 you as a home owner can legally design and build a shop with a standard block wall and slab on grade as per part 9 of the OBC however when it comes to piles or floating slabs you need an engineer's stamp to even get the city to look at it. Even if you find a canned drawing for a floating slab designed by a Canadian engineer you still need to get the engineer to stamp the drawing and under the current law the engineer is supposed to inspect and direct the construction as well.

                                In the real world you can can get an engineer to stamp your design .... what they do is just review the drawing, maybe run the numbers, stamp it and charge you a couple of hundred bucks. The guy I use doesn't feel he needs to supervise me.

                                This is the best simplified guide to part 9 of the Canadian building code that I know of https://chbanl.ca/wp-content/uploads...nstruction.pdf

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