Helical Pier Foundation

[nick_m]

Hello,

I'm planning to use helical piers to support a timber frame cabin, with sills supported by piers under every post, and conventional joists hung between them, running perpendicular to the bents. Should the posts rest directly on the sills (as shown below) or on top of the plywood sub-floor? I've seen more illustrations with the post on the sub-floor, but that material seems to be more compressible.

Also, I plan to enclose the cabin using conventional 2x6 framing with DIY modular panels fastened to the frame, offset using 5/8" furring strips to allow for interior installation of drywall (as described elsewhere on the forum). Since the framing will be fastened to the sills, rather than a rim joist, can I use a simple 2x4 ledger to support the panel instead of a sill plate? 

 

 

Thanks,
Nick 

[esarratt]

Normally helical piers are used in difficult soils (or slopes).  This is not an expense I would incur unless it was required by code (or an engineer).  I would talk to the local building department.

[Mooseherder]

We used them for an existing cabin this summer.   My original thought was to remove the front porch, pour concrete pad there then pull the cabin onto the pad, rebuild porch and add a bunkroom.  Instead I hired Postech and helped them with install.  I opted for 3 steel beams to put on top of the 6 piers.  Milled some 4x6 Spruce beams to go across the steel.  The cabin sits on the wood Beams.  I was able to save the porch on the lift and will complete the bunk room next time.  The nice part is it's done in less than a day.  The cost for the whole job was 4800.00.  Probably be less for you.  The charge for lifting and leveling was about 1200.  I have pics in phone and will post them later.  I wasn't happy with the job at first and had to do some work to correct things.  I'll write about it later. 

[Mooseherder]

Looks like she took more video than pics.  My wife was filming while we worked.  Can't wrestle her phone away from her at the moment. Here's one from my phone.  
There was some sway created after the job.  I had the guy come out and weld some steel cross pcs. That helped but not enough.  I also Cribbed under the wood stove and under the porch.  That helped some but still not enough.  I tied in some wood pcs. Temporarily.  I'll do more cross piecing and bracing after building the bunk room.  

[esarratt]

Mooseherder,

Would you post the exact name of the pier if you know it?  I am a contractor and I am always looking for a good quality, less expensive way of doing things.

[Mooseherder]

This is the one we used from Postech.  This is the middle size Pier.  They have 2 smaller piers and 2 sizes bigger.
2017 03 17 ALL PILES V2018- EN.pdf (postechpiles.com)

[Don P]

Mooseherder,

Would you post the exact name of the pier if you know it?  I am a contractor and I am always looking for a good quality, less expensive way of doing things.

Notice the comment on unacceptable sway, very common. Check their lateral capacity, 1kN at best, 225 lbs lateral load max.
Take tha largest face of the building total width x total height x wind pressure, full tilt storm use 20psf then divide that by their allowable lateral (158-225 lbs) to get the minimum number of piers needed to take care of the lateral without using welded bracing or some other means they fail to tell you about. I wouldn't touch these without a good engineer and inspector's ok. Their in house seems to consistently come up short.

[mike_belben]

Hmm.. Never seen those before.  Wouldnt work for us without a rock drill.. And maybe after the drilling disturbance couldnt work at all. Idk..


 whatre yalls thoughts on pouring a continous footer and a block or poured knee wall one on each side to lay the steel beams back down on?  I assume those steel piers have a threaded screw jack mechanism of some sort?  



Perhaps some X cables and turnbuckles or metal flatstock banding bolted at the flanges underneath could help prevent the house from racking?

[Don P]

A continuous perimeter (all 4 sides) masonry foundation takes any horizontal load and sends it down the length of the stiffest resisting wall(s). 2 parallel walls will only resist lateral loads from either in plane direction and will tip over if the load comes from out of plane. Better than piers which can overturn in any direction but still inadequate.

The helical piers have screw type flights of usually 3/8 steel at the bottom forming a "footing". They are screwed in until hydraulic system resistance says they have developed adequate force to resist the vertical loads. Then they are typically unbraced for lateral loads, attempting to develop lateral by using soil against a small diameter pipe.

Steel is quite capable of developing rigid connections. Design the pier posts so that they resist flexing, then weld an I beam frame, gusseted if necessary, into a box type frame on top of and rigidly welded to the stiff pipe piers. The joint from piers to frame has to be rigid whether by that method which is like a "moment frame" commercial steel building, X bracing, something, quite do-able, those companies are too lazy, stupid or cheap to do it. The sonotube piers are really no different there is simply more diameter in the soil. I think a 12" plays out at around 1300 lbs lateral but with unacceptable tipping by then.

One way to visualize a pier type foundation, I can put the family car on my dining room table, it will support it just fine (gravity). Now bump the table (wind or seismic). These companies only address gravity.

[mike_belben]

I get what youre saying.  Were back to the pole barn with no cross tie again.



I guess a bunch of X'd up rebar and gusset plates bonding the piers to the beams in multiple directions is how this redneck would handle it before covering the whole mess in porches and lattice. 

[Don P]

That would work, several ways to get there. The pole barn comment brings up another way. If the pier were driven then a tight fitting top of wall height square tube slid over it and welded/ bolted. The walls would then brace the piers. Its a viable technology being run by numbnuts, there's your stay at home million dollar opportunity ;D

[mike_belben]

I smell what yer cookin.