thoughts on spikes?

[muldoon]

I was looking at other cabin sites still trying to work out some details in my head around floorplans and the like and stumbled across a foundation system that I had not seen or considered before.  I was looking at

http://www.summerwood.com/construction/cabins/foundation.html
http://www.summerwood.com/information/foundation.html 

specifically what was new to me was what they called the super spike method.  I used something very similiar to this approach on my back porch in the city, but there is no real load on those posts.  For what I did, it works great and was easy to install.  I had not considered it much for a larger or freestanding structure like a cabin but now I am starting to think about it. 

I found a few commercial offerings, such as groundtech light duty and medium duty spikes:
http://www.hooksandlattice.com/groundtech-ground-master.html

and a simpson variety ground spike as well.. 
http://www.strongtie.com/products/connectors/ezfence.asp

4 pack for 10 each - 12 gauge powder coated steel. 
http://www.probuildingsupplies.com/item--Deck-Spikes-4x4-4-Count--pbs110.html

and here is a heavy duty version I found that comes in a 4pack for $60 (15 each)
http://www.probuildingsupplies.com/item--Heavy-Duty-Deck-Spikes-4x4--2270.html


Can anyone comment on the viability of this for a small cabin structure?  Could they be interchangable with the deck-block style of foundation for load calcs?  Seems to be a bit DIY friendly and offers some uplift protection over the blocks.  I would appreciate any insights from the board, especially if you see any red flags. 

[TheWire]

There is a heavier version of the spike footing.  Its a pin footing and info can be found at www.pinfoundations.com  It has 4 - 2' spikes that get driven at an angle through a center core.  The spikes then distribute the weight and provide uplift resistance.

[glenn kangiser]

Even the pin foundations required engineering (they provide for a fee if I recall correctly) if being inspected so I'd say it's a use at your own risk kind of thing unless you get engineering -

If the engineer is not familiar with local soil conditions then it may not do you much good.

[muldoon]

Thanks for those answers, I guess I should add some background information here to help go on. 

No building permits required, only a septic permit from the state.  Therefore no engineering documents required, nor do I have anyone necessarily looking out to make sure I dont do something really dumb.  No frost zone, but I do have expansive clay/sand loam soil.  Previous digs and the USGS soil report a limstone shelf about 4' down acting in a bedrock capacity.  Soil is well drained, sandy on top with a 1-3 degree slope that moves water away.  The slope is the reason for the posts. 

The pasture at the front leading in is very muddy with huge ruts, mostly from hogs rooting up the place.  The net affect being that getting a concrete truck in to pour will be a huge ordeal if possible at all.  My back is not as great as it once was so the idea of digging 15  holes (either by hand or 2 man auger) then mixing concrete in a wheelbarrow has me already cringing.  If these spikes are an option I am not opposed to the upfront cost to save myself alot of hurt.  To be honest I would rather spend more of my time on the inside finish work than heavy dirt work any day. 

The problem I see with these posts is that it doesn't really sit on anything.  As I understand it, at the bottom of a traditional footer you have the base be it concrete block or just the tube footing.  Pressure is directed from this base downwards and out at an angle transitioning the load evenly under it.  These spikes are pointed so there is no easy way I see to have the soil under it actually bear the weight except from the collar where the 4x4 connects at ground level.  The collar is the second issue, as it is a point of weakness because no matter how strong the 4x4 or steel is the entire assembly can only be as strong as the 4 inches or so where they meet.  Finally, the last question comes to placement.  I am pretty sure that the weakness in this system is the ground.  For other designs you can measure lengths of spans and determine lumber dimensiosn to meet them.  I think here you may need more posts because the ground itself (risk of sinking, loosening) is the primary concern. 

For sake of discussion, I am thinking that posts should be 4 foot apart for beam lengths, and that the spans between parallel beams should be at or less than 8 feet.  The posts would be PT 4x4, and the beams PT 4x6 over that. 

I am hoping these points spur some more discussion on this, anyone see any reason why this wont work?  Am I underestimating the weaknesses above? 

[glenn kangiser]

I think you have a good picture of it and that is also a reason I would like to get to the limestone shelf if it was me rather than floating in the mud.

Part of the reason the mud is so unstable and sloppy is that the limestone shelf impedes drainage causing an unstable bathtub of mud above it until the water slowly drains or evaporates.  Clay is slow to get wet and slow to drain prolonging the problem.

[muldoon]

Thanks Glen, I appreciate you sharing your knowledge on this.  Deep down I know your right and that sometimes the shortcuts just don't pan out in the long run. 

[MountainDon]

....sometimes the shortcuts just don't pan out in the long run. 

Very wise words in my opinion.

I don't know much about mud other than I hate it.

If I pretty much knew that bedrock was four feet away I'd dig, drill, whatever at least one test hole to confirm the presence or absence. Make the hole where it can be used later.

  For sake of discussion, I am thinking that posts should be 4 foot apart for beam lengths, and that the spans between parallel beams should be at or less than 8 feet.  The posts would be PT 4x4, and the beams PT 4x6 over that.

The distance between posts under the beams depends on the loads and what size the beams are. Smaller beams need more posts closer together.

Similarly the distance between the spans would partly depend on what you plan to use for the floor joists. By that I mean type and size of lumber, or other material.

Considering that you may be facing digging the post holes yourself you may want to explore the costs of increasing the beam size to reduce the number of posts. I looked at that when planning the foundation for my Little House. Johns plans call for 4x8 beams at 4 foot spacing. Changing the beams to 6x12 (built up) will allow 8 foot spacing and therefore fewer holes and posts. I ran the costs and the larger beams method does increase the materials cost some, but well worth the fewer number of holes to dig. In my case we're going to use concrete block piers, so that also means less concrete mixing.

Food for thought? I'm sorry, but I don't recall what you are planning to build; one story or two, size, etc. so can't make any suggestions for specifics.

[glenn kangiser]

If it really is only 4 feet I'd get help with a posthole digger or the kind on wheels and drill them...or someone with a Bobcat - tractor etc?

[Okie_Bob]

I think I'd consider building somewhere else. As Don said, I don't like mud either and it sounds like you are going to be
looking at a muddy bog year round? If that is correct, are you sure that is the best location on your property? Like Glenn said, this
is just like a bathtub with a very slow drain that is going to stay wet way too much for my taste. Just my opinion.
Okie Bob

[muldoon]

I think I'd consider building somewhere else. As Don said, I don't like mud either and it sounds like you are going to be
looking at a muddy bog year round? If that is correct, are you sure that is the best location on your property? Like Glenn said, this
is just like a bathtub with a very slow drain that is going to stay wet way too much for my taste. Just my opinion.
Okie Bob

No, not at all.  The ground drains very well, dont even get your boots muddy when it does rain.  It's sandy loam on top that slopes slightly and does not hold any standing water longer than an hour or so after a good storm.  It's under the topsoil that I have clay - which has expansive properties.  I do not have any frost depth at all here, just concerned about shrink/swell of the clay. 



here's a shot of the layer properties.  about 6 inches sand/loam, then clay


This shows the slope a bit, its higher ground on the right side:


It's good healthy soil, not muddy.  Springtime comes alive with a million flowers. 

[glenn kangiser]

Looks like the kids really love that.

[Okie_Bob]

Sorry, misunderstood Muldoon. So where are you located?
Okie Bob

[muldoon]

Food for thought? I'm sorry, but I don't recall what you are planning to build; one story or two, size, etc. so can't make any suggestions for specifics.

Well, I bought enchilada plans.  But to be honest I keep going back and forth on what I am going to do.  We have narrowed down on 16x24 but not sure what to put in after that.  I am also still working out the site stuff, which is a bigger effort than I first imagined. 

I finally have electric in and turned on with a 200 amp service panel and 4 gfci outside outlets.  I also got a deerstand built and elevated and feeder setup.  Did some pond cleanup work and got the stocking going for my goals later.  Next up is the gate and some fencework, and then a well.  Along the same time I would like to at least get the posts and beams in for a foundation in the spot figuring if I get a good foundation in now it will only make things easier later.  At this point I also have not ruled out a simple gambrel roof style barn with high enough walls to get a useful loft.  I can always use it no matter what else I decide to do later. 

Sorry, misunderstood Muldoon. So where are you located?

The place is in muldoon, texas.  Halfway between La Grange and Flatonia.  It's pretty much cattle country, with lots of big live oaks, pecans, some cedar and alot of hay production in the pastures.  I live and work in Houston. 

[glenn kangiser]

hmm Think I had barbecue at La grange, but I was trucking -- not at the little house.