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
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.
I always thought the same though we never have to deal with frost lines
where we build so I don't know. The way I understand is that SOMETHING has
to sit on solid ground that won't shift to much, so if the bottom is below
the frost line, the rest "should" stay relatively put. That's all pure
assumption though, so take it with a grain of salt.
Basically here in California the frost line is above where a standard
footing would be anyways, so we build em like normal. This makes me think
that it's the bottom that must sit below the frost line.
The frost line is an imaginary line and, hopefully, not the actual
depth of frost - otherwise you're in trouble. The frost line is a
design criteria and the footing should sit on undisturbed soil no less
than the stated depth.
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 /
Where were you building?
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
Architectural and topographical historian
That past few winters we've had little snow and brutal cold
temperatures. A couple of winters ago, almost everyone's septic systems
froze up. Frost down 7' in most places with a few reaching 8'.
Frost design depth here is 5'... But most people just opt for the
additional small expense and go 8+' with a basement (unless they have
water table issues).
Do sunflowers like to have "wet feet"? Maybe you should look into some
native plants that like wet/boggy conditions...?
Problems with sunflowers in wet soil:
How wet is your soil? Is it constantly wet, or intermittantly? Is the
area in full sun, part sun, part shade, or deep shade? IIRC, you're in
hardiness zone 6, is that correct:
THis part of the site allows you to enter as many (or as few) conditions
are you require, and then get back a linked listing of good candidates:
Since the footing supports the foundation wall or basement slab isn't it
logical that the footing should be below the frost line so as to not be
subject to the freeze/thaw cycles that occur above the said frost line?
That's the main reason...
The frost line is a design criteria, and, as with all design criteria,
incorporates a factor of safety. If you want to pay more to build in
an additional factor of safety by excavating deeper, well it's your
money. The primary problem is the moisture in the soil, so if you
have poorly draining soils, don't have foundation drains, and your
gutters dump water next to the foundation then I would agree that
going deeper is a good idea. Otherwise it's wasted money.
Backfilling should be done with a structural fill not susceptible to
freezing. A damp backfill with many fines just tossed back in will heave a
foundation just by being frozen to it. I always backfill with gravel to
within 8" of the surface, place a geofabric or tarpaper sloped strongly away
from the building for several feet, and complete with topsoil. The geofabric
or tarpaper keeps the fines from infiltrating the gravel and directs them
(and some moisture) away from the building. Any basement in our climate (New
England) should have drainage tiles set at the bottom of the excavation on a
substantial bed of gravel, sloped to an outlet. In some cases I've used 2
sets of drainage tiles, one half way down.
Just go down 4' and backfill same way. Usually no drainage tile needed. Most
of my work is commercial work, so houses may be a bit lighter. The 4' is a
given and I've done 6' in the Northeast Kingdom area of Vermont.
Slabs-on-grade make for cold feet.
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