28' x 36' log cabin project

[Don P]

Yup I've bought blem foam in the neighborhood. 

That faux truss over the spaced columns is not my proudest moment but i like the porches on this one.


  

The ridgebeam in your lower pic is a glulam with rafters over top, nothing in the code precludes that, it's actually better.

Center the chimney, offset the flue within the chimney to the lee side of the ridge. Read the rules in the chimney chapter on distance from flue to combustibles, I think its 8".

These are 4x10's on 4' centers. The collar ties are faux, the glulam ridge is doing the work, the actual upper ties are metal straps over the top, hidden. This roof could have been just the beams and planking overhead with no collar ties



 

[Don P]

I was looking for something else and passed by this page and remembered your comment on the collar tie/ridge connection. Here is the codebook language;
[color=rgba(0, 0, 0, 0.87)]R802.4.6 Collar ties.[/color]

[color=rgba(0, 0, 0, 0.87)]Where collar ties are used to connect opposing rafters, they shall be located in the upper third of the attic space and fastened in accordance with Table R602.3(1). Collar ties shall be not less than 1 inch by 4 inches (25 mm × 102 mm) nominal, spaced not more than 4 feet (1220 mm) on center. Ridge straps in accordance with Table R602.3(1) shall be permitted to replace collar ties.[/color]

I'm in one of the code referenced manuals, the WFCM, Wood Frame Construction Manual.

Notice the top of the page, the WFCM is divided into 2 parts "Engineered" and "Prescriptive". We are in the prescriptive part, you can cut and paste this part right into the codebook. This is giving the ridge connection requirement per foot of beam. Exposure B, typical, I'm assuming not on a ridge or lakeshore with a lot of fetch to the wind.

 

read the footnotes... always read the footnotes, at 4' rafter spacing multiply the connection requirement by 4. This is attaching the rafter pair together and down to the ridge, that uplift carries to the supports, take care of up as well as down.

The footnotes also talk about using 6psf dead load in calculating the uplift. this is closer to typical true roof dead load. Remember we typically design using 10psf or 15 for dead load when designing for down, for bending under gravity loads. Here we need to be conservative in the other direction, I don't want to assume I have 10 psf of dead weight when holding the roof down if that is less than what is there, always err conservative. They are saying that for typ use 6 psf DL. Some years ago an article in a trade mag came up with 7psf as being "typical". I have built many roofs that are something other than typical, the tin and spaced 1x4 roof on the sawshed is probably 2psf, there's the judgement part. Anyway connect well. Unless it is one old inspector, he has probably never seen this table but he will probably recognize the WFCM reference. There is another table a few pages away that lets a rafter tie be raised to mid height of the roof. The codebook table says no higher than the lower third of roof height. Complete with heel joint connection specs and prescriptive, it is law. Part of what led to this post is seeing that table go by and thinking, nobody knows where that body is buried. That is probably the most frustrating part, the info can be scattered far and wide.

[akadiesel]

 Busted!!!🙄 Coincidence?
  We could have bumped into each in the WFCM, but I've always drawn the line at helping bury one, ....but. I imagine you have most all this in books, versus my downloaded 2015 WFCM. That 700mph caught my eye but I didn't dwell there.
  A lot of this is sort of some new worms in the old can. Master code, referenced code, get in, get out. I was there in the 2015 knowing I should have been in the 2018, and was I there at the right place for the right reason, but it's a lot harder than you would think to download any, much less all of some of this stuff! Having only recently realized what a difference browsers make with the read only stuff, I can finally actually read the WSDD. The IRC displays different.
Back to the real world and liking your pictures, covered porches are pretty much a requirement!

 

[Don P]

That style has a lot going for it. It looks like one of the post and beam type, look at the corner posts. The logs are fixed and chinked between rather than a settlement system. The logs are infill in a post and beam "frame".

[akadiesel]

Yep, that caught my attention as a whole but saved it as a porch / roof example and moved on. Then later started looking at it, and what's really going on here? My neighbor across the road has some old cabin logs reassembled and some corners covered with boards to end up looking similar but totally different at the same time, if you know what I mean.

[Don P]

If you look at some old russian log homes they boarded over the corners as decorative protection of that end grain. That might be what your neighbor is doing.

Structurally (I'm speculating or daydreaming), the style above has vertical column members spaced around the perimeter close enough that the plate log acts as a beam. The infill logs can slide down with a trim at the top between the plate and upper log, or, they can be fixed to the column and chinked in between. The beauty of this method is that the wall height does not change. When you blend porches, plumbing, walls, on and on, with log, you can never turn your thinking cap off. Settlement, or in the case of a porch post and log wall, one element settling and the other not settling, now you have an issue that must be addressed $. This makes that go away

The Hudson Bay Company buildings utilized pretty much that method and it spread through places in the fur belt. James Mitchell "The Craft of Modular Post and Beam" is a good book.

This one was log "siding", 1/2 logs with 3/4 log corners applied to a frame wall. The round corner/log look could be done in full log without the frame using this method though. Imagine a tenon from the logs into a vertical groove in the corner post, either pinned or allowed to slide.



 

This is inside the living room in the house I liked the front porches of, they are left in this pic, unbuilt yet. I would call the logs fixed in the channels in the 10x10 post. I put a toe lag at a downward angle from each log top to post. The logs were in the lower 20% range IIRC and it has done fine.



 

This is the other end of that tie beam and another inside corner post, non settling master bedroom wall in green carrying the opposite side of the center roof. Although the code was evolving, this house was I knew, in the "special wind region". At first they painted the entire mountain chain red, then they started selecting the real high wind areas better. This house is on a bluff over a straight section of the New River looking out over about 5 or 6 miles of clear air coming off a big mountain. Those upper glass windows are protected by 12' of porch roof and I've seen them running water from top to bottom in a storm. Anyway, the plans called for a spliced log wall plate on that gable end. I knew that wall would get slammed by the wind, and they had supplied Florida/Dade, hurricane strength windows, so we plopped another 10x10 on top of the wall as a stiffener, sort of that horizontal beam hanging inside idea.



 

Which, the reality tv moment on that job. The BO wouldn't issue a CofO till the last of those special windows was done. 2 came in wrong. Anderson does not make mistakes, therefore the mistake must be us. Interest rates were going up, we're waiting on windows. Anyway, we got the deal done and to the bank with a half hour to spare. My clients could not afford what that rate hike would have done. I was ready to call Miss Lillian about the BO. Patience and karma worked, but that's another story  :D.

[akadiesel]

  That's all interesting to say the least! I'd thought about maybe a post beam to start with. Not really the way you're describing it but I was wondering if in the picture that was siding. There's the non-log inside walls and that one short log under the porch roof. Your daydream makes perfect sense now! Irregardless I like it and the way he framed the end windows is a lot like I was seeing to do.
  My neighbor short answer was the corners were too far gone and that was the easiest fix.
  A friend's father, way back, put up early Southland kit cabin and they used what we call push pull dogs so they wouldn't settle. Just chinking issues. Then he started building a chicken coop which turned into a guest cottage. He ran 2x12s around the perimeter with a gap to look like chinking. Had kind of the same look but not done as well.
  I was skeptical on the shrinkige to start with but have talked to enough people to know it's a concern. It's really good seeing and understanding all the different ways of doing stuff. I could end up changing the whole plan or not doing anything here and going elsewhere. Or do both if I live long enough!😂 Sure I'd like to already be doing something but I'm pretty used to figuring out the plan 1st, then starting late and finishing early!

[akadiesel]

  After the recent rafters over the ridge beam being equal or better, I'm thinking about how many ways are they going to let you skin that cat plus how should you. So with pictures of how I'd first think in mind, after a good while of looking around online,  I end up on a different forum from years ago and here's this guy using your name😂 with answers and references! I wonder how many more places I'm going to run into him??!!

[Don P]

You gotta watch your sources  :D

[akadiesel]

    Darned if it don't feel kinda ironic thinking about shrinkage, settling, adjustments, etc while sitting here in this old farmhouse looking at the stacks of shims under almost every piece of furniture and  appliance in it!!😂  
 Anyway, I've been using the calculators to figure post size and recheck beam sizes, having both the 2015 and 2018 NDS supplement beam charts. What am I not seeing or doing right? It can't be my source 🙄!
 Starting out with the simplified column calculator to understand the math, I input a #2 Doug fir 8x8, 144 in L, 25000 load. It passes with 521 psi allowable stress. Moving over to the other column calc and putting in values from the NDS, it passes with 568 allowable. It has to be the E, so I drop it down from 1.3 to 1 and it passes with a 518 allowable stress.
 So I move over to the beam calcs and the dropdowns are showing less than the NDS tables. So what fails there, passes in the other calculator with the NDS inputs. I'm not seeing any of the adjustment factors applying. What am I missing and why is dead load needed in one calculator and not in the other?

 

[Don P]

You are tracking year models more than anyone I've ever seen, are you seeing that many differences between years? My hard copies of most of this are from the turn of the century. It would take several grand per cycle to stay current in print. Most of it never changes, pay attention to the changes.

The column calcs is one place where there was a change between years and there is some difference in output.
E is an actual value rather than an allowable, it doesn't have a "safety factor" in the E number you see, it is the actual average stiffness of that species and grade. For beam calcs this is correct, we want a "true" deflection number and a "safe" bending and shear strength number.

Part of the math for determining column buckling requires the stiffness of the wood used in the column. In the older of those 2 calcs accepted practice was to input "E". This worked and through a fudge factor it gave a reasonably safe result and posts were sized this way for, about a century without event. However, it wasn't elegant, correctly there should be an "allowable" stiffness for a strength equation. A team of pocket protectors cyphered until they had added another column in the NDS supplement tables. Beside the value "E" is a column "E min"... to be used in the new column equation. I think this was between the 02 and 05 editions. I had to input those columns to the data for that calc, they had done a lot of work to fix something that was working just fine  :D

Correctly in beam type members deflection limits are for live load only, the dead load deflection is built in so is not going to crack tile, plaster, etc. I chose which adjustment factors to use where. Where I chose to let it err by not making an adjustment, it will do so conservatively. If you see otherwise let me know.

Likewise if you see erroneous design values anywhere let me know exactly what and exactly where. I need to find it to fix it, I want them right but don't care to chase snipe.

[akadiesel]

  Not seeing differences in the 2015 and 2018 tables, but some is blurry and pretty hard to read. I didn't really have a problem with column calculator as only did a few with one on rt that explained the process. I followed the formulas and did the math to verify it was calculating Emin.
  So I moved over to the other calculator and input several the same as in the other with NDS values. It was close enough to verify the Emin was calculated there too, The design values in your chart are pretty spot on with the NDS as best I can tell. So either I was not seeing something right or the other calculator is getting a different value from the dropdown than the charts have.
   That got me wondering and went to the beam chart, one that has the drop down. Hit #2 DF B+S and its 825Fb, 1E, & 165Fv. Off 50Fb, .3E, & 5Fv. #1 is low about the same. .4 on E. See pic.
  EWP is all the same on your chart, the NDS, and the drop down. That's as far as I've compared so far.
<br
 

[Don P]

It has been almost 20 years since I wrote these, recollection is getting into it :D. I believe you'll see several design values in the supplement for DF... North or South, interior/coastal,mixed DF-Larch or straight up DF. In the calcs I think I gave one choice and chose the lower design strengths. There are a few instances of that through the data array where I was trying to simplify the drop down list and in doing so chose the weaker, conservative, design values. Double check me and see if that is what is going on there. Is that my design value list on the left in your screenshot or the supplement's?

Depending on how deep into the weeds you want to go. One thing I was hoping for when writing those... I know diddly about computers, was that someone who does know computers would clean them up and add to them. Thus far bupkus  :D. But, if you want to lift the hood, those calcs are all open source. Right click and when the window pops up click "view source". All the code is right there, nothing is running in the background. You can go into the data arrays and add to or modify values. You can "save as" to your machine and have your changes. if there is an error, email me that copy for checking. I have done that and then saved the calcs back to the forum several times when an error is found. Feel free to poke around in the code there. If you have DA6 open, the awc's beam equations, you'll see the equations and my notes to myself (//!) under the hood. With the Supplement open and the data array's there, you can check or modify those values... or add to it, I didn't enter the entire Supplement in there. I do have for instance design values for poplar heavy timber done by an engineer that could be used there, but it is not official. Sure beats guessing. but more importantly at this moment, a dog wants to go for a walk, rather insistently :D.

[akadiesel]

  Hey, I'm all in for blaming Douglas!!😂 I bet Doug is the whole problem here! Go figure my second pick would be the problem child,!
  But it seems "they" have it or EWP beams to sell. And I can almost feel them looking at me like I'm stupid for asking, on the phone, why is it twice the price but all you know is it's #1, but no North/South/ or neither imfo? I know, it's from maybe N or S, but not E or W. And it's the dense one!!😂😂 But wait, there's no center I mean really?? Now tell me again that dense pine is Southern!!
  Seriously, in the picture, your chart on the left and your beam calculator with the dropdown on the right. Yeah I'll spend a little time later checking out the drop down values for more species. I relate well to the 20 years ago and computer illiterate thing. More than 20 years ago but back when I could have done those formulas in my head, a bunch of 0s & 1s made no sense and I didn't want it to. A Cummins under the hood would make more sense to me!

[Don P]

Welcome to my world :D. If no other info is given, err conservative, make it work with the weakest reasonable design values. Always mindful that forcing the math to work doesn't mean the building will, its smart that way.

 If better info is available and you want to use it, you've figured out where to find the design values in the supplement, the manual entry calc allows you to enter the design values, adjusted to whatever you want... so that option is there when you can't find it in the dropdown calc. Remember to shift over to the heavy timber tables in the supplement when it gets over 4x.

FOHC Dougfir is sweet stuff, is that for rafter material?

[akadiesel]

  I started looking for the ridge beam post that you mentioned needed to be trees. Then loft beams. Rafters will be after that. Been just using that 10 PSF dead load. I was planning to add up the actual dead load, but in his constant effort to help, my little kitty cat buddy laid on the laptop keyboard and deleted all my measurements and weights and everything. I need to expand my search but the only few places I know for logs and beams is pretty much Eastern white pine # 2 and Douglas fir #1 FOHC. DF cost about twice as much/ft, but if smaller size, we'll see.

[akadiesel]

FOHC Dougfir is sweet stuff, is that for rafter material?

  Twin Creek, one option in a reasonable distance, has Eastern White Pine - #2 Grade, Western Red Cedar - #1 Appearance Grade, and Douglas Fir - #1 Free of Heart Center (FOHC) Grade. I've read it may grade higher than #1 but don't know if that's true?

[Don P]

It may but you design based on the stamped grade. The interior shot of the very steeply pitched roof a few posts back, that was #1 FOHC DF 4x10's. A number of them were probably SS but design by the stamp and put the best ones where they will do the most good.

Something to think about. One rafter came in with a timber break, that co had a truck there within a day with a replacement. Keep your eyes open.


 

One thing with heavy timber. Everyone says how strong it is. Had I missed that, the rafters would have been effectively on 8' centers. Miss one on a stick frame and at worst you're on 4' centers. There's more than one way to look at strength. 

[akadiesel]

  True! I look at it a lot like rigging. You just don't fly a 10 ton load with 10 ton rigging! I guess that's a lot of why I like to know what the minimum is, so as to know what doubled the minimum is. And even the best sometimes have to get the books out!
  Which brings out several questions. On the posts, you originally said there were other factors that it was too soon to get into.
But the bottom post in the middle of a 28-ft span, so a 14-ft span whether two beams or one. With all the weight on tthe loft side, does that factor in & is it still technically a balanced load? Then the 16 ft beam from the rear wall to the post, which yes needs support in the middle at least, does any of that affect the post other than just the calculated midway weight on one side?
  Back to that minimum thing, or to be by the book, those beams should be measured support to support plus half the bearing length..Correct? Formula for that? One calculator gives the area after figuring it but that's not really the length. Or is it? If I can document the by the book beam size, then I can document or just know how much it's overdone. And do you have an opinion on how much over you'd like it to be? Like in rigging, 50% over is my minimum with 100% over preferred. But unlike with the wood they pay for the rigging! 😂
  Knowing how much you like Doug's wood, and yeah I'd love to use it all around, but it versus EWP?? For example, on the 14-ft beams, 8x12 EWP or 8x10 DF works. But the cost of one DF would almost buy two EWPs. I need to go back and look at how close to the line both were but other than size, and pretending we're spending your money, how do they really compare having knowledge and experience? Maybe I don't want to be under one of them? I don't know.

[Don P]

We've rambled long enough I'm liable to repeat myself but posts, or correctly, columns.
Back in the day they were classed as short or tall. If a wood column is l/12 or less it is considered short and will not fail by buckling, you'll have to crush it to kill it, use the compression parallel to grain values and that is the column design strength. Or, an 8x8 post standing 8' tall between floors is not going to fail by bucking, it is full compressive strength. It is 1" thick for each foot of height, burn that into your brain, that is safe and easy. However, also check that the end of the column will not bite into the beam it is supporting. Make sure there is sufficient bearing area on top of the column for the beam in compression perp to grain.

As the column becomes taller and more slender it fails by buckling. Push down on the end of a yardstick and it will bow out to the side, this is column buckling. The calcs are checking for that.

You are gut worried that the loft load is eccentric, it is not. It is still a vertical load and the calcs apply, the loft floor is a point of lateral support, the effective column length there is from loft floor to ridge beam... between points of lateral support.

Eccentric loading is not your friend, it encourages buckling. One example is a loaded knee brace, the horizontal component of that force is actively buckling the post. Then we're getting into combined loading with axial and bending. The NDS has sections on all of this and I think WSDD has a good chapter describing with examples.

The phone rang, I blew a bad hose yesterday and we need to move iron... my mind wandered, redirect if I missed there.