Non-timber framer with a dumb question.

[Old Greenhorn]

Caveats: I am not a carpenter. I am not a timber framer. I feel presumptuous even posting in this section. I can build stuff but usually seek good advice first. I am moving my mill behind my shop. The back wall is cinder block, 24' long. I would like to add a shed roof off the back in the spring, but I need to keep the long side open so I can get logs rolled up on the mill. I have a 24' bed on the mill. I am trying to figure out how to make this span and allow it to hold the roof, rafters, and snow load. I am spit balling ideas in my head and this is what seems workable to me. Now please don't laugh (too hard) at my sketch, as I said, jotting down ideas.



 

The uprights and top and bottom stringers are 8x8 as is the king post in the center (if that's the right term). The diagonal members are 2x6's or 2x8's. I am thinking through tenons on all joints except the diagonals.
 Please type any suggestions slowly and use plain language so I can try to follow along. If it's a dumb idea, tell me. This is something I think I can do.

[Don P]

The lack of scale of the sketch is making it look do-able. Your web members, the diagonals, will be too flat to do much good. They work better if they run at around 45 degrees.
I just pm'ed Scott this link a couple of days ago, it shows some nice sketches of parallel chord trusses. Notice how they lock in the heel of those web diagonals
https://www.carolinatimberworks.com/timber-frame-trusses/

[Brad_bb]

You might be able to get away with just and 8x12 beam.  I'd have braces on the ends that would reduce the span by 4 ft on each side but you should still be able to have a full 24' span just below those to bring logs in.  You need someone to do the math on the loading from the rafters and snow load, and to figure out if it can be pine, or if it needs to be oak.

For a parallel chord truss as you sketched, you'd need multiple diagonals in each side.  You probably want 3,4,5 triangles or even equal leg length triangles.    Again, it should be engineered.  You may also be able to get away with two 2x manufactured parallel chord trusses.  It depends on your loads and what the manufactured trusses are designed for.

This truss is way heavier than you would need, because it spans a much greater distance, but you can see the ratio of truss height to diagonal length and leg length.  


 

[Ljohnsaw]

You say you have 24' of bed but what is the biggest log you can actually mill?  How will you be loading logs on your mill?  Simple roll up or will you be using a tractor with a grapple?  If the latter, then you could get by with a smaller opening between posts.  You come in at an angle and turn when the first end of the log gets inside the post.  Saw it on a video posted on the FF for some massive logs.

Also, you could come way down on the posts with a brace - perhaps 2 or 3 feet from the ground leaving enough space to roll a log under.  Then, at 45°, the span would be way reduced to as little at 10', maybe even less if your true max log length is 21', 20' ??  You are not supposed to take the brace point as shortening the span, but...  However, snow load numbers would be needed to figure it all out.

[Old Greenhorn]

@Don P , thanks for the link. Do you know where I could find some dimensions for that jointing scheme? Is there a tenon involved? If not, how are they fastened?

@Brad_bb I like the brace idea, that could work. I also like the idea of a single 8x12 but I am not sure how I would get it up there. This will either be made from maple or oak. That's what I have. I'll have to work on a scale sketch.

@ljohnsaw The bed is 24' long, I can mill just under 22' but I can easily make an extension to get those 24' footers or longer done so I don't want to shorten the opening at all. Loading is a simple straight roll on, no equipment, so I can't do much manipulating without a lot more work.

Thank you all, this is very helpful. I have 6 months or more to plan this, too much other stuff to do. Then I have to find and cut logs. First I need a scale drawing and some snow loading data.

[Hilltop366]

Not sure what the existing building looks like but a gable end would be my first choice, then you can easily span 24'.

Not able to use a gable end, your current plan puts ½ of the roof load on the truss add a couple more trusses (4' oc) and you can make them shorter in height as well as reduce your rafter size.

Perhaps the load would be reduced enough that you may be able to use timbers instead. More head room, the load will be spread out more evenly, less chance of failure, not all your eggs in one basket.

[Don P]

It looks like I posted this a dozen years ago but fun to scroll through on a snowy morn. There are some parallel chord trusses in the pg 80-90's neighborhood but this is all good stuff.
https://www.woodworks.org/wp-content/uploads/2018-02-TX-Heavy-Timber-Trusses.pdf

@Sedgehammer this is Ben

[Sedgehammer]

Thanks @Don P ! I could see his features in some of the other pics, but that first one,   nope, no way!  :D

Many very beautiful designs and even more many, many dollars that they cost......

[Old Greenhorn]

if I moved the diagonals to 45° I think I can fit 11 of them. Then I could add two long braces up the posts at about 30° from vertical beginning about 3' from grade level. 
 The problem I am having is finding out what the snow load design requirements are. I can find calculators to tell me what the snow will weigh, but not what the design requirements are or what this roof can handle. I was hoping for a low pitch, but 8/12 might be workable. A foot of wet snow would be pretty heavy up there. I REALLY do not want to go to a 12 pitch (not sure I could anyway).

@Hilltop366 You typed too fast for me to understand. I don't like the gable end because it uses more than twice as much lumber and is a LOT more work (time I don't have). I did not follow what you were saying about adding more trusses. If I do that I won't have room for the mill. The 'shorter in height' comment was when I realized I didn't understand what you were suggesting.

@Don P thanks for another good link. Now my head hurts. ;D 

Maybe I will just go back to using a tarp.

[Hilltop366]

I'll try to type slower. :D

What I was referring to was instead of one truss along the 24' at the front of the building if you were to put two or three 24' trusses or beams to spread the rafter load out you may be able to reduce the truss depth and rafter depth and increase the head room at the opening and not have to rely on one truss to hold up half the roof.

The easiest way would be to put post under the beams but I'm guessing that you would like the ends open so that would not do, so If you think of your roof as ½ of a gable end with ½ of a timber truss on each end and 24' purlins with 12' rafters (probably can use 2x4")  you now have 1/3 of the area to support with your outer beam. (2' by 24' instead of 6' x 24').

Something like this.

 

 

[Old Greenhorn]

@Hilltop366 thank you for typing slower and taking the time to explain. I would have never thought of that on my own. Breaking the load up, of course, makes sense, but I can also use smaller lumber which saves material. I have to roll this around in my head for a few hours but I like the idea. I would need 3 bridge trusses all the same and the end frames would be 8x8's properly joined, correct? Where it meets the wall, I don't need a truss because that is bolted into concrete block. I have to check and see if I have enough wall height to do this because I may come up short. What pitch would you recommend for this?

[Hilltop366]

Not able to say what size timbers you would need but 8" x 8" could be good place to start to see, then adjust from there.

For pitch, the more the merrier, the steeper the pitch the smaller the framing can be but I tend to "over build" and use flat for my rafter size calculations. The code is the minimum required, I will usually try to surpass that if practical.

[Hilltop366]

I'm thinking that the outside beam would not need to be as large, it is holding up half of the load as the inner ones. an area of 2' x 24' vs 4' x 24', however it may be best to keep them the same. I figure the outside one is the most likely to get bumped so some extra sturdiness could prove handy.

I would try to size beams instead of trusses if you can get logs large enough, a lot less work if you can use beams.

Also I sure some bracing would be needed as well.

[Brad_bb]

I would try to size beams instead of trusses if you can get logs large enough, a lot less work if you can use beams.

Also I sure some bracing would be needed as well.

That's what I was also trying to say.  8x12 white pine tie beams are used in a white pine frame that is 24ft wide with a loft(with 3'x3' braces on each side).  So I'm thinking that a white oak 8x12 may work in that location since the only loading is the snow load which is only half of a 12' span.  It's definitely worth having the engineer run the numbers. That size may even be overkill? K.I.S.S.

Make a good sketch showing the views of the proposed design.  Get Firetower engineered Timber in Massachusetts review it and crunch the numbers.  The cost shouldn't be bad for something small like that and really worth it to do it right.  I've used them.  rjwoelk on here used them for his timberframed firewood processing shed and was happy.

[Don P]

Without loads its guesswork.
At 24' I think we're probably being optimistic thinking a manageable solid sawn timber will work but that is very easily checked when we have the load information. If a truss looks like the best option engineering is a good idea, especially if the truss is shallow which this needs to be. Another option for a long shallow span is an engineered beam, glulam if appearance matters, an LVL if strength/cost is more important, LVL also assembles easier since you would be lifting one ply at a time. The engineering for either of those is available online in tables and can be confirmed when you order. Those products are stronger and stiffer than solid sawn wood, I've got 24' lvl's spanning a shed opening on my barn. As an example white pine has a bending strength in #2 of 575 psi, lvl comes in at 2800 psi, that makes quite a difference. My shorter spans are in white oak and locust. Anyway that is all background at this point, find your snow load info, the local building department can give you that, and that will help narrow down some of the options.

Edit;
Here's a general map;
https://www.harrietstown.org/vertical/sites/%7B5D317D24-97FA-4BE7-AE35-555F0A30150D%7D/uploads/Ground_Snow_Loads_Map.gif

[Bruno of NH]

Build it with the beam or truss
When the mills not in use have a post cut that is put in at half way.
That way it covers your snow load when you get it.
Just stay on top of the snow build up with a roof rake.

[Bruno of NH]

Have the post made to be removable with all tread and plates to snug it up

[Nebraska]

It could be offset to the long side at say13 to 17 feet so unless you were milling a really long log you wouldn't have to take it out very often, I can mill 20 feet  just don't very often and 8 to 12 foot will be 95 % of what I will cut.

[Don P]

That post will soon be forgotten, don't ask how I know :D

[Nebraska]

You know even though I'm just full of great ideas, there's no way after milling in a hurry I would park the mill get it put to bed, throw the stuff I cut on the forks, go chase down stickers, put the chainsaw up, do the umpteen other steps involved, and remember to put the post in. Nope it would be 5° outside and blowing snow and I would be just dozing off in a warm bed then I would remember.....

[Old Greenhorn]

first, thanks everybody for all the ideas and teaching. I am not a construction guy either and can't seem to understand the snow loading or what I need to get, but that's OK. I have re-thought what I am doing. 
 I had always wanted a shed roof off the back of the shop, so I just went with that. But when I back up a bit I think the better course of action is to build a dog house at one end of the mill bed. I have a ground mounted Hud-Son 328 and the track is made of angle iron (1-1/2 I think). It would be pretty easy to make a 4' extension at the head end of the track and push the head in there at the end of the day and close the door. It would also serve as a place to store my blades and basic hand tools. I like this idea a lot better. It also gives me a full 24' cut length when I need it.
 I could bring the shed up (that I built last year) but that thing has to weigh 2,000# and it is a dangerous move up the steep skid road. I am leaving that as a gift for the landowner and a place to store logging tools and maybe party stuff or something.
 So I think I will sink 4x4 posts in concrete and build the dog house off of that with a back slanting shed roof (I am done with the 12/12 pitch roofs  ;D).

 Again, thanks for helping me get my head straight.

[ScottCC]

Go to the lumber yard.  Get a quote for a truss with design and price.  Be friendly , smile and go home and do it better.  My buddy likes to do it.  On mine I put in a 30' hole.  A tripled truss cost $1200 and a lot of nails.  Two weeks later done.