The Stump Ranch (Cabin Progress)

[jander3]

I am building a 22' x 20' (inside dimension) log cabin.  I will be moving the walls from my building yard to the cabin site near Hinckley, Mn.  My site is very remote, so getting materials to the area is very tough (I have to skid everything 1 mile with a tractor). 

I need to make a decision on the material for the main support beams soon.  I don't have access to the span tables I would need to calculate loads (live and dead), so if anyone can help based on experience, software, or calculation I sure would appreciate it.

Details are below:

Cabin is made of Red Pine, walls have about 40 logs (10 rounds per side), roof and loft structure will have about 20 more logs.   Logs are 22'-24' long with 12"-14" butts and 8"-10" tops.  They weigh about 500-600 lbs each.

I want to use Poplar for the main support beams and potentially the roof (here in Mn Poplar = Quaking Aspen).

I plan on three support beams; I dug 42" holes for footers so I can install 3 posts per beam (beams will be about 22' and span the 20' side of the cabin). On the beams I plan to use 2x10 floor joists with plenty of blocking covered with 3/4" plywood.  The logs will sit directly on the plywood.   I am hoping to use Poplar for the three main support beams as I have tons of it on my property. 

Specific Question:

Note: There are no building codes or inspectors to deal with on this project.

1. Will Poplar work for the support beams? What size?  I will, likely, flatten a few places for posts and use the whole log with shallow grooves cut in the top for the joists. 

2. Are three posts per beam enough?   I could go with 5, but  then I need to tote in more sack-crete. I would like to avoid installing more posts unless needed.

2. Are 2x10" floor joists on 12" centers enough?

Everything is manual, so I don't want to overbuild; however, I would like to make sure things are reasonably strong.

Jon

www.peelinglogs.blogspot.com

[Don P]

Looks like we need loft location and dimensions and local design snow load. You may have no inspector, you do have codes. We still obey the law even if there is no sheriff in town 

Quaking Aspen, what I would call popple has these design values in #2 grade, sawn such that sawing or shaving does not exceed 3/10 of the radius of the log at any point.
Fb-975 psi
E-.9*10⁶
Fv-115 psi
Fc perp-245 psi

Unsawn- allowable Fb jumps to 1400 psi


While waiting for info lets check the floor joists;
Looks like the joist span is 11' at 12" ctrs you're overbuilding I think I can set up the AWC calc to show the correct answer, you can play with it to adjust if you want.

Span Calc
So what I used there was #2 SPF 2x8's at a 40/10 loading 16" on center and it passed at typical deflection limits. You can go to 2x10's and 12" centers, it will hold more than our beams will I'll bet  . But it would be stiff.

Also is the loft going to have a post bearing down at midspan? Right now I'm envisioning the loft running 22'x10' If Im guessing right?

I knew the name of your town sounded familiar, the Great Fire,
http://www.americanheritage.com/articles/magazine/ah/1977/5/1977_5_90.shtml

[jander3]

Thanks for the help Don.  Info below:

Design snow load for Pine County, MN is 60 PSF.

The loft will be 11' x 20', it sits over a bedroom, so I could run a post (with screw jack) at mid-span.  I don't plan on running a post unless needed.  The loft joist logs will be about 22',  they will be lock-notched into the walls, and flattened for decking.  I will likely run 4 loft joists.

The main beams will be flattened just enough to sit on the pier (6" flat on the bottom) at each pier and a 4" flat or grooves on the top for the joists.  So, I won't be talking much off the log. 

[Don P]

Gotcha,
I'm understanding the loft joists running in the same direction as the beams underneath the house, the ridge runs perpendicular to them?

Also the dimensions of the roof in plan (birds eye) view... I'm guessing outside dimensions on the house are 22x24 and then 2' overhangs all around, for 26x28 of snow loaded area?

No post on loft joists, 20' span at 40" centers  I'm needing about a 15" diameter on those 

[jander3]

You are right on the joists and birds eye view.

Jon

[Don P]

There's my understanding so far. Brown lines are the beams underfloor. The red line is the ridge.

here's loads so far;
1st floor 440 sf@40/10=22,000 lbs
logs-24,000 lbs
loft-11,000 lbs
Roof+snow+extra logs=63,000 lbs
Total=120,000 lbs design load

Right now we have 9 piers the load on each is a bit different according to floor, roof ,loft areas but it looks like some of them are taking about 25,000 lbs. If the soils are good for 2,000 psf that's about a 42" square footing. It would need to be thick enough and reinforced to prevent punch thru. That is a pure guess on soil capacity, the range is huge.

Next thing I realized we need to know is the roof system. Is it purlins bearing on the gable walls or common rafters bearing on the eave walls?

You asked a simple question and I'm delving perhaps too deep, let me back up and give you some of my thoughts about the load paths. Being log construction we basically have beams transferring load to the perimeter piers irrespective of the beams below. This is true except where a doorway(s) break through the log wall. So really if there are piers on each side of any doors then the beams are really only taking the 1st floor load. The piers are taking all other loads, distributed through the log wall "beams" to them. This holds true as long as no internal posts land somewhere in a underfloor beam span other than over the middle post, (thinking midpost for the loft here, stack it over the underfloor pier if you do one).

If that makes sense, are you good with just sizing the underfloor beams for the main floor?  If you want to support sections of "broken" wall on the beams, then we need to keep going down this path, I'll need door locations, they would need to be over the beams.

I'm off to the showers but will check back with you tomorrow.

[jander3]

Don,

I really appreciate all your effort and input. I follow your logic.   I agree that the piers have some big time loads, more so than I was thinking to begin with.  I was very concerned with main support beam size; however, looking at your data it is clear that footing size and foot-print looks to be very critical.  I am ok with sizing beams for first floor loads.

On your drawing

If north is up, my loft will be on the east ½ of the building (you show it on the west).

North Wall - Two windows…on the west side of the wall the window is 4’ x 4’, on the east side of the wall the window is 2’ wide by 3’ tall.

East Wall – no windows or doors

West Wall - no windows or doors

South Wall – Two Windows and one door…each window is 4’ x 4’.  The door is on the east end of the wall.  Windows and doors are spaced roughly equal distant along the wall.

The roof system will be post and purlin (dimensional lumber will be used for common rafters on the purlins). 3 Posts will bear on each gable wall (one post for the ridge, and one post for each pulin). The rafter will rest on the ridge, the purlin, and the cap log (top log on the 22’ side).

Soil – I am not sure of the rating or how to find out.  I put a call into some local soil guys.  Near my cabin is a similar sized log cabin (square logs) without a loft.  This cabin sits on grade (with no footings) and is supported by standard concrete blocks.  It is built on 2” x 12” dimensional lumber with no main support beams.  There are 8 concrete blocks that support the perimeter and two blocks under the cabin.  The cabin has been in this configuration for years; everything is still level.

When I dug the holes at my property, there is a bit of rock near the surface, about 6” down I hit clay like soil that was not real sticky, the deeper I dug, the harder the clay.  At 42” the clay is very hard (and not much fun with a manual post-hole digger).

Additional questions:

1.   Will additional piers help me, or I am better off just increasing the size of the current piers and footings?
2.   42” square footing, man, that’s a lot of digging by hand and hauling in sack-crete.  Is there anyway to minimize this?   

I am heading to Hinckley this weekend to dig some more holes and start pouring footings.   So if you have any thoughts specific to the footing, let me know.  Right now, I’m thinking I will need big holes and a re-enforced footer that is pretty thick. Then, to minimize the sack-crete hauling, off the footers, I can install piers made of standard concrete block. Posts can then be installed on the concrete block piers.   

Jon

[Don P]

Jon,
I do run into the comparison to existing buildings dilemma frequently. Yes there are always old ones that have held up that we can point to, some have done well, many are gone, all I can say is these are the current standards. Most of these standards are concerned with natural events that might occur once every 50+ years. In one seminar the professor asked why these old buildings are still standing, he concluded that they have never seen design load. Usually there is at least a 2:1 safety margin on these types of things nowadays because failure can and has involved loss of life. To my knowledge only one house I've built has seen above design load, when a hurricane flattened every other building on the farm. I'd say we are pushing one side of the pendulum's swing. I also don't want to lead you astray, I've been trying to do a little reading here, to my understanding a pier type foundation is not addressed by code. My read is that using the prescriptive provisions of the code, they want them all to be on continuous footings. This is entering into an engineers territory.

Looking at the numbers and the possible pier sizes the other end of the pier column started worrying me. If we do hit those kinds of post loads the underfloor beams are going to be crushed by the posts unless they are about 10x10's, and the beams aren't going to be big enough to give us that kind of surface. I'm leaning towards more, smaller, piers. This also gives more redundancy and makes the floor stiffer. The redundancy means that if one pier is damaged or hit or whatever it is less critical to the building. I think the effort would be about the same, more, smaller, rather than few larger footings. It'll cost more posts but that's about it the way I'm seeing it. Checking the book I'm guessing we are talking a 2000 psf soil at best.

I need to go clean up this mornings work, been mixing and pouring concrete, I know your predicament  ,  but I figured I'd post this in case I miss you heading out.

[Don P]

If you go with 3 piers on the middle log beam I'm coming up with 11" midspan diameter with no more than 1/8" per foot taper, or 10-3/8" small end minimum log.

Lets look at 4 piers under each of the other beams;
120,000 lbs, we just put part of the main floor load on the middle pier under the floor, so less 5,500=114,500lbs

Divide that up among 10 perimeter piers= 11,450 pounds per if the load is uniform, the loft is heavier to one end, but I think we can say the logs do help spread the load more than I was giving them credit for last night, call it about 13,000 per pier  . divide that by the beam crush strength of 245 psi, we need at least 53 square inches bearing on the top of the pier posts. A dressed 6x6 is 30.25 square inches, a double post at each pier would be plenty or lose the posts, a 16" long piece of 2x6 on top of a block pier would be 88 square inches. I like that.

13,000 divided by 2000 psf soil = 6.5 sf of footing needed
square root that=2.54' on a side  x12= 30.59" on a side. I think that's getting pretty good.
Footing projection beyond the block cannot exceed thickness, 30-8=22, divide in half, 11 inches projection each side so 11 inches min footing thickness.
If they are about 11" deep we have 5.9 cu ft/hole. A 80lb sack is 2/3 cu ft, we just threw ~9 bags/hole. You should put a couple of bars each way in the footing as well.

I'm still not loving it, that's only about 2-1/2 yards for the whole deal but its around 2 pallets of sackrete  .  I've been using pea gravel, sand and portland here and doing about a yard a day. It sorta resembles prison labor  .

[jander3]

Don,

Thanks again for all the information; your input is very helpful.  I got your message on Friday that “more is better.”   Over the weekend I took a good look at what I had.  I decided to go with 5 piers on the outer two beams and will likely stay with 3 on the middle beam.  I’ve been thinking all along that 3 piers may not be enough.    And since I already dug three holes per beam, it will be easier to add two more holes to the outer beams. 

I spent the weekend hauling sack-crete, mixing sack-crete, and filling holes.  Oh, yeah, I have to haul in the water, too.   You said mixing cement by hand was like prison labor—that would be an understatement.  When I was looking for land I wanted remote, well I got remote.  Every weekend I get to test the capacity of my pick up hauling materials to Hinckley and then, thank god, I have an old Oliver 880 with a front end loader for skidding in materials.  It is slow as sin for hauling through the woods; however, when you compare this to hauling materials by hand, it is pretty quick.

I have 9 holes dug, 5 holes filled.  The holes are not quite where you calculate, a little smaller in diameter, a little deeper.  I have 2 to 2 ½ yards per hole.  The rebar I used was placed vertical.  On the remaining footers I will put some rebar in the horizontal direction and probably expand the holes a bit. 

The log size you mentioned for beams looks good, I happen to have a number of poplar that I cut to clear the cabin site, these trees are 12” butt and 11” at 25” so they should work.

I also have many pieces of oak that I will likely use for the piers. Since they are on the property (so the price is right) and I had to cut and haul them, I should probably make use of them.  I will probably peel them, treat them with some Penetreat, and then coat them with motor oil.  I’ve used this process on a number of log structures that sat directly on the ground (with no footing) for 10-15 years and the logs are still fine.

I do not fully understand your comment on surface area between the beam and post. Let me know if the following is correct:

I have 12” diameter oak piers.  I can probably cut a flat in the poplar beam that is 6” wide x 12” long without affecting the strength. That gives me ballpark 60 square inches of contact between the beam and the pier.  This is good, because it is more than the 53 square inches.  The same would hold true if I used my chainsaw and ripped the oak pieces into 6” x 10” piers. 

This week, I will put together the supplies and rigging for a portable gin pole that I will use to place the beams and logs.  I’m looking forward to this project, because I understand what I am doing and don’t have to think so hard.

Jon. 

[beenthere]

jander3
Very exciting project you have going.

I'm wondering why you don't have a heavy duty 2-wheel trailer to pull behind the Oliver, and haul as much as a pick-up load at a time into your site.

Just curious here...

[Don P]

Hey Jon,
Sounds like you had a right productive weekend. It sounds like you followed me on the minimum pier dimensions to avoid crushing the sides of the aspen beams.
I sure hope theres a math error in your pour quantity, a yard is 27 cubic feet 3'x3'x3'. I'm not saying it couldn't be done, but if you hauled, mixed, and poured 50,000lbs of concrete this weekend, I am not gonna call you Tiny 
I got one of those 250 gallon square plastic totes when we were doing our work. Then put a pair of lift pins thru the lower sides of a 55 gallon drum and a U shaped strap of steel at the top lip for the top link. It had a removeable lid. I put a hosebib near the bottom and would drive uphill of the tote, which was uphill of the site. I could then keep a good supply up by the house site.

[jander3]

Don,

Actually, I have about 10-12 60# bags per pier.


Beenthere,

I spent my trailer dollars on log arches.  I purchased one from Logrite (Jr. Arch) and had a local welder weld up an arch with a winch that I can hook up to my tractor.  That way I can tote 25' logs (supported on both ends) that are already cut and scribed into the site.  I have about 1/2 day invested in every log, so I don't want to screw them up hauling them in. 

 



For materials, I lash a couple of 2"x12" to the back of the tractor, secure the supplies with truck straps, and load up the bucket with extra things.   I can generally get one pickup load at time back to my cabin site.

[Dana]

I like the Oliver, is it diesel?

[jander3]

The tractor is an Oliver 880...gas powered. I don't know what year it is, but she starts every time in the Minnesota winter.  Even after sitting for a couple of weeks with temperature below zero (gotta plug up the water heater for 10 minutes or so first).

I purchased this tractor (with a front end loader) so I could lift the logs up on to my walls.  It has come in very handy for skidding supplies, toting cement, pulling stumps, and any other task that needs a little power.

Tractor cost $3,000; it cost me $360 to move it to Hinckely.  Best money I ever spent.  I can't imagine the time an effort it would take to do the log work by hand.




Corey lifting a 26' log that was notched and scribed.

 



Moved the tractor from the building yard to the cabin site near Hinckley, Minnesota.

[Dana]

I'm sure you know to be careful with using a narrow front ended tractor with a loader. They aren't real stable with the bucket high and a load slightly unbalanced, even worse on an incline and moving.

[Stephen1]

Nice balancing act with the log, Dana has a good point. Keep up the pictures we like to see what you are building.

[beenthere]

jander3
I see some additional write-up in your log cabin blog on your progress.  Good luck getting the material moved this week. I'm sure you are concerned over the 'mover' handling the logs with care so you don't end up with any breakage.

Appreciate your pics and story  (hope that truck fits down the road for you).
 

[jander3]

This gin pole was designed so one man can move it, raise it, and use it.  I kept the pole height at 12' so it can be moved around. 
 


Moving the gin pole around the work site.



Hooked up the rigging (main guy, chain-fall, and forward safety)



Equipment in position.



Raising the gin pole using the chain fall.



Adjusting the rear guy line.



Lifting an oak (about 550#).  I just needed to get it up off the ground so I could slide some stumps under the tree .  And, I wanted to test out the equipment.
 


This is the top of the gin pole.  The pulley is designed so I can install a winch; then, I have either chain-fall or winch for lifting.   

[StorminN]

Pretty slick, jander... keep the pics coming!

-Norm.