Brick question

[diovol]

So actually there are a few different topics in this but im really only worried about 1. I live in ottawa ontario so it gets like -40 in the winter and Im in the middle of building (or preparing) for a brick light post to be put up along the side of my driveway. My concern is that my friend who is gonna lay the bricks for me tells me I have to dig the hole about 1ft below the frost line, so around 4ft deep then make the form and poor the concrete footing for the brick.... Is this accurate.

thanks

 

[Stuart in MN]

Sounds about right, but confirm what the frost line depth is in your area. I did a quick google and it appears to be 1.5 meters, or nearly 5 feet.

 

[lilredex]

Even 4 Ft seems like over kill. Don't think you are ever going to see -40 there.

Our weather is not a lot different and I built something similar 30 years ago and it is still standing perfectly. It was a block corner post and the foundation was one existing block submerged in the ground.

If you were in Edm. or Wpg. maybe something to be concerned about............

This thing.......



Uploaded with ImageShack.us

 

[Zeke]

School me (a SoCal builder) on frozen soil. What's it gonna do to a post? Pinch it off like a pimple? Say he puts a bunch of steel in the thing, pours Type IV concrete and goes down 2 feet. What's the worst that will happen?

 

[diovol]

Even 4 Ft seems like over kill. Don't think you are ever going to see -40 there.

Our weather is not a lot different and I built something similar 30 years ago and it is still standing perfectly. It was a block corner post and the foundation was one existing block submerged in the ground.

If you were in Edm. or Wpg. maybe something to be concerned about............

This thing.......



Uploaded with ImageShack.us

not to start a ******* match by any means but do a weather history check of ottawa, we have seen -40(with the windchill) almost every year, I know you live in toronto but as far as canada goes vancouver and toronto might aswell be the canadian florida for winters, remember there is no comparisson because toronto is the same city that literally called in the army to help clean the roads after like a 6inch snow fall.



thanks though

 

[Eastpark]

Yup - Dig it deep or it will eventually heave and then lean. You sure can tell who didn't do that - looks like a lot of little 'leaning towers of Pizza'

Paul
(Navan, ON)

 

[Cougar]

School me (a SoCal builder) on frozen soil. What's it gonna do to a post? Pinch it off like a pimple? Say he puts a bunch of steel in the thing, pours Type IV concrete and goes down 2 feet. What's the worst that will happen?

Won't hurt the post, but if you don't get below the frost line it could start to lean after a few winters.
Same with building decks around here, I believe it's 42" deep for the posts.

 

[buildmyown]

School me (a SoCal builder) on frozen soil. What's it gonna do to a post? Pinch it off like a pimple? Say he puts a bunch of steel in the thing, pours Type IV concrete and goes down 2 feet. What's the worst that will happen?

If you dont go below the frost line as the soil freeze's and thaws between seasons the frozen soil will move or push things over. In your example over time it could push it right out of the ground or make it lean because the base is not set in solid ground. Soil below the frost line stays stable so by having stuff set in that it will allow the soil above the frost line to move around the object as it freeze and thaws. I might not be explaining it 100% correct but you should get the idea.

To the OP check local codes a simple phone call or net search should tell what your frost line is. I know here its 4 feet.

 

[tcianci]

For Milt and others who have been blessed to not have to deal with frost:

Any type of soil can and will retain moisture. When the temperature drops below freezing, the moisture will freeze and it causes the soil to expand. This is known as frost heaving. If a structure is not footed in the soil at a point where the temperature never goes below freezing, the heaving action can move, **** or otherwise wreck the structure. In a climate where frost is common, the closer the footing is to the surface, the worse off you are because the soil goes through more freeze/thaw cycles near the surface. So, in short, footing a structure on soild that never goes through the freeze/thaw cycles is good building practice and required by every code I've ever seen, but remember I'm in New England.

 

[theoldwizard1]

I don't understand exactly what is happening but ...

When we get our first "deep freeze" (temps below 20F for several days in a row) smoothly raked ground become very uneven. Little pieces of dirt are pushed up and some appears to have dropped.

In the old days, people poured concrete pads for A/C compressors and had to be sure they went down below the frost line. Then someone realized as long as the connection to the house could flex, the pad could just rest on the top of the ground and shift around with the freeze/thaw cycle.

 

[ishiboo]

I don't understand exactly what is happening but ...

When we get our first "deep freeze" (temps below 20F for several days in a row) smoothly raked ground become very uneven. Little pieces of dirt are pushed up and some appears to have dropped.

In the old days, people poured concrete pads for A/C compressors and had to be sure they went down below the frost line. Then someone realized as long as the connection to the house could flex, the pad could just rest on the top of the ground and shift around with the freeze/thaw cycle.

Yes. When you have a large slab, for example, it's important it doesn't move, because part of the slab can move up, part down, and you can get hollow spots, major breakage, etc.

An item like a post like that is not going to break apart from the movement (unless there's also terrible workmanship to go with it), but it can easily move and lean. Doesn't take much more than half an inch on one side, multiply that by X feet high and it'll look like **** in no time.

 

[koditten]

As for the opening post, is the temp. -40 degrees, *C or *F?

 

[ishiboo]

As for the opening post, is the temp. -40 degrees, *C or *F?

-40*C is -40*F

 

[koditten]

I was wondering if someone notice my lame attempt at humor I deal with compressed air driers and this is the benchmark temp we use, confuses the hell out of the new guys. (me too).

 

[Gary S]

Yes. When you have a large slab, for example, it's important it doesn't move, because part of the slab can move up, part down, and you can get hollow spots, major breakage, etc.

Exactly. A slab poured on the surface can "float" as the ground freezes and thaws. That is why it is called a floating slab. I also live where the temp drops to -40 to -45 and most garages here are still built on floating slabs with no deep footings. It works with no problems. You do need a thickened edge so the slab is strong enough to float as a unit instead of breaking up. Nobody cares if the garage moves an inch or so during the winter.
A house is different because it will be fully heated all the time so the temperature of the concrete cannot reach freezing temperatures. A fully heated house needs footings and a support wall 4' below grade.

 

[xrdad]

Just as important as getting below the frost line is the material you put back around the structure.
If you put clay soil back around it, that same moisture + hard packed dirt will 'grab' the structure and lift it.

Not hard to find that example.. just look at a poorly installed fence post.. happens all the time. Gravel is your friend here.. might even be other options (plastic tarp)?

In your case, the biggest problem may come from the traffic around that structure. When you compact the snow walking/driving by it because you'll drive the frost down. The snow is actually an insulator if it isn't compacted.

(Well, that's the way I learned it anyway )

 

[Rickstir]

I have a floating slab(new) that butts up agains another one. There is a conduit in the first slab and the electrick box is on the old one. In mid-winter the conduit bows out about 2 inches. Now in the summer it is straight as an arrow.

 

[Falcon67]

School me (a SoCal builder) on frozen soil. What's it gonna do to a post? Pinch it off like a pimple? Say he puts a bunch of steel in the thing, pours Type IV concrete and goes down 2 feet. What's the worst that will happen?

Called "frost heave". We don't usually have that problem here and there is no frost line. But last winter it stayed below freezing long enough that it heaved the sidewalk some in the front of our old house. In real cold winter areas, if your foundation is not down far enough it'll try to shove the house right out of the ground.

 

[Zeke]

Thanks everyone for the explanation of frost heave. I won't try to re-invent the wheel, but from the explanations it seems a foot or so below the ultimate frost line for a post would be terribly inadequate. One foot of non frozen soil vs. 4 feet of heaving soil doesn't compute to any stability to me. On a linear footing, yes, more so.

Sounds like he needs to go about 10' down and rebar the hell out of it. For all the trouble I would not build a brick post in snow country.

 

[iron_worker]

I know that here in Saskatoon, Saskatchewan we see -40C every year pretty much without fail for at least a few days (and sometimes a lot longer!).

The frost line here is around 6ft I believe and I know the requirement for deck piles(for decks which are over 6ft high ... and I'd assume it would be similar rules for basements etc) is that they have to be augered down to 8ft deep. It seemed extreme to me when I read it but themz the rules!

IW

 

[6768rogues]

In western NY our frost depth is 42 inches. Typically installations are done to about 4 feet. I think you need to go deeper as you're way north of us. Dirt does not heave, the water in the dirt freezes and causes heaving. I have seen well drained sandy soil that did not heave because there is not much moisture in it. Those are the lucky ones that are not deep enough but were ok.