Wood chip insulated footings

[hnash53]

There's always lots of talk on this forum about insulating footings in cold climates.  And it almost always involves digging down 36-48-60 inches and using concrete.  I have a cabin in Wyoming at 8000-8500 feet.  My footings are 6 inches to 10 inches deep, packed with gravel with an 18 inch patio paver on top.  They've never moved.  It gets cold up there, below zero.  So, what gives?

I noticed that some people we knew planted potatoes in their gardens in Montana.  Instead of digging up all the potatoes at the end of the growing season, they just put their lawn clippings over the still-buried potatoes, and then whenever they wanted some fresh garden-grown potatoes in winter, they just went and dug them up and they weren't frozen.

Hmmm. I thought.

Knowing that insulation works by retarding air movement, and that it needs to be kept dry, I came up with the idea of insulating my very shallow footings with wood chips.  I piled up about 6 inches of wood chips around each footing, sloped it away about 2 feet on all sides, then put down tarp material ... about a 4'x4' piece ... then added two inches of soil, then another 2 inches of wood chips.  You can see the piles of wood chips around the footings on the following link.  Scroll down about 1/3 of the page and you'll see the deck and the wood chips piled around the footings.

http://www.countryplans.com/nash.html

Snow accumulates under my cabin up to about 3-4' in depth ... yeah yeah I need to do something about that ... and then melts yet the footings remain stable.

I'm going to build another place sometime soon, a larger 20x40 and hope to use the same type of footing.  Of course soil type is a critical thing.  There are some places where concrete footings 5' deep are essential ... but then there are a lot of places where concrete isn't necessary.

In my opinion, concrete is over-rated, over-used, and in fact it appears that it is spontaneously generated in the hard-heads of inspectors and contractors.  A foundation with no concrete??!!  LOL

Anyway, there ARE other ways to create firm foundations without the use of concrete.

After 5 years of this, I've only had to add a little more wood chips to the footings.  The key, I think, is to keep them dry so rotting doesn't occur.

[optionguru]

I can't tell you how many times I've looked at your site in the last few years.  Your cabin was my original inspiration to buy some off-grid land and build a get-away cabin.  I know this has nothing to do with your footings but I had to take the opportunity to tell you the updates and pictures on your site are appreciated.

Peter

[glenn kangiser]

If it works you must be doing something right, Hal.

Drainage is one of the keys John mentions, so that water can get out of the gravel footings.  Sounds like you have that.

[John Raabe]

Thanks for that update Hal.

Concrete footings and foundations are often massively overbuilt for the worst case scenario.

When the soil is low in clay and well drained such expenses are not needed - a solid foundation can be much simpler as your project demonstrates.

For those who haven't seen it, the article on Post and Pier Foundations. Hal has combined this with insulation as he shows. His footings are above local forst depth, I expect.

[skiwest]

Speaking to a Civil Eng on this and per code you can insulate rather than going below the frost line but the area needed to be insulated for a small building might as well dig.  Now that might not nbe in the housing code but in the full blown code.

Actaully the code takes into account the type of soil for the size of footings. Big diffference between solid bedrock and loose clay .  Take a look at the big foot site and there is a calc sheet for it.  

The only problem with your insulated footing is that the chips will rot eventually and loss their R value.  Also it my be working now but if you got a very wet period followed by a week long -20 period you may have problems.  

I guess I look at the code differently.  To me its a minimum.  

[hnash53]

From my limited understanding of "codes" it seems that I have read ... maybe on this site ... that footing depths are usually double what the frost depth is...kind of a CYA (cover your ass) thing.

By the way, John, the frost depth around here is somewhere in the 24-36 inch range (others around here say even more)....my footings have been dug 6-10 inches.

I have protected the wood chips from moisture (and therefore rot) by covering the bulk of them with tarp material which then is covered by some soil and more wood chips.  Snow builds up deep around the footings but all has remained stable through 4 winters.

By the way, isn't a foundation like this an advantage in earthquake prone regions?

[Amanda_931]

In a cold climate--not mine--snow is a pretty good insulator.  I gather you're supposed to treasure it.

If it mostly turns to slush and run-off after three days it isn't.

IIRC, the shallow insulated frost free foundations can be pretty shallow.  With the insulation angling outwards as well as down or just going down and then out.  As shown here--with a slab 12" deep around the edges, angling up to half that a foot or so in.

http://www.cs.arizona.edu/people/jcropper/desguide.html



My recollection is that this is what the guy who sells the "plans" for the vertical log cabin calls the "alaska foundation."

[John Raabe]

The diagram Amanda has shown allows insulation to move horizontally to provide frost protection equal to going down the same distance. This traps the core heat of the earth. as well as heat from the building, and keeps the footings from freezing.

This detail can be interesting sometimes. If this is really an "Alaska" footing, and you are far enough north, then the same foundation can be used in permafrost areas to keep the footings from thawing and getting slushy in the summertime.  
(In an unheated building).

[Okie_Bob]

Seems to me you'd have a termite problem with the wood chips. How do you keep them under control?

I've often wonered myself, about the way we build foundations here in central Tx on clay soils. The expansion and contraction is bound to cause problems and I don't see how you can say 'if you dig it deep enough' you won't have a problem. We also have a saying around here that there are only two types of houses in Tx, those with foundation problems and those that are going to have problems! Guess that is why there are so many foundation repair companies here.
Okie Bob

[John Raabe]

Bob is right. If you build in expansive soil there can be long term problems no matter how deep you are. In some parts of Canada they have a lovely little problem called "ice lensing" where a concrete basement, well below frost depth, can be lifted out of the ground when expansive wet clay adheres and freezes to the basement wall and lifts the whole house (or maybe just part of the basement wall) out of the ground!