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Design Factors for the Pragmatist


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#1 Dook

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Posted 24 September 2014 - 02:38 AM

I'm planning a log home that will be as simple, cost-effective, long-lasting and problem free as possible. I know many don't like a plain old rectangle, but this design seems to fit the above criteria much better than any other. Besides, I don't have the wealth to build a sprawling, eight-corner notch per course mansion.

 

Around here in Western Montana, most people use standing dead lodgepole, as that is the most available. That suits me fine since I want a handcrafted home with full length logs and long walls (34x36'), and in order to make that work taper is a big issue. Most likely available logs will have 12" tips. I'd go larger if they were available.

I'd prefer to get the log package built by someone within 100 miles of here so I could check it's progress as it's being built to make sure they aren't taking  short cuts. This area is pretty remote and getting several bids the moment I'm ready to build will be difficult. There were a lot of log builders here five years ago but many have just faded away and found other ways to subsist.

My first choice would be a full scribe package with shrink fit saddle notch corners and large diameter logs, but when the time comes (when I sell my current home) I'll want to move quickly and get something dried in so I'll have to be somewhat flexible. The roof will be metal and 8 in 12 pitch with no dormers or valleys....no snow buildup and no loud crashing noise of snow sliding off a dormer on another roof below.

 

Here are some design considerations I'm hoping to get feedback on:

 

1) What is the shortest possible flyway length (not including dovetail) that would hold together without problems? I understand that horizontal wood members rot much faster than vertical ones so I want to keep them dry with generous overhangs, yet not so long that I can't see much out the eave side windows.  One local logdog told me two feet from centerlines, which seems exessive to me.  I can really appreciate why dovetail homes are so popular in rainy ares like the Southeast. But I want large round logs.

 

2) Is it standard procedure (if there is such a thing in this business) to use pins or dowels in handcrafted homes? With long walls it seems imperative to help prevent leaning walls.

 

3) Is it standard to refer to log centerline dimensions in this business?

 

4) How much settling should I expect from standing dead lodgepole in a full scribes home?

 

5) Should I put a treated 1x8 under the first course?

 

6) What roof span issues/limitations will I have to work with? The purlins will have to span the entire 36' length with only one truss around midway. That middle truss would have to span the 34' between eave walls without any vertical members in between supported by foundation. Is that within reason? It seems that most center trusses are the kingpost variety. What my plan calls for is a walk through truss. The top of the log staircase shall end at one side of the kingpost. I'm also considering a stick frame center truss as this would be the wall between the loft and the living room area. My gables will be stick framed. Could a stick framed center truss be made to span that 34" between eave walls?

 

7) I intend to use vinyl windows not because I love them but because they are energy efficient and economical. Compared to the thin frames of aluminum windows used in the past, vinyl windows use up much of the cutout for plastic frame I can't see out of. I was thinking of mitigating this problem by using flangeless windows and attaching them directly to the wooden splines on the log package. Has this ever been done with any degree of success?

 

8) If I'm going to build a log home I want log walls everywhere except the gables. I see many building log walls on top of chipboard bands/joists because they didn't think to build a step ledge on their stem wall and then scabbing in some log siding later to cover the chipboard. This will not be the case here since it will be a slab foundation. Another scab-in-siding-later is often seen at the top on eave walls. So here is the question: Can log dogs cut a "pacman" style slope log so I can use 2x12's over the living area and 2x6 on the eaves? Would that be asking a lot?

I realize I could avoid the issue by using thinner rafters and getting my R-value using closed cell foam, but when I build something I want to dry it in ASAP and not twiddle my thumbs watching it get rained on while waiting for a foam insulation contractor from Washington to show up when he gets around to it. Also fiberglass is less likely to have moisture condensation problems.



#2 Greg Steckler

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Posted 24 September 2014 - 02:33 PM

A couple of thoughts before I run off to work....  consider a standard footing and stemwall foundation, TJI subfloor above the stemwall, thru bolts for the walls, doug fir for the species (larger diameter), 5' flyway (overhang), taller eave walls if needed and even an outrigger log for say a 5' roof to wall distance.  Foundation as I've described allows access to underfloor plumbing/electrical/HVAC systems/thru bolts and the ability to change things.  Doug fir is stronger, straighter than lodgepole (pinus contortus..there is a reason they named it that).  taller walls upstairs give more headroom and usable space.  5' overhang protects the walls.  I'd even recommend a complete walk-around covered porch if you can manage it.  gotta go...more later.

 

Okay, job got rained out, plumber didn't show so nothing for me today...

On to specifics:

1.  2' for large logs is too short.  In time, even 2' will just split and fall away.  Minimum is 3' or more.

2.  Pins or dowels can be used but i like thru bolts.

3.  No (or rarely).  All dimensions should be pulled from the perimeter of the foundation/stemwall.

4.  Depends on moisture content of wood and relative humidity of your site.  Anywhere from 2" to 6" is what I've seen typically depending on species.

5.  Yes (if its wood to concrete), non-treated if wood to wood.

6.  If the truss is is "W" style (Fink) as opposed to Palladian and located say 3'-5' above loft floor there would be lots of head clearance for loft entry from top of stairs.  What is your snow load?  that determines span and log diameter.  DF is better than Lodgepole.

7.  Don't use aluminum windows under any circumstances.  Window trim/installation is not a big problem as long as you provide for settling/shrinkage.

8.  Sure.  :) A good logdog can do anything with a chain saw.  Use TJI's for rafters...lighter, faster, probably cheaper.  (Glu-lams are now cheaper than almost any nominal lumber...so I would expect TJI's are less expensive than 2x12's.)

 

In almost all cases, by the time you get your dig out, foundation/subfloor/subfloor plumbing & wiring done your log shell will be ready to ship.  So it doesn't really matter if it is 100 miles or less from your site.  Could be anywhere in North America or Canada...simply freight + shell cost.

 

Well, just my 2 cents...


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#3 Dook

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Posted 24 September 2014 - 07:37 PM

Thanks for the reply, Greg. I would prefer a stem wall, but the site is on a flattened ridgetop and there are bedrock spines sticking up all around. I'm afraid the jackhammering would make stemwalls cost prohibitive. I plan to do a FPSF.

 

Is it possible to have those long through bolts in the walls on a slab?

 

I guess I have my log terminology cornfused. I though "flyway" meant the log end that sticks out beyond the corners.

 

I agree about long overhangs, but the limiting factor is visibility. With an 8 in 12 pitch I wouldn't be able to see much out the eave side windows besides the underside of the overhangs.

 

A factor that limits size is the septic system. If I had more room upstairs, I would have to make the downstairs smaller and actually use the stairs, which my bad knee doesn't need.

 

The fir trees on the steep terrain around here grow with a sweep the first 12 feet or so. It may be straighter than lodgepole in other regions but not here.  The log companies here seldom use them. I would be more likely to find straight larch here than Doug fir. The Lodgepoles grow close together and thus few branches and straight up.  When they get taller they kill each other off in competition for moisture, then stressed out from lack of water they succomb to the pine beetles.



#4 Dook

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Posted 24 September 2014 - 11:46 PM

Thanks for the additional info.

Good idea about the W truss, I could have the stairway go straight to the middle instead of off to one side of a kingpost.

The snow load is 115 Pg, whatever that means.

TJI rafters are easy if you have the same thickness roof throughout, but when you have 12" roof and 6" thick overhangs, it's a lot of work to attach the rafter tails. Considering that they will be longer than 20', I suppose it will be TJI anyway.

 

The distance of the log package contractor is not an issue if I trust him, but why would I? This might be the subject of another thread...how to deal with that contractor. So much at stake and up front. If he trusted me instead and did not demand payment until I accept the package, then that would work.



#5 Greg Steckler

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Posted 25 September 2014 - 02:35 PM

but the site is on a flattened ridgetop and there are bedrock spines sticking up all around. I'm afraid the jackhammering would make stemwalls cost prohibitive. I plan to do a FPSF.

 

You need to look into what the frostdepth is at your site.  If you truly have bedrock, you just clean it off (air blow) and pour stemwall directly on to it.  the whole purpose of a foundation is to spread the load down to the ground and not have frost heave.  Keep water out from under the concrete and deep enough and you're home free.

 

Is it possible to have those long through bolts in the walls on a slab?

 

yes, altho' difficult...you have to box out for it.

 

I agree about long overhangs, but the limiting factor is visibility. With an 8 in 12 pitch I wouldn't be able to see much out the eave side windows besides the underside of the overhangs.

 

Raise the wall higher(gives you more headroom in the loft) or reduce the pitch.  A cross section drawing through the house will show exactly what will be visible.  I always favor a wrap around porch.  Your septic system is usually defined by the number of bedrooms.  The loft can be declared a storage loft only.

 

The snow load is 115 Pg, whatever that means.

 

I would guess your snow load is 115 lbs/sq. ft.  which is substantial.

 

The distance of the log package contractor is not an issue if I trust him, but why would I? This might be the subject of another thread...how to deal with that contractor. So much at stake and up front. If he trusted me instead and did not demand payment until I accept the package, then that would work.

 

Whoa...  do your homework, get references, ask for photos, talk to folks... way before you lay your money down.  Log Builders (good ones) are a small tight knit community.  We all know each other and respect each other as well.  there are a lot more unscrupulous buyers than producers which is why almost all log home builders will insist on 1/2 down to start and the balance F.O.B. plus more if they are the ones doing the re-erection (which most insist on as well).


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Greg Steckler
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Here is my temporary email:  stecklergreg@gmail.com

2253 NE Edgewater Dr.
Bend OR 97701
541-389-4887
Designer
Log Rhythms, Inc.

"Only Nixon could go to China" ~ Mr. Spock


#6 Dook

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Posted 25 September 2014 - 04:26 PM

The locals call these bedrock outcroppings "spines". Maybe named after the spines on a dinosaurs back. That's about how it layers. It's definitely not a flat bedrock site.  It would cost dearly to dig away the decomposed shale and fractured bedrock areas to see what I really have. There is silt mixed in with it so heaving is a possibility. Getting deep enough is uncertain and likely costly. FPSF seems like the easiest and most cost-effective solution.

How do you box out for thru bolts?  I suppose I could embed some of those long 5/8" NC nuts used for connecting allthread rod, using a bolt underneath to anchor it. Has that been tried?

I had thought about raising the walls, but that carries some disadvantages like cost, and having more area to heat. The non-loft area will have extremely high cielings and I have no other motive to raise it even higher.

If I were building a log home down in Texas with a 4 in 12 pitch roof I would love to have a wraparound porch.

The septic is going to be limited to 1500 feet as I understand it. Every state has different rules on this.



#7 Greg Steckler

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Posted 25 September 2014 - 05:37 PM

Okay, if you think FPSF will work (I'm not convinced, however) and if your local building official allows (if you even have a building code...lots of MT does not).  A plastic of P.T. wood box similar to a plastic vent can be installed prior to pour 6-8" down from slab surface on the outside of the perimeter of the concrete.  I would add a 1" PVC hole from slab surface to box for the thru bolt which is installed later (or drill out later).  This would require very accurate placement of both the PVC and the bolt holes in the logs.  At least (2) #4 bars in that conc. "header" between the box and slab surface.  You are building a reverse lentil.  I have seen this done by Mark Fritch out of Sandy Oregon to good effect, although he did it on a regular stemwall because he wanted to hang the joists from the PT mudsill, not set them on top of the mudsill.  The box out was 12" down, if I remember correctly.  Pictures are on this website somewhere.

 

How about a 6/12 pitch?  What is the size you want?  34x36?  Do they count the loft?  Without being too nosy, where is the site?


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Greg Steckler
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Here is my temporary email:  stecklergreg@gmail.com

2253 NE Edgewater Dr.
Bend OR 97701
541-389-4887
Designer
Log Rhythms, Inc.

"Only Nixon could go to China" ~ Mr. Spock


#8 Dook

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Posted 25 September 2014 - 06:12 PM

Thanks, Greg.

Yes, that thru bolt box sounds like a complex project. The FPSF will be very complicated as it is with the foam perimeter covered in concrete board (usually done inside the form) and the pex tubing for hydronic heat.  I can see where the thru bolts would help a lot on a 36 foot long wall not having any intersecting log wall. It's going to be a tough call. 

If I tried to dig around to see where the spines are, I would then have disturbed ground to deal with if I decide to go FPSF anyway, plus be out that expense. The FPSF only needs to be 14" below grade. That much I can handle with a jackhammer mounted on a skid steer loader without falling in a deep trench. I can rent that for $240 a day including a quick detach bucket and operate myself.  An excavator with a mounted jackhammer would have to be hauled in from afar, include operator and be additional to the excavator which digs the foundation, very expensive.

 

34x36 plus the loft (which they do count) is going to be right at 1500 square feet. If I went 6 in 12 pitch, I would have more expense in taller walls and need a stout roof system for snow load. I don't want any vertical logs inside, the spans are probably easier to manage with greater pitch. It's going to be in Mineral County, Mt.

 

Is 34x36 without intersecting log walls stretching the limits? They are going to be big logs. The middle truss should help stabilize the 36' walls. Inside walls and loft floor will be stick framed.



#9 Greg Steckler

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Posted 25 September 2014 - 11:13 PM

I once watched a concrete pour that had insulation under the slab.  As the pour progressed the 2" foam boards started popping up right through the "liquid" concrete.  What a mess.

 

Just for fun I did a beam calc. on a 18' purlin with a 6' tributary load at 115 lbs/ sq. ft. in Lodgepole then in DF/L.  8/12

 

Lodgepole:  19" diameter at 1/3 point.  (Western Woods design criteria)

DF/L:  15" diameter at 1/3 point.  (old Haney design criteria, may not be the most current)

 

If the foundation is only 14" down, what happens when that ground heaves?  BTW, the intersecting framed walls can be built to brace the log walls and still slip for settling.  Scribe fit logs are more stable than round on round chinkers.  Also, if you elect to do window boxes as a window subframe they can be done with splines which stabilize the wall, too.


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Greg Steckler
Webmaster at
Lhoti.com

Here is my temporary email:  stecklergreg@gmail.com

2253 NE Edgewater Dr.
Bend OR 97701
541-389-4887
Designer
Log Rhythms, Inc.

"Only Nixon could go to China" ~ Mr. Spock


#10 Dook

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Posted 25 September 2014 - 11:39 PM

I once watched a concrete pour that had insulation under the slab.  As the pour progressed the 2" foam boards started popping up right through the "liquid" concrete.  What a mess.

 

Just for fun I did a beam calc. on a 18' purlin with a 6' tributary load at 115 lbs/ sq. ft. in Lodgepole then in DF/L.  8/12

 

Lodgepole:  19" diameter at 1/3 point.  (Western Woods design criteria)

DF/L:  15" diameter at 1/3 point.  (old Haney design criteria, may not be the most current)

 

If the foundation is only 14" down, what happens when that ground heaves?  BTW, the intersecting framed walls can be built to brace the log walls and still slip for settling.  Scribe fit logs are more stable than round on round chinkers.  Also, if you elect to do window boxes as a window subframe they can be done with splines which stabilize the wall, too.

That must be why they put visqueen on top of the foam panels....to keep concrete from sneaking under. The theory about the FPSF is that the ground cannot heave under it because the foam traps geothermal heat. Crawl down into a mine shaft when it's below zero outside. It will still be 60 above down there. The ridge site percolates pretty well, standing puddles after a hard rain are always gone in less than 24 hours.

 

Thanks for the calculations. Does "6' tributary load" mean purlins every 6 feet? Even if the walls are Lodgepole, Dougfir/Larch purlins are a good idea. I'm about 30 miles from the site and have 8 in 12 and 10 in 12 pitch on my barn and house. Both are metal and no valleys. The snow seldom accumulates  at all, one time it got up to about 17" on the barn but usually it slides right off. I can understand how a shingle roof could get four feet of buildup and that's probably how they calculate the loads.

 

I would like to learn the method of bracing log walls with stick frame walls.

 

EDIT: Found another source for snow load in Montana : http://www.coe.monta...12105noMaps.pdf which shows 60 psf for the town of Superior, ten miles away and 700 feet lower than my site.






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