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kebwi 09-07-2009 09:10 PM

Seattle frostline
I'm curious if any other Seattle builders used a footer or sonotube piles or anything else like that? I was planning on the original Pompeii directions: dug just deep enough to level the ground, couple inches of pebbles, rebar/mesh slab (still unsure about the mesh). I liked the simplicity. Grrr.

I believe the Seattle frostline is 18", which would be two or three blocks deep.

Is it necessary? :-/


dmun 09-08-2009 03:55 AM

Re: Seattle frostline
A well drained bed of crushed stone, then a slab, should be fine if you chimney won't stand much taller than you. Well drained is the key: water in contact with the foundation is what causes frost heave. If you're building in the low spot in your yard where the water runs when it rains, you will need footings, or if you are building a tall chimney.

Sonotubes under the slab is the worst of both worlds, unless you use the special flared footing they sell for them. It just gives something for the ice lenses to grab on to.

ThisOldGarageNJ 09-08-2009 04:59 AM

Re: Seattle frostline
Hi Keb,
I built mine on a 12" slab using rebar and wire, over about 4-6 inches of gravel, I also have an 18" frostline (i believe) of course its too early to tell as I havent been thru a winter yet, but I dont forsee any problems as I have a 10 year old 8x8 shed built on a 6x6 pressure treated rr tie foundation and that hasnt budged in all that time,,
Good luck and start digging,

kebwi 09-08-2009 05:38 AM

Re: Seattle frostline
Holy smokes, your foundation is a foot thick? May I ask why?

Thanks for the input guys.

kebwi 09-08-2009 06:13 AM

Re: Seattle frostline
@dmun, I was referring to Neil2's "pile" comments in this thread:

dmun 09-08-2009 06:57 AM

Re: Seattle frostline

@dmun, I was referring to Neil2's "pile" comments in this thread: (Cold climate foundations)
The quote in question:

Easy to do. I just dug down 4 feet with an ordinary hand held post hole digger. Put in a couple of 3/8 rebar, filled with concrete to about 6 inches of the surface. A second pour, from there up to the bottom of the structural slab I used 7 inch diameter "sonotube" cardboard tube forms - available at any builder supply.
If I understand correctly, Neil2 did put proper footings at the bottoms of the sonotubes. Most people just dig and fill, and it's not a cure for frost heave, it can even make the situation worse. The tube makers do make a flared plastic bottom for the tubes that provide proper footings in one pour, or you can pour your own footings.

But really, in most cases, its' not necessary.

ThisOldGarageNJ 09-08-2009 07:51 AM

Re: Seattle frostline

Originally Posted by kebwi (Post 63946)
Holy smokes, your foundation is a foot thick? May I ask why?

I framed it out with 2 x 12's and poured on top of the rock, I just wanted to make sure it wasnt gonna move, It might have been easier to just pour footings, but his is another thing more experience has taught me


papavino 09-08-2009 10:59 AM

Re: Seattle frostline

I just poured some pea gravel (about a yard) and then built a 6" slab, which is probably overkill.

kebwi 09-08-2009 11:36 AM

Re: Seattle frostline
Thanks guys.

Wiley 09-08-2009 12:00 PM

Re: Seattle frostline
Well as you don't need a building permit I ask a question, perhaps a few:
How long have you lived in Seattle? In all the time you have lived in Seattle have you ever found that your yard froze long and hard enough that you had problems with your sidewalk heaving? Your driveway? I live further north than you and perhaps more maritime than some parts of Seattle, (seeing as how I'm on an island surrounded by water to the west less than 2000ft and perhaps a bit more to the east). But inspite of once every 7 years or so it freezing such that shallow ponds freeze over enough to skate on, I really think the 18 inches is major overkill and perhaps simply a COA on the part of the building department. But then I think the IBC is inane, one building code for all climes, gov't at its worst.

Just my opinion, and no I made no such thickness for my WFO (which wasn't inspected) or either of my shops or my home (which were).


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