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Jacking a cabin

KHWillets's picture

We have an old 25x25' cabin in Northern California that's rotted its footings a bit. It was originally set on piers with pads of various types, including cedar rounds which I can now dig out with a shovel. After almost 100 years the supports on both uphill and downhill (3-4' of drop) sides have rotted to the point that the floor bows several inches (the middle supports stayed dry). The doors now jam against the floor, and we did some minor jacking to get a sliding door square.

The cabin is of fairly lightweight construction, with a corrugated roof, 48" OC studs (!) standing directly on the subfloor (no bottom plate), and minimal finish materials. The floor is 2x6 joists at 16"OC, sitting directly on shims on the uphill side (redwood and cedar throughout). From looking up the lumber weights I guess it's 8-15,000 pounds.

From looking around the web I've found permanent screw jacks which we could probably install for a few hundred dollars, with enough capacity to lift the downhill side and get it onto concrete pads, instead of the buried cedar log it's resting on now. I'd like to put a purlin across the bottom of all the joists (they run uphill/downhill) and jack the whole side level instead of jacking each joist and fitting a pier under it (labor-intensive).

My questions are:

Is there a way to "sanity check" my weight estimate? Is there a ballpark figure I could use for psf?

Is there a safety procedure to follow? If I use screw jacks I'll have to get several feet under the structure and turn the jacks.

Is there a problem putting the purlin, etc., a couple of feet uphill (farther under) from the downhill sill? The aforementioned cedar log is suspect at this point and I'm thinking the pads should be on soil, above the log at least.

Thanks for any perspective people might have to offer.

(post #105339, reply #1 of 5)

Greetings KH,


This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.


Perhaps it will catch someone's attention that can help you with advice.


Cheers


 

 

(post #105339, reply #2 of 5)

Well, I have to admit I didn't see this until Rez bumped it.


And, my first thought was under-serious--something about sneaking up on either side with a couple fire teams to provide cover for the Engineers to come and run off with the structure . . .


Now, given your description, I'd be very inclined to go as little and slow as possible, really.   You have widse-spaced studs, potenitally dubious framing connections, and what can best be described as a "quaint" foundation system.


Now, I'm guessing that this building has "character" (certainly sounds like it was built by characters).  Whether that character is worth the effort to preserve is a question well beyond what text on a computer screen from hundreds of mile away can provide.


But, having dealt with some old buildings on ranch property before, it's the "might as well as's" you have to watch for--they add up quickly.  Suppose we build a temporary wall to hold things as they are.  Well, that's when you discover that the roof is only indifferently wattached to the walls--so, "might as well as" reinforce the roof to wall joint.  Then, you notice that there's a bit of rack in the building--well "might as well as" put another temporary stiffening wall in.  All of the sudden the project has enough temporary lumber in it to properly frame a brand new copy (except we chopped it all up to make temporary framing--chicken-egg-chicken).


But, I could be jaded.  We worked to save and restore an old cabin out on this ranch.  Customer was bound and determined to do this, no matter what.  Three weeks into jury-rigging this beast to not fall on us, the customer's GGF wanders up and comments that we sure were putting in a lot of work on what had been a chicken coop rescued from a flooded creek, and I've been waiting for the blame thing to fall down to give an excuse the replace it . . . ah, crusty old Texas ranchers . . .


Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)

(post #105339, reply #3 of 5)

I dont think the weight is a big issue.Sounds like car jack would lift up that thing.Ur basic problem will be keeping it all in one pc..unless u jack a lil bit everywhere a lil bit at a time.Its like sleeping on a bad mattress for 50 years..thimgs may not go back so easily.


 Joist and boards have short term memory not long term.They maynot want to return to thier  installed shape licketysplit. But thank heavens  wood is resiliant.


We do alot of what ur talking about doing here in WV. Got to be careful tho cuz we have a saying.....Like putting a golden saddle on a mule!!

(post #105339, reply #4 of 5)

The problem with jacking a building when you have no experience, is the basic lack of "feel" for how much danger you're in since much of the danger isn't readily apparent until something breaks and falls.   Falling buildings = bad.  Even experienced guys sometimes have mental blocks and do dangerous things.


Okay, with the disclaimer out of the way I'll share what we've done before, not necessarily what is best for your building since suggestion such is silly without seeing it firsthand.


The walls need to be stabilized so the rotted crapola can be dug out and replaced.  Using LVL's extended a few feet out past the corners it's possible to rather safely attach them to the outside of the existing stud walls with multiple timberloc/ledgerloc or simpson 1/4" structrual screws.  Cribbing on the ends of the LVL's holds the weight of the house.  A second set of LVL's can be placed above the first for more shear strength (double the attachments) and less LVL deflection.


At corners, the LVL's are all allowed to extend past the corner, with two sides over and two sides under.  Most yards have 40' LVL's that are cut into smaller lengths as needed so you're easily able to span the distance.


30' is a long span so don't think the house will lift with only support on the ends.  You'll want a support every 8' or so, which can be a 4x4 post.


LVL deflection will provide a good measure of weight and how well it's braced.  It's critical that you understand how much weight the screws holding the LVL's on can take.


Now that the house will hold together if you don't get carried away, lift a little, block underneith, lift a little, block underneith.  The theory is your never lifting much above a solid support so worst case it can't hurt you or itself. 


Don't lift the whole works at once or there is a huge risk of it all falling sideways if your cribs aren't built right, which is something you'll want to become familar with. 


Stabilize the house at the level you want it, wich is only a few inches higher than it currently is to level the floor.  Bock under the floor joists as a secondary support.


In small sections, say 10', dig out the crappy areas, install a proper beam under the walls and any post bases.  Secure that section, let the house weight rest on the new supports before moving to the next section.  Repeat as needed.


The risk to a structure is quite small and if small sections are worked on and people stay out of harms way as much as possible there is also very little risk if the guys have an educated feel for the work.


There are other ways to do such things, but that is a pretty common approach to it.  LVL's are relatively cheap, easy to work with, quick to screw on, and long enough to hold everything together from end to end.


Check out http://www.ellisok.com/ellisok/timberjackproducts_screwjacks.html for these little gizmo's.


Ellis Timber Jack


 


Happy Holidays!


 


 


Beer was created so carpenters wouldn't rule the world.

 

Beer was created so carpenters wouldn't rule the world.

(post #105339, reply #5 of 5)

Thanks for the replies. I guess I did get a feel for the danger when I went under there the first time and found the joists hanging in space - the piers had rotted to the point where I pulled them out by hand. There were some mid-span supports that appeared to be taking the load, and the corner posts keeping it from toppling, but definitely some sag in the middle of the downhill wall.

We cut some new piers and jacked the joists slightly to get them in, but didn't level across the house fully.

It seems like the place isn't too badly built if it took the cantilevering, but I've been taking off the siding and checking for rot. The original problem was moisture splattering from a deck onto the siding and soaking into the joist ends and piers -- they didn't even put tar paper under the siding, so we fixed that, and gutters are in the works. The sag is relatively recent and I think we'll be fine with re-squaring the doorways.

Those Ellis jacks are on my list, or something similar. Next time up there I'm planning on measuring and taking pictures. I'll set up a fluid level too and measure the amount of sag.