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  • guitarchitect
    replied
    Originally posted by Rusty View Post
    A floating slab is exactly that! The key word is "floating"!

    Geshka if your description of soil and water conditions are as difficult as you say then your biggest enemy is hydraulic pressure. Geshka I'm from Ontario and I've built lots of houses in Ontario. I'm now building in the west and I've been in your shoes many times.

    Following the building code is good sound advice but it is not rocket science. You need to determine your problem and work around it with a solution. Determine the specific issues that will cause failure and eliminate them. If one is frost then you have no option but to float or get below it. Floating is a crap shoot in your situation if your description of the ground is correct. I think you have already seen the results with your present structure which appears to be moving inconsistently year after year. When you said you had to cut off your middle post and adjust others it told me that hydraulic pressure was in play. Water is below your piles and pushing upwards on those piles. If you are as deep as you suggest with your present piles it is not frost heaving them upwards it is hydraulics.

    If you have bedrock down 8 feet that's where your piles should sit. In the west I drill 10 inch round piles 12 feet deep and fill the holes with reinforced concrete to final grade or slightly above. Water does not flow through clay very well so you have a soil condition under the clay which allows the water flow. You have to get below that if you want stability. Getting below it may require a soil test to prove what exactly is there and that may prove some building sites are just not good enough to support structures we want to build. That's the reason you see major excavations under many structures. They are removing the soils they can't use as a base for construction.

    Going by what you describe I think you can get around it but it won't be easy and even a monolithic slab can and probably will fail in time. Most assuredly it will move. At the very least it will move unevenly and when this happens with any structure the only saving of that structure is generally underpinning. Now you're talking real money!

    A wooden structure could be built on beams with adjustable post supports BTW. That's a whole different discussion though.
    It's hydrostatic pressure that you're referring to, not hydraulic.

    As I've said in a number of posts now it is far more likely that, all things being equal and assuming his last shop wasn't built very poorly, the issues he's seeing are the result of expansive clays, and not hydrostatic pressure alone. Only way to know (and work around it) is a proper soils test and the advise of a structural and geotechnical engineer.

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  • Rusty
    replied
    A floating slab is exactly that! The key word is "floating"!

    Geshka if your description of soil and water conditions are as difficult as you say then your biggest enemy is hydraulic pressure. Geshka I'm from Ontario and I've built lots of houses in Ontario. I'm now building in the west and I've been in your shoes many times.

    Following the building code is good sound advice but it is not rocket science. You need to determine your problem and work around it with a solution. Determine the specific issues that will cause failure and eliminate them. If one is frost then you have no option but to float or get below it. Floating is a crap shoot in your situation if your description of the ground is correct. I think you have already seen the results with your present structure which appears to be moving inconsistently year after year. When you said you had to cut off your middle post and adjust others it told me that hydraulic pressure was in play. Water is below your piles and pushing upwards on those piles. If you are as deep as you suggest with your present piles it is not frost heaving them upwards it is hydraulics.

    If you have bedrock down 8 feet that's where your piles should sit. In the west I drill 10 inch round piles 12 feet deep and fill the holes with reinforced concrete to final grade or slightly above. Water does not flow through clay very well so you have a soil condition under the clay which allows the water flow. You have to get below that if you want stability. Getting below it may require a soil test to prove what exactly is there and that may prove some building sites are just not good enough to support structures we want to build. That's the reason you see major excavations under many structures. They are removing the soils they can't use as a base for construction.

    Going by what you describe I think you can get around it but it won't be easy and even a monolithic slab can and probably will fail in time. Most assuredly it will move. At the very least it will move unevenly and when this happens with any structure the only saving of that structure is generally underpinning. Now you're talking real money!

    A wooden structure could be built on beams with adjustable post supports BTW. That's a whole different discussion though.

    Leave a comment:


  • guitarchitect
    replied
    Originally posted by dave_k View Post

    It's nice that this is still published. It was used in my apprenticeship back in the 1970's in Alberta and it's used in the current curriculum in Ontario. It's not meant to teach you how to cite the BC but it give a good overview of how to build a house that conforms to part 9 anywhere in Canada .... and it's free. I'm in NB now and use the NBC..... before that I spent 35 years in Ontario ... I see no difference between the two in broad strokes. I'm sure there are differences but it would be deep in the details. All the big stuff like foundations, framing and building envelope are the same.

    I'm not surprised architects study the NBC as opposed to the OBC. they have to be able to design federal projects .... military bases and ports for example .... which are designed to the NBC. Since college the only section of the BC I've opened is part 9. In the trades our certification is national and the NBC is the national standard. In reality there is so little difference between the provincial codes and the NBC that it makes no difference. The big difference is that the NBC costs $435 while the OBC can be downloaded and printed for free.
    I disagree that there's little difference - it's just that the differences are not necessarily related to Part 9. the OBC has an entire section dealing with renovations of existing buildings (part 11) that the NBC doesn't have, note to mention a number of SB's which are unique to provincial policy and direction (energy efficiency for example, which does affect Part 9). Provinces like BC and Ontario also go much further than the NBC when it comes to accessibility. By design the NBC is a model building code - it is intended to be modeled upon. Many provinces only use it , whereas up until the mid 70's Ontario let municipalities develop and use their own building codes. Vancouver has its own and BC has its own, both modeled on the NBC... BC has a very unique climate compared to the rest of Canada.

    We don't study it because of federal projects - typically the government has its own architecture division that does those, although sometimes it gets contracted out. The exams used to be part of the NCARB system (using the International Building Code) which would let you apply for a license anywhere in north america, but that just didn't fit how people wanted to practice after going to school in canada. So, Canadians have the option of now writing the ExACs which let you apply for a license anywhere in Canada (you're still held to the local body's licensing requirements though so it's not a rubber-stamp process).

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  • dave_k
    replied
    Originally posted by guitarchitect View Post
    From page xiii - "Though Canadian Wood-Frame House Construction is based on the requirements of the 2010 edition of the National Building Code (NBC)..." ;) The two codes are lined up in many ways, but the OBC is more restrictive. Many licensing exams (including the ExACs which one has to write to get an OAA license) are, paradoxically, based on National rather than Provincial codes.
    It's nice that this is still published. It was used in my apprenticeship back in the 1970's in Alberta and it's used in the current curriculum in Ontario. It's not meant to teach you how to cite the BC but it give a good overview of how to build a house that conforms to part 9 anywhere in Canada .... and it's free. I'm in NB now and use the NBC..... before that I spent 35 years in Ontario ... I see no difference between the two in broad strokes. I'm sure there are differences but it would be deep in the details. All the big stuff like foundations, framing and building envelope are the same.

    Originally posted by guitarchitect View Post
    Many licensing exams (including the ExACs which one has to write to get an OAA license) are, paradoxically, based on National rather than Provincial codes.
    I'm not surprised architects study the NBC as opposed to the OBC. they have to be able to design federal projects .... military bases and ports for example .... which are designed to the NBC. Since college the only section of the BC I've opened is part 9. In the trades our certification is national and the NBC is the national standard. In reality there is so little difference between the provincial codes and the NBC that it makes no difference. The big difference is that the NBC costs $435 while the OBC can be downloaded and printed for free.

    Leave a comment:


  • guitarchitect
    replied
    Originally posted by dave_k View Post
    I would be calling city hall first. I did mine in 1990 and even then I needed a stamped drawing. The 2006 code revision brought draconian changes as to who can design and submit drawings.
    I did mine two years ago and I didn't need a stamped drawing I advise a lot of my wife's friends and they do their own drawings to submit for certain things and it's rare that the city wants anything stamped. I submitted my own drawings (including the slab which was not designed by an engineer) as a homeowner and they didn't require a stamp. Again... TACBOC is the committee of chief building officials. it'd be pretty funny if they didn't approve their own approved drawings! The caveat with geshka is his soil condition and the performance he wants, which is why i've said several times now that he should get an engineer.

    Originally posted by dave_k View Post
    There is nothing in the CMHC book that doesn't conform to the OBC .... I used to use it to prepare carpenters for the C of Q exam.
    From page xiii - "Though Canadian Wood-Frame House Construction is based on the requirements of the 2010 edition of the National Building Code (NBC)..." ;) The two codes are lined up in many ways, but the OBC is more restrictive. Many licensing exams (including the ExACs which one has to write to get an OAA license) are, paradoxically, based on National rather than Provincial codes.
    Last edited by guitarchitect; 05-18-2019, 04:57 PM.

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  • dave_k
    replied
    Originally posted by guitarchitect View Post
    The link I sent earlier (TACBOC) has a bunch of canned details including a monolithic slab on grade, all to OBC but as I clarified it's not to Ottawa climate. The reason to hire an engineer is to ensure it'll perform the way he wants.
    I would be calling city hall first. I did mine in 1990 and even then I needed a stamped drawing. The 2006 code revision brought draconian changes as to who can design and submit drawings.

    In 2008 I had to have a stamped drawing for a lintel that was carrying a point load of 80 lbs .... it was a field decision. I had 2-2x12 in the framing but the inspector wouldn't accept it because part 9 doesn't cover point loads on a lintel. I went to the engineer and he ran the numbers and a single 2x4 was sufficient to carry the load. I came back with a letter and a stamped dwg and he accepted it. Good luck with an engineered foundation.

    There is nothing in the CMHC book that doesn't conform to the OBC .... I used to use it to prepare carpenters for the C of Q exam.

    Leave a comment:


  • guitarchitect
    replied
    Originally posted by dave_k View Post

    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
    Not to be tooooo picky but he needs to design to Part 9 of the OBC and the CMHC book deals with the NBC (National Building Code) It's a great resource though!
    The link I sent earlier (TACBOC) has a bunch of canned details including a monolithic slab on grade, all to OBC but as I clarified it's not to Ottawa climate.
    The reason to hire an engineer is to ensure it'll perform the way he wants. Using a canned detail will give him a safe inhabitable shop but his performance criteria is "i want it to stay in place on expansive clay near a high spring water table" which is what points to "engineer". His current shop was probably done to code, but his site conditions are what made it go haywire.

    Luckily for something simple like a slab-on-grade (even with a fancy design) the engineer won't need to inspect/direct construction, the inspector will do that by inspecting after excavation and after the formwork is in, before the pour starts (and again after the pour is done to ensure the concrete cured properly).

    Leave a comment:


  • dave_k
    replied
    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

    Leave a comment:


  • dave_k
    replied
    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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  • sgbotsford
    replied
    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.

    Leave a comment:


  • Rusty
    replied
    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!

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  • Egon
    replied
    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.

    Leave a comment:


  • Les@Brownsville
    replied
    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.

    Leave a comment:


  • guitarchitect
    replied
    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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  • geshka
    replied
    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.

    Leave a comment:

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