Remote Cabin Foundation Repair

[rifleman]

I have a twenty-year-old remote cabin built on what I think are utility pole piers. Most are about 20 inches in diameter. They are all short, about 6 to 12 inches above grade. I think they are creosote-treated. At least one is rotting and needs replacement (from roof runoff, probably). I don’t know yet how deep the piers are.

One long side of the 20x30 cabin floor is about 5 inches lower than the other long side. Judging by the sagging of the porch where it attaches to the sill log of the lower long wall, most of the 5 inch drop is from pier settling rather than from the original state of the foundation.

So, I plan on jacking the low side up. I want what I do to the foundation to remain sound for another 40 or 50 years.

So, do I:

1. Keep the original piers if they seem sound and install five inches of “shimming”, or

2. Keep the original piers and compact more earth beneath them to prop them up, or

3. Replace all five piers on the low long side.


If I replace all five piers, should I use:

1. Creosote utility poles again, or

2. Install 8x8 or 12x12 pressure treated timbers that I paint with copper naphthenate (dock and fence post preservative)


Or, instead of subsurface piers, should I use 1/3 steel drums filled with concrete for above ground pads (resting on mineral earth)?


Do AKDoug or others have any thoughts about it?

 

[Akheloce]

I don't have a strong opinion one way or the other on your suggestions sans actually looking at it, but a foundation for a building in AK should either be totally above the frost line, or totally below.

i made the mistake of burying drill stem 4' to add on a mud room onto my cabin. I had not yet bolted the drill stem (pipe) to the joists, just had them resting on the bracket. when I came back in winter, my mud room was 12" off the pipes, with no support! NMy cabin is on pier blocks, on the surface.

 

[cdubbin]

Need more info about your site, such as soils and drainage conditions, and your pier spacing; pics would help. I'm assuming 7.5' or so spacing, and fairly boggy, but let's hear it. Sonatubes would probably be your best option, if you can get bags of Redi-Mix there. Treated wood is not rated for a 50-year life span, although it definitely can last longer than that under perfect conditions.

 

[otternorth]

Before you start check all the piers to their centers. I have seen the outside of beams and posts look good and then discovered the inside was bad. Check them close to the ground level.

If replacement is needed you should treat all the posts in an identical way/depth/base pads. Use .80 treated material that has been wrapped in ice&water or plastic....some thing to help prevent ground water from freezing to wooden posts and moving them.
If the ground has high water content, or you can not get down to decent/draining earth, surface pads with steel bar will support the building and give you a jacking surface when you do need to level. I have used 2'x2'x1' pads with a double #5 bar grid buried level to the ground. This was for a building on wet ground with no hope of getting a proper foundation down.
A site visit would be help full for details.

 

[rifleman]

cdubbin,

You’re right, the spacing is approximately 7 1/2 feet on center. The cabin sits on a hundred foot wide shelf on a hillside. The shelf has about a 5 percent grade. The hill is 25% grade upslope, and 100% grade downslope from the cabin. There are some bedrock exposures visible downslope.

I haven’t done much digging yet. I know that nearby, it’s loamy for at least the first foot down. There are large white spruce and birch trees growing within 50 feet of the cabin. That indicates good drainage. I’ll just have to start digging around the piers...if the hole starts to fill with water, I’ll have an answer.

otternorth,

That’s a good tip about checking the centers of the piers. I’ve noticed that the center seems to be the first place that standing trees begin to rot. Could you describe what the rebar grid looked like when you poured the pads, and what kind of hardware you used to connect the pads to the piers and/or beams?

 

[FamilyMan]

foundation

foundation

Could you describe what the rebar grid looked like when you poured the pads, and what kind of hardware you used to connect the pads to the piers and/or beams?

I got looped into doing a deal like you describe almost 2 years ago; this is how I did it:

sonotubes: I used an assortment between 10 inch and 24 inch diameter tubes, all 4 feet long.

rebar cage: My 6 year old and I (you just need a third hand to do it) assembled the rings (each one a couple inches smaller than its sonotube's diameter) to the 45 inch long posts with bailing wire-like stuff which the rebar guy knew well (its used in that trade for doing exactly that). We did 3 rings per tube, with the upper and lower a good 6 inches from the upper and lower ends of the posts. We used 4 of the vertical posts per cage.

I'm really glad I went with the adjustable saddles (SBS has them in 6x6; no one else I've seen) so that you can later in life just twist a big nut on the saddle to raise/lower it. But to do that you need a vertical hole in the cement for the saddle's threaded end to go into as you lower things with your big wrench. So, take a foot of 1 inch pvc, duct tape one end closed, and just after your pour your concrete re-set your strings that represent the centerlines of your foundation, and right where the string hits the thickest part of each sonotube (in a perfect world this would be its center), and dunk one of your little pipes into just that spot, perfectly vertical. You can use a 4 foot long 3/4 inch dowel to aid you in getting each one just so; then remove the dowel - I taped my dowel into and onto the pvc loosely then cut it apart when its time to remove the dowel.

I used 6 inch saddles; many use 4. Into each of my saddles went a 6x6 vertical support that went up to where beams and joists live. At the bottom of each 6x6 where the saddle is on both sides of it, a 7 inch long 1/2 inch bolt with nut go clear thru to the far side of the saddle ensuring the saddle will stay with the wood.

My sonotubes protude up just a few inches, then I have 3 inches or so of big bolt visible, then the vertical beam begins. Even though we had a record snowfall last winter I never had snow that would continue to be in contact with wood; the snow always melted itself way away from each vertical support - so, no constant water contact on wood, so I'm thinking it will last a good long time.

I suspect what I did was a bit of overkill. But hey it sure has been solid, and the movement has been sub-inch per year so far - did I mention its nice to have those adjustable saddles?