Pier Foundation

[AKDon]

I have been searching and scowering the past couple days trying find out if the foundation I put in last fall will be sufficient for the cabin I am building this summer.

First the size of the cabin:
24 x 32 - 9 ft walls, 12:12 pitch roof. Log gables with a ridgepole and 2 purlins. Logs will be milled on 2 sides and will use the butt and pass method. I have the Logosol M7 so I could mill 4 sides to lose a bit of the weight if needed. But I really don't want to do that.

Now for the foundation that is already in. Timber pilings (treated, wrapped in plastic, plus a layer of blue insulation foam to prevent heaving) are set below the frost line (36") with a base of sakrete. They are arranged in a 5 x 4 array for a total of 20 pilings. Diameter is between 9 - 12 inches for each piling. The four corner piers are the largest of the piers. Right now I am thinking about leaving them about 36" off the ground to leave a little crawl space, but prevent a ton of movement. We have a clay/gravel mixture for soil here.

So, experienced foundationists & log builders- does this cabin stand a chance of staying up? What can I do to improve her odds? What would you do in my shoes. This is off the road and on a tiiiiight budget, bear in mind. Thanks a lot!

-Don

[loghousenut]

Don,

If it was me I would change a few things. You won't like what I know has to be said so I will let you hear it from the next member.

PS... Sounds like a fun project and the tight budget is right up our alley.

[Mosseyme]

Lhn,
You have always been kind to me when I needed a little help along the way.

[Basil]

can you tell us more about the concrete base? thickness, diameter, etc? log diameter? stacking green or cured? might get more answers with more info! Sounds fun, but in my area of the country I'd never use wood for foundation work. Interested to hear what others say. Is rockengeneer around?

[AKDon]

The base is 12 inches of sakrete about 3 inches deep, plus about 4 inches alonge the side of each pier. Piers are around 10 inches each. The logs I am stacking are going to be roughly 12 inches in diameter and will be more cured than green (a lot of standing dead that isn't rotten). I was looking at maybe sticking another pier in between the ones that are set in place on the perimeter to give it more stability (for a total of 26 piers around the perimeter and 6 on the inside). I am not worried about them rotting- a lot of people up here use this method (even without treating, wrapping in plastic, etc) and they last as long as they can keep them dry. My concern isn't the rot, it's the weight. Thanks so far.

[StressMan79]

if you have a footing, I don't know what the bearing capability of your soil is... but say it is 2500 psf, (from http://www.concretenetwork.com/concrete/footing_fundamentals/footing_dimensions.htm), I would assume in your case, logs are ~ the same weight as a "4-Inch Brick Veneer Over Wood Frame or 8-Inch Hollow Concrete Masonry" you need between a 12 and 15 inch wide footer. You have around an 18" disc you are setting all your piers on. so you have 20 of them, or about 5090 sq inches (35sqft) of bearing area. that means that you can bear 88kip (thousand pounds) of weight. the corresponding footer has a minimum of 112 sqft, more than 3 times your bearing area. You could not get the recommended bearing area for a 1 story stick built home on 4000psf soil...

In short, I would not trust that foundation as far as I could throw it.

[edkemper]

> In short, I would not trust that foundation as far as I could throw it.

The problem you're having is asking us to guess. Most of us do not have the math expertise that StressMan has. But, from experience, I'd believe anything he says on this subject.

Now comes the question of how to fix the problem. The best I can offer is that our "taught" style of piers is far different than what you built. I'd also like to share that the cost of the class is substantially cheaper than the foundation you built and probably cheaper than what it'll cost you to salvage the work you've already completed. I'm betting that the fix will require far more than a simple inexpensive solution. A reason to consider the class before going forward. Delaying any more work might be the cheapest way to go.

I'm glad you're here and hope this will all work out for you.

[StressMan79]

the problem besides the bearing issues is that you are building it out of wood. dirt has lots of nasty bacteria that cause rot. It also has plenty of water to let them grow. If you trust the backteria not to eat the piers, you can do the following.

You said you had 20 of these piers. If you dug in between each so that you had say 40 of them and poured an 8" thick pad that was 36 inches on a side, reinforced with some rebar, then built a stack of cinder blocks (tied down to the base with L bar), and filled the blocks (with crete) to the height you wanted, then put down the recommended 2x PT and 90# felt, You'd be OK.

However, like Ed says, just spend the money. learn the best way to build (piers or otherwise) and you'll be much happier in the long run.

-Peter