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Author Topic: I want to try building a timber frame wood shed, need to confirm design  (Read 796 times)

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Offline stumper

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I am looking to build a post and beam woodshed.  It is the first post and beam structure I will have built.  I am an experience furniture maker and an engineer so  understand the principles but Need to check my plans.  the structure would be 9 feet by 22 feet.  Three posts along the length 11 feet apart.  I think a simple ridge beam rafter design with the roof overhanging the sides by 18 inched and the ends by 2  feet for a total roof size of 12 by 26 feet.  I plan on a steel roof, 12/12 pitch, no heat or even walls.  I am in an area with a snow ground load of 70 to 80 lbs.

I am thinking of using 8 by 8's for all the posts, beams and braces.  Is 8 by 8 strong enough for the beams, or overkill?   Could I drop back to 6 by 6 beams and posts or 6 by 8 beams and 6 by 6 posts.

As some of posts will be subject to splashing from the roof I planned on using hemlock, but using white pine for the beams and braces.  Any issues with mixing species?

Thanks

Offline ljohnsaw

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If it were me, without doing ANY calculations, I would use the 6x6 posts and 6x10 beams.  A 4x10 would probably suffice but then it wouldn't be a real timber frame now, would it? :D  The braces can be 4x6 - no need to go so heavy on them.  Your rafters? 2x8 or 2x10 rough?  With that steep of a roof slope, you *shouldn't* have any snow accumulation, but just in case, make it stout!  With no walls, make sure you anchor it well because of uplift.  You will have one heck of a sail there!

Now, with the tool box, it is pretty easy to do the calcs...
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline stumper

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Thanks

"Now, with the tool box, it is pretty easy to do the calcs..."

Is there an onsite tool box for these calculations? 

Offline ljohnsaw

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yep  Scroll down to the bottom of the sponsors on the left and you will see a little red toolbox.  Dig around in there and you will find some "beam calculators".  Figure out what your dead load (wood/roofing) and snow load will be and plug in some beam sizes to see if it flies!  If you need more guidance, we are here to help!
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64' - using it all to build a timber frame cabin.

Offline Brad_bb

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Posting a picture of your design would really help.  Is there a specific reason for it only being 9 feet wide (like limited space to put it etc?)?  As you have described it, you have 3 bents in 22 feet.  So only a 7 foot span between bents.  Your tie beams are only 9 ft.   8x material would bi overkill for these sizes.  As ljohnsaw said, sounds like 6x post and beams, and 3x or braces and rafters would find.  A pic of your design would be really helpful.  8x material is more typical but would look odd for such a small span. 
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline D L Bahler

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A significant potion of Europe's timber framing tradition uses 4x and 5x material all the time for posts and beams, so don't feel like you have to use oversized timbers to make it a 'true' timber frame. Of course, I'm probably annoying some times with my advocacy of Central European/German timber framing, so take what I say with a grain of salt!

IF it were me, making a woodshed, I'd probably not use bents at all, just frame two parallel walls, one taller than the other, and stick beams on top of them, crossbeams between them, and make a shed roof. Either that, or I'd frame it as two walls (even height) with a beam on top of them, lay crossbeams over top of those with simple cog joints (super easy to cut) that hold up ridge posts, and stick a ridge beam atop those posts (hope my description is clear enough), then hang rafters from the ridge.
I think such a narrow building foregoes the necessity and practicality of bent framing. 

Offline Don P

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3 bents, 2 bays in 22', so 11' per bay. A picture is worth a thousand words. I'm not disagreeing with DL either, just running down one rabbit :)
If there is a ridge beam 22' long with a center support, that support is carrying 4.5'x11'x90lbs/sf + ~4500lbs. If there isn't a post to ground supporting the ridge beam then a crown post on a 9' beam that runs from front post to back post. Or, a 9' center point loaded beam carrying a 4500 lb load.

As an aside, using the same total load, the bending force on a beam (the maximum bending moment)is twice as great if the same load is concentrated in the center of a beam's span vs being uniformly spread out along the span. There are 2 different calcs in the toolbox, one for uniformly distributed load and one for center point loaded beams. I'm sure stumper knows that, just putting it out there.

Given the options I'd use good hemlock over white pine in bending members, the beams. In #2 an Fb of 750 vs 575, and better shear, which rarely controls but if there is a beam situation where it could, it is in a relatively short relatively heavily loaded beam. Then there is the growth habit of the trees. EWP grows 2-3' per year and throws out a complete whorl of branches then grows another 2-3' and does it again the next year. Basically there is a knot cluster every 2-3'. The hemlock has scattered knots. After all the cyphering is done, you are more likely to drop below #2 in EWP and are more likely to rise above #2 in hemlock in the real world.

Offline Roger Nair

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So I'm just spit balling, no calcs.  I would suggest 8 x 8 posts, mainly because lack of specific plans to comment on and brace joinery will remove significant grain in a 6 x 6.  I would prefer 3 bents with a dropped tie 8 inches min.  Bents aid rack strength resistance.  3 x 6 braces should be fine.  For a roof 3 x 6 half lapped rafters, spiked and clinched at peak.  Ceiling joist every other rafter couple, again spiked and clinched.  Wall plates by calc maybe 8 x 8.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Offline stumper

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I will work on putting a design on paper so that I can scan it in for all to see.  Unfortunately, playing with the tool box I think I may need to have to change front a common bent to a king post bent to lighten the load.  Or change to 8 by 10's. 

I do want to stay with white pine as I have white pine on my property suitable but not hemlock.  I can find #1 pine easier than I can find #2 hemlock.

Offline D L Bahler

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By all means use white pine. I am an advocate of white pine, and if it were entirely up to me, I'd use it exclusively.
It's easy to work and has a fantastic strength to weight ratio.

Offline plantman

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Re: I want to try building a timber frame wood shed, need to confirm design
« Reply #10 on: March 13, 2017, 07:32:27 am »
Of possible interest are these wood preservatives. I'm new to this but have been trying to gather as much info as possible

http://www.alsnetbiz.com/homeimprovement/homemade.html