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Author Topic: 12' High Log Walls?  (Read 643 times)

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Offline Yoter

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12' High Log Walls?
« on: October 20, 2021, 11:43:07 AM »
I'm still kicking around ideas for my guest/office cabin but am leaning away from building it exclusively in locust from my property just due to the logistics of taking down the amount of trees needed at once, etc...  I had a thought recently about buying wholesale logs and building a log cabin, which is not entirely unexpected since I grew up in one:





That's me on the floor at about four years old with my dad in the background-he and his cousin did most of the work.  My parents bought a kit through Lincoln Logs out of Lake George, NY and built that log Cape Cod about 35 years ago and are are still living there today.  They of course bought an entire kit complete with windows, doors, fixtures, etc...but I'm looking to put up a simple 16' x 20' box.  The catch is I need high walls in order to have a standup loft.  Any reason that I cannot stack 8x8 logs 12' high?  I would be using 8x12 locust beams from the property to support the loft and 8x10 locust rafters for the roof.  Here is a simple sketch:





I figure the process would be to anchor the first course of logs (with some kind of rot resistant sill underneath) to the concrete pad and begin stacking to build the 16' x 20' box.  At the the appropriate course the logs would be notched to accept the 8x12 locust loft beams, and then the stacking would resume to a height of 12'-0"  At that point the logs would be capped off with a locust 2x8 to provide a bearing surface for the 8x10 locust rafters.  The loft and ground floor flooring would be 5/4 locust boards.  Locust would be used wherever else it would be needed as trim, framing, etc...of which there will be minimal need.  Again, my biggest concern is building log walls this high-my parents' place only has log walls stacked to 8'-0" and then everything above is stick frame platform construction with log siding.  Thoughts?

Offline jake pogg

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Re: 12' High Log Walls?
« Reply #1 on: October 20, 2021, 12:20:10 PM »
I see nothing wrong with going higher with the log-wall in Principle(and i do see it done on occasion around about).

I'd pay particular attention to Pegging the logs,which is an entirely separate issue from Fastening them,having to do with resistance to buckling.

Also,since your "ties" will end up lower-ish down on your wall,and you'll not want to intersect your upper living space with tie-beams,i'd consider buying/building scissor trusses for the roof,vs rafters,to prevent the out-thrust moment.
(unless some sufficient collar-ties can be employed higher up).

Other than that i see no issues,not with the height per se.
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Offline snobdds

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Re: 12' High Log Walls?
« Reply #2 on: October 20, 2021, 12:45:55 PM »
You're going to need collar ties and rafter ties for a rafter roof and high walls.  I did the same design, more or less, with high walls and the loft at 8 feet.   I did not want the rafter ties in the main living space, so we put them on the outside of the building with walk around porches. I had to have an enginer design it, but it was well worth it. 

Offline Yoter

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Re: 12' High Log Walls?
« Reply #3 on: October 20, 2021, 12:51:19 PM »
I see nothing wrong with going higher with the log-wall in Principle(and i do see it done on occasion around about).

I'd pay particular attention to Pegging the logs,which is an entirely separate issue from Fastening them,having to do with resistance to buckling.

Also,since your "ties" will end up lower-ish down on your wall,and you'll not want to intersect your upper living space with tie-beams,i'd consider buying/building scissor trusses for the roof,vs rafters,to prevent the out-thrust moment.
(unless some sufficient collar-ties can be employed higher up).

Other than that i see no issues,not with the height per se.
Thanks-I could do 2x6 collar ties on both sides of each rafter with about 7' of headroom:

Offline Yoter

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Re: 12' High Log Walls?
« Reply #4 on: October 20, 2021, 01:03:50 PM »
You're going to need collar ties and rafter ties for a rafter roof and high walls.  I did the same design, more or less, with high walls and the loft at 8 feet.   I did not want the rafter ties in the main living space, so we put them on the outside of the building with walk around porches. I had to have an enginer design it, but it was well worth it.
I'm not really understanding what you mean by putting the rafter ties on the outside of the building?  As far as snow load goes the roof is basically 12/12 pitch and will be steel so I can't see any appreciable amount of snow ever sticking to it.  Plus I'm in New Jersey.  Any chance you can post some pictures of your build?  The loft space is critical to what I want to do.  My hope is that by locating the collar tie near almost the middle of the rafter (whereas collar ties are usually in the upper third) that it would provide both uplift AND down pressure resistance.  Since I'm planning on using 8x10s for the rafters I could let in the 2x6s on either side so that they're flush and bolt them with some attractive looking hardware creating a homebuilt truss of sorts.  I could also lower the collar ties to 6'-6" but that would not be preferable.  Final thought:  I suppose I could also incorporate a ridge beam with king posts.  King posts just at the gable ends would require a 20' long and very substantial beam so maybe not feasible, but I could set a king post at the edge of the loft over the tie beam which would allow for a two piece ridge of about 13'-6" and 6'-6" which would much easier to procure not to mention set.  A nice 8x8 post at the end of the loft might be a nice visual effect too.  

Offline snobdds

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Re: 12' High Log Walls?
« Reply #5 on: October 20, 2021, 02:04:36 PM »
I wish I could post the pdf from my engineer showing how he tied in the rafter ties to the roof and wall.  It was ingenious. However, the forum does not recognize a .pdf as an acceptable format. Just look on the wrap around porches for the ties from the roof to the walls. 

Here is my cabin thread. 

https://forestryforum.com/board/index.php?topic=113025.msg1776752#msg1776752

Offline firefighter ontheside

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Re: 12' High Log Walls?
« Reply #6 on: October 20, 2021, 07:33:56 PM »
My log walls are 10' high.  The second floor is at about the 8' mark on the walls.  The loft does not have a lot of stand up room, maybe 8' before your head hits a purlin.  The master bedroom and bath are made with 2 dormers.  I would think about using dormers upstairs instead of building such high walls.  The dormer walls are just stud framed on top of the log walls.  I have log purlins that span about 24' from gable end wall to a bearing wall in the middle of the house. With a purlin roof theres no need for collar ties.

 

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Offline Don P

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Re: 12' High Log Walls?
« Reply #7 on: October 20, 2021, 07:42:41 PM »
It does and I'd like to see how he did it. In the reply window, just above the box that says "Click here to add Photos to post" is a line that says "Attach documents and other options". Click on that to post a pdf.

A collar tie and a rafter tie are two different roof members. The rafter tie is in the lower third of roof height and is what restrains spreading thrust. The collar tie is in the upper third and ties the rafter tops and upper roof together in uplift. At midheight the spreading force on the connections is high and it also puts an additional bending force on the rafter. There is a calc in the toolbox here that gives the thrust at whatever height in the roof you input. The building code in the rafter chapter has span tables, at the bottom of each is the span derate as the tie is raised, for the bending force. The last table gives the tie to rafter connection and how many more nails to add as the tie is raised. That is all for stick frame but the physics is the same.

Up to the compression limit it really isn't about the overall wall height it is the unsupported wall height. You have a supporting floor diaphragm at 8' so your effective wall heights are under 8'. If you go up to 5' on the upper walls that is usually about the time you can put ties in the lower third of roof height and everything starts to work. And then there is the ridgebeam, or purlins, option.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline snobdds

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Re: 12' High Log Walls?
« Reply #8 on: October 20, 2021, 11:54:50 PM »
It does and I'd like to see how he did it. In the reply window, just above the box that says "Click here to add Photos to post" is a line that says "Attach documents and other options". Click on that to post a pdf.

A collar tie and a rafter tie are two different roof members. The rafter tie is in the lower third of roof height and is what restrains spreading thrust. The collar tie is in the upper third and ties the rafter tops and upper roof together in uplift. At midheight the spreading force on the connections is high and it also puts an additional bending force on the rafter. There is a calc in the toolbox here that gives the thrust at whatever height in the roof you input. The building code in the rafter chapter has span tables, at the bottom of each is the span derate as the tie is raised, for the bending force. The last table gives the tie to rafter connection and how many more nails to add as the tie is raised. That is all for stick frame but the physics is the same.

Up to the compression limit it really isn't about the overall wall height it is the unsupported wall height. You have a supporting floor diaphragm at 8' so your effective wall heights are under 8'. If you go up to 5' on the upper walls that is usually about the time you can put ties in the lower third of roof height and everything starts to work. And then there is the ridgebeam, or purlins, option.
I have the file on my work computer, which may be the problem.  I'll email it to my house laptop and do it that way.

Offline Joe Hillmann

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Re: 12' High Log Walls?
« Reply #9 on: October 21, 2021, 10:07:01 AM »
I plan to build a cabin with similarly tall walls.  All my plans are just rough ideas, nothing will be finalized until I actually start stacking logs to see how it will really be built.

How many logs I have will decide how far above the second floor I go.  I have enough long logs to run at least two full length rows above the second floor joists.  I think the floor joists should help keep the walls from pushing out and setting the rafters on full length logs will also help resist pushing the logs out.  If more support is needed I can run several cables from side to side in between the second floor joists.

If even more support is needed I can build a wall perpendicular to the ridge in the middle of the loft and then run a cable inside that wall from top  log to top log while going above, under or through the door in the wall.  The door can be framed out with steel beams so the cable can go from the top log, to the door frame on both sides.

  Or the cable can go from the top log down under the central beam that supports the second floor than back up to the other top log.  All while staying inside the wall or floor cavity.

It doesn't have to be cable I have seen it done with hammered steel bar to look like wrought iron that was threaded on the end to be able to bolt it tight.


Offline snobdds

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Re: 12' High Log Walls?
« Reply #10 on: October 21, 2021, 10:23:14 AM »
I hope this works. 

Here is the plans showing the ties on the outside of the main building.  

Offline Joe Hillmann

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Re: 12' High Log Walls?
« Reply #11 on: October 21, 2021, 10:53:26 AM »
I hope this works.

Here is the plans showing the ties on the outside of the main building.  
Those are stud walls, and it looks like the studs are 12 foot long with no break where it can flex at the second floor floor joists.  Whereas a log wall has a possible flex point at every log.  So the design may not work as well on a log wall.
Also for that design to work the house roof and porch roof need to be a single piece of timber and the same pitch.  Which is no problem as long as it is planned for and the builder has access to long enough logs. 

That method could be reinforced even more by extending the floor joists through the wall until they intersect with the rafters and tie them together out there.  Or my idea of a cable could be run from one rafter end, through the building and floor and back out to the other rafter end.

Offline Don P

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Re: 12' High Log Walls?
« Reply #12 on: October 21, 2021, 11:00:45 AM »
Yup, it worked.
I typed slower than Joe so a lot of this is repeat.
He provided what the code is calling for, a "continuous tie across the building" which is also what Joe is describing. Do be careful with the detailing, at the porch ceiling joist to wall in snobdds drawing, that connection should be detailed to restrain whatever the design thrust is, figure out what it takes, whether a strap or lap or whatever to restrain that. In Joe's I'm hearing a  line of force that has to climb up a steel door jamb and run across the header and back down the other side, again just confirm that the members are up to the stresses. Frank Lloyd Wright did a number of roofs with wide soffits that acted as horizontal beams which avoided a ridgebeam but accomplished the same thrust restraint. When running the load around raised beams the ends of those beams, the end walls, are the points of support, detail that connection and then follow the load down the walls to support. If the thrust simply pushes the entire beam or log off the wall it didn't work. We would refer to that as plate log roll on log homes.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline snobdds

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Re: 12' High Log Walls?
« Reply #13 on: October 21, 2021, 11:11:19 AM »
Yes this is a stud framed building as it's hard to get long straight logs to build a building of any size.

The topic was how do you install high walls and keep them from bowing out.  This is just an example of how to have ties and not have them in the living space.

I had a neighbor by my cabin build a true log cabin with high walls for a loft.  He didn't think he needed ties as the logs were considered "beams".  Well about five years later his roof started to sag because the top of his wall were bowing out.  He had to use cables and turnbuckles to bring them back into plum. The problem was, the logs developed a material memory and did not want to stay plum anymore and created tension in other areas. He had to use so many simpson ties that he should have bought stock in the company.  He had to leave the cables in so he could retension them every year to keep his roof from sagging.  

True log cabins still need the walls and roof framed with proper tieing and this gives the OP an option to have an open cabin with a porch.

Offline Joe Hillmann

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Re: 12' High Log Walls?
« Reply #14 on: October 21, 2021, 11:28:31 AM »
 In Joe's I'm hearing a  line of force that has to climb up a steel door jamb and run across the header and back down the other side
And below.  The door would be framed with steel on all four sides.  Kind of like some old silo door openings.  The door was heavily framed with steel and the tie rod went from the door frame, around the silo and back to the other side of the door frame.

Offline Joe Hillmann

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Re: 12' High Log Walls?
« Reply #15 on: October 21, 2021, 11:35:21 AM »
Yes this is a stud framed building as it's hard to get long straight logs to build a building of any size.

The topic was how do you install high walls and keep them from bowing out.  This is just an example of how to have ties and not have them in the living space.

I had a neighbor by my cabin build a true log cabin with high walls for a loft.  He didn't think he needed ties as the logs were considered "beams".  Well about five years later his roof started to sag because the top of his wall were bowing out.  He had to use cables and turnbuckles to bring them back into plum. The problem was, the logs developed a material memory and did not want to stay plum anymore and created tension in other areas. He had to use so many simpson ties that he should have bought stock in the company.  He had to leave the cables in so he could retension them every year to keep his roof from sagging.  

True log cabins still need the walls and roof framed with proper tieing and this gives the OP an option to have an open cabin with a porch.
I think that is a very common problem with log cabins that have rafters instead of trusses.  In some cases it is just accepted.  I assume that it is less of a problem in a smaller building than a big building. 

Offline jake pogg

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Re: 12' High Log Walls?
« Reply #16 on: October 21, 2021, 12:41:34 PM »
Here is the plans showing the ties on the outside of the main building


That's a cool idea,to take the rafter tails Elsewhere,to bear at least in part not on the long walls in question.

Possibly something of the sort can be done without those extra walls/additions outside the main structure,by tying the rafter tails back into the building,to lock things on itself by triangulation.
But that in effect will be a form of a truss,so why not truss up the roof to begin with?

The idea(-s) employing steel tension members is a funky one,no offense,but it seems over-thought to my(admittedly non-engineer ) pea-brain.

In the past once i've dealt with an old building,log first story/framed second,where 1" dia. rod-rigging(scavanged from an old gold dredge in the late 1920-ies) was used in an attempt to keep the log walls from bowing out.
It was successful only partially,and that building sagged and bagged in some quite fascinating ways...It Did hold up for nearly 100 years,until we restructured it completely.

As a blacksmith i must say that i did admire the hand-forge-welded turnbuckles in the middle of each rod run(there were 4 all together),those were Way cool,visually!:)
"You can teach a pig anything,it just takes time;but what's time to a pig?"
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Offline Joe Hillmann

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Re: 12' High Log Walls?
« Reply #17 on: October 21, 2021, 01:09:44 PM »
Here is the plans showing the ties on the outside of the main building


That's a cool idea,to take the rafter tails Elsewhere,to bear at least in part not on the long walls in question.

Possibly something of the sort can be done without those extra walls/additions outside the main structure,by tying the rafter tails back into the building,to lock things on itself by triangulation.
But that in effect will be a form of a truss,so why not truss up the roof to begin with?

The idea(-s) employing steel tension members is a funky one,no offense,but it seems over-thought to my(admittedly non-engineer ) pea-brain.

In the past once i've dealt with an old building,log first story/framed second,where 1" dia. rod-rigging(scavanged from an old gold dredge in the late 1920-ies) was used in an attempt to keep the log walls from bowing out.
It was successful only partially,and that building sagged and bagged in some quite fascinating ways...It Did hold up for nearly 100 years,until we restructured it completely.

As a blacksmith i must say that i did admire the hand-forge-welded turnbuckles in the middle of each rod run(there were 4 all together),those were Way cool,visually!:)
The reason I suggest the steel cables is because I know it works.  I have helped pull sag out of or stop worse sag on at least 3 buildings using steel cables.  And because I can get used elevator cable for less than 5 cents a foot and grader blades to make huge washers/load bearing plates to tighten the cables into for free.  In my situation it is the most economical solution.  For others it could be prohibitively expensive.

Offline Don P

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Re: 12' High Log Walls?
« Reply #18 on: October 21, 2021, 01:29:44 PM »
Use materials where they shine, steel is a better tension element. I've used the scrap wooden silo rods laying in the weeds around a couple of barns to pull them back together. Both of those had widely spaced ties pegged to the plate with ~1-1/4" pegs that had failed letting the rafters slide the plates outward.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline TW

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Re: 12' High Log Walls?
« Reply #19 on: November 12, 2021, 08:12:23 AM »
In my Nordic log building tradition the normal way of building a roof without tie beams is to build log built gable ends and notch in a pair of purlins for every second or third log course on the gables. As the gables are pegged together with 1 1/2 inch pegs and normally scribe fitted as well they can carry the whole roof weight as long as each room isn't longer than about 7 metres at which point it also becomes difficult to find thick enough trees for purlins. Therefore traditional log houses have partition walls going all the way up to the ridge log.



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