Jack Sobon's Timber Frame Project (Modification)

[CJ]

  Hi Everyone,   As a greenhorn who has only seen the light to timber frame construction early 2018, I have had the bug to build a small timber frame bunkie on my waterfront property that I purchased back in late '17.
Last May when I took two two week courses, I was presented with two types of structures; one being a 16' X 20' rafter style, and the other a 14' X 20' King truss and hammer beam model. Although I found both very stunning and would truly wouldn't mind either, I have since opted for the rafter style frame as it will allow me to have a loft. The extra little bit of room will surely be valued.
This past Christmas, my son gave me Jack Sorbon's Learn to Timber Frame book, and in it is a layout pattern for a 12' X 16' rafter style frame. Go figure! However, my wife and I both agree that making it a tad larger would be ideal. Soooo...I was going to modify it to a 14' X 18' layout. That said, my dimensional cuts will change on some of the structure members; ie: rafters, top plate, tie beams. The one that I want to be sure of that I don't screw up would be the rafter measurements. Being this my first project, and being by myself on this project, I don't have anyone to concur with, or to double-check my work and I certainly don't want to make a mistake on cutting the timbers.
So to make a long story short, I calculated my rafter length as follows; for a 14' wide frame, I calculated my rafter to be an overall length of 12'-9 3/4" and 11'-3 3/4" to the step-lap. Is my calculation right?? Although I did use an online calculator to arrive at my answer, it would be nice to have someone confirm. In Jack's design his overall rafter length for a 12' wide frame is 9-11 13/16" and 8-3 13/16" to the step-lap.
Also will by floor joists (5" X 7") have to increase in size for the extra two feet of width? Thank you for any help and input that you can provide this novice. - Cheers!

[Dave Shepard]

To calculate the rafter length of a 12/12 pitch roof, multiply the run, 7' in this case, by 1.414213562. This will be the length from the peak to the arris of the plate. Jack gives the length to the step lap, which is safer if you are just cutting the part in the book, but a little confusing if you are modifying the frame dimensions. 

I am cutting a 12x16 now,  and in 2016 I cut a 16x20 version.

  

[CJ]

You are absolutely right!! Thank you for that. I inadvertently did the calculations for an 8' run rather than a 7' run. This is why I am leery about doing this project on my own. One simple miscalculation, or placing cut layouts where they shouldn't be. It is, what it is. I'll just have to forge on.
I love that picture! Nice!! I see that your overhangs are minimal. In Jack's book, he states that you can have an 18" overhang with a 2" thick rafter tail. Is going a little further beyond that really an issue if a roof is going atop of that? I'm thinking that the pitch of the roof with the thickness of the added T & G, plywood, foam board insulation plywood would distribute the weight and not placing all the weight on the rafter tail? Furthermore, if a metal roof is added to the final product, I don't think that snow accumulation will be a real factor taking into account the slope of the roof. Again, I am just guessing. This is my first build of any sort.

[curved-wood]

CJ if you are not sure of any calculations, just do a drawing to scale. Do it with precision and as large as you need. You will see all the detailing and where the measurements are going

[doc henderson]

CJ.  Welcome to the forum.  I am not a timber frame person, but had a couple comments.. I am from Ks, but spent time in Albany.  I do not see from where you come,  But if the building is unheated, or if so but you have extended overhangs, you might get freeze up at the edges and then build up above.  Also you don't have to tell anyone if you take an old scrap and make the cut to check yourself.  I have also drawn on a concrete slab to full scale to see if my math is ok.  I know that all the math can be done with a framing square or can use the A squared + B squared = C squared.  You may know this already but in other words, take the run times itself, and add the rise times itself, then take the Square root of that total for the length.  Look forward to seeing your progress, sounds like you are well on your way to becoming a Timber Frame expert.

[CJ]

Hi Lads, thanks for the input. I appreciate any knowledge that I can attain from people who have been there and done that. If you're dishing it, I'll surely take it.
As a greenhorn I truly love this old traditional way of building, and I wish I would have been introduced to it years ago, however, I still have a few more good years (God willing) and put some heart and soul into building something I can be proud of, put a signature to it, along with a time piece and hand it down to my kids. You know, the good Lord isn't making any more waterfront property, so just to be able to have a piece of property on the water with a self constructed timber frame that is overlooking the vista is what life is all about.
I know that this project will take me a bit of time to complete, as I am slow and methodical about everything that I do. The plus side is I have all winter to start doing piece by piece out of my garage, except of course for the longer timbers that won't fit. Those I will probably have to wait for the Spring weather in April, so that I can do it outside.
I may have to lean on you guys from time to time to help me along. I think that this site is just ingenious! A support system for people who are wanting to learn and construct, all done through technology. Love it! Thanks again. - Cheers!!

[Don P]

Oh you and Doc are pups, I keep telling myself that cause I'm the same age. Dad taught me the same way, loft it on the floor full scale if possible and if not take some scrap and mock it up, if it is heavy make the test piece out of a full length 2x4 with full sized stock screwed to the ends to make your trials. With sketchup you can pretty much draw and try anything and then zoom in and print the critical parts. I think there is some of that kind of drawing in my gallery under "24' kingpost truss" where I've played around and then dimensioned stuff.

[Brian_Weekley]

This past Christmas, my son gave me Jack Sorbon's Learn to Timber Frame book, and in it is a layout pattern for a 12' X 16' rafter style frame. Go figure! However, my wife and I both agree that making it a tad larger would be ideal. Soooo...I was going to modify it to a 14' X 18' layout.

I up-sized Sobon's design to 14x20 and added a 6' leanto on one side.  If you have Sketchup, you can download my drawing and take measurements:

http://forestryforum.com/board/index.php?topic=71838.0

You can see the build in this thread:  

http://forestryforum.com/board/index.php?topic=68551.0

[scouter Joe]

CJ you say that you are in northern Ontario . I'm also in Northern Ontario which is a very big place . I'm in Hanmer just north of Sudbury And if you are any where near me I'd be glad to help out . I've been doing log and timber framing for the last 38 years and should be able to answer all of your questions . Let me know . Thanks scouter Joe

[CJ]

  Hi Joe,  Yeah...I'm in Sudbury. What are the chances! 8)    I will surely look you up for advice and as a resource. I appreciate the gesture. It's nice to know that there is someone close by. Thanks!!

[doc henderson]

Hey CJ.  Lots of good info.  I hope I am not over killing this, but here are some pics of a quick way to calculate for a shed, and or check your math,

 




 




 


So rough idea is about 9 feet 11 inches
sorry if I am beating a dead horse.

[CJ]

Absolutely not overkill. As a matter of fact, that is ingenious. I would never have thought of a method like that. You see, you can teach an old dog new tricks! Thanks for that idea, Doc.
When I took my timber frame course last May (2018), I actually showed the instructor who has been doing timber framing since the early 90's, how to use a speed square to figure out the slope of a roof. He thought that it was luck, but came back a while later to say that he had tried it on multiple examples only to find out that it wasn't hokum. You see, even the experienced can learn a thing or two.

[doc henderson]

Glad it may be of use to you.. Of course I will give credit to my dad and our family friend, Kenny Skeels.  Kenny would hire kids he knew to help build houses even though it would take us much longer to do any thing.  Making things simple is much harder sometimes than working on something complex.  when I was 14 or so, I was working with Kenny's sons David and Doug and another teen hanging sheet rock on a ceiling.  It took us 20 minutes a sheet and in the end, had a half inch gap at one end.  It had to come down and Kenny filled his mouth full of nails, picked up a 4 x 12 x 1/2 inch sheet of rock on his head, jumped up on a saw horse and nailed it perfectly in place.  I was amazed.  In later years he came and stayed at my house to do remodeling.  At night he was moaning and groaning.  I finally asked him if he was dreaming about his lovely wife Rosie.  He just laughed and said his knees hurt so bad from all the work he had done. Anyway thanks for the comments and we all look forward to pics and play by play on your build. 

[doc henderson]

Be careful using the framing square.  In a book I read years ago titled tools of the trade.  Each chapter is titled by a different hand tool.  It is written by a master carpenter from his years as an apprentice to an old German carpenter.  In the chapter titled, "faming square" he states he was cautioned that this was the most dangerous tool he would ever use...They  were cutting in stairs and laying out the stringers.  The apprentice asked to borrow the square of the master carpenter who warned him in a thick accent, " This is the most dangerous tool you can use, cause if you drop it and knock it out of square, it will be my sad duty to kill you".  God Bless.


smiley_swinging_board

[CJ]

  :D Good one!

[Dave Shepard]

I've got a little trick to convert decimal to fractions of an inch. Using your 7' run:

7×1.414213562=9.899494934

That's a rafter length of 9 feet and some inches. To get the exact inches, subtract the 9 and multiply by 12.

.899494934×12=10.79393921

Now we know that the rafter is 9 feet 10 and a little bit inches. To convert that little bit to sixteenths, subtract the 10 and multiply by 16.

.79393921×16=12.70302733

So,  now we have a rafter that is 9 feet, 10 and a little over 12/16 of an inch. 12.70 is close enough to 13/16 for me,  so 9' 10-13/16" it is. 


If you want to work to greater accuracy, like in cabinet work, substitute 32, or 64 at the final step in place of 16. Working any finer than 16ths, and some would argue, finer then eigths, in timber framing is unnecessary. 

[CJ]

 Holy Cow Dave!! I'm going to have to write that one down somewhere, cause I don't think I have the braincells to remember all that. Although, if I have less decimal places, then there might be a chance. That's pretty slick, I must say. The stuff I've learned so far. I'm glad I joined this site. Very informative and a ton of database from knowledgeable people. 

[Dave Shepard]

The number of decimals don't matter, because you are doing it all in a calculator. Just subtract the whole number in the front each time until you get feet, inches, and fractions. 

[Dana Stanley]

Throughout my carpentry career I carried the swanson blue book. I think I still have a copy in my truck. I have stepped out rafters with a framing square using those little clamp on lugs. I used them a lot for stairs too. But an old time carpenter warned against using a framing square as if your off you can get progressively worse. Using the mathematical formula, or a reference is the most accurate! https://www.olpl.org/documents/SpeedSquareInstructionBook2.pdf  Using this book I could layout and cut a whole hip roof on the ground. If you do use a framing square for rafter length, use one with a rafter table and use the number they give you on the rafter table as a reference.

[Don P]

Very true, when stepping off rafters or stairs setting the square nuts off a little or even the accumulated width of a pencil line over and over can add up to more than you think, I like doing it by Mr Pythagoras, a table or by math, and since sketchup arrived I've done more that way than anything. I've got a few rafter calcs down in the toolbox, on most I tried to put the math equations there so you can see what they are doing to arrive at the result. BTW you can adjust your framing square if it does get off, but if you tweak someone else's they probably are going to kill you first :D

[CJ]

 Dually noted. I have those set pins for my framing square, but have never used them. I could also just buy a Construction Pro calculator that has all the functions on it to do the calculations, but these calculators are a bit pricey.  
Those of you who say you use Sketchup, do you have the free version of it or did you actually pay for the software. I watched how it works on line yesterday and thought that I would try the free version of it. However, the free version seems a bit difficult to use, as it only has a few of the available functions available to allow you to do certain tasks. I am pretty tech savvy, but trying this free software application was a bit tedious. I was very impressed with the product overall after having watched the tutorials.

[flyingparks]

Free version of sketcup is great. Watch the official sketchup tutorials...in order. It does not work like other drafting software. It can get really frustrating if you try to teach yourself...but it is a wonderful program.

[Don P]

I use the free version too, I'm stuck at the 2016 version, that's as modern as my graphics card can handle. It does everything I need. I got Sketchup for dummies and it helped me get going.

One trick with square nuts, set the square with the marks you want in line with the edge of the board where you want them to be. Then while holding the square there, slide the nuts on till they hit the board and are bedded on the square and tighten. They may not be quite on the marks depending on the angles you are setting up but they are holding the square on the marks. To avoid pencil thickness accumulated error when stepping off I use a knife to scribe my marks on the wood. Be careful, a knife can hop up on the square and take the side of your thumb off in a heartbeat.

[curved-wood]

Well,  if you have a lot of fun to play around with software there is quite a few out there and the number are growing : revit, auto cad, solidworks, etc . I like to built in curve  ( see some of my constructions  at : claudedrolet.com ) so Sketchup is a bit limited for my use. But I know quite a few people that are well satisfied with it.  I use more complex software and the learning curve goes with it. So for a square building, straight line that is, I am much faster to use a scale drawing on the standard 1/4 '' graph paper than trying to learn the steps of a new software. I will get all the info I want,  providing you have a little bit of math knowledge. But when I am dealing with curved roof or even just a curved door, the software will give me a precision that will take me hours to calculate. My point is that if you are a tech passionate go for it,  but just don't forget that a simple graph paper with a scale drawing could do a very good job specially with a structure like yours. Choose your way and have fun

[Brad_bb]

FYI it's "Sobon", pronounced So-bun.  Not Sorbon.