Stupid footer question

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

Reply to
Bill
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Top of the footing.

Reply to
Pierre Levesque

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

Reply to
EDS

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.

Reply to
Edgar

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.

R
Reply to
RicodJour

Didn't you know that this is a question that you have to ask your engineer????? He would design the footing correctly and the correct size.

CID..

Reply to
Chuck News

How do you know the OP requires an engineer for a garage where he is? His is a question, yours is an assumption.

R
Reply to
RicodJour

"Chuck News" wrote in news:vtGdnffuAoWiLmDanZ2dnUVZ snipped-for-privacy@comcast.com:

Now that you got that off your chest do you have a real answer?

If I could afford an engineer I wouldn't be asking this here and since buildings have been built for quite a long time before there were engineers I expect that with the right input I can get by without one now.

Bill

Reply to
Bill

Does that mean that you are supposed to get a permit and you won't, or that one is not required?

R
Reply to
RicodJour

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

Reply to
EDS

More complete information:

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R

Reply to
RicodJour

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...

Reply to
Pierre Levesque

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.

R
Reply to
RicodJour

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. EDS

Reply to
EDS

"EDS" wrote in news:KKudnSMgwcokxWPanZ2dnUVZ snipped-for-privacy@comcast.com:

How do you guys handle a non-basement foundation?

Bill

Reply to
Bill

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:

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Where were you building?

Reply to
++

The North Slope, DEW line facilities. Also a "hotel" at Thule AFB in Greenland. EDS

Reply to
EDS

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. EDS

Reply to
EDS

On 10 Apr 2008, EDS wrote

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...)

Reply to
HVS

consider doing an FPSF "Frost Protected Shallow Foundation" where you are basically doing a flat slab but you place rigid insulation on teh outside face of the foundation and then a foot or so below grade you lay more rigid insulation in a horizontal position and extending out a few feet around the entire perimeter of the foundation

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An excellent design guide in pdf format:
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Reply to
Pierre Levesque

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