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Installing Windows (bucks) to roundwood post and beam walls

Started by Andy2018, November 04, 2017, 04:42:34 PM

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Andy2018

Hello all

could you share please what is the best practice to install windows into log post and beam wall. The wall is made of a pine approx. 20 inch diameter...
Should i attach a window buck to posts? And should i consider a shrinkage of a vertical posts? Or i can just make a  flat surface from inside part of posts and use them as a buck?

Thanks in advance for inputs!

Don P

A log won't shrink noticeably in length as it dries, it will shrink in diameter a bit. From my guess of what you are doing (post some pics) I'd skim that side of the log flat, attach buck enough to nail the flange or brickmold to and provide trim dimension between window and log. I don't see a reason why you couldn't mill that into the log. Any work you do to the log is going to weaken that area and so encourage the major drying check to form there. If you plow a vertical kerf lengthwise up the post behind a buck it will encourage the check to form there hidden by the buck and with the buck made from an independent seasoned stick, it won't be affected by any log movement so much. ... watch the grain in timbers around millwork, straight rather than spiral will help with twisting during seasoning.

Andy2018

Thanks Don!
And what if i install windows just to flatted vertical posts without buck?
Please see attached pic of post and beam part... 

 

MbfVA

Don, hi, how about relating your comments on checking to timbers as well as logs--does it help to make that (hidden) cut on them?  I know you don't approve of green timber for TF, but wondering that will help.

I have seen some hellacious settling in a large log home in Bath County (sourced with a NW log home company, now out of business) that seriously wracked a bunch of the windows and doors in the 7800 SF structure.  Some would barely open, and this was 3 years later.

Foreclosure, cost over $1.5 MM plus 72 ac land and 2 big Morton buildings (neighbor said they cost over $400K cs), sold by BB&T for $825K.  We lost it while trying to finance it.  Insurance was going to be over $5000 per yr, BTW.
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Don P

Andy, I'm assuming you are talking about fixed panes of insulated glass mounted and trimmed to those openings. This is fairly high risk, you may pop some seals or break some panes over time. Looking around, just about every seal in this stick framed house has failed. So, just to define high risk, they all fail eventually.

I'd flatten and wait as long as possible. Use the largest rubber setting blocks and largest trim/gap around the glass you can get away with. A twist or bow during seasoning is the risk.

MBF, yes a kerf in a timber does the same thing as a kerf in a log. Usually... the major check forms at the shortest distance from heart to bark. Cutting that kerf shortens that stress relief path, sort of like making a control joint in a slab.

MbfVA

 Comparing it to a concrete control joint was especially helpful to me.  Almost a word picture.

You have a good clear way of explaining things ;).

Makes me wonder how we avoid the problems using green wood, as others around here using green have no doubt been able to do.  I have some ideas but need to ask lots of questions.
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MbfVA

BTW, I  do not recall seeing any broken glass or actual damaged doors or windows in that log cabin home. The main problem was sticking.  I also suspect that the heat was not carefully controlled during time it was vacant.
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Roger Nair

I have not, in general, followed the writings on log building, however, the one book I could recommend is The Art of Log Building by Hermann Phleps in which Phleps documents the Germanic log building practices.  Much is written on the various techniques used in constructing green wood log homes that have practical non binding doors and windows.  I would suspect Robert Chambers books would also cover the same ground from a modern point of view.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Don P

We're heading off into the weeds  :D. Above I was describing direct set glazing in a post and beam assembly. That gable is really no different than a stick or timberframe. There is one horizontal member, at best a foot of horizontal wood subject to shrinkage, ~1/4" there. The timbers happen to be round.

Conversely, a typical stacked log wall rough opening is the window rough opening height plus the settlement allowance for the horizontal wood of that opening height. The bucks themselves are the rough opening height given for the millwork, generally the jamb height plus ~1/2". The rough opening is several inches taller than the bucks, the settlement allowance. If settlement is shrinkage alone (milled logs stacked tightly flat on flat), from the green condition, in white woods, the allowance is 2-2.6% depending on climate zone. Settlement may not be shrinkage alone, in Chambers and Phleps scribed logs will experience crushing of the coped edge until it reaches bearing for the load and, we're back to that stress relief, the major check will tend to form inside that cope, which will then spread as the check opens and the logs will settle deeper, known as slumping. As long as we are in this deep, the shrinkage allowances above are from the log home code, I and a group of others commented when it was written. Chambers sat on that panel. The numbers are greater than reality. Here's why, if a check forms in a face the wood has certainly shrunk but the log may not lose any height if the shrinkage has been accommodated by the checking. So one way to look at code shrinkage and settlement allowances is that they are quite conservative.

I digressed  ::)

Inside of those bucks the window or door frame is set. That finished frame is shorter than the bucks by the manufacturer RO allowance. So, in a perfect world even if the logs try to settle more than was allowed for, the header log will land on the bucks before it can settle on the window or door frame. Widthwise the rough opening is usually 1/2" larger than the unit on each side, again it accommodates more movement than a direct set piece of glass.

There are any number of ways to screw that up I suppose but most commonly someone affixes the head trim to the window and header log. The trim comes down as the logs settle, putting load on the window or door frame itself. Generally it is nails but it doesn't have to be, caulk is an adhesive. Another way to bind them is to fill the gap above the jambs with rigid foam or tightly stuffed fiberglass. Again as the logs above settle there is no free gap and the load begins to land on the jambs. That is typically the binding issues and if so, relatively easily fixed.

When you design for settlement you have to be thorough. You cannot quit thinking about how to accommodate settlement when it gets tough. On the barn project I've been sharing we've blended green log and timber construction, one settles the other doesn't. It all has to plane in when it seasons out.

Some more thinking exercises. Look at Andy's gable. Imagine if he had built it with stacked logs that would settle. Instead of purlins imagine a rafter couple associated with that settling gable.

Steps cannot vary in height or depth more than 3/8" from each other and treads must be within 2° of level. Now drop the upper floor 2%.

Rambling as I listen to the voting returns  :D Drag us back out of the underbrush if I missed Andy.

MbfVA

 If I interpreted some of the references on Chambers download page & what you said correctly, "floating" (my term) the dimensional lumber in making "the box" for the fenestration, again my lay term, that is used to frame window openings, seems to be what you're talking about.

In other words the way the window openings are framed in a log structure, and perhaps this would be applicable to green wood timber framing as well, there's an allowance for settling, shrinkage & other movement of the logs by this "floating" of the framing.  No one wants popping glass.

Do I come close to understanding this?  Or are the (my) weeds getting higher n higher?
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Don P

Do you know how many times I just wrote "window or door" just to avoid the confusion of a big word like fenestration  :D

A timber isn't going to shrink in length just as Andy's log posts aren't going to shrink in height. A floating buck is not necessary for that reason.

If you work green the wood is going to move a fair amount during drying though. If it works well everything stays sealed and is accommodated by the rough opening gaps. If not pull the window and work on the opening.

Unrelated but popping glass reminded me of another thing we experienced. I contracted for 7 log homes in the Black Hills in the early 90's, around a mile high. The windows came from the east coast and it was before they installed the relief tubes. We actually got to where we could see that a window was going to break the day before they would crack. The pressure trapped inside the double pane glass would begin to bulge the glass a little on the larger panes and usually the next morning we'd have another one to take to the local glass shop.

Looks like we've put another election to bed, me too, Michelle was up at 4 to work at a local precinct.

Andy2018

Hi Don and others!
Many thanks for shared thoughts and suggestions! Very much appreciate!
I could not understand everything written as it has some building specifics and English is not my native, but what i could get is that installing windows into flatten post and beam log structure brings up a hight risk of windows crushing mainly in case of horizontal log settlement. So the best in that case is to install bucks into vertical posts keeping space between buck and upper beam.
I hope that is correct understanding :-)



MbfVA

why don't you fill out your profile so we will know where you are, etc
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Don P

No, the buck is needed in a typical horizontal log wall opening BUT in your post and beam gable the vertical posts are holding the horizontal log in place so it is not required.

The main job of a buck is to keep the stacked logs in line vertically.

Ask about anything you don't understand... It took me three years to fail French 2 times, if English is second language I'm impressed

MbfVA

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Don P

I found a pic of bucks going into a stacked log wall. The 2x6 buck was recessed on the log side to hold one leg of a 2x2x1/4" angle iron. The logs had a groove cut in them to accept the other leg of the steel. This holds the log stack in line but allows it to settle. The bucks were cut about 1/2" taller than the window frames and then a settlement space was left above that.



To connect to another log home conversation, this was in Marathon Co, WI around '93. We had a local independent third party inspector on that job.

Andy2018

Hi Don,

Thanks a lot! Now all is clear! I had understanding about the buck in stacked logs, but didn't have any clue for post and beam. I'm from Russia, Moscow area and Post and Beam contstuction is fairly new especially nowdays, when all old traditional skills are almost lost and builders are starting almost from scratch...

Thanks a lot, i got the final understanding how to proceed with my case. So we agreed with the crew that we take a small quarter from outside of posts and attach windowd frames to them from exterior, so that to keep a natural nice look of logs from inside.

@MbfVA, thank you! I updated the profile with some personal details.

Don P

  You are quite welcome.
My father has travelled to your country several times to teach American style construction. One of my old building code books is somewhere in Tver  :D.

Edit;
There is a good book on building log/post and beam "The craft of modular post and beam", James Mitchell

For those interested in pics mostly of Russian log buildings,
I was looking up a book I have to see if it is still available, it is, but if you hit the images tab in google there is more there are more pictures there than there are in the book. google;
The Wooden Architecture of Russia
then click images.

A traditional Russian buck for a stacked log wall is a thicker timber standing upright, it looks to be about 4"... 10cm thick with a groove up the center of the log face, maybe 5cmx5cm. The ends of the stacked logs have a corresponding tenon that can slide in that groove in the buck.

MbfVA

Given Russia's cold climate, do you use any added insulation?  Lots of commentary about the thermal mass of logs v insulation.  Russia seems like a great laboratory for research on the question.

Andy, wish I spoke Russian but glad you can handle English which is about as treacherous a tongue to learn as any out there.  Thanks for bringing perspective from a less well represented side of the globe to this forum.  If it works in Russia, our VA/USA climate should be a pushover (in other words, easy).

In fact if so it might also make it through a winter in Grayson County, VA, on Mt Rogers!

BTW, I am betting that Andy read in history class about the Defenestration of Prague which "started" the Thiry Years War in Europe.  Sometimes a unique word like that transcends the language of the book it appears in.

During my one year at W&L in Lexington, a note appeared on the bulletin board in the Old Quad announcing that unidentitfied parties would be re-enacting the DOP with a classmate who was annoying them by constantly playing his Country Joe & the Fish Records too loud.  His stereo system and records would be included.
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