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Stupid footer question Bill 04-09-2008
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Posted by EDS on April 10, 2008, 10:48 am



>
>>
>>
>>
>>>
>>>> Ok, here comes the stupid footer question of the month. I've been
>>>> researching info on constructing a garage and know that I have to have
>>>> a
>>>> footer below the frost line, which in my neck of the woods is 32
>>>> inches, my
>>>> question is exactly WHAT has to be below that line. Does the entire
>>>> footer
>>>> need to be below as in a 8 inch thick footer has the top of the footer
>>>> at
>>>> 32 inches or does the footer just have to sit or have its bottom at the
>>>> frost line.
>>>>
>>>> I originally thought it was the first way but have since seen some
>>>> inferences that it might be the second way. I want to do this correctly
>>>> but
>>>> if I can start the footer 8 inches higher I save on hand digging 16 x 8
>>>> inches of dirt and save on 8 x 8 inches of concrete for the stem wall
>>>> thus
>>>> lightening the load on my wallet and back.
>>>>
>>>> Bill
>>>
>>> Top of the footing.
>>>
>> Around here it is a 48" frost line and to the BOTTOM of the footing. Why
>> the top? What if the footing is 2' thick?
>> EDS
>
> If its 2' thick than the ditch has to be 2' deeper.
> What the point in putting the bottom of the footer ABOVE the frost line?
>
>
Not above, at or below. I just checked with a structural engineer and the
local Code. As Rico said it's an imaginary line, just get below it. As you
get further North into deep snow country, it never gets below 6' as the snow
is an insulator. However even further North in permafrost areas, the
buildings must be insulated from the earth to avoid melting the permafrost.
I worked on one project where we put in 2' of stone on the permafrost, and
built a wood frame sitting on the stone to support the building, with a 3'
space between building and stone. Another way is to set wood piles into the
ground down to below the permafrost summer melt line, and build your
structure several feet above grade.
EDS



Posted by RicodJour on April 10, 2008, 10:56 am
>
>
>
>
>
>
> >>>> Ok, here comes the stupid footer question of the month. I've been
> >>>> researching info on constructing a garage and know that I have to have
> >>>> a
> >>>> footer below the frost line, which in my neck of the woods is 32
> >>>> inches, my
> >>>> question is exactly WHAT has to be below that line. Does the entire
> >>>> footer
> >>>> need to be below as in a 8 inch thick footer has the top of the footer
> >>>> at
> >>>> 32 inches or does the footer just have to sit or have its bottom at the
> >>>> frost line.
>
> >>>> I originally thought it was the first way but have since seen some
> >>>> inferences that it might be the second way. I want to do this correctly
> >>>> but
> >>>> if I can start the footer 8 inches higher I save on hand digging 16 x 8
> >>>> inches of dirt and save on 8 x 8 inches of concrete for the stem wall
> >>>> thus
> >>>> lightening the load on my wallet and back.
>
> >>>> Bill
>
> >>> Top of the footing.
>
> >> Around here it is a 48" frost line and to the BOTTOM of the footing. Why
> >> the top? What if the footing is 2' thick?
> >> EDS
>
> > If its 2' thick than the ditch has to be 2' deeper.
> > What the point in putting the bottom of the footer ABOVE the frost line?
>
> Not above, at or below. I just checked with a structural engineer and the
> local Code. As Rico said it's an imaginary line, just get below it. As you
> get further North into deep snow country, it never gets below 6' as the snow
> is an insulator. However even further North in permafrost areas, the
> buildings must be insulated from the earth to avoid melting the permafrost.
> I worked on one project where we put in 2' of stone on the permafrost, and
> built a wood frame sitting on the stone to support the building, with a 3'
> space between building and stone. Another way is to set wood piles into the
> ground down to below the permafrost summer melt line, and build your
> structure several feet above grade.

More complete information:
http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd026_e.html

R

Posted by ++ on April 10, 2008, 3:12 pm


EDS wrote:

>>
>>
>>
>>
>Not above, at or below. I just checked with a structural engineer and the
>local Code. As Rico said it's an imaginary line, just get below it. As you
>get further North into deep snow country, it never gets below 6' as the snow
>is an insulator. However even further North in permafrost areas, the
>buildings must be insulated from the earth to avoid melting the permafrost.
>I worked on one project where we put in 2' of stone on the permafrost, and
>built a wood frame sitting on the stone to support the building, with a 3'
>space between building and stone. Another way is to set wood piles into the
>ground down to below the permafrost summer melt line, and build your
>structure several feet above grade.
>
>

I've read some interesting things about floating foundations on
permafrost in Siberia where the permafrost is becoming not so "perma" in
some areas. In one ara what is made secure below the frost line is made
secure by not disturbing the frost line.

study: http://www.springerlink.com/content/qj9v8exf77ger3xb/
on: http://en.wikipedia.org/wiki/Permafrost
scary:
http://www.thewe.cc/weplanet/news/arctic/permafrost_melting.htm#this_is_real


Where were you building?

>EDS
>
>
>
>
>


Posted by EDS on April 10, 2008, 5:05 pm



>
>
> EDS wrote:
>
>>>
>>>
>>>
>>Not above, at or below. I just checked with a structural engineer and the
>>local Code. As Rico said it's an imaginary line, just get below it. As
>>you get further North into deep snow country, it never gets below 6' as
>>the snow is an insulator. However even further North in permafrost areas,
>>the buildings must be insulated from the earth to avoid melting the
>>permafrost. I worked on one project where we put in 2' of stone on the
>>permafrost, and built a wood frame sitting on the stone to support the
>>building, with a 3' space between building and stone. Another way is to
>>set wood piles into the ground down to below the permafrost summer melt
>>line, and build your structure several feet above grade.
>>
>
> I've read some interesting things about floating foundations on permafrost
> in Siberia where the permafrost is becoming not so "perma" in some areas.
> In one ara what is made secure below the frost line is made secure by not
> disturbing the frost line.
>
> study: http://www.springerlink.com/content/qj9v8exf77ger3xb/
> on: http://en.wikipedia.org/wiki/Permafrost
> scary:
> http://www.thewe.cc/weplanet/news/arctic/permafrost_melting.htm#this_is_real
>
>
> Where were you building?
>
>>EDS
>>
>>
>>
The North Slope, DEW line facilities. Also a "hotel" at Thule AFB in
Greenland.
EDS



Posted by HVS on April 10, 2008, 5:15 pm
On 10 Apr 2008, EDS wrote

> However even further North in permafrost areas, the
> buildings must be insulated from the earth to avoid melting the
> permafrost. I worked on one project where we put in 2' of stone
> on the permafrost, and built a wood frame sitting on the stone
> to support the building, with a 3' space between building and
> stone.

And it's a real risk: I took a photograph in the late 1970s of a new
house in Yellowknife that had tilted about 15 degrees at one corner
when the developer got it wrong.

(My parents were working in Yellowknife at the time, and I went up
there from Edmonton, where I was living, for Christmas. I moved to
England in 1982, and I *still* have zilch nostalgia for that
climate...)

--
Cheers, Harvey
Architectural and topographical historian



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