Re: Standalone 20x24 workshop foundation questions

[guitarchitect]

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).

[dave_k]

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.

[guitarchitect]

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.

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.

[dave_k]

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.

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.

[guitarchitect]

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).

[Rusty]

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.

[guitarchitect]

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.

[Egon]

Movement winter - spring sounds like frost heave.

If piles are out then ecavate material to below to below the frost line and back fill with material that will not support capillary action. Then go for a slab on grade.

[John Bartley]

I think maybe it would help if we knew a bit more about the area that OP is building in .... urban, suburban, country estate lot, rural? Elevations, grading, ditches nearby?

I guess what I am getting at is :: can the area be excavated to get rid of the water bearing clay?, replaced with clear stone and weepers below the frost line? Does it have to be a sump pump or can it be gravity from the weepers to a nearby lower elevation?

Where do you want to build?

cheers

[Rusty]

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.

Perhaps an explanation of the difference between hydro static and hydraulic is in order. I'm not interested in an argument it's a discussion to aid the original poster.

Expansive clays will not lift piles if you are below the clay.

I agree with Egon. Excavate and eliminate the problem soil or get your foundation below it. Advising of a geotechnical advisor is like buck passing. If you have been in construction long enough you should be aware of certain situations and their cure. I mean no offence, but quoting and depending on the OBC or the NBC by you or any others in this discussion will not answer the questions posed here by the OP.

I know some people think I'm a bit blunt but you guys really need to decide whether you want answers to your issues or do you want to reference a building code which will not answer anything to do with this OP's question. Yes it's a great idea to follow the building code but the building code does not say " if you have this problem do this!" So I'm just saying to advise the guy to read the code is not helpfull at all. Offer a solution and let's discuss it for him!

If what he is telling us is true and I have no doubt that it is, I know that I can overcome his issues several ways.

[guitarchitect]

Perhaps an explanation of the difference between hydro static and hydraulic is in order. I'm not interested in an argument it's a discussion to aid the original poster.

Expansive clays will not lift piles if you are below the clay.

I agree with Egon. Excavate and eliminate the problem soil or get your foundation below it. Advising of a geotechnical advisor is like buck passing. If you have been in construction long enough you should be aware of certain situations and their cure. I mean no offence, but quoting and depending on the OBC or the NBC by you or any others in this discussion will not answer the questions posed here by the OP.

I know some people think I'm a bit blunt but you guys really need to decide whether you want answers to your issues or do you want to reference a building code which will not answer anything to do with this OP's question. Yes it's a great idea to follow the building code but the building code does not say " if you have this problem do this!" So I'm just saying to advise the guy to read the code is not helpfull at all. Offer a solution and let's discuss it for him!

If what he is telling us is true and I have no doubt that it is, I know that I can overcome his issues several ways.

If he wants to solve his problem, it won't happen listening to a bunch of guys on the internet. There are a variety of ways to build something, but to really meet certain performance criteria (such as "I never want it to move out of place") you sometimes need professional help. He's described enough challenges that it's pretty clear he needs to take that path. It's not about passing the buck, it's about recognizing the complexity of the issue.

OBC/NBC was a tangent - no one referenced it as a way to solve his problem.

To your question about hydraulic/hydrostatic - Hydraulic pressure deals with hydraulic fluid. Hydrostatic pressure deals with the pressure exerted by a fluid at equilibrium. think of it this way... if you know your water table is at 2' below the surface, that's where it is at equilibrium. if you put your foundation and floor down at 4', hydrostatic pressure is the pressure exerted "up" by the water because it wants to be at equilibrium - at 2'. That's where the "static" part of the phrase comes from. Let it be known that this is just for visualizing it... the actual force at work is gravity, which is exerting a downward force on the water table, so the force "up" by the water is actually equal to the "downward" force of water by gravity, blah blah blah... the deeper you go, the higher the pressure because there's more water weight pushing down, and so on.

The problem with excavating the problem soil is that (a) he's surrounded by it and who knows how deep it goes, and (b) his water table is at 2' in the spring. i don't think he's in good shape if he digs out say 6' of soil that then holds 4' of water in the spring, whether it's full of gravel or not. The best solution is for him to drill piles down to bedrock (it's only 8' away) and put a slab at grade that will resist the uplift caused by his soil. But how you design that solution (and how much it costs) is beyond the userbase here. If his only problem is frost heaving, a FPSF and a monolithic slab (probably with a beam down the middle in each direction) will solve that easily.

[Rusty]

If he wants to solve his problem, it won't happen listening to a bunch of guys on the internet. There are a variety of ways to build something, but to really meet certain performance criteria (such as "I never want it to move out of place") you sometimes need professional help. He's described enough challenges that it's pretty clear he needs to take that path. It's not about passing the buck, it's about recognizing the complexity of the issue.

OBC/NBC was a tangent - no one referenced it as a way to solve his problem.

To your question about hydraulic/hydrostatic - Hydraulic pressure deals with hydraulic fluid. Hydrostatic pressure deals with the pressure exerted by a fluid at equilibrium. think of it this way... if you know your water table is at 2' below the surface, that's where it is at equilibrium. if you put your foundation and floor down at 4', hydrostatic pressure is the pressure exerted "up" by the water because it wants to be at equilibrium - at 2'. That's where the "static" part of the phrase comes from. Let it be known that this is just for visualizing it... the actual force at work is gravity, which is exerting a downward force on the water table, so the force "up" by the water is actually equal to the "downward" force of water by gravity, blah blah blah... the deeper you go, the higher the pressure because there's more water weight pushing down, and so on.

The problem with excavating the problem soil is that (a) he's surrounded by it and who knows how deep it goes, and (b) his water table is at 2' in the spring. i don't think he's in good shape if he digs out say 6' of soil that then holds 4' of water in the spring, whether it's full of gravel or not. The best solution is for him to drill piles down to bedrock (it's only 8' away) and put a slab at grade that will resist the uplift caused by his soil. But how you design that solution (and how much it costs) is beyond the userbase here. If his only problem is frost heaving, a FPSF and a monolithic slab (probably with a beam down the middle in each direction) will solve that easily.

Now that's a helpful answer. I understand the tangent. It's just not helpfull but you can discuss and argue it's merits for how ever long you want.

As to a bunch of guys on the internet,,,,some of us are professionals and can describe solutions. Egon described a fix way back at the start of this thread and I have no clue as to wether he's a professional or not but piles were discounted as a poor option and no discussion followed,, when in fact that might be his best option. The point is he needs to be presented with solutions that he can easily understand and assess. I daresay piles were discounted because most of this bunch of guys doesn't know a thing about them or their ability to carry a load when connected to a grade beam.

[guitarchitect]

yeah and i even gave him a monolithic slab detail early in the thread too, along with the principles that he probably wants to adhere to no matter what he does.

not to discount what egon said but it wasn't detailed enough - most people (even many of my architect colleagues) don't know the difference between piles and piers and use the terms interchangably. from what he said it wasn't clear if he was referring to piers (which is what it sounded like) or piles connected to a slab on grade, or friction piles.

All of that aside, given the sound of the clay and water situation (likely expansive but who knows), I would be wary of piles (unless connected to bedrock) or piers. Friction piles (which is any pile that doesn't go to bedrock) and piers both rely on friction with the soil, and expansive clay with a high shrink-swell capacity will pull away from them over time. Neither are especially good in higher water table conditions because the wetting of the soil reduces friction with the pile.

Is that to say none of them will work? Of course not - piles are used for large slab-on-grade industrial buildings all the time, and you can't always pick the best site for your building... but you have to design for your needs based on the site condition, and tricky sites need more consideration (an engineer). i also gave geshka a good lead for a company that does slab-on-grade systems and do the engineering as part of the process (they gave me a tonne of free advice that helped me design my monolithic slab), so I think he's well-equipped to make an informed decision at this point.

[dave_k]

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).

Lets just back this up a little. This thread is about a guy who is looking for a solution to his foundation problem. In the conversation he states he is looking for a guide to the building code and I suggest the CMHC guide to wood frame construction.

You say it's no good to him because it's based on the NBC. I say it's close enough ... it hits all the main points which seeing as the provincial codes are based on the NBC makes it a good Canada wide resource.

So is the guy going to find the answers to his questions in part 11 of the OBC? Nope.

Does the provincial policy on energy efficiency affect his proposed floating foundations ability to support a 1.5 ton milling machine without that side of the building sinking into the soil making his shop look like a listing oil tanker? Nope.

What it gives him a good knowledge of what's required by the BC and what he can and cannot do without the help of design professionals. At worst it gives him enough knowledge to ask the right questions of city hall so he can build his shop and start milling metal.

The CMHC guide has been a great resource for Canadians for generations. As a teaching tool it's main strength over the OBC or NBC is that it's simple, plain language and it's illustrated. This may not be advantageous to architects and engineers but to those visual learners among us and to people who need an overview of Canadian construction standards that lays out the BC requirements without having to wade through legalese it's a godsend.

[dave_k]

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.

So the fed's architectural division doesn't hire Canadian architects?

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).

Common issue in Canada. Nursing for example, uses US exams. There was a big debate over it a few years back and there is a problem with Canadian trained nurses failing the exams because of the differences between the US and Canadian systems. The reason for using US exams it's cheaper to buy exams than write them.