foundation depths and frost lines

The_Surveyor · Apr 3, 2013

I have decided to try to get my garage built this year, a 26' deep x 30' wide gem with 9' eves and 15' roof peak to call my own. :drool:

In my quest for an awesome garage space I had several contractors come by to provide quotes. My main problem with this has been several of the garage "specialists" have suggested that I do not require footings to be 4' below grade (live in Calgary, Canada. It gets cold!). This seams odd to me as it is my understanding that getting footings at or below the frost line helps to prevent frost heaving of the walls and adds to the stability of the structure.

If it were you and you wanted to install in slab heating would you want footings at or below the frost line with fully insulated foundation walls?

Why would you not want footings to be at the frost line?

Thanks so much for any input even if it is contradictory to my current thinking.

srmofo · Apr 4, 2013

In my area the frost line is at 34" . However I have heard more than once that canadian codes dont require footings that deep when a monolithic slab is poured. Personally I would want footings below the frost line regardless of what MINIMUM code is. The reason the builders dont want to do it, is because it is cheaper and easier to just pour a slab with minimal depth. Find another builder.

BTW welcome to GJ

ForceFed70 · Apr 4, 2013

You absolutely need footings below the frost line. In fact, that is code in Calgary so you MUST do it if you are getting the building permitted.

Check with your inspector regarding the depth. I had to go down a min of 2 feet in Kelowna but I think code for your area is 4 feet.

The guys saying you dont need footing are either building disposable buildings (sheds) or are in areas with a mild climate.

Sureshot · Apr 4, 2013

Better check with local codes. Our weather is colder than yours but you can do a floating slab up to a certain size and not attached to the house of course. It all depends on the soil conditions and slope in the area.

GYPSY400 · Apr 4, 2013

I'm building this year in Sudbury Ontario.. My contractor told me the footing has to be at 4.5 feet (54") below surface.. One way to cheat is to raise the ground level outside the structure if I go less than 54".. But that's probably more work than just digging the initial hole deeper.

Check with your local codes to see if your contractor is screwing you.. If he wants to cheat on the foundation, who knows what he'll do the rest of the build.

Gary S · Apr 4, 2013

Sureshot said:
Better check with local codes. Our weather is colder than yours but you can do a floating slab up to a certain size and not attached to the house of course. It all depends on the soil conditions and slope in the area.

It is the same here. My frost line is 72". A floating slab does not need to be down that deep as long as the garage is not attached to the house. House foundations need to be below frost line, but detatched garages do not. Attached garage is considered part of the house obviously, so house rules apply.
Check your local building codes. I suspect that if your contractors are saying you don't need to go deep, they are right.

readhead · Apr 4, 2013

Do you have a set of plans so that everyone that looks at this is quoting the same thing? Plans will clarify questions like this. If a builder wants to offer an alternate that is fine. Without plans you will get prices all over the map.

The_Surveyor · Apr 4, 2013

The interesting thing in Calgary is that the city does not require a permit for foundation work for garages as long as you are not building a retaining that holds back more then 3'. Thanks for the input on the footings, it looks like I will be calling more more concrete guys today and even a city building inspector.

Trevor454 · Apr 4, 2013

I built in Strathmore, 28x29 detached. You don't need footings, they made a killer slap for me though, 24" thick for 3' around the entire perimeter and 6" concrete depth in middle. They then poured a 1' curb wall around entire pad (minus where overhead door was). The pad has had 0 issues in the 6 years I had it. If you doing a deck, thats a different story you NEED to have footings that go below the frost line, or it will heave and your deck be wavy, and unlevel. My new house - they obviously did not do them deep enough, so that is my spring project, do new deck footings at least 4' below ground level, with 8 or 12" sonotubes.

ForceFed70 · Apr 4, 2013

Trevor454 said:
I built in Strathmore, 28x29 detached. You don't need footings, they made a killer slap for me though, 24" thick for 3' around the entire perimeter and 6" concrete depth in middle. They then poured a 1' curb wall around entire pad (minus where overhead door was). The pad has had 0 issues in the 6 years I had it. If you doing a deck, thats a different story you NEED to have footings that go below the frost line, or it will heave and your deck be wavy, and unlevel. My new house - they obviously did not do them deep enough, so that is my spring project, do new deck footings at least 4' below ground level, with 8 or 12" sonotubes.

So basically the slab was designed to handle the heaving? Interesting.

In my neck of the woods, I had to have the building very small before they would let me do a floating slab. Something in the neighborhood of max 150sqft.

bygasper · Apr 4, 2013

srmofo said:
Personally I would want footings below the frost line regardless of what MINIMUM code is. The reason the builders dont want to do it, is because it is cheaper and easier to just pour a slab with minimal depth. Find another builder.

BTW welcome to GJ

HERE HERE!!! That is why I put footings down to either 1) 36-40" (NW Missouri), or 2) until I hit undisturbed/virgin soil (one corner to 60")

pantera1 · Apr 4, 2013

http://www.huduser.org/portal/publications/PDF/FPSFguide.pdf

In the past few years my township/county in MN has ammended the code requirements for a detached building for use as a garage/shop.

If one wanted a stick built shop, you were stuck getting an expensive foundation below the frost line. The only option then was building a pole barn with a monolithic slab.

The technology of insulated slab foundations has advanced, and there is plenty of long term data coming in from Norway, Alaska, etc. showing great results.

If the shop is to be heated, my county will now allow a stick built building on an insulated monolithic slab.

Who knows, basements may become a thing of the past in northern homes!

Sureshot · Apr 4, 2013

ForceFed70 said:
So basically the slab was designed to handle the heaving? Interesting.

In my neck of the woods, I had to have the building very small before they would let me do a floating slab. Something in the neighborhood of max 150sqft.

I think you need to look at the soil and drainage.

Also be sure to put slip pipes in the slab where any lines or wires will come through. A slab may move but unless it rips the wires or pipes off it won't matter or be noticable.

Charles (in GA) · Apr 4, 2013

Why 9 ft tall? Not enough in my opinion.

If doing a monolith slab on ground that will be heaving, the slab needs to be stiff enough to not crack or break. That would mean, as someone noted, deep wide edges and probably "beams" poured under it also.

Charles

nehog · Apr 4, 2013

Sureshot said:
Better check with local codes. Our weather is colder than yours but you can do a floating slab up to a certain size and not attached to the house of course. It all depends on the soil conditions and slope in the area.

Agreed, I have a floating slab on my building and have had zero problems with it.

6768rogues · Apr 4, 2013

We are in a cold climate (42" frost depth) and it is acceptable to build an accessory structure on a monolithic slab with thicker haunches along the perimeter. A lot has to do with how well your site drains. Soil does not cause heaving, water in the soil freezes and heaves. If you have a very well drained site, you will get little heaving. That said, if it were mine, I would put in the deep footers and foundation. I have several barns and garages and they are all resting below the frost depth.

The_Surveyor · Apr 4, 2013

I have to do 9' tall eves (no higher) as the city requires this in the building codes (but not foundations, looks like they have there priorities straight). I would think about a monolithic slab for my garage but I have about 3' of grade change from the rear lane to the back of the house so a monolithic slab is out.

This is what I am working with and looking to accomplish.

Al36rx7 · Aug 7, 2013

We've built a couple houses in Calgary, and I can confirm Calgary's minimum footing depth is 4ft (1.2m), unless engineer approved foundation at specified shallower depth that is protected from frost with specified insulation. As with anywhere, footing is always placed on virgin / undisturbed soil.

sparky36000 · Aug 7, 2013

I'm in North Dakota and it gets cold here too. Built my 24x36 with a loft detached on a floating slab with 12" thickened edges. The only thing required was at least two #4 rebar in the edges. No cracking, no heaving and no problems.

Gary S · Aug 7, 2013

Same here. In my part of North Dakota, the frost line is at 72". My garage and just about every other one here sits on a floating slab, and they don't heave or move.
If your contractors say you don't need to go deep, believe them. They will save you money.

brownbagg · Aug 7, 2013

my frost line is 6 inches above the soil, when ever we get a frozen mud puddle it make the nightly news. and you think I'm joking.

GYPSY400 · Aug 9, 2013

GYPSY400 said:
I'm building this year in Sudbury Ontario.. My contractor told me the footing has to be at 4.5 feet (54") below surface.. One way to cheat is to raise the ground level outside the structure if I go less than 54".. But that's probably more work than just digging the initial hole deeper.

Check with your local codes to see if your contractor is screwing you.. If he wants to cheat on the foundation, who knows what he'll do the rest of the build.

UPDATE: my garage is in the paper trail process.. It is going to be a floating slab with a "thickened perimeter" drawn up by an engineer.. It's ok to do floating slabs if its not attached to the house.

OldGarageChris · Feb 27, 2014

Al36rx7 said:
We've built a couple houses in Calgary, and I can confirm Calgary's minimum footing depth is 4ft (1.2m), unless engineer approved foundation at specified shallower depth that is protected from frost with specified insulation. As with anywhere, footing is always placed on virgin / undisturbed soil.

Does anyone have any product links for this insulation and/or how shallow a foundation wall can be used with this insulation?

I live near Toronto, Canada (clay ground) and currently have a being house built. My foundation wall will step down from front to the back and the builder told me I was 1 step away (from the 1st floor kitchen walkout to backyard) from them giving me a basement walkout as apart of the build. Now I'm forced to put in a basement walkout post construction. I've got the rim joist doubled where I will be putting the walkout to strengthen above, but I'm wondering whether I need to underpin or if I can get away with cutting 2 of the 4 feet away and using this insulation?

Ultimately, I'll be getting an engineer to do the drawing and contracting the work...but I'm trying to budget whether I need to underpin the foundation (expensive) or if I can get away with the cheaper insulation route. Cant find anything in the building code, although I've been told this insulation can be used.

EDIT: Incase anyone is interested, here are pics before the fill...I think I'll need to get 2 feet cut...
http://i1240.photobucket.com/albums/gg481/OldGarageChris/cbe49172-bb2a-4b7c-9964-2a6699b8211a_zps636d6bf1.jpg
http://i1240.photobucket.com/albums/gg481/OldGarageChris/Foundation3_zpsd607882f.jpg

brownbagg · Feb 27, 2014

but no matter what the contractor says, you have to do what the county inspector sat

MN4x4 · Feb 27, 2014

You can definitely do a floating slab as long as your garage is not connected to anther building. But you might want to check out the concept of a Frost Protected Shallow Footing. It has the potential to save you a bunch of money and make your building easier to heat.

I re-did my shop to incorporate it. You can view my project here:

OldGarageChris · Feb 27, 2014

brownbagg> I was under the impression that the inspector inspects against the approved permit? In other words, the engineer that signs off on the drawing is responsible with the city approving the proposal and giving the permit.

MN4x4> I'm talking about a house. The foundation wall will be 4' around the entire house, except where I want to cut the foundation for a walkout basement. I've been told that insulating the foundation will reduce the depth required by code and I'm trying to confirm how much this insulation allows you to go below the building code 3' 11" frost level. The Ontario building code mentions foundation insulation but doesnt give adjusted frost deth levels based on R insulation value/etc.

OldGarageChris · Feb 28, 2014

Does nobody have experience using this insulation on foundations to get away with less than code bare cement frost depths?

srmofo · Feb 28, 2014

OldGarageChris said:
Does nobody have experience using this insulation on foundations to get away with less than code bare cement frost depths?

start a new thread. This one was pretty old when you bumped it, and your topic really doesnt apply to the thread title so many people might just be skipping over it. Make sure your thread title is descriptive and you'll get some hits

also insulation on a foundation is not going to do anything for frost heave.

The ground freezes, expands, and pushes anything that isnt firmly anchored below the frozen portion out of the ground. Thats what minimum depths are for

OldGarageChris · Mar 1, 2014

My Q about insulated foundation reducing the need to go down to build code frost line doesn't apply to "foundation depths and frost lines"? I figured it was worth combining...but I guess I'll create a dedicated thread

John Kay · Apr 15, 2024

The_Surveyor said:
I have decided to try to get my garage built this year, a 26' deep x 30' wide gem with 9' eves and 15' roof peak to call my own.

In my quest for an awesome garage space I had several contractors come by to provide quotes. My main problem with this has been several of the garage "specialists" have suggested that I do not require footings to be 4' below grade (live in Calgary, Canada. It gets cold!). This seams odd to me as it is my understanding that getting footings at or below the frost line helps to prevent frost heaving of the walls and adds to the stability of the structure.

If it were you and you wanted to install in slab heating would you want footings at or below the frost line with fully insulated foundation walls?

Why would you not want footings to be at the frost line?

Thanks so much for any input even if it is contradictory to my current thinking.

Hi there So how did your garage build go ?

foundation depths and frost lines

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