new post/pier for existing cabin

[dulatoag]

Hello!
I live in a 24x32 "cabin" that my wife's grandfather built 50 or so years ago. We live a bit north of Binghamton NY, so the winter's can be quite cold, windy and nasty. There are 8 old oil drums filled with concrete along the perimeter of the house, 3 on each side and 2 on the ends. The house currently rests on blocking that was stacked on these barrels, with another 3 "supports" underneath the house up the middle. Needless to say, with frost heave, there is nothing level about the house. The front 12 feet of the house rises about 2.5 inches from the rest, and the "rest" is all over the place.

We are preparing some upgrades to the house interior, new flooring, ceiling, etc., and I need to stabilize the house as best as possible before investing that money. The best answer, of course, would be to burn the place down and build new, but I'm not interested in that debt load.

My idea is to install a new post-pier framework underneath the house. There is a bout a 36 inch clearance under the house. I'm thinking of building 6 concrete piers, 4' deep, three in the front of the house (on the 24' side) and 3 in the back. Then putting beams that run between them perpendicular to the floor joists.

My questions are these:
1. I don't believe there is significant freezing under the house. So how far down should I place the post footers under the floor joists? I figure I'll need three of these per run underneath. Obviously I can't do any serious excavation under there with minimal height clearance between the earth and the floor joists.
2. My plan would be to run the two beams on the sides about 24" in from the exterior, 36' walls. This is because of the supports that are currently in place would be in the way. I'd like to build out the beam runs as close to the joists as possible, then jack up each side of the house in turn, remove the current support stacks, then gently bring it down on top of the new beams. Would it be cool not to have the new side beams directly under the exterior walls?
3. Obviously my other problem would be the beam running beneath the center of the house, with the current supports in the way. I might need to run two lengths of beam, on on each side of the current supports.
4. What size wood for the beams? I'm looking at 4x6 pressure treated beams, or should I go with double 2x8's or 2x10's or 6x6?
5. Am I just nuts for contemplating this at all??

Thanks for any tips on this ... would be enormously helpful.

[Bob S.]

I would look into  replacing the barrels one ar a time? That way you will not need to change the structure and it would be a more manageable project. You could block up around a barrel the remove it and dig down below the frost depth, pour a footing and build a pier wth blocks.


Bob

[dulatoag]

Hi Bob .. thanks for your thoughts. So having a beam structure to support along the length of the building doesn't provide any good benefits as opposed to supports at individual points? What would you suggest for fixing or replacing the three support points under the house? Dig down as far as possible, put in a footing and a pier?

[MountainDon]

1. I don't believe there is significant freezing under the house.

With the cabin positioned above ground like that there is nothing to prevent the ground frsszing deep. In fact if the surrounding area has deep snow cover and under the cabin there is little or no snow then there is a chance the ground might freeze deeper there. Not saying it will for sure, but snow cover does insulate to some degree. Best thing is to use the frost depth for the area as the depth required for any new or remedial work, IMO.

IMO, what you really need is an engineer's opinion on whether or not this is practical and how it should be accomplished. Also check locally as to what permits might be required and if there are any code requirements for this type of work.

Any pictures?

[comanche]

here's a company we up here in Alaska that does them for around $430/ pile. Maybe a similar company around your neck of the woods?

http://tmpalaska.com/2012/06/20/using-techno-metal-post-alaska-to-save-a-failing-cabin-foundation/

[dulatoag]

I'm beginning to rethink the relative extremity of the project. I might try to work with the piers that are in place, at least those that appear sound, and not install beams. Of course my big fear is spending the time and money to put in a new foundation of some type only to have some heave continue. Mountain Don ... great thoughts there. Only one of the three supports under the cabin along the center line are actually above ground ... concrete blocks with various pieces of wood shim on top that are on grade. The third support is blocking on top of a concrete barrel. Any wisdom in surrounding the supports with rigid foam a few inches beneath the surface to help prevent freezing/heave? For that matter, putting that around the perimeter barrels as well?

[JRR]

I agree with working with what you have in place already.  Have you thought about trying to add a perimeter (around each individual barrel or other pier) of subsurface insulation (rigid foam) to make use of the "frost protected shallow insulated foundation" concept.  I would think that would be fairly easy to do, and should mimize/eliminate continued heaving in the future.  Info: http://countryplans.com/smf/index.php?topic=79.0

And it should be a "doable" project to level the current structure by jacking and adding spacers between supports and structure.

[dulatoag]

Yes, I think that's my new approach. Do you think a couple feet horizontal 2" foam insulation around the piers would be sufficient, or do you think I also need vertical foam around them as well going deeper?

Thanks for your thoughts!

[John Raabe]

It might come down to a question of how much the preservation is worth.

The "heritage way" to do this is get the big boys in and crib the whole structure up in the air and pour a full and proper concrete stemwall foundation with drainage, full soil bearing and an anchored sill plate. Then you would lower the cabin down and relevel and repair your way to the top of the roof.

You can make some calls and find out what something like that will cost (there are likely specialty contractors). Since it will be a lot of money you would want a structural and soils engineer to review the work plan.

This is how Grandpa lives a 2nd hundred years.

[dulatoag]

One more thought ... even with potential for minimized heaving, am I asking for replacing my ceiling tiles with drywall? Am I asking for cracks or is there enough flexibility in that where a couple of minor sways each spring wouldn't be a problem.

[dulatoag]

John ... yes, that is the cadillac option. But the place isn't worth that kind of cash. If I was to go that route, I'd grab some ballparks, light a match and when the smoke cleared, build a whole new house. 

[Squirl]

Yes, I think that's my new approach. Do you think a couple feet horizontal 2" foam insulation around the piers would be sufficient, or do you think I also need vertical foam around them as well going deeper?

Thanks for your thoughts!

The engineering and design behind FPSF works only on full foundations.  It uses the heat of the house to force under the footings to keep the soil under the footings from freezing. 

There are designs for unheated frost protected shallow foundations, which requires more insulation and excavation than a full foundation.
For this climate it would take 4 feet of wing insulation in all directions around each pier and under each pier at least 12 inches deep.  That requires over 50 square feet (pi*r^2) of insulation and excavation per pier.  I am building in Otsego county.  I have researched this a lot already for this climate zone.  Don't waste the money.

Don is right.  Under the house has no snow cover as ground insulation or direct sunlight.  It will freeze to the full depth of four feet.

I don't mean offense by this, but you are in this predicament because someone cut a corner a long time ago.  Cutting the corners now, will leave you in the same place.

Post and pier foundations are designed by calculating the load distributions from the roof down.  Then building large beams or girders to distribute the even loads from wall framing to points on the ground.  The amount of footing size and pier spacing depends on the loads above.  I do know that you are in 50 lb snow load area.

My understanding from your OP is that there are only three points of contact that there are only 3 points of contact with the ground for the 32 ft span?!

I did a quick guide once for girder span charts in the ICC (the NY building code). 
http://countryplans.com/smf/index.php?topic=10511.0

4-2x12 dimensional lumber girders can't span 16 ft under the building code.  This sounds way over span.  Also, unless the soil is solid rock it can't handle that kind of concentrated load.

Dig each pier down four feet.
Make sure the soil bearing capacity can handle the concentrated load.
The less piers, the larger the girders and footings you need.

Major renovations such as foundation work requires a permit in Otsego county. I assume Broome County does too.  Even in my rural area, the building department got a half dozen from calls from my nice sweet neighbors to make sure my permits were in order.  Just giving you a heads up.

[MountainDon]

Do you know if the structure continues to shift every year? Or has the movement be mostly in the past? If the structure is not worth spending the big dollars on, doing a proper foundation suitable for the climate, perhaps money should be saved for a new project rather apply a series of band aids and performing renovations that will have a limited life span. 

If the lack of being level is a real bother perhaps some jacking and new blocking might give temporary relief and perhaps could be done without getting tangled in permits. I am NOT a house jacking expert and want that to be clear. House jacking can be dangerous. I would not want to have one fall on me or anyone else. The pros that do this sort of thing have a small fortune invested in timbers they use.

[JRR]

It may be true that using "frost protected ..." techniques would not be cost effective for your situation.  I have not done the math.  But we must understand the method does not only depend on heat from the building .... as found in the guide:
.
"The effect of heat from the building is magnified when insulation is strategically placed around
the foundation. Frost protection of an insulated foundation also works for an unheated building by
conserving ground geothermal heat beneath the building. Unheated areas of homes, such as
garages, may be constructed in this manner."

My editing/bold.

[dulatoag]

Unfortunately, it hasn't been until the wife wanted to make some improvements that I have really dug into this problem. So I do not know the level of shift each year. In that regard I'm starting at year 1. I'm going to level it all out with blocking and track it from there.

It does appear however that the heaving, past or present, has mostly occurred in the northwest facing side of the house ... this is where the wind/weather blows in from across the field (I live on a hill in Whitney Point Squirl ... can get quite windy). That is where the 2.5" heave is. The house gets lower as you move towards the back. So I'm not certain I'm getting much heave from under the house, more from where the piers in the NW front, and N side are, which makes sense.

Squirl - there are 5 supports along the center of the 32' span. Three are concrete piers, two are on grade cement/wood blocks. Four supports along the outside walls along that span. The original sin came from the grandfather who put the cabin on a perimeter block foundation 45 or so years ago, but didn't go below the frost line, so it all ultimately crumbled. That was replaced by the next generation by the post/beam. Apparently he could not always dig down to 4' because we have a shale bed 3 or so feet down. I believe the holes were dug by a lucky nephew by hand at that time.

[JRR]

I have this mental image of your situation that may be way off the mark ... but is it possible that after making corrections in level, you could help resist heat loss to the air stream by ... laying down a ground cover of tarp, and then stacking hay bales underneath, around the perimeter underneath, in such a way to restrict air flow and preserve some ground heat? 

[dulatoag]

Yes, I'm going to lay plastic sheeting on the ground below the cabin and work on some better skirting. That will certainly help with cold inside the cabin as well.

Hay bales kind of freak me out a bit ... like kindling under my bed lol.

[JRR]

Good point! ...though the bales may actually slow the burn rate.  Sand bags?